Effects of chlorpyrifos on soil carboxylesterase activity at an aggregate-size scale.

PubMed

Sanchez-Hernandez, Juan C; Sandoval, Marco

2017-08-01

The impact of pesticides on extracellular enzyme activity has been mostly studied on the bulk soil scale, and our understanding of the impact on an aggregate-size scale remains limited. Because microbial processes, and their extracellular enzyme production, are dependent on the size of soil aggregates, we hypothesized that the effect of pesticides on enzyme activities is aggregate-size specific. We performed three experiments using an Andisol to test the interaction between carboxylesterase (CbE) activity and the organophosphorus (OP) chlorpyrifos. First, we compared esterase activity among aggregates of different size spiked with chlorpyrifos (10mgkg -1 wet soil). Next, we examined the inhibition of CbE activity by chlorpyrifos and its metabolite chlorpyrifos-oxon in vitro to explore the aggregate size-dependent affinity of the pesticides for the active site of the enzyme. Lastly, we assessed the capability of CbEs to alleviate chlorpyrifos toxicity upon soil microorganisms. Our principal findings were: 1) CbE activity was significantly inhibited (30-67% of controls) in the microaggregates (<0.25mm size) and smallest macroaggregates (<1.0 - 0.25mm), but did not change in the largest macroaggregates (>1.0mm) compared with the corresponding controls (i.e., pesticide-free aggregates), 2) chlorpyrifos-oxon was a more potent CbE inhibitor than chlorpyrifos; however, no significant differences in the CbE inhibition were found between micro- and macroaggregates, and 3) dose-response relationships between CbE activity and chlorpyrifos concentrations revealed the capability of the enzyme to bind chlorpyrifos-oxon, which was dependent on the time of exposure. This chemical interaction resulted in a safeguarding mechanism against chlorpyrifos-oxon toxicity on soil microbial activity, as evidenced by the unchanged activity of dehydrogenase and related extracellular enzymes in the pesticide-treated aggregates. Taken together, these results suggest that environmental risk assessments of OP-polluted soils should consider the fractionation of soil in aggregates of different size to measure the CbE activity, and other potential soil enzyme activities. Copyright © 2017 Elsevier Inc. All rights reserved.

Effects of vegetation restoration on the aggregate stability and distribution of aggregate-associated organic carbon in a typical karst gorge region

NASA Astrophysics Data System (ADS)

Tang, F. K.; Cui, M.; Lu, Q.; Liu, Y. G.; Guo, H. Y.; Zhou, J. X.

2015-08-01

Changes in soil utilization significantly affect aggregate stability and aggregate-associated soil organic carbon (SOC). A field investigation and indoor analysis were conducted in order to study the soil aggregate stability and organic carbon distribution in the water-stable aggregates (WSA) of the bare land (BL), grassland (GL), shrubland (SL), and woodland (WL) in a typical karst gorge region. The results indicated that the BL, GL, SL, and WL were dominated by particles with sizes > 5 mm under dry sieving treatment, and that the soil aggregate contents of various sizes decreased as the particle size decreased. In addition, the BL, GL, SL, and WL were predominantly comprised of WSA < 0.25 mm under wet sieving treatment, and that the WSA contents initially increased, then decreased, and then increased again as the particle size decreased. Furthermore, at a soil depth of 0-60 cm, the mean weight diameter (MWD), geometrical mean diameter (GMD), and fractal dimensions (D) of the dry aggregates and water-stable aggregates in the different types of land were ranked, in descending order, as WL > GL > SL > BL. The contents of WSA > 0.25 mm, MWD and GMD increased significantly, in that order, and the percentage of aggregate destruction (PAD) and fractal dimensions decreased significantly as the soil aggregate stability improved. The results of this study indicated that, as the SOC contents increased after vegetation restoration, the average SOC content of WL was 2.35, 1.37, and 1.26 times greater than that in the BL, GL, and SL, respectively. The total SOC and SOC associated in WSA of various sizes were the highest at a soil depth of 0-20 cm. In addition, the SOC contents of the WSA increased as the soil aggregate sizes decreased. The SOC contents of the WSA < 0.25 mm were highest except in the bare land, and the SOC contents of the aggregates < 0.25 mm, which ranged from 18.85 to 41.08 %, comprised the majority of the total aggregate SOC contents. The woodland and grassland facilitated WSA stability and SOC protection, thus, promoting the natural restoration of vegetation by reducing artificial disturbances could effectively restore the ecology of and prevent soil erosion in karst regions.

Sediment composition for the assessment of water erosion and nonpoint source pollution in natural and fire-affected landscapes.

PubMed

Carkovic, Athena B; Pastén, Pablo A; Bonilla, Carlos A

2015-04-15

Water erosion is a leading cause of soil degradation and a major nonpoint source pollution problem. Many efforts have been undertaken to estimate the amount and size distribution of the sediment leaving the field. Multi-size class water erosion models subdivide eroded soil into different sizes and estimate the aggregate's composition based on empirical equations derived from agricultural soils. The objective of this study was to evaluate these equations on soil samples collected from natural landscapes (uncultivated) and fire-affected soils. Chemical, physical, and soil fractions and aggregate composition analyses were performed on samples collected in the Chilean Patagonia and later compared with the equations' estimates. The results showed that the empirical equations were not suitable for predicting the sediment fractions. Fine particles, including primary clay, primary silt, and small aggregates (<53 μm) were over-estimated, and large aggregates (>53 μm) and primary sand were under-estimated. The uncultivated and fire-affected soils showed a reduced fraction of fine particles in the sediment, as clay and silt were mostly in the form of large aggregates. Thus, a new set of equations was developed for these soils, where small aggregates were defined as particles with sizes between 53 μm and 250 μm and large aggregates as particles>250 μm. With r(2) values between 0.47 and 0.98, the new equations provided better estimates for primary sand and large aggregates. The aggregate's composition was also well predicted, especially the silt and clay fractions in the large aggregates from uncultivated soils (r(2)=0.63 and 0.83, respectively) and the fractions of silt in the small aggregates (r(2)=0.84) and clay in the large aggregates (r(2)=0.78) from fire-affected soils. Overall, these new equations proved to be better predictors for the sediment and aggregate's composition in uncultivated and fire-affected soils, and they reduce the error when estimating soil loss in natural landscapes. Copyright © 2015 Elsevier B.V. All rights reserved.

Aggregate stability as an indicator of soil erodibility and soil physical quality: review and perspectives

NASA Astrophysics Data System (ADS)

Le Bissonnais, Yves; Chenu, Claire; Darboux, Frédéric; Duval, Odile; Legout, Cédric; Leguédois, Sophie; Gumiere, Silvio

2010-05-01

Aggregate breakdown due to water and rain action may cause surface crusting, slumping, a reduction of infiltration and interrill erosion. Aggregate stability determines the capacity of aggregates to resist the effects of water and rainfall. In this paper, we evaluated and reviewed the relevance of an aggregate stability measurement to characterize soil physical properties as well as to analyse the processes involved in these properties. Stability measurement assesses the sensitivity of soil aggregates to various basic disaggregation mechanisms such as slaking, differential swelling, dispersion and mechanical breakdown. It has been showed that aggregate size distributions of structural stability tests matched the size distributions of eroded aggregates under rainfall simulations and that erosion amount was well predicted using aggregate stability indexes. It means stability tests could be used to estimate both the erodibility and the size fractions that are available for crust formation and erosion processes. Several studies showed that organic matter was one of the main soil properties affecting soil stability. However, it has also been showed that aggregate stability of a given soil could vary within a year or between years. The factors controlling such changes have still to be specified. Aggregate stability appears therefore as a complex property, depending both on permanent soil characteristics and on dynamic factors such as the crusting stage, the climate and the biological activity. Despite, and may be, because of this complexity, aggregate stability seems an integrative and powerful indicator of soil physical quality. Future research efforts should look at the causes of short-term changes of structural stability, in order to fully understand all its aspects.

Reduction in soil aggregation in response to dust emission processes

NASA Astrophysics Data System (ADS)

Swet, Nitzan; Katra, Itzhak

2016-09-01

Dust emission by aeolian (wind) soil erosion depends on the topsoil properties of the source area, especially on the nature of the aggregates where most dust particles are held. Although the key role of soil aggregates in dust emission, the response of soil aggregation to aeolian processes and its implications for dust emission remain unknown. This study focuses on aggregate size distribution (ASD) analyses before and after in-situ aeolian experiments in semiarid loess soils that are associated with dust emission. Wind tunnel simulations show that particulate matter (PM) emission and saltation rates depend on the initial ASD and shear velocity. Under all initial ASD conditions, the content of saltator-sized aggregates (63-250 μm) increased by 10-34% due to erosion of macro-aggregates (> 500 μm), resulting in a higher size ratio (SR) between the saltators and macro-aggregates following the aeolian erosion. The results revealed that the saltator production increases significantly for soils that are subjected to short-term (anthropogenic) disturbance of the topsoil. The findings highlight a decrease in soil aggregation for all initial ASD's in response to aeolian erosion, and consequently its influence on the dust emission potential. Changes in ASD should be considered as a key parameter in dust emission models of complex surfaces.

Study of soil aggregate breakdown dynamics under low dispersive ultrasonic energies with sedimentation and X-ray attenuation**

PubMed Central

Schomakers, Jasmin; Zehetner, Franz; Mentler, Axel; Ottner, Franz; Mayer, Herwig

2016-01-01

It has been increasingly recognized that soil organic matter stabilization is strongly controlled by physical binding within soil aggregates. It is therefore essential to measure soil aggregate stability reliably over a wide range of disruptive energies and different aggregate sizes. To this end, we tested high-accuracy ultrasonic dispersion in combination with subsequent sedimentation and X-ray attenuation. Three arable topsoils (notillage) from Central Europe were subjected to ultrasound at four different specific energy levels: 0.5, 6.7, 100 and 500 J cm−3, and the resulting suspensions were analyzed for aggregate size distribution by wet sieving (2 000-63 μm) and sedimentation/X-ray attenuation (63-2 μm). The combination of wet sieving and sedimentation technique allowed for a continuous analysis, at high resolution, of soil aggregate breakdown dynamics after defined energy inputs. Our results show that aggregate size distribution strongly varied with sonication energy input and soil type. The strongest effects were observed in the range of low specific energies (< 10 J cm−3), which previous studies have largely neglected. This shows that low ultrasonic energies are required to capture the full range of aggregate stability and release of soil organic matter upon aggregate breakdown. PMID:27099408

Study of soil aggregate breakdown dynamics under low dispersive ultrasonic energies with sedimentation and X-ray attenuation

NASA Astrophysics Data System (ADS)

Schomakers, Jasmin; Zehetner, Franz; Mentler, Axel; Ottner, Franz; Mayer, Herwig

2015-10-01

It has been increasingly recognized that soil organic matter stabilization is strongly controlled by physical binding within soil aggregates. It is therefore essential to measure soil aggregate stability reliably over a wide range of disruptive energies and different aggregate sizes. To this end, we tested highaccuracy ultrasonic dispersion in combination with subsequent sedimentation and X-ray attenuation. Three arable topsoils (notillage) from Central Europe were subjected to ultrasound at four different specific energy levels: 0.5, 6.7, 100 and 500 J cm-3, and the resulting suspensions were analyzed for aggregate size distribution by wet sieving (2 000-63 μm) and sedimentation/X-ray attenuation (63-2 μm). The combination of wet sieving and sedimentation technique allowed for a continuous analysis, at high resolution, of soil aggregate breakdown dynamics after defined energy inputs. Our results show that aggregate size distribution strongly varied with sonication energy input and soil type. The strongest effects were observed in the range of low specific energies (< 10 J cm-3), which previous studies have largely neglected. This shows that low ultrasonic energies are required to capture the full range of aggregate stability and release of soil organic matter upon aggregate breakdown.

Organic carbon, water repellency and soil stability to slaking at aggregate and intra-aggregate scales

NASA Astrophysics Data System (ADS)

Jordán López, Antonio; García-Moreno, Jorge; Gordillo-Rivero, Ángel J.; Zavala, Lorena M.; Cerdà, Artemi; Alanís, Nancy; Jiménez-Compán, Elizabeth

2015-04-01

Water repellency (WR) is a property of some soils that inhibits or delays water infiltration between a few seconds and days or weeks. Inhibited or delayed infiltration contributes to ponding and increases runoff flow generation, often increasing soil erosion risk. In water-repellent soils, water infiltrates preferentially through cracks or macropores, causing irregular soil wetting patterns, the development of preferential flow paths and accelerated leaching of nutrients. Although low inputs of hydrophobic organic substances and high mineralization rates lead to low degrees of WR in cropped soils, it has been reported that conservative agricultural practices may induce soil WR. Although there are many studies at catchment, slope or plot scales very few studies have been carried out at particle or aggregate scale. Intra-aggregate heterogeneity of physical, biological and chemical properties conditions the transport of substances, microbial activity and biochemical processes, including changes in the amount, distribution and chemical properties of organic matter. Some authors have reported positive relationships between soil WR and aggregate stability, since it may delay the entry of water into aggregates, increase structural stability and contribute to reduce soil erosion risk. Organic C (OC) content, aggregate stability and WR are therefore strongly related parameters. In the case of agricultural soils, where both the type of management as crops can influence all these parameters, it is important to evaluate the interactions among them and their consequences. Studies focused on the intra-aggregate distribution of OC and WR are necessary to shed light on the soil processes at a detailed scale. It is extremely important to understand how the spatial distribution of OC in soil aggregates can protect against rapid water entry and help stabilize larger structural units or lead to preferential flow. The objectives of this research are to study [i] the OC content and the intensity of WR in aggregates of different sizes. [ii] the intra-aggregate distribution of OC and the intensity of WR and [iii] the structural stability of soil aggregates relative to the OC content and the intensity of WR in soils under different crops (apricot, citrus and wheat) and different treatments (conventional tilling and mulching). Soil samples were collected from an experimental area (Luvic Calcisols and Calcic Luvisols) in the province of Sevilla (Southern Spain) under different crops (apricot, citrus and wheat) and different management types (conventional tillage with moldboard plow) and mulching (no-tilling and addition of wheat residues at rates varying between 5 and 8 Mg/ha/year). At each sampling site, soil blocks (50 cm long × 50 cm wide × 10 cm deep) were carefully collected to avoid disturbance of aggregates as much as possible and transported to the laboratory. At field moist condition, undisturbed soil aggregates were separated by hand. In order to avoid possible interferences due to disturbance by handling, aggregates broken during this process were discarded. Individual aggregates were arranged in paper trays and air-dried during 7 days under laboratory standard conditions. After air-drying, part of each sample was carefully divided for different analyses: [i] part of the original samples was sieved (2 mm) to eliminate coarse soil particles and homogenized for characterization of OC and N contents, C/N ratio and texture; [ii] part of the aggregates were dry-sieved (0.25-0.5, 0.5-1 and 1-2 mm) or measured with a caliper (2-5, 5-10 and 10-15 mm) and separated in different sieve-size classes for determination of WR and OC content; [iii] aggregates 10-15 mm in size were selected for obtaining aggregate layers using a soil aggregate erosion (SAE) apparatus and WR and OC content were determined at each layer; finally, [iv] in order to study the relation between stability to slaking, WR and OC, these properties were determined in 90 air-dried aggregates (about 10 mm in size) selected per treatment (mulched or conventional tillage) and crop (apricot, citrus and wheat). In this case, every set of aggregates was randomly divided in three groups (n = 30) for assessing stability to slaking, WR and OC, respectively. OC content in the fine earth fraction of soils under different crops did not show important variations, although it increased significantly from conventionally tilled to mulched soils. The distribution of OC content in aggregates with different size varied among soils under different crops, generally increasing with decreasing size. At the intra-aggregate level, OC concentrated preferably in the exterior layer of differently sized aggregates and of aggregate coatings and interior from conventionally tilled soils, probably because of recent organic inputs or leachates. In the case of mulched soils, higher concentrations were observed, but no significant differences among aggregate regions were found. The intensity of water repellency, determined by the ethanol method, did not show great variations among differently sized aggregates under different crops in the 0-10 cm layer, but increased significantly from conventionally tilled to mulched soils. Coarser aggregates were generally wettable, while finer aggregates showed slight water repellency. Regardless of variations in the distribution of OC in different layers of aggregate from conventionally tilled soils, great or significant differences in the distribution of water repellency at the intra-aggregate level were not found. In case of mulched soils such differences were not significant. Finally, the intensity of water repellency was much more important than the concentration of OC in the stability to slaking of aggregates.

[Splash erosion of black soil with different reclamation years and its relations to soil aggregates selective characteristics].

PubMed

Zhou, Yi-Yang; Wang, En-Heng; Chen, Xiang-Wei

2009-10-01

Taking the typical black soil with a reclamation history of 8, 30, and 50 years and the un-reclaimed secondary forest land as test objects, a simulation study was made on the process of splash erosion and the selective characteristics of soil aggregates under artificial rainfall condition, with the effects of reclamation on the splash erosion in black soil region analyzed. The splash amount of reclaimed black soil was evidently higher than that of un-reclaimed secondary forest land, and increased with increasing reclamation years, with a variation range of 0.95-7.06 g x cm(-1). There was a significant exponential correlation between splash amount and splash distance, and the percentages of small size water-stable aggregates increased with increasing splash distance. The critical particle size of soil aggregates for the enrichment and depletion of splash erosion was 1.0 mm. Soil water-stable aggregates larger than 2 mm and smaller than 0.25 mm in size and soil organic matter content were the main factors affecting the splash erosion characteristics of typical black soil.

The Role of Management in Enrichment Ratio Dynamics and Resilience of Aggregate Fractions Via Raindrop Impact within Agricultural Hillslopes

NASA Astrophysics Data System (ADS)

Wacha, K.; Papanicolaou, T.; Hatfield, J.; Cambardella, C.; Abban, B. K.; Wilson, C. G.; Filley, T. R.; Hou, T.; Dold, C.

2017-12-01

The abundance and distribution of surface soil size fractions has been shown to be reflective of changes in management practices and landscape position. Soil size fractions exist in both un-aggregated and aggregated forms that differ in textural and biological composition, which can impact soil hydrology and aggregation processes. Soils with higher stocks of soil organic matter (SOM) promote higher biological activity, infiltration, and soil structure due to stronger, more resilient aggregates. Within ag-systems, intensive cultivation and steep gradients can negatively impact the formation/stability of aggregates and amplify erosion processes, which redistributes material along downslope flowpathways to varying degrees, based on the amount of available surface cover during a rainfall event. The innate variability in SOM composition found amongst the size fractions combined with these highly active flowpathways, produces a symphony of interactive biogeochemical and hydrologic processes, which promote spatial landscape heterogeneity. Due to this intricacy, accurately assessing changes in SOM stocks within high energy ag-systems is extremely challenging, and could greatly impact soil carbon budgets at the hillslope and greater spatial scales. To address this, in part, we utilize a systematic approach that isolates the role of management in building aggregate resilience to hydrologic forcing. Soil samples were collected from farm fields with varying slopes (1-20%) and management conditions, and then isolated into seven aggregate size fractions. Each aggregate fraction was tested for resilience to raindrop impact with corresponding SOM composition and biological activity. Rainfall simulations were conducted on plots under representative management and gradient to capture the dynamicity of the size fractions being transported during an applied rainfall event. Results found that small macroaggregate fractions were most indicative of changes in management, and erosion rates from plots were inversely proportional to SOM enrichment. These experiments not only promote our fundamental understanding on the dynamics of surface soil and SOM redistribution but also can provide guidance into best management practices that promote aggregate stability, decrease soil loss, and enhance soil health.

Soil aggregate and organic carbon distribution at dry land soil and paddy soil: the role of different straws returning.

PubMed

Huang, Rong; Lan, Muling; Liu, Jiang; Gao, Ming

2017-12-01

Agriculture wastes returning to soil is one of common ways to reuse crop straws in China. The returned straws are expected to improve the fertility and structural stability of soil during the degradation of straw it selves. The in situ effect of different straw (wheat, rice, maize, rape, and broad bean) applications for soil aggregate stability and soil organic carbon (SOC) distribution were studied at both dry land soil and paddy soil in this study. Wet sieving procedures were used to separate soil aggregate sizes. Aggregate stability indicators including mean weight diameter, geometric mean diameter, mean weight of specific surface area, and the fractal dimension were used to evaluate soil aggregate stability after the incubation of straws returning. Meanwhile, the variation and distribution of SOC in different-sized aggregates were further studied. Results showed that the application of straws, especially rape straw at dry land soil and rice straw at paddy soil, increased the fractions of macro-aggregate (> 0.25 mm) and micro-aggregate (0.25-0.053 mm). Suggesting the nutrients released from straw degradation promotes the growing of soil aggregates directly and indirectly. The application of different straws increased the SOC content at both soils and the SOC mainly distributed at < 0.53 mm aggregates. However, the contribution of SOC in macro- and micro-aggregates increased. Straw-applied paddy soil have a higher total SOC content but lower SOC contents at > 0.25 and 0.25-0.053 mm aggregates with dry land soil. Rape straw in dry land and rice straw in paddy field could stabilize soil aggregates and increasing SOC contents best.

An alternative method for determining particle-size distribution of forest road aggregate and soil with large-sized particles

Treesearch

Hakjun Rhee; Randy B. Foltz; James L. Fridley; Finn Krogstad; Deborah S. Page-Dumroese

2014-01-01

Measurement of particle-size distribution (PSD) of soil with large-sized particles (e.g., 25.4 mm diameter) requires a large sample and numerous particle-size analyses (PSAs). A new method is needed that would reduce time, effort, and cost for PSAs of the soil and aggregate material with large-sized particles. We evaluated a nested method for sampling and PSA by...

Influence of pore size distributions on decomposition of maize leaf residue: evidence from X-ray computed micro-tomography

NASA Astrophysics Data System (ADS)

Negassa, Wakene; Guber, Andrey; Kravchenko, Alexandra; Rivers, Mark

2014-05-01

Soil's potential to sequester carbon (C) depends not only on quality and quantity of organic inputs to soil but also on the residence time of the applied organic inputs within the soil. Soil pore structure is one of the main factors that influence residence time of soil organic matter by controlling gas exchange, soil moisture and microbial activities, thereby soil C sequestration capacity. Previous attempts to investigate the fate of organic inputs added to soil did not allow examining their decomposition in situ; the drawback that can now be remediated by application of X-ray computed micro-tomography (µ-CT). The non-destructive and non-invasive nature of µ-CT gives an opportunity to investigate the effect of soil pore size distributions on decomposition of plant residues at a new quantitative level. The objective of this study is to examine the influence of pore size distributions on the decomposition of plant residue added to soil. Samples with contrasting pore size distributions were created using aggregate fractions of five different sizes (<0.05, 0.05-0.1, 0.10-05, 0.5-1.0 and 1.0-2.0 mm). Weighted average pore diameters ranged from 10 µm (<0.05 mm fraction) to 104 µm (1-2 mm fraction), while maximum pore diameter were in a range from 29 µm (<0.05 mm fraction) to 568 µm (1-2 mm fraction) in the created soil samples. Dried pieces of maize leaves 2.5 mg in size (equivalent to 1.71 mg C g-1 soil) were added to half of the studied samples. Samples with and without maize leaves were incubated for 120 days. CO2 emission from the samples was measured at regular time intervals. In order to ensure that the observed differences are due to differences in pore structure and not due to differences in inherent properties of the studied aggregate fractions, we repeated the whole experiment using soil from the same aggregate size fractions but ground to <0.05 mm size. Five to six replicated samples were used for intact and ground samples of all sizes with and without leaves. Two replications of the intact aggregate fractions of all sizes with leaves were subjected to µ-CT scanning before and after incubation, whereas all the remaining replications of both intact and ground aggregate fractions of <0.05, 0.05-0.1, and 1.0-2.0 mm sizes with leaves were scanned with µ-CT after the incubation. The µ-CT image showed that approximately 80% of the leaves in the intact samples of large aggregate fractions (0.5-1.0 and 1.0-2.0 mm) was decomposed during the incubation, while only 50-60% of the leaves were decomposed in the intact samples of smaller sized fractions. Even lower percent of leaves (40-50%) was decomposed in the ground samples, with very similar leaf decomposition observed in all ground samples regardless of the aggregate fraction size. Consistent with µ-CT results, the proportion of decomposed leaf estimated with the conventional mass loss method was 48% and 60% for the <0.05 mm and 1.0-2.0 mm soil size fractions of intact aggregates, and 40-50% in ground samples, respectively. The results of the incubation experiment demonstrated that, while greater C mineralization was observed in samples of all size fractions amended with leaf, the effect of leaf presence was most pronounced in the smaller aggregate fractions (0.05-0.1 mm and 0.05 mm) of intact aggregates. The results of the present study unequivocally demonstrate that differences in pore size distributions have a major effect on the decomposition of plant residues added to soil. Moreover, in presence of plant residues, differences in pore size distributions appear to also influence the rates of decomposition of the intrinsic soil organic material.

[Effects of cotton straw returning on soil organic carbon, nitrogen, phosphorus and potas-sium contents in soil aggregates].

PubMed

Wang, Shuang Lei; Liu, Yan Hui; Song, Xian Liang; Wei, Shao Bin; Li, Jin Pu; Nie, Jun Jun; Qin, Du Lin; Sun, Xue Zhen

2016-12-01

To clarify the effects of cotton straw returning on the composition and contents of nu-trients in different particle sizes of aggregates, two treatments with or without cotton straw returning were tested in continuous three years. After three years straw treatments, we collected undisturbed soil within 0-5, 5-10, 10-20 and 20-30 cm soil layers, and to measure the composition, soil organic carbon, nitrogen, phosphorus and potassium contents in different particle sizes of aggregates classified using dry sieving. Returning cotton straw into the field significantly increased particle contents of 2-5 mm and >5 mm aggregates in 0-5 cm soil layer, while the content of <0.25 mm micro-aggregates was decreased. Cotton straw returning significantly improved soil organic carbon, nitrogen, and potassium contents by 19.2%, 14.2% and 17.3%, respectively, compared to no returning control. In 5-10 cm soil layer, cotton straw returning increased the contents of 2-5 mm and >5 mm aggregates, reduced the content of <0.25 mm micro-aggregate, but significantly increased contents of soil organic carbon, available nitrogen and potassium by 19.6%, 12.6% and 23.4%, compared to no straw returning control. In 10-20 cm soil layer, cotton straw returning significantly reduced the content of <0.25 mm micro-aggregates, and significantly enhanced soil organic carbon, nitrogen, and potassium contents by 8.4%, 10.9% and 11.5%, compared to the control. However, in 20-30 cm soil layer, cotton straw returning only increased soil available potassium content by 12.0%, while there were no significant changes in particle size, organic carbon, nitrogen and phosphorus contents. We concluded that cotton straw returning could significantly improve the structure of surface soil by increasing the number of macro-aggregates, contents of organic carbon, available nitrogen and potassium in aggregates, while decreasing micro-aggregate content. The enhancement of the contribution of macro-aggregates to soil fertility by returning cotton straw could improve soil physical structure, fertility and then increase cotton yield.

PM10 emissions from aggregate fractions of an Entic Haplustoll under two contrasting tillage systems

NASA Astrophysics Data System (ADS)

Mendez, Mariano J.; Aimar, Silvia B.; Buschiazzo, Daniel E.

2015-12-01

Tillage systems affect physical and chemical properties of soils modifying its aggregation. How changes of the aggregate size distribution affect the capacity of the soil to emit fine particulate matter (PM10) to the atmosphere during wind erosion processes, is a less investigated issue. In order to answer this question, PM10 emissions from an Entic Haplustoll submitted to 25 years of continuous conventional tillage (LC) and no-till (NT) were analyzed. Soil samples were sieved with a rotary sieve in order to determine the aggregate size distribution (fractions : <0.42 mm, 0.42-0.84 mm, 0.84-2 mm, 2-6.4 mm, 6.4-19.2 mm, and >19.2 mm), the dry aggregate stability (DAS) and the erodible fraction (EF). The organic matter contents (OM), the particle size composition and the PM10 emission of each aggregate fraction were also measured. Results showed that NT promoted OM accumulations in all aggregate fractions which favored DAS and soil aggregation. The <0.42 mm sized aggregates (27%) predominated in CT and the >19.2 mm (41.7%) in NT, while the proportion of the other aggregate fractions was similar in both tillage systems. As a consequence of the smaller proportion of the <0.42 mm aggregates, the erodible fraction was lower in NT (EF: 17.3%) than in CT (30.8%). PM10 emissions of each aggregate fraction (AE) decreased exponentially with increasing size of the fractions in both tillage systems, mainly as a consequence of the smaller size and higher specific surface. AE was higher in CT than in NT for all aggregate fractions, but the higher differences were found in the <0.42 mm aggregates (18 μg g-1 in CT vs 8 μg g-1 in NT). The PM10 emission of the whole soil was three times higher in CT than in NT, while the emission of the erodible fraction (EFE) was in CT four times higher than in NT. PM10 emissions of the <0.42 mm aggregates represented over 50% of SE and 90% of EFE. We concluded that NT reduced the capacity of soils of the semiarid Pampas to emit PM10 because it produced a better aggregation that reduced the proportion and emission of the <0.42 mm aggregates. These aggregates had, by far, the highest emission potential.

Feedbacks Between Soil Structure and Microbial Activities in Soil

NASA Astrophysics Data System (ADS)

Bailey, V. L.; Smith, A. P.; Fansler, S.; Varga, T.; Kemner, K. M.; McCue, L. A.

2017-12-01

Soil structure provides the physical framework for soil microbial habitats. The connectivity and size distribution of soil pores controls the microbial access to nutrient resources for growth and metabolism. Thus, a crucial component of soil research is how a soil's three-dimensional structure and organization influences its biological potential on a multitude of spatial and temporal scales. In an effort to understand microbial processes at scale more consistent with a microbial community, we have used soil aggregates as discrete units of soil microbial habitats. Our research has shown that mean pore diameter (x-ray computed tomography) of soil aggregates varies with the aggregate diameter itself. Analyzing both the bacterial composition (16S) and enzyme activities of individual aggregates showed significant differences in the relative abundances of key members the microbial communities associated with high enzyme activities compared to those with low activities, even though we observed no differences in the size of the biomass, nor in the overall richness or diversity of these communities. We hypothesize that resources and substrates have stimulated key populations in the aggregates identified as highly active, and as such, we conducted further research that explored how such key populations (i.e. fungal or bacterial dominated populations) alter pathways of C accumulation in aggregate size domains and microbial C utilization. Fungi support and stabilize soil structure through both physical and chemical effects of their hyphal networks. In contrast, bacterial-dominated communities are purported to facilitate micro- and fine aggregate stabilization. Here we quantify the direct effects fungal versus bacterial dominated communities on aggregate formation (both the rate of aggregation and the quality, quantity and distribution of SOC contained within aggregates). A quantitative understanding of the different mechanisms through which fungi or bacteria shape aggregate formation could alter how we currently treat our predictions of soil biogeochemistry. Current predictions are largely site- or biome-specific; quantitative mechanisms could underpin "rules" that operate at the pore-scale leading to more robust, mechanistic models.

[Effects of Tillage on Distribution of Heavy Metals and Organic Matter Within Purple Paddy Soil Aggregates].

PubMed

Shi, Qiong-bin; Zhao, Xiu-lan; Chang, Tong-ju; Lu, Ji-wen

2016-05-15

A long-term experiment was utilized to study the effects of tillage methods on the contents and distribution characteristics of organic matter and heavy metals (Cu, Zn, Pb, Cd, Fe and Mn) in aggregates with different sizes (including 1-2, 0.25-1, 0.05-0.25 mm and < 0.05 mm) in a purple paddy soil under two tillage methods including flooded paddy field (FPF) and paddy-upland rotation (PR). The relationship between heavy metals and organic matter in soil aggregates was also analyzed. The results showed that the aggregates of two tillage methods were dominated by 0.05-0.25 mm and < 0.05 mm particle size, respectively. The contents of organic matter in each aggregate decreased with the decrease of aggregate sizes, however, compared to PR, FPF could significantly increase the contents of organic matter in soils and aggregates. The tillage methods did not significantly affect the contents of heavy metals in soils, but FPF could enhance the accumulation and distribution of aggregate, organic matter and heavy metals in aggregates with diameters of 1-2 mm and 0.25-1 mm. Correlation analysis found that there was a negative correlation between the contents of heavy metals and organic matter in soil aggregates, but a positive correlation between the amounts of heavy metal and organic matter accumulated in soil aggregates. From the slope of the correlation analysis equations, we could found that the sensitivities of heavy metals to the changes of soil organic matters followed the order of Mn > Zn > Pb > Cu > Fe > Cd under the same tillage. When it came to the same heavy metal, it was more sensitive in PR than in FPF.

Dynamics of soil biogeochemical gas emissions shaped by remolded aggregate sizes and carbon configurations under hydration cycles.

PubMed

Ebrahimi, Ali; Or, Dani

2018-01-01

Changes in soil hydration status affect microbial community dynamics and shape key biogeochemical processes. Evidence suggests that local anoxic conditions may persist and support anaerobic microbial activity in soil aggregates (or in similar hot spots) long after the bulk soil becomes aerated. To facilitate systematic studies of interactions among environmental factors with biogeochemical emissions of CO 2 , N 2 O and CH 4 from soil aggregates, we remolded silt soil aggregates to different sizes and incorporated carbon at different configurations (core, mixed, no addition). Assemblies of remolded soil aggregates of three sizes (18, 12, and 6 mm) and equal volumetric proportions were embedded in sand columns at four distinct layers. The water table level in each column varied periodically while obtaining measurements of soil GHG emissions for the different aggregate carbon configurations. Experimental results illustrate that methane production required prolonged inundation and highly anoxic conditions for inducing measurable fluxes. The onset of unsaturated conditions (lowering water table) resulted in a decrease in CH 4 emissions while temporarily increasing N 2 O fluxes. Interestingly, N 2 O fluxes were about 80% higher form aggregates with carbon placement in center (anoxic) core compared to mixed carbon within aggregates. The fluxes of CO 2 were comparable for both scenarios of carbon sources. These experimental results highlight the importance of hydration dynamics in activating different GHG production and affecting various transport mechanisms about 80% of total methane emissions during lowering water table level are attributed to physical storage (rather than production), whereas CO 2 emissions (~80%) are attributed to biological activity. A biophysical model for microbial activity within soil aggregates and profiles provides a means for results interpretation and prediction of trends within natural soils under a wide range of conditions. © 2017 John Wiley & Sons Ltd.

Impacts of Cropping Systems on Aggregates Associated Organic Carbon and Nitrogen in a Semiarid Highland Agroecosystem

PubMed Central

Chu, Jiashu; Zhang, Tianzhe; Chang, Weidong; Zhang, Dan; Zulfiqar, Saman; Fu, Aigen; Hao, Yaqi

2016-01-01

The effect of cropping system on the distribution of organic carbon (OC) and nitrogen (N) in soil aggregates has not been well addressed, which is important for understanding the sequestration of OC and N in agricultural soils. We analyzed the distribution of OC and N associated with soil aggregates in three unfertilized cropping systems in a 27-year field experiment: continuously cropped alfalfa, continuously cropped wheat and a legume-grain rotation. The objectives were to understand the effect of cropping system on the distribution of OC and N in aggregates and to examine the relationships between the changes in OC and N stocks in total soils and in aggregates. The cropping systems increased the stocks of OC and N in total soils (0–40 cm) at mean rates of 15.6 g OC m-2 yr-1 and 1.2 g N m-2 yr-1 relative to a fallow control. The continuous cropping of alfalfa produced the largest increases at the 0–20 cm depth. The OC and N stocks in total soils were significantly correlated with the changes in the >0.053 mm aggregates. 27-year of cropping increased OC stocks in the >0.053 mm size class of aggregates and N stocks in the >0.25 mm size class but decreased OC stocks in the <0.053 mm size class and N stocks in the <0.25 mm size class. The increases in OC and N stocks in these aggregates accounted for 99.5 and 98.7% of the total increases, respectively, in the continuous alfalfa system. The increases in the OC and N stocks associated with the >0.25 mm aggregate size class accounted for more than 97% of the total increases in the continuous wheat and the legume-grain rotation systems. These results suggested that long-term cropping has the potential to sequester OC and N in soils and that the increases in soil OC and N stocks were mainly due to increases associated with aggregates >0.053 mm. PMID:27764209

To what extent clay mineralogy affect soil aggregation? Insights from fractionation analyses conducted on soils under different land-uses.

NASA Astrophysics Data System (ADS)

Fernandez-Ugalde, O.; Barré, P.; Hubert, F.; Virto, I.; Girardin, C.; Ferrage, E.; Caner, L.; Chenu, C.

2012-04-01

Aggregation is a key process for soil functioning as it influences C storage, vulnerability to erosion and water holding capacity. While the influence of soil C content or tillage on aggregation has been documented, much less is known about the role of soil mineralogy. The aim of this study is to determine quantitatively if different clay minerals of a temperate soil contribute differently to aggregation and if their contribution is modulated by soil management. We compared the aggregate-size distribution of three cropping systems in a silt loam soil in Versailles (France): organic cropping system (ORG, tilled yearly), direct seeding mulch-based cropping system (DMC, tilled every 4 years), both from a long-term trial, and a nearby grassland. Soil samples from 0-5 cm were wet-sieved to 5 mm and air-dried before aggregate-size separation. For each aggregate class, fraction <2 µm was separated and analysed using X-ray diffraction. Organic C content was determined both in aggregates and <2-µm fractions. C content was lower in ORG than in the two other treatments. The proportion of large-macroaggregates (500-5000 µm) was greater in DMC and grassland; while microaggregates (50-250 µm) showed greater proportions in ORG. In the three treatments, microaggregates had the greatest amount of clays, with preferential accumulation of smectitic phases. In grassland, clays from all aggregated fractions showed more smectitic phases than free-clay fraction. The results indicate that smectitic phases contributed particularly to the microaggregates dynamics. Their contribution to aggregation was lower for larger aggregate sizes where the influence of organic matter was preponderant. Moreover, it was observed that cultivation (ORG and DMC treatments) reduced the relative enrichment of smectitic phases in stable aggregates which makes them more vulnerable to slaking erosion and alters their physico-chemical functions.

Influence of calcium carbonate and charcoal application on aggregation processes and organic matter retention at the silt-size scale

NASA Astrophysics Data System (ADS)

Asefaw Berhe, Asmeret; Kaiser, Michael; Ghezzehei, Teamrat; Myrold, David; Kleber, Markus

2013-04-01

The effectiveness of charcoal and calcium carbonate applications to improve soil conditions has been well documented. However, their influence on the formation of silt-sized aggregates and the amount and protection of associated organic matter (OM) against microbial decomposition is still largely unknown. For sustainable management of agricultural soils, silt-sized aggregates (2-53 µm) are of particularly large importance because they store up to 60% of soil organic carbon with mean residence times between 70 and 400 years. The objectives are i) to analyze the ability of CaCO3 and/or charcoal application to increase the amount of silt-sized aggregates and associated OM, ii) vary soil mineral conditions to establish relevant boundary conditions for amendment-induced aggregation processes, iii) to determine how amendment-induced changes in formation of silt-sized aggregates relate to microbial decomposition of OM. We set up artificial high reactive (HR, clay: 40%, sand: 57%, OM: 3%) and low reactive soils (LR, clay: 10%, sand: 89%, OM: 1%) and mixed them with charcoal (CC, 1%) and/or calcium carbonate (Ca, 0.2%). The samples were adjusted to a water potential of 0.3 bar and sub samples were incubated with microbial inoculum (MO). After a 16-weeks aggregation experiment, size fractions were separated by wet-sieving and sedimentation. Since we did not use mineral compounds in the artificial mixtures within the size range of 2 to 53 µm, we consider material recovered in this fraction as silt-sized aggregates, which was confirmed by SEM analyses. For the LR mixtures, we detected increasing N concentrations within the 2-53 µm fractions of the charcoal amended samples (CC, CC+Ca, and CC+Ca+MO) as compared to the Control sample with the strongest effect for the CC+Ca+MO sample. This indicates an association of N-containing microbial derived OM with silt-sized aggregates. For the charcoal amended LR and HR mixtures, the C concentrations of the 2-53 µm fractions are larger than those of the respective fractions of the Control samples but the effect is several times stronger for the LR mixtures. The C concentrations of the 2-53 µm fractions relative to the total C amount of the LR and HR mixtures are between 30 and 50%. The charcoal amended samples show generally larger relative C amounts associated with the 2-53 µm fractions than the Control samples. Benefits for aggregate formation and OM storage were larger for sand (LR) than for clay soil (HR). The gained data are similar to respective data for natural soils. Consequently, the suggested microcosm experiments are suitable to analyze mechanisms within soil aggregation processes.

Roundup Ready soybean gene concentrations in field soil aggregate size classes.

PubMed

Levy-Booth, David J; Gulden, Robert H; Campbell, Rachel G; Powell, Jeff R; Klironomos, John N; Pauls, K Peter; Swanton, Clarence J; Trevors, Jack T; Dunfield, Kari E

2009-02-01

Roundup Ready (RR) soybeans containing recombinant Agrobacterium spp. CP4 5-enol-pyruvyl-shikimate-3-phosphate synthase (cp4 epsps) genes tolerant to the herbicide glyphosate are extensively grown worldwide. The concentration of recombinant DNA from RR soybeans in soil aggregates was studied due to the possibility of genetic transformation of soil bacteria. This study used real-time PCR to examine the concentration of cp4 epsps in four field soil aggregate size classes (>2000 microm, 2000-500 microm, 500-250 microm and <250 microm). Aggregates over 2000 microm in diameter had significantly greater gene concentrations than those with diameters under 2000 microm. The >2000 mum fraction contained between 66.62% and 99.18% of total gene copies, although it only accounted for about 30.00% of the sampled soil. Aggregate formation may facilitate persistence of recombinant DNA.

Soil Aggregates and Organic Carbon Distribution in Red Soils after Long-term Fertilization with Different Fertilizer Treatments

NASA Astrophysics Data System (ADS)

Tang, J.; Wang, Y.

2013-12-01

Red soils, a typical Udic Ferrosols, widespread throughout the subtropical and tropical region in southern China, support the majority of grain production in this region. The red soil is naturally low in pH values, cation exchange capacity, fertility, and compaction, resulting in low organic matter contents and soil aggregation. Application of chemical fertilizers and a combination of organic-chemical fertilizers are two basic approaches to improve soil structure and organic matter contents. We studied the soil aggregation and the distribution of aggregate-associated organic carbon in red soils with a long-term fertilization experiment during 1988-2009. We established treatments including 1) NPK and NK in the chemical fertilizer plots, 2) CK (Control), and 3) CK+ Peanut Straw (PS), CK+ Rice Straw (RS), CK+ Fresh Radish (FR), and CK + Pig Manure (PM) in the organic-chemical fertilizer plots. Soil samples were fractionated into 6 different sized aggregate particles through the dry-wet sieving method according to the hierarchical model of aggregation. Organic carbon in the aggregate/size classes was analyzed. The results showed that the distribution of mechanically stable aggregates in red soils after long-term fertilization decreased with the size, from > 5mm, 5 ~ 2 mm, 2 ~ 1 mm, 1~ 0.25 mm, to < 0.25 mm, but the distribution of water-stable aggregates did not follow this pattern. Compared with the chemical fertilizer application alone, the addition of pig manure and green manure can significantly improve the distribution of aggregates in the 5-2 mm, 2-1 mm and 1-0.25 mm classes. The organic carbon (OC) contents in red soils were all increased after the long-term fertilization. Compared with Treatment NK, soil OC in Treatment NPK was increased by 45.4%. Compared with Treatment CK (low chemical fertilizer), organic fertilizer addition increased soil OC. The OC in the different particle of water-stable aggregates were all significantly increased after long-term fertilization. OC mainly existed in the macroaggregate (> 0.25 mm) of red soils after the long-term fertilization, and the organic matter was the most important colloid material for macroaggregates. We conclude that the long-term, appropriate application of chemical fertilizer and the combination with organic manure were the most effective measures to improve soil structure and organic carbon contents in red soil regions.

Differences in SOM decomposition and temperature sensitivity among soil aggregate size classes in a temperate grasslands.

PubMed

Wang, Qing; Wang, Dan; Wen, Xuefa; Yu, Guirui; He, Nianpeng; Wang, Rongfu

2015-01-01

The principle of enzyme kinetics suggests that the temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is inversely related to organic carbon (C) quality, i.e., the C quality-temperature (CQT) hypothesis. We tested this hypothesis by performing laboratory incubation experiments with bulk soil, macroaggregates (MA, 250-2000 μm), microaggregates (MI, 53-250 μm), and mineral fractions (MF, <53 μm) collected from an Inner Mongolian temperate grassland. The results showed that temperature and aggregate size significantly affected on SOM decomposition, with notable interactive effects (P<0.0001). For 2 weeks, the decomposition rates of bulk soil and soil aggregates increased with increasing incubation temperature in the following order: MA>MF>bulk soil >MI(P <0.05). The Q10 values were highest for MA, followed (in decreasing order) by bulk soil, MF, and MI. Similarly, the activation energies (Ea) for MA, bulk soil, MF, and MI were 48.47, 33.26, 27.01, and 23.18 KJ mol-1, respectively. The observed significant negative correlations between Q10 and C quality index in bulk soil and soil aggregates (P<0.05) suggested that the CQT hypothesis is applicable to soil aggregates. Cumulative C emission differed significantly among aggregate size classes (P <0.0001), with the largest values occurring in MA (1101 μg g-1), followed by MF (976 μg g-1) and MI (879 μg g-1). These findings suggest that feedback from SOM decomposition in response to changing temperature is closely associated withsoil aggregation and highlights the complex responses of ecosystem C budgets to future warming scenarios.

Total organic carbon in aggregates as a soil recovery indicator

NASA Astrophysics Data System (ADS)

Luciene Maltoni, Katia; Rodrigues Cassiolato, Ana Maria; Amorim Faria, Glaucia; Dubbin, William

2015-04-01

The soil aggregation promotes physical protection of organic matter, preservation of which is crucial to improve soil structure, fertility and ensure the agro-ecosystems sustainability. The no-tillage cultivation system has been considered as one of the strategies to increase total soil organic carbono (TOC) contents and soil aggregation, both are closely related and influenced by soil management systems. The aim of this study was to evaluate the distribution of soil aggregates and the total organic carbon inside aggregates, with regard to soil recovery, under 3 different soil management systems, i.e. 10 and 20 years of no-tillage cultivation as compared with soil under natural vegetation (Cerrado). Undisturbed soils (0-5; 5-10; and 10-20 cm depth) were collected from Brazil, Central Region. The soils, Oxisols from Cerrado, were collected from a field under Natural Vegetation-Cerrado (NV), and from fields that were under conventional tillage since 1970s, and 10 and 20 years ago were changed to no-tillage cultivation system (NT-10; NT-20 respectively). The undisturbed samples were sieved (4mm) and the aggregates retained were further fractionated by wet sieving through five sieves (2000, 1000, 500, 250, and 50 μm) with the aggregates distribution expressed as percentage retained by each sieve. The TOC was determined, for each aggregate size, by combustion (Thermo-Finnigan). A predominance of aggregates >2000 μm was observed under NV treatment (92, 91, 82 %), NT-10 (64, 73, 61 %), and NT-20 (71, 79, 63 %) for all three depths (0-5; 5-10; 10-20 cm). In addition greater quantities of aggregates in sizes 1000, 500, 250 and 50 μm under NT-10 and NT-20 treatments, explain the lower aggregate stability under these treatments compared to the soil under NV. The organic C concentration for NV in aggregates >2000 μm was 24,4; 14,2; 8,7 mg/g for each depth (0-5; 5-10; 10-20 cm, respectively), higher than in aggregates sized 250-50 μm (7,2; 5,5; 4,4 mg/g) for all depths. Although, with lower organic C contents, NT-10 and NT-20 presented the same behavior, i.e., greater amounts of organic C in bigger aggregates, (NT-10: 10,7; 9,5; 9,0 mg/g and NT-20: 18,8; 15,7; 8,6 mg/g, for each depth respectively 0-5; 5-10; 10-20 cm), and lower C contents in smaller aggregates (NT-10: 5,7; 6,1; 5,6 mg/g and NT-20: 8,2; 7,9; 6,3 mg/g , for each depth respectively 0-5; 5-10; 10-20 cm). The aggregates > 2000 μm, at 10-20 cm depth, showed similar C contents for NV, NT-10 and NT-20 (8,7; 9,0; 8,6 mg/g, respectively) suggesting that the C supply, even in natural environment, is not enough to increase organic C at 10-20 cm depth. The organic C concentration for aggregates sized 250-50 μm, in all three evaluated depths, is similar. Therefore, under NT-10 and NT-20 the smaller aggregates are not influenced by cultivation system, suggesting that the organic C inside the smaller aggregates can be retained for longer time in soil system. The results suggest, with regard to aggregate distribution and organic carbon content under NV, that soil under NT-20 is recovering. Acknowledgement: This study received financial support from CNPq

Solid-state 13C NMR experiments reveal effects of aggregate size on the chemical composition of particulate organic matter in grazed steppe soils

NASA Astrophysics Data System (ADS)

Steffens, M.; Kölbl, A.; Kögel-Knabner, I.

2009-04-01

Grazing is one of the most important factors that may reduce soil organic matter (SOM) stocks and subsequently deteriorate aggregate stability in grassland topsoils. Land use management and grazing reduction are assumed to increase the input of OM, improve the soil aggregation and change species composition of vegetation (changes depth of OM input). Many studies have evaluated the impact of grazing cessation on SOM quantity. But until today little is known about the impact of grazing cessation on the chemical quality of SOM in density fractions, aggregate size classes and different horizons. The central aim of this study was to analyse the quality of SOM fractions in differently sized aggregates and horizons as affected by increased inputs of organic matter due to grazing exclusion. We applied a combined aggregate size, density and particle size fractionation procedure to sandy steppe topsoils with different organic matter inputs due to different grazing intensities (continuously grazed = Cg, winter grazing = Wg, ungrazed since 1999 = Ug99, ungrazed since 1979 = Ug79). Three different particulate organic matter (POM; free POM, in aggregate occluded POM and small in aggregate occluded POM) and seven mineral-associated organic matter fractions were separated for each of three aggregate size classes (coarse = 2000-6300 m, medium = 630-2000 m and fine =

Effects of Pedogenic Fe Oxides on Soil Aggregate-Associated Carbon

NASA Astrophysics Data System (ADS)

Asefaw Berhe, A.; Jin, L.

2017-12-01

Carbon sequestration is intimately related to the soil structure, mainly soil aggregate dynamics. Carbon storage in soil aggregates has been recognized as an important carbon stabilization mechanism in soils. Organic matter and pedogenic Fe oxides are major binding agents that facilitate soil aggregate formation and stability. However, few studies have investigated how different forms of pedogenic Fe oxides can affect soil carbon distribution in different aggregate-size fractions. We investigated sequentially extracted pedogenic Fe oxides (in the order of organically complexed Fe extracted with sodium pyrophosphate, poorly-crystalline Fe oxides extracted with hydroxylamine hydrochloride, and crystalline Fe oxides extracted with dithionite hydrochloride) and determined the amount and nature of C in macroaggregates (2-0.25mm), microaggregates (0.25-0.053mm), and two silt and clay fractions (0.053-0.02mm, and <0.02mm) in Musick soil from Sierra Nevada mountain in California. We also determined how pedogenic Fe oxides affect soil carbon distribution along soil depth gradients. Findings of our study revealed that the proportion of organic matter complexed Fe decreased, but the proportion of crystalline Fe increased with increasing soil depths. Poorly crystalline Fe oxides (e.g. ferrihydrite) was identified as a major Fe oxide in surface soil, whereas crystalline Fe oxides (e.g. goethite) were found in deeper soil layers. These results suggest that high concentration of organic matter in surface soil suppressed Fe crystallization. Calcium cation was closely related to the pyrophosphate extractable Fe and C, which indicates that calcium may be a major cation that contribute to the organic matter complexed Fe and C pool. Increasing concentrations of extractable Fe and C with decreasing aggregate size fractions also suggests that Fe oxides play an important role in formation and stability of silt and clay fractions, and leading to further stabilization of carbon in soil. Our findings provide mechanistic understanding of how pedogenic Fe oxides play important role in carbon stabilization in different aggregate-size fractions in soil.

Soil organic carbon response to shrub encroachment regulated by soil aggregates

NASA Astrophysics Data System (ADS)

Zhu, Y.; Li, H.; Shen, H.; Feng, Y.; Fang, J.

2017-12-01

Shrub encroachment leads to change in soil organic carbon content, but there still exists a lot of uncertainty in its mechanism as it relates to deep soil research. Soil organic carbon is usually associated with stable aggregate quantity. In this study, we conducted a field investigation for typical steppe and desert steppe in Inner Mongolia with the view to examining the impact of shrub encroachment on soil organic carbon with soil aggregate at a depth of 0-500 cm. The results show that in the desert steppe, the particle size of soil aggregate content level in different depth are presented the trend of shrub patches is lower than the herb matrix, organic carbon content of soil aggregate under 50 cm deeper presents the trend of shrub patches is higher than herb matrix, eventually leading to shrub patches whole soil organic carbon in the 0 to 50 cm depth lower than the herb matrix, and in deeper soil below 50 cm higher than the herb matrix. In the typical steppe, there is no significant difference between soil aggregate structure of shrub patches and herb matrix, but organic carbon content of soil aggregate, especially large aggregate organic carbon content in the shrub patches is significantly higher than the herb matrix, so that the whole soil organic carbon content in the shrub patches is significantly higher than herb matrix. The rate of soil organic carbon content change (0-100 cm) by shrub encroachment showed significant negative correlation with the mean weight diameter of soil aggregate of herb matrix. We also found that the variations of soil organic carbon in desert steppe is not dominant by aggregates of some size, but the change of the typical steppe soil organic carbon mainly contributed by > 0.25 mm and 0.053-0.25 mm aggregates. The results suggested that the effects of shrub encroachment on soil organic carbon is regulated by soil aggregate, but it is varied for different type of grassland, which should provide some insights into our understanding on regional carbon budget under global environment change.

No tillage effect on water retention characteristics of soil aggregates in rainfed semiarid conditions.

NASA Astrophysics Data System (ADS)

Blanco-Moure, Nuria; López, M. Victoria; Moret, David

2010-05-01

The evaluation of changes in soil moisture retention characteristics associated to alterations in soil structure is of great interest in tillage studies. Most of these studies have evaluated soil properties in samples of total soil but not in individual aggregates. However, soil behavior at a macroscale level depends on the aggregate properties. A better knowledge of aggregate characteristics, as the water retention properties, will help to explain, for example, the response of soil to tillage, compaction and crop growth, and hence, to plan adequate soil management practices. In this study we determine the water retention curve of soil aggregates of different sizes from a soil under two tillage systems (conventional and no tillage). The study was carried out in a silty clay loam soil of semiarid Aragon (NE Spain). Two tillage systems were compared: no tillage (NT) and conventional tillage with mouldboard plough (CT). Water retention curves (WRC) were determined for soil surface aggregates (0-5 cm) of three different sizes (8-4, 4-2 and 2-1 mm in diameter) by using the TDR-pressure cell (Moret et al. 2008. Soil Till. Res, 100, 114-119). The TDR-pressure cell is a non-destructive method which permits determining WRC with the only one and same soil sample. Thus, the pressure cell was filled with aggregates up to 4 cm height, weighted and wetted to saturation from the bottom. Pressure steps were sequentially applied at -0.5, -1.5, -3, -5, -10, -33, -100, -300 kPa, and water content of each aggregate sample was measured gravimetrically and by TDR 24 h after starting each pressure head step. The volume of the sample within the cell was also determined at this moment in order to obtain the bulk density and thus calculate the volumetric water content. A good relationship was obtained between the volumetric water content calculated from the gravimetric water content and the corresponding values measured by TDR (r2=0.907; p≤0.05). Within the same tillage treatment, no significant differences in WRC were found among soil aggregate sizes. Soil aggregates under CT retained more water at lower pressure heads in all aggregate sizes; in contrast the retention was more effective in those from NT at high pressure level. The extensive structural degradation of the CT aggregates observed during wetting with the consequent decrease in the soil volume within the transparent cell, can help to explain the different behaviour of both soils. The CT aggregates were probably disintegrated by slaking, causing a reduction in water drainage and, therefore, an increase in soil water content at low pressure heads. This idea was also confirmed with the application of the double exponential function proposed by Dexter et al. (2008. Geoderma 173, 243-253). The WRC curves measured by TDR were successfully fitted to the theoretical model proposed by Dexter (r2=0.986; p≤0.05). Thus, the model estimated that the large porosity between aggregates retain slightly more water under CT (0.36-0.39 m3 m-3) than under NT (0.31-0.35 m3 m-3). On the contrary, pores inside the aggregates tend to storage more water in NT (0.16-0.20 m3 m-3vs. 0.13-0.17 m3 m-3 in CT). These results show the suitability of NT to reduce the risk of soil crusting and compaction in agricultural lands of Aragón.

Effect of aggregate structure on VOC gas adsorption onto volcanic ash soil.

PubMed

Hamamoto, Shoichiro; Seki, Katsutoshi; Miyazaki, Tsuyoshi

2009-07-15

The understanding of the gaseous adsorption process and the parameters of volatile organic compounds such as organic solvents or fuels onto soils is very important in the analysis of the transport or fate of these chemicals in soils. Batch adsorption experiments with six different treatments were conducted to determine the adsorption of isohexane, a gaseous aliphatic, onto volcanic ash soil (Tachikawa loam). The measured gas adsorption coefficient for samples of Tachikawa loam used in the first three treatments, Control, AD (aggregate destroyed), and AD-OMR (aggregate destroyed and organic matter removed), implied that the aggregate structure of volcanic ash soil as well as organic matter strongly enhanced gas adsorption under the dry condition, whereas under the wet condition, the aggregate structure played an important role in gas adsorption regardless of the insolubility of isohexane. In the gas adsorption experiments for the last three treatments, soils were sieved in different sizes of mesh and were separated into three different aggregate or particle size fractions (2.0-1.0mm, 1.0-0.5mm, and less than 0.5mm). Tachikawa loam with a larger size fraction showed higher gas adsorption coefficient, suggesting the higher contributions of macroaggregates to isohexane gas adsorption under dry and wet conditions.

Biological framework for soil aggregation: Implications for ecological functions.

NASA Astrophysics Data System (ADS)

Ghezzehei, Teamrat; Or, Dani

2016-04-01

Soil aggregation is heuristically understood as agglomeration of primary particles bound together by biotic and abiotic cementing agents. The organization of aggregates is believed to be hierarchical in nature; whereby primary particles bond together to form secondary particles and subsequently merge to form larger aggregates. Soil aggregates are not permanent structures, they continuously change in response to internal and external forces and other drivers, including moisture, capillary pressure, temperature, biological activity, and human disturbances. Soil aggregation processes and the resulting functionality span multiple spatial and temporal scales. The intertwined biological and physical nature of soil aggregation, and the time scales involved precluded a universally applicable and quantifiable framework for characterizing the nature and function of soil aggregation. We introduce a biophysical framework of soil aggregation that considers the various modes and factors of the genesis, maturation and degradation of soil aggregates including wetting/drying cycles, soil mechanical processes, biological activity and the nature of primary soil particles. The framework attempts to disentangle mechanical (compaction and soil fragmentation) from in-situ biophysical aggregation and provides a consistent description of aggregate size, hierarchical organization, and life time. It also enables quantitative description of biotic and abiotic functions of soil aggregates including diffusion and storage of mass and energy as well as role of aggregates as hot spots of nutrient accumulation, biodiversity, and biogeochemical cycles.

Influence of pore structure on carbon retention/loss in soil macro-aggregates

NASA Astrophysics Data System (ADS)

Quigley, Michelle; Kravchenko, Alexandra; Rivers, Mark

2017-04-01

Carbon protection within soil macro-aggregates is an important component of soil carbon sequestration. Pores, as the transportation network for microorganisms, water, air and nutrients within macro-aggregates, are among the factors controlling carbon protection through restricting physical accessibility of carbon to microorganisms. The understanding of how the intra-aggregate pore structure relates to the degree of carbon physical protection, however, is currently lacking. This knowledge gap can lead to potentially inaccurate models and predictions of soil carbon's fate and storage in future changing climates. This study utilized the natural isotopic difference between C3 and C4 plants to trace the location of newly added carbon within macro-aggregates before and after decomposition and explored how location of this carbon relates to characteristics of intra-aggregate pores. To mimic the effect of decomposition, aggregates were incubated at 23˚ C for 28 days. Computed micro-tomographic images were used to determine pore characteristics at 6 μm resolution before and after incubation. Soil (0-10 cm depth) from a 20 year continuous corn (C4 plant) experiment was used. Two soil treatments were considered: 1) "destroyed-structure", where 1 mm sieved soil was used and 2) "intact-structure", where intact blocks of soil were used. Cereal rye (Secale cereale L.) (C3 plant) was grown in the planting boxes (2 intact, 3 destroyed, and one control) for three months in a greenhouse. From each box, ˜5 macro-aggregates of ˜5 mm size were collected for a total of 27 macro-aggregates. Half of the aggregates were cut into 5-11 sections, with relative positions of the sections within the aggregate recorded, and analyzed for δ13C. The remaining aggregates were incubated and then subjected to cutting and δ13C analysis. While there were no significant differences between the aggregate pore size distributions of the two treatments, the roles that specific pores sizes played in carbon protect were disparate. In intact-structure aggregates, prior to incubation, there was no association between carbon distribution and pores. After incubation, significant correlations (α=0.05) were observed between abundance of 6-40 μm pores and both soil organic carbon (SOC) and δ13C. Sections containing more 6-40 μm pores also had increased amounts of SOC (r2=0.23) with higher presence of C4 carbon (r2=0.27). This indicates preferential preservation of older carbon in the pores of this size range. Prior to incubation, destroyed-structure aggregates had higher amounts of C3 carbon associated with 40-95 μm pores (r2=0.14), pointing to a greater presence of newly added carbon within these pores. However, after incubation there was a significant loss of SOC from these pores (r2=0.22) and, specifically, the loss of C3 carbon (r2=0.16). In the studied soil, pores of 6-40 μm size range appeared to control the preservation of older carbon, while 40-95 μm pores controlled the fate of newly added carbon. Older carbon preservation in 6-40 μm pores was mostly observed in macro-aggregates from the soil with intact structure, while the associations between 40-95 μm pores and gains and losses of newly added carbon were primarily observed in the macro-aggregates that were formed anew in the sieved soil during the plant growing experiment.

Changes in carbon stability and microbial activity in size fractions of micro-aggregates in a rice soil chronosequence under long term rice cultivation

NASA Astrophysics Data System (ADS)

Pan, Genxing; Liu, Yalong; Wang, Ping; Li, Lianqinfg; Cheng, Kun; Zheng, Jufeng; Zhang, Xuhui; Zheng, Jinwei; Bian, Rongjun; Ding, Yuanjun; Ma, Chong

2016-04-01

Recent studies have shown soil carbon sequestration through physical protection of relative labile carbon intra micro-aggregates with formation of large sized macro-aggregates under good management of soil and agricultural systems. While carbon stabilization had been increasingly concerned as ecosystem properties, the mechanisms underspin bioactivity of soil carbon with increased carbon stability has been still poorly understood. In this study, topsoil samples were collected from rice soils derived from salt marsh under different length of rice cultivation up to 700 years from eastern China. Particle size fractions (PSF) of soil aggregates were separated using a low energy dispersion protocol. Carbon fractions in the PSFs were analyzed either with FTIR spectroscopy. Soil microbial community of bacterial, fungal and archaeal were analyzed with molecular fingerprinting using specific gene primers. Soil respiration and carbon gain from amended maize as well as enzyme activities were measured using lab incubation protocols. While the PSFs were dominated by the fine sand (200-20μm) and silt fraction (20-2μm), the mass proportion both of sand (2000-200μm) and clay (<2μm) fraction increased with prolonged rice cultivation, giving rise to an increasing trend of mean weight diameter of soil aggregates (also referred to aggregate stability). Soil organic carbon was found most enriched in coarse sand fraction (40-60g/kg), followed by the clay fraction (20-24.5g/kg), but depleted in the silt fraction (~10g/kg). Phenolic and aromatic carbon as recalcitrant pool were high (33-40% of total SOC) in both coarse sand and clay fractions than in both fine sand and silt fractions (20-29% of total SOC). However, the ratio of LOC/total SOC showed a weak decreasing trend with decreasing size of the aggregate fractions. Total gene content in the size fractions followed a similar trend to that of SOC. Bacterial and archaeal gene abundance was concentrated in both sand and clay fractions but that of fungi in sand fraction, and sharply decreased with the decreasing size of aggregate fraction. Gene abundance of archaeal followed a similar trend to that of bacterial but showing an increasing trend with prolonged rice cultivation in both sand and clay fractions. Change in community diversity with sizes of aggregate fractions was found of fungi and weakly of bacterial but not of archaeal. Soil respiration ratio (Respired CO2-C to SOC) was highest in silt fraction, followed by the fine sand fraction but lowest in sand and clay fractions in the rice soils cultivated over 100 years. Again, scaled by total gen concentration, respiration was higher in silt fraction than in other fractions for these rice soils. For the size fractions other than clay fraction, soil gene concentration, Archaeal gen abundance, normalized enzyme activity and carbon sequestration was seen increased but SOC- and gene- scaled soil respiration decreased, more or less with prolonged rice cultivation. As shown with regression analysis, SOC content was positively linearly correlated to recalcitrant carbon proportion but negatively linearly correlated to labile carbon, in both sand and clay fractions. However, soil respiration was found positively logarithmically correlated to total DNA contents and bacterial gen abundance in both sand and clay fractions. Total DNA content was found positively correlated to SOC and labile carbon content, recalcitrant carbon proportion and normalized enzyme activity but negatively to soil respiration, in sand fraction only. Our findings suggested that carbon accumulation and stabilization was prevalent in both sand and clay fraction, only the coarse sand fraction was found responsible for bioactivity dynamics in the rice soils. Thus, soil carbon sequestration was primarily by formation of the macro-aggregates, which again mediated carbon stability and bioactivity in the rice soils under long term rice cultivation.

AggModel: A soil organic matter model with measurable pools for use in incubation studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Segoli, Moran; De Gryze, S.; Dou, Fugen

2013-01-01

Current soil organic matter (SOM) models are empirical in nature by employing few conceptual SOM pools that have a specific turnover time, but that are not measurable and have no direct relationship with soil structural properties. Most soil particles are held together in aggregates and the number, size and stability of these aggregates significantly affect the size and amount of organic matter contained in these aggregates, and its susceptibility to decomposition. While it has been shown that soil aggregates and their dynamics can be measured directly in the laboratory and in the field, the impact of soil aggregate dynamics onmore » SOM decomposition has not been explicitly incorporated in ecosystem models. Here, we present AggModel, a conceptual and simulation model that integrates soil aggregate and SOM dynamics. In AggModel, we consider unaggregated and microaggregated soil that can exist within or external to macroaggregated soil. Each of the four aggregate size classes contains particulate organic matter and mineral-associated organic matter fractions. We used published data from laboratory incubations to calibrate and validate the biological and environmental effects on the rate of formation and breakdown of macroaggregates and microaggregates, and the organic matter dynamics within these different aggregate fractions. After calibration, AggModel explained more than 70% of the variation in aggregate masses and over 90% of the variation in aggregate-associated carbon. The model estimated the turnover time of macroaggregates as 32 days and 166 days for microaggregates. Sensitivity analysis of AggModel parameterization supported the notion that macroaggregate turnover rate has a strong control over microaggregate masses and, hence, carbon sequestration. In addition to AggModel being a proof-of-concept, the advantage of a model that is based on measurable SOM fractions is that its internal structure and dynamics can be directly calibrated and validated by using experimental data. In conclusion, AggModel successfully incorporates the explicit representation for the turnover of soil aggregates and their influence on SOM dynamics and can form the basis for new SOM modules within existing ecosystem models.« less

Limited protection of macro-aggregate-occluded organic carbon in Siberian steppe soils

NASA Astrophysics Data System (ADS)

Bischoff, Norbert; Mikutta, Robert; Shibistova, Olga; Puzanov, Alexander; Silanteva, Marina; Grebennikova, Anna; Fuß, Roland; Guggenberger, Georg

2017-05-01

Macro-aggregates especially in agricultural steppe soils are supposed to play a vital role for soil organic carbon (OC) stabilization at a decadal timescale. While most research on soil OC stabilization in steppes focused on North American prairie soils of the Great Plains with information mainly provided by short-term incubation experiments, little is known about the agricultural steppes in southwestern Siberia, though they belong to the greatest conversion areas in the world and occupy an area larger than that in the Great Plains. To quantify the proportion of macro-aggregate-protected OC under different land use as function of land use intensity and time since land use change (LUC) from pasture to arable land in Siberian steppe soils, we determined OC mineralization rates of intact (250-2000 µm) and crushed (< 250 µm) macro-aggregates in long-term incubations over 401 days (20 °C; 60 % water holding capacity) along two agricultural chronosequences in the Siberian Kulunda steppe. Additionally, we incubated bulk soil (< 2000 µm) to determine the effect of LUC and subsequent agricultural use on a fast and a slow soil OC pool (labile vs. more stable OC), as derived from fitting exponential-decay models to incubation data. We hypothesized that (i) macro-aggregate crushing leads to increased OC mineralization due to an increasing microbial accessibility of a previously occluded labile macro-aggregate OC fraction, and (ii) bulk soil OC mineralization rates and the size of the fast OC pool are higher in pasture than in arable soils with decreasing bulk soil OC mineralization rates and size of the fast OC pool as land use intensity and time since LUC increase. Against our hypothesis, OC mineralization rates of crushed macro-aggregates were similar to those of intact macro-aggregates under all land use regimes. Macro-aggregate-protected OC was almost absent and accounted for < 1 % of the total macro-aggregate OC content and to a maximum of 8 ± 4 % of mineralized OC. In accordance to our second hypothesis, highest bulk soil OC mineralization rates and sizes of the fast OC pool were determined under pasture, but mineralization rates and pool sizes were unaffected by land use intensity and time since LUC. However, at one chronosequence mean residence times of the fast and slow OC pool tended to decrease with increasing time since establishment of arable use. We conclude that the tillage-induced breakdown of macro-aggregates has not reduced the OC contents in the soils under study. The decline of OC after LUC is probably attributed to the faster soil OC turnover under arable land as compared to pasture at a reduced plant residue input.

Effect of Soil Water Content on the Distribution of Diuron into Organomineral Aggregates of Highly Weathered Tropical Soils.

PubMed

Regitano, Jussara B; Rocha, Wadson S D; Bonfleur, Eloana J; Milori, Debora; Alleoni, Luís R F

2016-05-25

We evaluated the effects of soil water content on the retention of diuron and its residual distribution into organomineral aggregates in four Brazilian oxisols. (14)C-Diuron was incubated for days at 25, 50, and 75% of maximum water-holding capacity for each soil. After 42 days, the physical fractionation method was used to obtain >150, 53-150, 20-53, 2-20, and <2 μm aggregate sizes. Diuron retention increased with increasing soil water content for all soils. At lower soil water content, diuron's retention was higher in the sandier soil. It was mostly retained in the fine (<20 μm) aggregates of sandier soil, and for clayed soils, retention was higher in the coarse aggregates (>53 μm). The sorption coefficients (Kd and Koc) generated by batch studies should be carefully used because they do not provide information about aggregation and diffusion effects on pesticides soil sorption.

Aggregate distribution and associated organic carbon influenced by cover crops

NASA Astrophysics Data System (ADS)

Barquero, Irene; García-González, Irene; Benito, Marta; Gabriel, Jose Luis; Quemada, Miguel; Hontoria, Chiquinquirá

2013-04-01

Replacing fallow with cover crops during the non-cropping period seems to be a good alternative to diminish soil degradation by enhancing soil aggregation and increasing organic carbon. The aim of this study was to analyze the effect of replacing fallow by different winter cover crops (CC) on the aggregate distribution and C associated of an Haplic Calcisol. The study area was located in Central Spain, under semi-arid Mediterranean climate. A 4-year field trial was conducted using Barley (Hordeum vulgare L.) and Vetch (Vicia sativa L.) as CC during the intercropping period of maize (Zea mays L.) under irrigation. All treatments were equally irrigated and fertilized. Maize was directly sown over CC residues previously killed in early spring. Composite samples were collected at 0-5 and 5-20 cm depths in each treatment on autumn of 2010. Soil samples were separated by wet sieving into four aggregate-size classes: large macroaggregates ( >2000 µm); small macroaggregates (250-2000 µm); microaggregates (53-250 µm); and < 53 µm (silt + clay size). Organic carbon associated to each aggregate-size class was measured by Walkley-Black Method. Our preliminary results showed that the aggregate-size distribution was dominated by microaggregates (48-53%) and the <53 µm fraction (40-44%) resulting in a low mean weight diameter (MWD). Both cover crops increased aggregate size resulting in a higher MWD (0.28 mm) in comparison with fallow (0.20 mm) in the 0-5 cm layer. Barley showed a higher MWD than fallow also in 5-20 cm layer. Organic carbon concentrations in aggregate-size classes at top layer followed the order: large macroaggregates > small macroaggregates > microaggregates > silt + clay size. Treatments did not influence C concentration in aggregate-size classes. In conclusion, cover crops improved soil structure increasing the proportion of macroaggregates and MWD being Barley more effective than Vetch at subsurface layer.

Spatial distribution of soil water repellency in a grassland located in Lithuania

NASA Astrophysics Data System (ADS)

Pereira, Paulo; Novara, Agata

2014-05-01

Soil water repellency (SWR) it is recognized to be very heterogeneous in time in space and depends on soil type, climate, land use, vegetation and season (Doerr et al., 2002). It prevents or reduces water infiltration, with important impacts on soil hydrology, influencing the mobilization and transport of substances into the soil profile. The reduced infiltration increases surface runoff and soil erosion. SWR reduce also the seed emergency and plant growth due the reduced amount of water in the root zone. Positive aspects of SWR are the increase of soil aggregate stability, organic carbon sequestration and reduction of water evaporation (Mataix-Solera and Doerr, 2004; Diehl, 2013). SWR depends on the soil aggregate size. In fire affected areas it was founded that SWR was more persistent in small size aggregates (Mataix-Solera and Doerr, 2004; Jordan et al., 2011). However, little information is available about SWR spatial distribution according to soil aggregate size. The aim of this work is study the spatial distribution of SWR in fine earth (<2 mm) and different aggregate sizes, 2-1 mm, 1-0.5 mm, 0.5-0.25 mm and <0.25 mm. The studied area is located near Vilnius (Lithuania) at 54° 42' N, 25° 08 E, 158 masl. A plot with 400 m2 (20 x 20 m with 5 m space between sampling points) and 25 soil samples were collected in the top soil (0-5 cm) and taken to the laboratory. Previously to SWR assessment, the samples were air dried. The persistence of SWR was analysed according to the Water Drop Penetration Method, which involves placing three drops of distilled water onto the soil surface and registering the time in seconds (s) required for the drop complete penetration (Wessel, 1988). Data did not respected Gaussian distribution, thus in order to meet normality requirements it was log-normal transformed. Spatial interpolations were carried out using Ordinary Kriging. The results shown that SWR was on average in fine earth 2.88 s (Coeficient of variation % (CV%)=44.62), 2-1mm 1.73 s (CV%=45.10), 1-0.5 mm 2.02 s (CV%=93.75), 0.5-0.25 mm 3.12 s (CV%=233.68) and in <0.25 mm 15.54 mm (CV%=240.74). This suggests that SWR persistence and CV% is higher in small size aggregates than in the coarser aggregate sizes. The interpolated maps showed that in fine earth SWR was higher in the western part of the studied plot and lower in the central area. In the 2-1 mm aggregate size it was higher in the southwest and lower at north and northwest area. In the 1-0.5 mm aggregate size it was lower in the central area and higher in the southwest. In the 0.5-0.25 mm aggregate size it was higher in the west part and lower in the north of the plot and. In the <0.25 mm no specific pattern was identified and the SWR was heterogeneously distributed. This suggests that the spatial distribution of SWR is very different according to the aggregate size. Future studies are needed in order to identify the causes and consequences of such dynamic. Acknowledgements The authors appreciated the support of the project "Litfire", Fire effects in Lithuanian soils and ecosystems (MIP-048/2011) funded by the Lithuanian Research Council References Diehl, D. (2013) Soil water repellency: Dynamics of heterogeneous surfaces, Colloids and surfaces A: Physicochem. Eng. Aspects, 432, 8-18. Doerr, S.H., Shakesby, R.A., and Walsh, R.P.D. (2000) Soil water repellency: its causes, characteristics and hydro-geomorphological significance, Earth-Science Reviews, 51, 33-65. Jordan, A., Zavala, L., Mataix-Solera, J., Nava, A.L., Alanis, N. (2011) Effects of fire severity on water repellency and agregate stability on mexican volcanic soils, Catena, 84, 136-147. Mataix-Solera, J., Doerr, S. (2004) hydrophobicity and agregate stability in calcareous topsoils from fire-affected pine forests in south-easthern Spain, Geoderma, 118, 77-88. Wessel, A.T. (1988) On using the effective contact angle and the water drop penetration time for classification of water repellency in dune soils, Earth Surfaces Process. Landforms, 13, 555-562, 1988.

Effect of long-term combined application of organic and inorganic fertilizers on soil nematode communities within aggregates

PubMed Central

Zhang, Zhiyong; Zhang, Xiaoke; Mahamood, Md.; Zhang, Shuiqing; Huang, Shaomin; Liang, Wenju

2016-01-01

A long-term fertilization experiment was conducted to examine the effects of different fertilization practices on nematode community composition within aggregates in a wheat-maize rotation system. The study was a randomized complete block design with three replicates. The experiment involved the following four treatments: no fertilizer, inorganic N, P and K fertilizer (NPK), NPK plus manure (NPKM) and NPK plus maize straw (NPKS). Soil samples were taken at 0–20 cm depth during the wheat harvest stage. Based on our results, NPKS contributed to soil aggregation and moisture retention, with a positive effect on soil total nitrogen accumulation, particularly within small macroaggregates (0.25–1 mm) and microaggregates (<0.25 mm). The C/N ratio was correlated to the distribution of the soil nematode community. Both manure application and straw incorporation increased the nematode functional metabolic footprints within all aggregates. Additionally, the functional metabolic footprints decreased with a decline in aggregate size. The accumulation of total nitrogen within <1 mm aggregates under NPKS might play a key role in maintaining the survival of soil nematodes. In our study, both crop straw incorporation and inorganic fertilizer application effectively improved soil physicochemical properties and were also beneficial for nematode survival within small aggregate size fractions. PMID:27502433

Effect of long-term combined application of organic and inorganic fertilizers on soil nematode communities within aggregates.

PubMed

Zhang, Zhiyong; Zhang, Xiaoke; Mahamood, Md; Zhang, Shuiqing; Huang, Shaomin; Liang, Wenju

2016-08-09

A long-term fertilization experiment was conducted to examine the effects of different fertilization practices on nematode community composition within aggregates in a wheat-maize rotation system. The study was a randomized complete block design with three replicates. The experiment involved the following four treatments: no fertilizer, inorganic N, P and K fertilizer (NPK), NPK plus manure (NPKM) and NPK plus maize straw (NPKS). Soil samples were taken at 0-20 cm depth during the wheat harvest stage. Based on our results, NPKS contributed to soil aggregation and moisture retention, with a positive effect on soil total nitrogen accumulation, particularly within small macroaggregates (0.25-1 mm) and microaggregates (<0.25 mm). The C/N ratio was correlated to the distribution of the soil nematode community. Both manure application and straw incorporation increased the nematode functional metabolic footprints within all aggregates. Additionally, the functional metabolic footprints decreased with a decline in aggregate size. The accumulation of total nitrogen within <1 mm aggregates under NPKS might play a key role in maintaining the survival of soil nematodes. In our study, both crop straw incorporation and inorganic fertilizer application effectively improved soil physicochemical properties and were also beneficial for nematode survival within small aggregate size fractions.

Lignin characteristics in soil profiles of different plant communities in a subtropical mixed forest in Central China

NASA Astrophysics Data System (ADS)

Liu, F.; Wang, X.

2016-12-01

Lignin is widely considered as a major source of stable soil carbon, its content and degradation states are important indicators of soil carbon quality and stability. Few studies have explored the effects of plant communities on lignin characteristics in soils, and studies on lignin characteristics across soil depths resulted in contradictory findings. In this study, we investigated the lignin contents, their degradation states in the soil aggregates across three soil depths for four major plant communities in a subtropical mixed forest in central China. We found that lignin content in the litter of two deciduous species (Carpinus fargesii CF and Fagus Lucida FL) are higher than that in the two evergreen species ( Cyclobalanopsis multinervis CM and Schima parviflora SP). These differences maintained in the soil with a diminished scale. Lignin content showed a decreased trend in soil profiles of all plant communities, but no significant differences of degradation states were observed. The distribution of aggregation fractions was significantly different among plant communities, the SP community have higher percent of >2000 μm fraction (50.46%) and lower percent of <0.25 μm fraction (12.87%) than the CF community (40.05%, 21.90% respectively). The lignin content increased with decreasing aggregations size, however, no significant differences of lignin degradation states was observed among the four size aggregations. These results collectively reveal the influence of plant communities on lignin characteristics in soil, probably through litter input. Similar degradation states of lignin across soil profile and different size aggregates emphasized the importance of lignin movements association with soil water. This knowledge of lignin characteristics across soil profile can improve our understanding of soil carbon stability at different depths and how it may respond to changes in soil conditions.

[Profile distribution of soil aggregates organic carbon in primary forests in Karst cluster-peak depression region].

PubMed

Lu, Ling-Xiao; Song, Tong-Qing; Peng, Wan-Xia; Zeng, Fu-Ping; Wang, Ke-Lin; Xu, Yun-Lei; Yu, Zi; Liu, Yan

2012-05-01

Soil profiles were collected from three primary forests (Itoa orientalis, Platycladus orientalis, and Radermachera sinica) in Karst cluster-peak depression region to study the composition of soil aggregates, their organic carbon contents, and the profile distribution of the organic carbon. In the three forests, >2 mm soil aggregates were dominant, occupying about 76% of the total. The content of soil total organic carbon ranged from 12.73 to 68.66 g x kg(-1), with a significant difference among the forests. The organic carbon content in <1 mm soil aggregates was slightly higher than that in >2 mm soil aggregates, but most of soil organic carbon was stored in the soil aggregates with greater particle sizes. About 70% of soil organic carbon came from >2 mm soil aggregates. There was a significant positive relationship between the contents of 2-5 and 5-8 mm soil aggregates and the content of soil organic carbon. To increase the contents of 2-8 mm soil aggregates could effectively improve the soil carbon sequestration in Karst region. In Itoa orientalis forest, 2-8 mm soil aggregates accounted for 46% of the total, and the content of soil total organic carbon reached to 37.62 g x kg(-1), which implied that Itoa orientalis could be the suitable tree species for the ecological restoration in Karst region.

Leaching characteristics of EDTA-enhanced phytoextraction of Cd and Pb by Zea mays L. in different particle-size fractions of soil aggregates exposed to artificial rain.

PubMed

Lu, Yayin; Luo, Dinggui; Lai, An; Liu, Guowei; Liu, Lirong; Long, Jianyou; Zhang, Hongguo; Chen, Yongheng

2017-01-01

Chelator-assisted phytoextraction is an alternative and effective technique for the remediation of heavy metal-contaminated soils, but the potential for heavy metal leaching needs to be assessed. In the present study, a soil column cultivation-leaching experiment was conducted to investigate the Cd and Pb leaching characteristics during assisted phytoextraction of metal-contaminated soils containing different particle-size soil aggregates. The columns were planted with Zea mays "Zhengdan 958" seedlings and treated with combined applications of EDTA and simulated rainfall (pH 4.5 or 6.5). The results were as follows: (1) The greatest uptake of Cd and Pb by Z. mays was observed after treatment with EDTA (2.5 mmol kg -1 soil) and soil aggregates of <1 mm; uptake decreased as the soil aggregate size increased. (2) Simulated rainfall, especially acid rain (pH 4.5), after EDTA applications led to the increasing metal concentrations in the leachate, and EDTA significantly increased the concentrations of both Cd and Pb in the leachate, especially with soil aggregates of <1 mm; metal leachate concentrations decreased as soil particle sizes increased. (3) Concentrations of Cd and Pb decreased with each continuing leachate collection, and data were fit to linear regression models with coefficients of determination (R 2 ) above 0.90 and 0.87 for Cd and Pb, respectively. The highest total amounts of Cd (22.12%) and Pb (19.29%) were observed in the leachate of soils treated with EDTA and artificial acid rain (pH 4.5) with soil aggregates of <1 mm. The application of EDTA during phytoextraction method increased the leaching risk in the following order: EDTA 2.5-1 (pH 4.5) > EDTA 2.5-1 (pH 6.5) > EDTA 2.5-2 (pH 4.5) > EDTA 2.5-4 (pH 4.5) > EDTA 2.5-2 (pH 6.5) > EDTA 2.5-4 (pH 6.5).

Bacterial diversity of soil aggregates of different sizes in various land use conditions

NASA Astrophysics Data System (ADS)

Ivanova, Ekaterina; Azida, Thakahova; Olga, Kutovaya

2014-05-01

The patterns of soil microbiome structure may be a universal and very sensitive indicator of soil quality (soil "health") used for optimization and biologization of agricultural systems. The understanding of how microbial diversity influenses, and is influenced by, the environment can only be attained by analyses at scales relevant to those at which processes influencing microbial diversity actually operate. The basic structural and functional unit of the soil is a soil aggregate, which is actually a microcosm of the associative co-existing groups of microorganisms that form characteristic ecological food chains. It is known that many important microbial processes occur in spatially segregated microenvironments in soil leading to a microscale biogeography. The Metagenomic library of typical chernozem in conditions of different land use systems was created. Total genomic DNA was extracted from 0.5 g of the frozen soil after mechanical destruction. Sample preparation and sequencing was performed on a GS Junior ("Roche»", Switzerland) according to manufacturer's recommendations, using the universal primers to the variable regions V4 gene 16S - rRNA - F515 (GTGCCAGCMGCCGCGGTAA) and R806 (GGACT-ACVSGGGTATCTAAT). It is shown that the system of land use is a stronger determinant of the taxonomic composition of the soil microbial community, rather than the size of the structural units. In soil samples from different land use systems the presence of accessory components was revealed. They may be used as indicators of processes of soil recovery, soil degradation or soil exhaustion processes occuring in the agroecosystems. The comparative analysis of microbial communities of chernozem aggregates investigated demonstrates the statistically valuable differences in the amount of bacterial phyla and Archean domain content as well as the species richness in aggregates of various size fractions. The occurrence of specific components in the taxonomic structure of micro-and macro-aggregates may indicate the presence of a certain size fraction in the structure of the investigated soil. The study of soils' metagenome is promising for the development of both soil microbiology, and for the soil processes trends in soils of anthropogenic origin.

The structure of microbial community in aggregates of a typical chernozem aggregates under contrasting variants of its agricultural use

NASA Astrophysics Data System (ADS)

Ivanova, E. A.; Kutovaya, O. V.; Tkhakakhova, A. K.; Chernov, T. I.; Pershina, E. V.; Markina, L. G.; Andronov, E. E.; Kogut, B. M.

2015-11-01

The taxonomic structure of microbiomes in aggregates of different sizes from typical chernozems was investigated using sequencing of the 16S rRNA gene. The aggregate fractions of <0.25, 2-5, and >7 mm obtained by sieving of the soil samples at natural moisture were used for analysis. The highest prokaryote biomass (bacteria, archaea) was determined in the fractions <0.25 and aggregates 2-5 mm; the bacterial and archaeal biomass decreased in the following series: fallow > permanent black fallow > permanent winter wheat. The greatest number of fungi was recorded in the fraction <0.25 mm from the soils of the permanent black fallow and in all the studied aggregate fractions in the variant with permanent wheat. The system of agricultural use affected more significantly the structure of the prokaryote community in the chernozem than the size of aggregate fractions did. The most diverse microbial community was recorded in the soil samples of the fallow; the statistically significant maximums of the Shannon diversity indices and indices of phylogenetic diversity (PD) were recorded in the fractions <0.25 and 2-5 mm from the fallow soil. On the whole, the fine soil fractions (<0.25 mm) were characterized by higher diversity indices in comparison with those of the coarser aggregate fractions.

Measurement of particle size distribution of soil and selected aggregate sizes using the hydrometer method and laser diffractometry

NASA Astrophysics Data System (ADS)

Guzmán, G.; Gómez, J. A.; Giráldez, J. V.

2010-05-01

Soil particle size distribution has been traditionally determined by the hydrometer or the sieve-pipette methods, both of them time consuming and requiring a relatively large soil sample. This might be a limitation in situations, such as for instance analysis of suspended sediment, when the sample is small. A possible alternative to these methods are the optical techniques such as laser diffractometry. However the literature indicates that the use of this technique as an alternative to traditional methods is still limited, because the difficulty in replicating the results obtained with the standard methods. In this study we present the percentages of soil grain size determined using laser diffractometry within ranges set between 0.04 - 2000 μm. A Beckman-Coulter ® LS-230 with a 750 nm laser beam and software version 3.2 in five soils, representative of southern Spain: Alameda, Benacazón, Conchuela, Lanjarón and Pedrera. In three of the studied soils (Alameda, Benacazón and Conchuela) the particle size distribution of each aggregate size class was also determined. Aggregate size classes were obtained by dry sieve analysis using a Retsch AS 200 basic ®. Two hundred grams of air dried soil were sieved during 150 s, at amplitude 2 mm, getting nine different sizes between 2000 μm and 10 μm. Analyses were performed by triplicate. The soil sample preparation was also adapted to our conditions. A small amount each soil sample (less than 1 g) was transferred to the fluid module full of running water and disaggregated by ultrasonication at energy level 4 and 80 ml of sodium hexametaphosphate solution during 580 seconds. Two replicates of each sample were performed. Each measurement was made for a 90 second reading at a pump speed of 62. After the laser diffractometry analysis, each soil and its aggregate classes were processed calibrating its own optical model fitting the optical parameters that mainly depends on the color and the shape of the analyzed particle. As a second alternative a unique optical model valid for a broad range of soils developed by the Department of Soil, Water, and Environmental Science of the University of Arizona (personal communication, already submitted) was tested. The results were compared with the particle size distribution measured in the same soils and aggregate classes using the hydrometer method. Preliminary results indicate a better calibration of the technique using the optical model of the Department of Soil, Water, and Environmental Science of the University of Arizona, which obtained a good correlations (r2>0.85). This result suggests that with an appropriate calibration of the optical model laser diffractometry might provide a reliable soil particle characterization.

The distribution of microplastics in soil aggregate fractions in southwestern China.

PubMed

Zhang, G S; Liu, Y F

2018-06-09

Plastic particle accumulation in arable soils is a growing contaminant of concern with unknown consequences for soil productivity and quality. This study aimed to investigate abundance and distribution of plastic particles among soil aggregate fractions in four cropped areas and an established riparian forest buffer zone at Dian Lake, southwestern China. Plastic particles (10-0.05 mm) from fifty soil samples were extracted and then sorted by size, counted, and categorized. Plastic particles were found in all soil samples. The concentration of plastic particles ranges from 7100 to 42,960 particles kg -1 (mean 18,760 particles kg -1 ). 95% of the sampled plastic particles are in the microplastic size (1-0.05 mm) range. The predominant form is plastic fibers, making up on average 92% of each sample followed by fragments and films that contributed with to 8%. Results of this study also show that 72% of plastic particles are associated with soil aggregates, and 28% of plastic particles are dispersed. The abundance of aggregate-associated plastic fibers is significantly greater in the micro-aggregate than that in the macro-aggregate, whereas the less concentrations of plastic films and fragments are found in the micro-aggregate. Compared to the adjacent vegetable soil, the less concentration of plastic particles in the buffer soil implicates that application of soil amendments and irrigation with wastewater must be controlled to reduce accumulation of microplastics in agricultural soils. While the implications of microplastic on ecological and human health are poorly understood, the staggering number of microplastic in agricultural soils should be continually concerned in the future. Copyright © 2018 Elsevier B.V. All rights reserved.

Predicting the mineral composition of dust aerosols: Insights from elemental composition measured at the Izaña Observatory

NASA Astrophysics Data System (ADS)

Pérez García-Pando, Carlos; Miller, Ron L.; Perlwitz, Jan P.; Rodríguez, Sergio; Prospero, Joseph M.

2016-10-01

Regional variations of dust mineral composition are fundamental to climate impacts but generally neglected in climate models. A challenge for models is that atlases of soil composition are derived from measurements following wet sieving, which destroys the aggregates potentially emitted from the soil. Aggregates are crucial to simulating the observed size distribution of emitted soil particles. We use an extension of brittle fragmentation theory in a global dust model to account for these aggregates. Our method reproduces the size-resolved dust concentration along with the approximately size-invariant fractional abundance of elements like Fe and Al in the decade-long aerosol record from the Izaña Observatory, off the coast of West Africa. By distinguishing between Fe in structural and free forms, we can attribute improved model behavior to aggregation of Fe and Al-rich clay particles. We also demonstrate the importance of size-resolved measurements along with elemental composition analysis to constrain models.

To what extent clay mineralogy affects soil aggregation? Consequences for soil organic matter stabilization

NASA Astrophysics Data System (ADS)

Fernandez-Ugalde, O.; Barré, P.; Hubert, F.; Virto, I.; Chenu, C.; Ferrage, E.; Caner, L.

2012-12-01

Aggregation is a key process for soil functioning as it influences C storage, vulnerability to erosion and water holding capacity. While the influence of soil organic C on aggregation has been documented, much less is known about the role of soil mineralogy. Soils usually contain a mixture of clay minerals with contrasted surface properties, which should result on different abilities of clay minerals to aggregation. We took advantage of the intrinsic mineral heterogeneity of a temperate Luvisol to compare the role of clay minerals (illite, smectite, kaolinite, and mixed-layer illite-smectite) in aggregation. In a first step, grassland and tilled soil samples were fractionated in water in aggregate-size classes according to the hierarchical model of aggregation (Tisdall and Oades, 1982). Clay mineralogy and organic C in the aggregate-size classes were analyzed. The results showed that interstratified minerals containing swelling phases accumulated in aggregated fractions (>2 μm) compared to free clay fractions (<2 μm) in the two land-uses. The accumulation increased from large macro-aggregates (>500 μm) to micro-aggregates (50-250 μm). C concentration and C/N ratio followed the opposite trend. These results constitute a clay mineral-based evidence for the hierarchical model of aggregation, which postulates an increasing importance of the reactivity of clay minerals in the formation of micro-aggregates compared to larger aggregates. In the latter aggregates, formation relies on the physical enmeshment of particles by fungal hyphae, and root and microbial exudates. In a second step, micro-aggregates from the tilled soil samples were submitted to increasingly disaggregating treatments by sonication to evaluate the link between their water stability and clay mineralogy. Micro-aggregates with increasing stability showed an increase of interstratified minerals containing swelling phases and C concentration for low intensities of disaggregation (from 0 to 5 J mL-1). This suggests that swelling phases promote their stability. Swelling phases and organic C decreased for greater intensities of disaggregation. These results and the SEM images taken at different disaggregation intensities indicate that when increasing disaggregation intensity above 5 J mL-1, the recovered material consists on sand particles covered by physical coatings of illite and kaolinite. Our results show that different clay minerals have different contribution to soil aggregation. Swelling phases are especially important for water-stable aggregates formation, whereas illite and kaolinite can either contribute to aggregation or been coated to sand grains in "mineral aggregates", without porosity and organic C protection capability. In conclusion, soils with large proportion of swelling clay minerals have greater potential for carbon storage by occlusion in aggregates and greater resistance to erosion. Tisdall JM, Oades JM (1982) Organic matter and water-stable aggregates in soils. J Soil Sci 62: 141-163.

Monitoring aggregate disintegration with laser diffraction: A tool for studying soils as sediments

NASA Astrophysics Data System (ADS)

Mason, Joseph; Kasmerchak, Chase; Liang, Mengyu

2016-04-01

One of the more important characteristics of soil that becomes hillslope, fluvial, or aeolian sediment is the presences of aggregates, which disintegrate at varying rates and to varying degrees during transport. Laser diffraction particle size analyzers allow monitoring of aggregate disintegration as a sample of soil or sediment suspended in water is circulated continuously through the measurement cell (Bieganowski et al., 2010, Clay Minerals 45-23-34; Mason et al., Catena 87:107-118). Mason et al. (2011) applied this approach to aeolian sedimentary aggregates (e.g. clay pellets eroded from dry lakebeds), immersing dry samples in DI water and circulating them through a Malvern Mastersizer 2000 particle size analyzer for three hours while repeated size distribution (SD) measurements were made. A final measurement was made after sonication and treatment with Na-metaphosphate. In that study, most samples approached a steady SD within three hours, which included both primary mineral grains and persistent aggregates. The disintegration process could be modeled with a first-order rate law representing the disintegration of a single population of aggregates. A wide range of model parameters were observed among the samples studied, and it was suggested that they could be useful in predicting the behavior of these aggregates, under rainfall impact and during slopewash or fluvial transport. Addition of Ca++ to the suspension altered aggregate behavior in some but not all cases. We applied the same method to dry, unground material from upper horizons of soils sampled along a bioclimatic gradient in northern Minnesota, USA, all formed in lithologically similar glacigenic sediment. These ranged from Alfisols (Luvisols) formed under forest since the last deglaciation, to Alfisols under forest that more recently replaced grassland, and Mollisols (Chernozems) that formed entirely under grassland vegetation. Few of these soil samples approached a steady SD within three hours, and modeling aggregate disintegration required the assumption of at least two aggregate populations. Upper horizons of soils formed under grassland displayed relatively slow disintegration throughout the procedure, with a large proportion of aggregates remaining after three hours. E horizons from forest soils, with low organic matter (OM) and clay content, displayed rapid early distintegration of a large portion of the aggregates, followed by much slower breakdown of the remainder (i.e. the two populations modeled had very different rate constants). OM content is clearly the overriding control on aggregate behavior, but we are also exploring effects of clay content and mineralogy, cation chemistry, and other factors. The differences in aggregate behavior are likely to be relevant to transport and deposition of sediment eroded from these soils, and possibly to the transport of OM or nutrients with eroded soil. We hope to incorporate this method into ongoing field studies of soil erosion with colleagues at UW-Madison.

Rainfall-induced soil aggregate breakdown in field experiments at different rainfall intensities and initial soil moisture conditions

NASA Astrophysics Data System (ADS)

Shi, Pu; Thorlacius, Sigurdur; Keller, Thomas; Keller, Martin; Schulin, Rainer

2017-04-01

Soil aggregate breakdown under rainfall impact is an important process in interrill erosion, but is not represented explicitly in water erosion models. Aggregate breakdown not only reduces infiltration through surface sealing during rainfall, but also determines the size distribution of the disintegrated fragments and thus their availability for size-selective sediment transport and re-deposition. An adequate representation of the temporal evolution of fragment mass size distribution (FSD) during rainfall events and the dependence of this dynamics on factors such as rainfall intensity and soil moisture content may help improve mechanistic erosion models. Yet, little is known about the role of those factors in the dynamics of aggregate breakdown under field conditions. In this study, we conducted a series of artificial rainfall experiments on a field silt loam soil to investigate aggregate breakdown dynamics at different rainfall intensity (RI) and initial soil water content (IWC). We found that the evolution of FSD in the course of a rainfall event followed a consistent two-stage pattern in all treatments. The fragment mean weight diameter (MWD) drastically decreased in an approximately exponential way at the beginning of a rainfall event, followed by a further slow linear decrease in the second stage. We proposed an empirical model that describes this temporal pattern of MWD decrease during a rainfall event and accounts for the effects of RI and IWC on the rate parameters. The model was successfully tested using an independent dataset, showing its potential to be used in erosion models for the prediction of aggregate breakdown. The FSD at the end of the experimental rainfall events differed significantly among treatments, indicating that different aggregate breakdown mechanisms responded differently to the variation in initial soil moisture and rainfall intensity. These results provide evidence that aggregate breakdown dynamics needs to be considered in a case-specific manner in modelling sediment mobilization and transport during water erosion events.

Estimation of soil saturated hydraulic conductivity by artificial neural networks ensemble in smectitic soils

NASA Astrophysics Data System (ADS)

Sedaghat, A.; Bayat, H.; Safari Sinegani, A. A.

2016-03-01

The saturated hydraulic conductivity ( K s ) of the soil is one of the main soil physical properties. Indirect estimation of this parameter using pedo-transfer functions (PTFs) has received considerable attention. The Purpose of this study was to improve the estimation of K s using fractal parameters of particle and micro-aggregate size distributions in smectitic soils. In this study 260 disturbed and undisturbed soil samples were collected from Guilan province, the north of Iran. The fractal model of Bird and Perrier was used to compute the fractal parameters of particle and micro-aggregate size distributions. The PTFs were developed by artificial neural networks (ANNs) ensemble to estimate K s by using available soil data and fractal parameters. There were found significant correlations between K s and fractal parameters of particles and microaggregates. Estimation of K s was improved significantly by using fractal parameters of soil micro-aggregates as predictors. But using geometric mean and geometric standard deviation of particles diameter did not improve K s estimations significantly. Using fractal parameters of particles and micro-aggregates simultaneously, had the most effect in the estimation of K s . Generally, fractal parameters can be successfully used as input parameters to improve the estimation of K s in the PTFs in smectitic soils. As a result, ANNs ensemble successfully correlated the fractal parameters of particles and micro-aggregates to K s .

Changes on aggregation in mine waste amended with biochar and marble mud

NASA Astrophysics Data System (ADS)

Ángeles Muñoz, María; Guzmán, Jose; Zornoza, Raúl; Moreno-Barriga, Fabián; Faz, Ángel; Lal, Rattan

2016-04-01

Mining activities have produced large amounts of wastes over centuries accumulated in tailing ponds in Southeast Spain. Applications of biochar may have a high potential for reclamation of degraded soils. Distribution, size and stability of aggregates are important indices of soil physical quality. However, research data on aggregation processes at amended mining tailings with biochar are scanty. Therefore, the aim of this study was to determine the effects of seven different treatments involving biochar and marble mud (MM) on the aggregation in mine waste (MW). Seven different treatments were tested after 90 days of incubation in the laboratory. These treatments were the mix of MW and: biochar from solid pig manure (PM), biochar from cotton crop residues (CR), biochar from municipal solid waste (MSW), marble mud (MM), PM+MM, CR+MM, MSW+MM and control without amendment. High sand percentages were identified in the MW. The biochars made from wastes (PM, CR, MSW) were obtained through pyrolysis of feedstocks. The water stability of soil aggregates was studied. The data on total aggregation were corrected for the primary particles considering the sandy texture of the MW. Moreover, partial aggregation was determined for each fraction and the mean weight diameter (MWD) of aggregates was computed. Soil bulk density and total porosity were also determined. No significant differences were observed in total aggregation and MWD among treatments including the control. For the size range of >4.75 mm, there were significant differences in aggregates > 4.75 mm between CR+MM in comparison with that for CT. There were also significant differences between MSW and PM+MM for the 1-0.425 mm fraction, and between CT and MM and CR for 0.425-0.162 mm aggregate size fractions. Therefore, CR-derived biochar applied with MM enhanced stability of macro-aggregates. Furthermore, soil bulk density was also the lowest bulk density and total porosity the highest for the CR-derived biochar treatment because macro aggregate stability is largely responsible for macro-porosity. The decrease in bulk density may be an indication of a positive effect for mine waste reclamation. Conversely, no differences were observed among treatments in micro-aggregate stability. Apparently, low organic matter contents in MW needed to be co-amended with labile organic amendments to effectively increase soil aggregation. Furthermore, the presence of Fe hydroxides could also increase the micro-aggregation. Additional research is needed to understand the mechanisms of mine soil reclamation. Acknowledgement : This work has been funded by Fundación Séneca (Agency of Science and Technology of the Region of Murcia, Spain

Assessing the dynamics of the upper soil layer relative to soil management practices

NASA Astrophysics Data System (ADS)

Hatfield, J.; Wacha, K.; Dold, C.

2017-12-01

The upper layer of the soil is the critical interface between the soil and the atmosphere and is the most dynamic in response to management practices. One of the soil properties most reflective to changes in management is the stability of the aggregates because this property controls infiltration of water and exchange of gases. An aggregation model has been developed based on the factors that control how aggregates form and the forces which degrade aggregates. One of the major factors for this model is the storage of carbon into the soil and the interaction with the soil biological component. To increase soil biology requires a stable microclimate that provides food, water, shelter, and oxygen which in turn facilitates the incorporation of organic material into forms that can be combined with soil particles to create stable aggregates. The processes that increase aggregate size and stability are directly linked the continual functioning of the biological component which in turn changes the physical and chemical properties of the soil. Soil aggregates begin to degrade as soon as there is no longer a supply of organic material into the soil. These processes can range from removal of organic material and excessive tillage. To increase aggregation of the upper soil layer requires a continual supply of organic material and the biological activity that incorporates organic material into substances that create a stable aggregate. Soils that exhibit stable soil aggregates at the surface have a prolonged infiltration rate with less runoff and a gas exchange that ensures adequate oxygen for maximum biological activity. Quantifying the dynamics of the soil surface layer provides a quantitative understanding of how management practices affect aggregate stability.

Interactions between extracellular polymeric substances and clay minerals affect soil aggregation

NASA Astrophysics Data System (ADS)

Vogel, Cordula; Rehschuh, Stephanie; Kemi Olagoke, Folasade; Redmile Gordon, Marc; Kalbiltz, Karsten

2017-04-01

Soil aggregation is crucial for carbon (C) sequestration and microbial processes have been recognised as important control of aggregate turnover (formation, stability, and destruction). However, how microorganisms contribute to these processes is still a matter of debate. An enthralling mechanism determining aggregate turnover and therefore C sequestration may be the excretion of extracellular polymeric substances (EPS) as microbial glue, but effects of EPS on aggregation is largely unknown. Moreover, interdependencies between important aggregation factors like the amount of fine-sized particles (clay content), the decomposability of organic matter and the microbial community (size and composition, as well as the excretion of EPS) are still poorly understood. Therefore, we studied the complex interactions between these factors and their role in aggregate turnover. It was hypothesized that an increase in microbial activity, induced by the input of organic substrates, will stimulate EPS production and therefore the formation and stability of aggregates. To test this hypothesis, an incubation experiment has been conducted across a gradient of clay content (montmorillonite) and substrate decomposability (starch and glucose) as main drivers of the microbial activity. A combination of aggregate separation and stability tests were applied. This results will be examined with respect to the obtained microbial parameters (amount and composition of EPS, CO2 emission, microbial biomass, phospholipid fatty acid), to disentangle the mechanisms and factors controlling aggregate turnover affected by soil microorganisms. This study is expected to provide insights on the role of EPS in the stability of aggregates. Thus, the results of this study will provide an improved understanding of the underlying processes of aggregate turnover in soils, which is necessary to implement strategies for enhanced C sequestration in agricultural soils.

40 CFR 796.2750 - Sediment and soil adsorption isotherm.

Code of Federal Regulations, 2011 CFR

2011-07-01

... size analysis” is the determination of the various amounts of the different particle sizes in a sample... °C. (iii) Replications. Three replications of the experimental treatments shall be used. (iv) Soil...) Decrease the water content, air or oven-dry soils at or below 50 °C. (B) Reduce aggregate size before and...

40 CFR 796.2750 - Sediment and soil adsorption isotherm.

Code of Federal Regulations, 2010 CFR

2010-07-01

... size analysis” is the determination of the various amounts of the different particle sizes in a sample... °C. (iii) Replications. Three replications of the experimental treatments shall be used. (iv) Soil...) Decrease the water content, air or oven-dry soils at or below 50 °C. (B) Reduce aggregate size before and...

Relationship between chemical structure of soil organic matter and intra-aggregate pore structure: evidence from X-ray computed micro-tomography

NASA Astrophysics Data System (ADS)

Kravchenko, Alexandra; Grandy, Stuart A.

2014-05-01

Understanding chemical structure of soil organic matter (SOM) and factors that affect it are vital for gaining understanding of mechanisms of C sequestration by soil. Physical protection of C by adsorption to mineral particles and physical disconnection between C sources and microbial decomposers is now regarded as the key component of soil C sequestration. Both of the processes are greatly influenced by micro-scale structure and distribution of soil pores. However, because SOM chemical structure is typically studied in disturbed (ground and sieved) soil samples the experimental evidence of the relationships between soil pore structure and chemical structure of SOM are still scarce. Our study takes advantage of the X-ray computed micro-tomography (µ-CT) tools that enable non-destructive analysis of pore structure in intact soil samples. The objective of this study is to examine the relationship between SOM chemical structure and pore-characteristics in intact soil macro-aggregates from two contrasting long-term land uses. The two studied land use treatments are a conventionally tilled corn-soybean-wheat rotation treatment and a native succession vegetation treatment removed from agricultural use >20 years ago. The study is located in southwest Michigan, USA, on sandy-loam Typic Hapludalfs. For this study we used soil macro-aggregates 4-6 mm in size collected at 0-15 cm depth. The aggregate size was selected so as both to enable high resolution of µ-CT and to provide sufficient amount of soil for C measurements. X-ray µ-CT scanning was conducted at APS Argonne at a scanning resolution of 14 µm. Two scanned aggregates (1 per treatment) were used in this preliminary study. Each aggregate was cut into 7 "geo-referenced" sections. Analyses of pore characteristics in each section were conducted using 3DMA and ImageJ image analysis tools. SOM chemistry was analyzed using pyrolysis/gas chromatography-mass spectroscopy. Results demonstrated that the relationships between SOM chemical structure and pore characteristics differed in the aggregates of the two treatments. For example, in the agricultural treatment, the aggregate sections with prevalence of small pores had lower relative lignin abundance, while higher lignin abundances occurred in aggregate sections with more large pores. This relationship could be reflecting the low accessibility of the sections dominated by small pores to plant roots. It is interesting to note that no relationship between pores and lignin were observed in the aggregate from the native succession treatment. In the native succession aggregate we found that a larger presence of protein and N-bearing compounds was associated with sections with greater presence of 35-90 µm pores. This could be a result of fungal activities, as pores of this size constitute a primary fungal habitat and fungi are known for secreting proteins. Fewer fungi in the soil under agricultural management are likely the reason that no such relationship was observed in the aggregate from the agricultural treatment. Our preliminary results indicate that substantial spatial variability patterns in SOM chemical structure can exist even within a single macro-aggregate and that pores are likely a main driver of intra-aggregate SOM chemistry.

Biosolids increase soil aggregation and protection of soil carbon five years after application on a crested wheatgrass pasture.

PubMed

Wallace, Brian M; Krzic, Maja; Forge, Tom A; Broersma, Klaas; Newman, Reg F

2009-01-01

Biosolids application to rangelands and pastures recycles nutrients and organic matter back to soils. The effects of biosolids (20 and 60 dry Mg ha(-)(1)) and N+P fertilizer on soil aggregate stability, bulk density, aeration porosity, and total C and N of stable aggregates were evaluated 4 and 5 yr after surface application to a crested wheatgrass [Agropyron cristatum (L.) Gaertn.] pasture in the southern interior of British Columbia (BC). The experiment was established in 2001 in a randomized complete block design with four replications. The 60 Mg ha(-1) biosolids treatment (Bio 60) had a greater aggregate mean weight diameter (MWD) and proportion of water-stable soil aggregates > 1 mm relative to the control and fertilizer treatments. Temporal variation in aggregate stability was attributed to seasonal variations in soil water content. Surface application of 60 Mg ha(-1) of biosolids increased C concentrations within water-stable aggregates relative to the control from 29 to 104, 24 to 79, and 12 to 38 g kg(-1) for the 2 to 6, 1 to 2, and 0.25 to 1 mm size fractions, respectively. The concentration of N within aggregates increased in similar proportions to C. Neither soil bulk density, nor aeration porosity were affected by biosolids application. Increased aggregation and the accumulation of soil C within aggregates following biosolids application creates a potential for better soil C storage, soil water retention, nutrient availability, and ultimately the overall health of semiarid perennial pastures.

Effects of long-term grassland management on the carbon and nitrogen pools of different soil aggregate fractions.

PubMed

Egan, Gary; Crawley, Michael J; Fornara, Dario A

2018-02-01

Common grassland management practices include animal grazing and the repeated addition of lime and nutrient fertilizers to soils. These practices can greatly influence the size and distribution of different soil aggregate fractions, thus altering the cycling and storage of carbon (C) and nitrogen (N) in grassland soils. So far, very few studies have simultaneously addressed the potential long-term effect that multiple management practices might have on soil physical aggregation. Here we specifically ask whether and how grazing, liming and nutrient fertilization might influence C and N content (%) as well as C and N pools of different soil aggregate fractions in a long-term grassland experiment established in 1991 at Silwood Park, Berkshire, UK. We found that repeated liming applications over 23years significantly decreased the C pool (i.e. gCKg -1 soil) of Large Macro Aggregate (LMA>2mm) fractions and increased C pools within three smaller soil aggregate fractions: Small Macro Aggregate (SMA, 250μm-2mm), Micro Aggregate (MiA, 53-250μm), and Silt Clay Aggregate (SCA<53μm). Soil C (and N) accrual in smaller fractions was mainly caused by positive liming effects on aggregate fraction mass rather than on changes in soil C (and N) content (%). Liming effects could be explained by increases in soil pH, as this factor was significantly positively related to greater soil C and N pools of smaller aggregate fractions. Long-term grazing and inorganic nutrient fertilization had much weaker effects on both soil aggregate-fraction mass and on soil C and N concentrations, however, our evidence is that these practices could also contribute to greater C and N pools of smaller soil fractions. Overall our study demonstrates how agricultural liming can contribute to increase C pools of small (more stable) soil fractions with potential significant benefits for the long-term C balance of human-managed grassland soils. Copyright © 2017 Elsevier B.V. All rights reserved.

[Effects of Land Use Type on Soil Microbial Biomass Carbon and Nitrogen in Water-Stable Aggregates in Jinyun Mountain].

PubMed

Li, Zeng-quan; Jiang, Chang-sheng; Hao, Qing-ju

2015-11-01

In this study, four land use types including subtropical evergreen broad-leaved forest (abbreviation: forest), sloping farmland, orchard and abandoned land were selected to collect soil samples from 0 to 60 cm depth at the same altitude in Jinyun Mountain. Four sizes of large macroaggregates (> 2 mm), small macroaggregates (0.25-2 mm), microaggregates (0.053-0.25 mm) and silt + clay (< 0.053 mm) were achieved by wet sieving method and the contents of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in each aggregate fraction were measured to study the impacts of the different land use types on MBC and MBN in soil aggregates. The results showed that the contents of MBC and MBN in all aggregates in the four land use types decreased with the increasing soil depth. Except large macroaggregetes, the contents of MBC and MBN in the other three soil aggregates decreased when the forest was reclamated into orchard and sloping farmland. MBC and MBN contents in large macroaggregates, small macroaggregates and microaggregates all increased when the sloping farmland was abandoned. The storages of organic carbon and nitrogen in soil depth of 0-60 cm in the four proportions were calculated by the equivalent soil mass method. The results revealed that MBC storages in the other three sizes except silt + clay were higher in the forest than those in orchard and sloping land. And MBC storages in the all aggregates were higher in the abandoned land than those in the sloping land. MBN storages in small macroaggregates and microaggregates were higher in the forest than those in orchard and sloping land. And MBN storages in the other three aggregates except silt + clay were higher in the abandoned land than those in the sloping land. Generally speaking, the storages of MBC in soil aggregates of forest and abandoned land were higher than in orchard and sloping land, MBN storage in soil aggregates of forest was nearly equal to the storage in orchard. However, the storages of MBN in soil aggregates of forest and abandoned land were higher than those in sloping land. The results showed that the reclamation of the forest resulted in the loss of MBC and MBN in soil aggregates of sloping land. However, the abandon of the sloping land contributed to the acumulation of MBC and MBN in soil aggregates. In the process of land use change, the direction and quantity of change in MBC in the soil aggregates were not consistent with those of the total soil organic carbon, which meant the microbial quotient in soil aggregates was not suitable for using to evaluate the impact of land use change on soil quality, using the total organic carbon as an index to express the sensitivity of the land use change may be better.

Linking Intra-Aggregate Pore Size Distribution with Organic Matter Decomposition Status, Evidence from FTIR and X-Ray Tomography

NASA Astrophysics Data System (ADS)

Toosi, E. R.; Quigley, M.; Kravchenko, A. N.

2014-12-01

It has been reported that conversion of intensively cultivated lands to less disturbed systems enhances soil OM storage capacity, primarily through OM stabilization in macroaggregates. We hypothesized that the potential for OM stabilization inside macro-aggregates is influenced by presence and abundance of intra-aggregate pores. Pores determine microbial access to OM and regulate diffusion of solution/gases within aggregates which drives microbial functioning. We investigated the influence of longterm disturbance intensity on soil OM composition and its relation to pore size distribution within macroaggregates. We used quantitative FTIR to determine OM decomposition status and X-ray micro-tomography to assess pore size distribution in macroaggregates as affected by management and landuse. Macroaggregates 4-6 mm in size where selected from topsoil under long term conventional tillage (CT), cover-crop (CC), and native succession vegetation (NS) treatments at Kellogg Biological Station, Michigan. Comparison of main soil OM functional groups suggested that with increasing disturbance intensity, the proportion of aromatic and carboxylic/carbohydrates associated compounds increased and it was concomitant with a decrease in the proportion of aliphatic associated compounds and lignin derivatives. Further, FTIR-based decomposition indices revealed that overall decomposition status of macroaggregates followed the pattern of CT > CC ≈ NS. X-ray micro-tomography findings suggested that greater OM decomposition within the macroaggregates was associated with i) greater percent of pores >13 micron in size within the aggregates, as well as ii) greater proportion of small to medium pores (13-110 micron). The results develop previous findings, suggesting that shift in landuse or management indirectly affects soil OM stabilization through alteration of pore size distribution within macroaggregates that itself, is coupled with OM decomposition status.

Mercury porosimetry for comparing piece-wise hydraulic properties with full range pore characteristics of soil aggregates and porous rocks

NASA Astrophysics Data System (ADS)

Turturro, Antonietta Celeste; Caputo, Maria C.; Gerke, Horst H.

2017-04-01

Unsaturated hydraulic properties are essential in the modeling of water and solute movement in the vadose zone. Since standard hydraulic techniques are limited to specific moisture ranges, maybe affected by air entrapment, wettability problems, limitations due to water vapor pressure, and are depending on the initial saturation, the continuous maximal drying curves of the complete hydraulic functions can mostly not reflect the basic pore size distribution. The aim of this work was to compare the water retention curves of soil aggregates and porous rocks with their porosity characteristics. Soil aggregates of Haplic Luvisols from Loess L (Hneveceves, Czech Republic) and glacial Till T (Holzendorf, Germany) and two lithotypes of porous rock C (Canosa) and M (Massafra), Italy, were analyzed using, suction table, evaporation, psychrometry methods, and the adopted Quasi-Steady Centrifuge method for determination of unsaturated hydraulic conductivity. These various water-based techniques were applied to determine the piece-wise retention and the unsaturated hydraulic conductivity functions in the range of pore water saturations. The pore-size distribution was determined with the mercury intrusion porosimetry (MIP). MIP results allowed assessing the volumetric mercury content at applied pressures up to 420000 kPa. Greater intrusion and porosity values were found for the porous rocks than for the soil aggregates. Except for the aggregate samples from glacial till, maximum liquid contents were always smaller than porosity. Multimodal porosities and retention curves were observed for both porous rocks and aggregate soils. Two pore-size peaks with pore diameters of 0.135 and 27.5 µm, 1.847 and 19.7 µm, and 0.75 and 232 µm were found for C, M and T, respectively, while three peaks of 0.005, 0.392 and 222 µm were identified for L. The MIP data allowed describing the retention curve in the entire mercury saturation range as compared to water retention curves that required combining several methods for limited suction ranges. Although the soil aggregates and porous rocks differed in pore geometries and pore size distributions, MIP provided additional information for characterizing the relation between pore structure and hydraulic properties for both.

Flow Partitioning in Fully Saturated Soil Aggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Xiaofan; Richmond, Marshall C.; Scheibe, Timothy D.

2014-03-30

Microbes play an important role in facilitating organic matter decomposition in soils, which is a major component of the global carbon cycle. Microbial dynamics are intimately coupled to environmental transport processes, which control access to labile organic matter and other nutrients that are needed for the growth and maintenance of microorganisms. Transport of soluble nutrients in the soil system is arguably most strongly impacted by preferential flow pathways in the soil. Since the physical structure of soils can be characterized as being formed from constituent micro aggregates which contain internal porosity, one pressing question is the partitioning of the flowmore » among the “inter-aggregate” and “intra-aggregate” pores and how this may impact overall solute transport within heterogeneous soil structures. The answer to this question is particularly important in evaluating assumptions to be used in developing upscaled simulations based on highly-resolved mechanistic models. We constructed a number of diverse multi-aggregate structures with different packing ratios by stacking micro-aggregates containing internal pores and varying the size and shape of inter-aggregate pore spacing between them. We then performed pore-scale flow simulations using computational fluid dynamics methods to determine the flow patterns in these aggregate-of-aggregates structures and computed the partitioning of the flow through intra- and inter-aggregate pores as a function of the spacing between the aggregates. The results of these numerical experiments demonstrate that soluble nutrients are largely transported via flows through inter-aggregate pores. Although this result is consistent with intuition, we have also been able to quantify the relative flow capacity of the two domains under various conditions. For example, in our simulations, the flow capacity through the aggregates (intra-aggregate flow) was less than 2% of the total flow when the spacing between the aggregates was larger than 18 micron. Inter-aggregate pores continued to be the dominant flow pathways even at much smaller spacing; intra-aggregate flow was less than 10% of the total flow when the inter- and intra-aggregate pore sizes were comparable. Such studies are making it possible to identify which model upscaling assumptions are realistic and what computational methods are required for detailed numerical investigation of microbial carbon cycling dynamics in soil systems.« less

Aggregate-associated carbon and nitrogen in reclaimed sandy loam soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wick, A.F.; Stahl, P.D.; Ingram, L.J.

2009-11-15

Minimal research has been conducted on aggregate, C, and N in coarse-textured soils used to reclaim surface coal mine lands. Furthermore, little is known about the contribution different plant communities make to the recovery of aggregation in these soils. Two chronosequences of semiarid reclaimed sites with sandy loam soils were sampled under shrub- and grass-dominated communities. Aggregation, aggregate fractions, and associated C and N were measured. No definitive trends of increasing macroaggregates between sites were observed undershrubs; however, macro- and microaggregation was greater in the 16-yr-old (0.20 and 0.23 kg aggregate kg{sup -1} soil, respectively) than in the 5-yr-old soilsmore » (0.02 and 0.08 kg aggregate kg{sup -1} soil, respectively) under grasses. Although C and N concentrations were drastically reduced (50-75%) with mining activity between the <1-yr-old and native soils, aggregate C and N concentrations tinder shrubs and grasses were similar to each other and to the native soils in the 5-yr-old site. Sods under grass in the 16-yr-old site had lower available and aggregate-occluded C and N concentrations than the 5-yr-old site, while C and N concentrations did not change between 5- and 16-yr-old soils under shrubs. Conversely, aggregate C and N pool sizes under shrubs and grasses both increased with site age to conditions similar to those observed in the native soil. Reclaimed shrub site soils had consistently higher C concentrations in the older reclaimed sites (10 and 16 yr old) than the soils under grasses, indicating greater accumulation and retention of C and N in organic material under shrub than grass communities in semiarid reclaimed sites.« less

Effects of land conversion from native shrub to pistachio orchard on soil erodibility in an arid region.

PubMed

Yakupoglu, Tugrul; Gundogan, Recep; Dindaroglu, Turgay; Kara, Zekeriya

2017-10-29

Land-use change through degrading natural vegetation for agricultural production adversely affects many of soil properties particularly organic carbon content of soils. The native shrub land and grassland of Gaziantep-Adiyaman plateau that is an important pistachio growing eco-region have been cleared to convert into pistachio orchard for the last 50 to 60 years. In this study, the effects of conversion of natural vegetation into agricultural uses on soil erodibility have been investigated. Soil samples were collected from surface of agricultural fields and adjacent natural vegetation areas, and samples were analyzed for some soil erodibility indices such as dispersion ratio (DR), erosion ratio (ER), structural stability index (SSI), Henin's instability index (I s ), and aggregate size distribution after wet sieving (AggSD). According to the statistical evaluation, these two areas were found as different from each other in terms of erosion indices except for I s index (P < 0.001 for DR and ER or P < 0.01 for SSI). In addition, native shrub land and converted land to agriculture were found different in terms of AggSD in all aggregate size groups. As a contrary to expectations, correlation tests showed that there were no any interaction between soil organic carbon and measured erodibility indices in two areas. In addition, significant relationships were determined between measured variables and soil textural fractions as statistical. These obtaining findings were attributed to changing of textural component distribution and initial aggregate size distribution results from land-use change in the study area. Study results were explained about hierarchical aggregate formation mechanism.

Soil Aggregate Stability and Grassland Productivity Associations in a Northern Mixed-Grass Prairie

PubMed Central

Reinhart, Kurt O.; Vermeire, Lance T.

2016-01-01

Soil aggregate stability data are often predicted to be positively associated with measures of plant productivity, rangeland health, and ecosystem functioning. Here we revisit the hypothesis that soil aggregate stability is positively associated with plant productivity. We measured local (plot-to-plot) variation in grassland community composition, plant (aboveground) biomass, root biomass, % water-stable soil aggregates, and topography. After accounting for spatial autocorrelation, we observed a negative association between % water-stable soil aggregates (0.25–1 and 1–2 mm size classes of macroaggregates) and dominant graminoid biomass, and negative associations between the % water-stable aggregates and the root biomass of a dominant sedge (Carex filifolia). However, variation in total root biomass (0–10 or 0–30 cm depths) was either negatively or not appreciably associated with soil aggregate stabilities. Overall, regression slope coefficients were consistently negative thereby indicating the general absence of a positive association between measures of plant productivity and soil aggregate stability for the study area. The predicted positive association between factors was likely confounded by variation in plant species composition. Specifically, sampling spanned a local gradient in plant community composition which was likely driven by niche partitioning along a subtle gradient in elevation. Our results suggest an apparent trade-off between some measures of plant biomass production and soil aggregate stability, both known to affect the land’s capacity to resist erosion. These findings further highlight the uncertainty of plant biomass-soil stability associations. PMID:27467598

Soil Aggregate Stability and Grassland Productivity Associations in a Northern Mixed-Grass Prairie.

PubMed

Reinhart, Kurt O; Vermeire, Lance T

2016-01-01

Soil aggregate stability data are often predicted to be positively associated with measures of plant productivity, rangeland health, and ecosystem functioning. Here we revisit the hypothesis that soil aggregate stability is positively associated with plant productivity. We measured local (plot-to-plot) variation in grassland community composition, plant (aboveground) biomass, root biomass, % water-stable soil aggregates, and topography. After accounting for spatial autocorrelation, we observed a negative association between % water-stable soil aggregates (0.25-1 and 1-2 mm size classes of macroaggregates) and dominant graminoid biomass, and negative associations between the % water-stable aggregates and the root biomass of a dominant sedge (Carex filifolia). However, variation in total root biomass (0-10 or 0-30 cm depths) was either negatively or not appreciably associated with soil aggregate stabilities. Overall, regression slope coefficients were consistently negative thereby indicating the general absence of a positive association between measures of plant productivity and soil aggregate stability for the study area. The predicted positive association between factors was likely confounded by variation in plant species composition. Specifically, sampling spanned a local gradient in plant community composition which was likely driven by niche partitioning along a subtle gradient in elevation. Our results suggest an apparent trade-off between some measures of plant biomass production and soil aggregate stability, both known to affect the land's capacity to resist erosion. These findings further highlight the uncertainty of plant biomass-soil stability associations.

Predicting the Mineral Composition of Dust Aerosols. Part 1; Representing Key Processes

NASA Technical Reports Server (NTRS)

Perlwitz, J. P.; Garcia-Pando, C. Perez; Miller, R. L.

2015-01-01

Soil dust aerosols created by wind erosion are typically assigned globally uniform physical and chemical properties within Earth system models, despite known regional variations in the mineral content of the parent soil. Mineral composition of the aerosol particles is important to their interaction with climate, including shortwave absorption and radiative forcing, nucleation of cloud droplets and ice crystals, heterogeneous formation of sulfates and nitrates, and atmospheric processing of iron into bioavailable forms that increase the productivity of marine phytoplankton. Here, aerosol mineral composition is derived by extending a method that provides the composition of a wet-sieved soil. The extension accounts for measurements showing significant differences between the mineral fractions of the wetsieved soil and the emitted aerosol concentration. For example, some phyllosilicate aerosols are more prevalent at silt sizes, even though they are nearly absent at these diameters in a soil whose aggregates are dispersed by wet sieving. We calculate the emitted mass of each mineral with respect to size by accounting for the disintegration of soil aggregates during wet sieving. These aggregates are emitted during mobilization and fragmentation of the original undispersed soil that is subject to wind erosion. The emitted aggregates are carried far downwind from their parent soil. The soil mineral fractions used to calculate the aggregates also include larger particles that are suspended only in the vicinity of the source. We calculate the emitted size distribution of these particles using a normalized distribution derived from aerosol measurements. In addition, a method is proposed for mixing minerals with small impurities composed of iron oxides. These mixtures are important for transporting iron far from the dust source, because pure iron oxides are more dense and vulnerable to gravitational removal than most minerals comprising dust aerosols. A limited comparison to measurements from North Africa shows that the model extensions result in better agreement, consistent with a more extensive comparison to global observations as well as measurements of elemental composition downwind of the Sahara, as described in companion articles.

Predicting the mineral composition of dust aerosols - Part 1: Representing key processes

NASA Astrophysics Data System (ADS)

Perlwitz, J. P.; Pérez García-Pando, C.; Miller, R. L.

2015-10-01

Soil dust aerosols created by wind erosion are typically assigned globally uniform physical and chemical properties within Earth system models, despite known regional variations in the mineral content of the parent soil. Mineral composition of the aerosol particles is important to their interaction with climate, including shortwave absorption and radiative forcing, nucleation of cloud droplets and ice crystals, heterogeneous formation of sulfates and nitrates, and atmospheric processing of iron into bioavailable forms that increase the productivity of marine phytoplankton. Here, aerosol mineral composition is derived by extending a method that provides the composition of a wet-sieved soil. The extension accounts for measurements showing significant differences between the mineral fractions of the wet-sieved soil and the emitted aerosol concentration. For example, some phyllosilicate aerosols are more prevalent at silt sizes, even though they are nearly absent at these diameters in a soil whose aggregates are dispersed by wet sieving. We calculate the emitted mass of each mineral with respect to size by accounting for the disintegration of soil aggregates during wet sieving. These aggregates are emitted during mobilization and fragmentation of the original undispersed soil that is subject to wind erosion. The emitted aggregates are carried far downwind from their parent soil. The soil mineral fractions used to calculate the aggregates also include larger particles that are suspended only in the vicinity of the source. We calculate the emitted size distribution of these particles using a normalized distribution derived from aerosol measurements. In addition, a method is proposed for mixing minerals with small impurities composed of iron oxides. These mixtures are important for transporting iron far from the dust source, because pure iron oxides are more dense and vulnerable to gravitational removal than most minerals comprising dust aerosols. A limited comparison to measurements from North Africa shows that the model extensions result in better agreement, consistent with a more extensive comparison to global observations as well as measurements of elemental composition downwind of the Sahara, as described in companion articles.

Physical soil architectural traits are functionally linked to carbon decomposition and bacterial diversity.

PubMed

Rabbi, S M F; Daniel, H; Lockwood, P V; Macdonald, C; Pereg, L; Tighe, M; Wilson, B R; Young, I M

2016-09-12

Aggregates play a key role in protecting soil organic carbon (SOC) from microbial decomposition. The objectives of this study were to investigate the influence of pore geometry on the organic carbon decomposition rate and bacterial diversity in both macro- (250-2000 μm) and micro-aggregates (53-250 μm) using field samples. Four sites of contrasting land use on Alfisols (i.e. native pasture, crop/pasture rotation, woodland) were investigated. 3D Pore geometry of the micro-aggregates and macro-aggregates were examined by X-ray computed tomography (μCT). The occluded particulate organic carbon (oPOC) of aggregates was measured by size and density fractionation methods. Micro-aggregates had 54% less μCT observed porosity but 64% more oPOC compared with macro-aggregates. In addition, the pore connectivity in micro-aggregates was lower than macro-aggregates. Despite both lower μCT observed porosity and pore connectivity in micro-aggregates, the organic carbon decomposition rate constant (Ksoc) was similar in both aggregate size ranges. Structural equation modelling showed a strong positive relationship of the concentration of oPOC with bacterial diversity in aggregates. We use these findings to propose a conceptual model that illustrates the dynamic links between substrate, bacterial diversity, and pore geometry that suggests a structural explanation for differences in bacterial diversity across aggregate sizes.

Physical soil architectural traits are functionally linked to carbon decomposition and bacterial diversity

PubMed Central

Rabbi, S. M. F.; Daniel, H.; Lockwood, P. V.; Macdonald, C.; Pereg, L.; Tighe, M.; Wilson, B. R.; Young, I. M.

2016-01-01

Aggregates play a key role in protecting soil organic carbon (SOC) from microbial decomposition. The objectives of this study were to investigate the influence of pore geometry on the organic carbon decomposition rate and bacterial diversity in both macro- (250–2000 μm) and micro-aggregates (53–250 μm) using field samples. Four sites of contrasting land use on Alfisols (i.e. native pasture, crop/pasture rotation, woodland) were investigated. 3D Pore geometry of the micro-aggregates and macro-aggregates were examined by X-ray computed tomography (μCT). The occluded particulate organic carbon (oPOC) of aggregates was measured by size and density fractionation methods. Micro-aggregates had 54% less μCT observed porosity but 64% more oPOC compared with macro-aggregates. In addition, the pore connectivity in micro-aggregates was lower than macro-aggregates. Despite both lower μCT observed porosity and pore connectivity in micro-aggregates, the organic carbon decomposition rate constant (Ksoc) was similar in both aggregate size ranges. Structural equation modelling showed a strong positive relationship of the concentration of oPOC with bacterial diversity in aggregates. We use these findings to propose a conceptual model that illustrates the dynamic links between substrate, bacterial diversity, and pore geometry that suggests a structural explanation for differences in bacterial diversity across aggregate sizes. PMID:27615807

Influences of composted hazelnut husk on some physical properties of soils.

PubMed

Zeytin, Serhat; Baran, Abdullah

2003-07-01

Some physical properties of clay loam and sandy loam soils amended with hazelnut husk (HH) were investigated. HH collected from hazelnut trees were dried, ground and composted for four months. Before use the composted material obtained was separated to three different aggregate sizes, smaller than 0.84 mm, 0.84-2.38 mm and bigger than 2.38 mm. Then these fractions were mixed with soil samples, at 0%, 1%, 2%, 4% and 8% by weight. Huzelnut husk compost-soil mixtures were placed to plastic pots and kept in an incubator at 25+/-5 degrees C for 45 and 90 days. At the end of incubation periods, water stable aggregate (WSA), hydraulic conductivity, total porosity, aeration porosity and macro- and micro-pore percentages of the mixtures were determined. Results obtained showed that composted HH increased the WSA, hydraulic conductivity, total porosity and macro-pore percentage in both clay loam and sandy loam soils depending on the incubation time and aggregate sizes.

Rainfall kinetic energy controlling erosion processes and sediment sorting on steep hillslopes: A case study of clay loam soil from the Loess Plateau, China

NASA Astrophysics Data System (ADS)

Wang, L.; Shi, Z. H.; Wang, J.; Fang, N. F.; Wu, G. L.; Zhang, H. Y.

2014-05-01

Rainfall kinetic energy (KE) can break down aggregates in the soil surface. A better understanding of sediment sorting associated with various KEs is essential for the development and verification of soil erosion models. A clay loam soil was used in the experiments. Six KEs were obtained (76, 90, 105, 160, 270, and 518 J m-2 h-1) by covering wire screens located above the soil surface with different apertures to change the size of raindrops falling on the soil surface, while maintaining the same rainfall intensity (90 ± 3.5 mm h-1). For each rainfall simulation, runoff and sediment were collected at 3-min intervals to investigate the temporal variation of the sediment particle size distribution (PSD). Comparison of the sediment effective PSD (undispersed) and ultimate PSD (dispersed) was used to investigate the detachment and transport mechanisms involved in sediment mobilization. The effective-ultimate ratios of clay-sized particles were less than 1, whereas that of sand-sized particles were greater than 1, suggesting that these particles were transported as aggregates. Under higher KE, the effective-ultimate ratios were much closer to 1, indicating that sediments were more likely transported as primary particles at higher KE owing to an increased severity of aggregate disaggregation for the clay loam soil. The percentage of clay-sized particles and the relative importance of suspension-saltation increased with increasing KE when KE was greater than 105 J m-2 h-1, while decreased with increasing KE when KE was less than 105 J m-2 h-1. A KE of 105 J m-2 h-1 appeared to be a threshold level beyond which the disintegration of aggregates was severe and the influence of KE on erosion processes and sediment sorting may change. Results of this study demonstrate the need for considering KE-influenced sediment transport when predicting erosion.

The Effect of Thermal Convection on Earth-Atmosphere CO2 Gas Exchange in Aggregated Soil

NASA Astrophysics Data System (ADS)

Ganot, Y.; Weisbrod, N.; Dragila, M. I.

2011-12-01

Gas transport in soils and surface-atmosphere gas exchange are important processes that affect different aspects of soil science such as soil aeration, nutrient bio-availability, sorption kinetics, soil and groundwater pollution and soil remediation. Diffusion and convection are the two main mechanisms that affect gas transport, fate and emissions in the soils and in the upper vadose zone. In this work we studied CO2 soil-atmosphere gas exchange under both day-time and night-time conditions, focusing on the impact of thermal convection (TCV) during the night. Experiments were performed in a climate-controlled laboratory. One meter long columns were packed with matrix of different grain size (sand, gravel and soil aggregates). Air with 2000 ppm CO2 was injected into the bottom of the columns and CO2 concentration within the columns was continuously monitored by an Infra Red Gas Analyzer. Two scenarios were compared for each soil: (1) isothermal conditions, representing day time conditions; and (2) thermal gradient conditions, i.e., atmosphere colder than the soil, representing night time conditions. Our results show that under isothermal conditions, diffusion is the major mechanism for surface-atmosphere gas exchange for all grain sizes; while under night time conditions the prevailing mechanism is dependent on the air permeability of the matrix: for sand and gravel it is diffusion, and for soil aggregates it is TCV. Calculated CO2 flux for the soil aggregates column shows that the TCV flux was three orders of magnitude higher than the diffusive flux.

Bioaccessible Porosity: A new approach to assess residual contamination after bioremediation of hydrophobic organic compounds in sub-surface microporous environments

NASA Astrophysics Data System (ADS)

Akbari, A.; Ghoshal, S.

2016-12-01

We define a new parameter, "bioaccessible porosity", the fraction of aggregate volume accessible to soil bacteria, towards a priori assessment of hydrocarbon bioremediation end points. Microbial uptake of poorly soluble hydrocarbons occurs through direct uptake or micellar solubilzation/emulsification associated with biosurfactant production, and requires close proximity of bacteria and hydrocarbon phase. In subsurface microporous environments, bioremediation rates are attenuated when residual hydrophobic contamination is entrapped in sterically restrictive environments which is not accessible to soil bacteria. This study presents new approaches for characterization of the microstructure of porous media and as well, the ability of indigenous hydrocarbon degraders to access to a range of pore sizes. Bacterial access to poorly soluble hydrocarbons in soil micro pores were simulated with bioreactors with membranes with different pore sizes containing the hydrocarbon degrading bacteria, Dietzia maris. D. maris is Gram-positive, and nonmotile that we isolated as the major hydrocarbon degrader from a fine-grained, weathered, hydrocarbon-contaminated site soil. Under nutritional stress, planktonic D. maris cells were aggregated and accessed 5 µm but not 3 µm and smaller pores. However, when hexadecane was available at the pore mouth, D. maris colonized the pore mouth, and accessed pores as small as 0.4 µm. This suggests bacterial accessibility to different pore sizes is regulated by nutritional conditions. A combination of X-ray micro-CT scanning, gas adsorption and mercury intrusion porosimetry was used to characterize the range of pore sizes of soil aggregates. In case of the studied contaminated soil, the bioaccessible porosity were determined as 25% , 27% and 29% (assuming 4, 1, 0.4 µm respectively as accessibility criteria), and about 2.7% of aggregate volume was attributed to 0.006-0.4 µm pores. The 2% aggregate volume at an assumed saturation of 10% could accommodate 1000 mg/ kg soil of oil. The remediation endpoint after extended biotreatment was at similar order of magnitude of 600 mg/kg. The approach introduced here could be used for qualitative assessment of attainable bioremediation endpoint in soils with different microstructure and hydrocarbon degrading bacterial community.

Soil-Structural Stability as Affected by Clay Mineralogy, Soil Texture and Polyacrylamide Application

USDA-ARS?s Scientific Manuscript database

Soil-structural stability (expressed in terms of aggregate stability and pore size distribution) depends on (i) soil inherent properties, (ii) extrinsic condition prevailing in the soil that may vary temporally and spatially, and (iii) addition of soil amendments. Different soil management practices...

Microbial activity promoted with organic carbon accumulation in macroaggregates of paddy soils under long-term rice cultivation

NASA Astrophysics Data System (ADS)

Liu, Yalong; Wang, Ping; Ding, Yuanjun; Lu, Haifei; Li, Lianqing; Cheng, Kun; Zheng, Jufeng; Filley, Timothy; Zhang, Xuhui; Zheng, Jinwei; Pan, Genxing

2016-12-01

While soil organic carbon (SOC) accumulation and stabilization has been increasingly the focus of ecosystem properties, how it could be linked to soil biological activity enhancement has been poorly assessed. In this study, topsoil samples were collected from a series of rice soils shifted from salt marshes for 0, 50, 100, 300 and 700 years from a coastal area of eastern China. Soil aggregates were fractioned into different sizes of coarse sand (200-2000 µm), fine sand (20-200 µm), silt (2-20 µm) and clay (< 2 µm), using separation with a low-energy dispersion protocol. Soil properties were determined to investigate niche specialization of different soil particle fractions in response to long-term rice cultivation, including recalcitrant and labile organic carbon, microbial diversity of bacterial, archaeal and fungal communities, soil respiration and enzyme activity. The results showed that the mass proportion both of coarse-sand (2000-200 µm) and clay (< 2 µm) fractions increased with prolonged rice cultivation, but the aggregate size fractions were dominated by fine-sand (200-20 µm) and silt (20-2 µm) fractions across the chronosequence. SOC was highly enriched in coarse-sand fractions (40-60 g kg-1) and moderately in clay fractions (20-25 g kg-1), but was depleted in silt fractions (˜ 10 g kg-1). The recalcitrant carbon pool was higher (33-40 % of SOC) in both coarse-sand and clay fractions than in fine-sand and silt fractions (20-29 % of SOC). However, the ratio of labile organic carbon (LOC) to SOC showed a weakly decreasing trend with decreasing size of aggregate fractions. Total soil DNA (deoxyribonucleic acid) content in the size fractions followed a similar trend to that of SOC. Despite the largely similar diversity between the fractions, 16S ribosomal gene abundance of bacteria and of archaeal were concentrated in both coarse-sand and clay fractions. Being the highest generally in coarse-sand fractions, 18S rRNA gene abundance of fungi decreased sharply but the diversity gently, with decreasing size of the aggregate fractions. The soil respiration quotient (ratio of respired CO2-C to SOC) was the highest in the silt fraction, followed by the fine-sand fraction, but the lowest in coarse-sand and clay fractions in the rice soils cultivated over 100 years, whereas the microbial metabolic quotient was lower in coarse-sand-sized fractions than in other fractions. Soil respiration was higher in the silt fraction than in other fractions for the rice soils. For the size fractions other than the clay fraction, enzyme activity was increased with prolonged rice cultivation, whereas soil respiration appeared to have a decreasing trend. Only in the coarse-sand fraction was both microbial gene abundance and enzyme activity well correlated to SOC and LOC content, although the chemical stability and respiratory of SOC were similar between coarse-sand and clay fractions. Thus, biological activity was generally promoted with LOC accumulation in the coarse-sand-sized macroaggregates of the rice soils, positively responding to prolonged rice cultivation management. The finding here provides a mechanistic understanding of soil organic carbon turnover and microbial community succession at fine scale of soil aggregates that have evolved along with anthropogenic activity of rice cultivation in the field.

Life cycle of soil sggregates: from root residue to microbial and physical hotspots

NASA Astrophysics Data System (ADS)

Ghezzehei, T. A.; Or, D.

2017-12-01

Soil aggregation is a physical state of soil in which clumps of primary soil particles are held together by biological and/or chemical cementing agents. Aggregations plays important role in storage and movement of water and essential gases, nutrient cycling, and ultimately supporting microbial and plant life. It is also one of the most dynamic and sensitive soil qualities, which readily responds to disturbances such as cultivation, fire, drought, flooding, and changes in vegetation. Soil aggregation that is primarily controlled by organic matter generally exhibits hierarchical organization of soil constituents into stable units that range in size from a few microns to centimeters. However, this conceptual model of soil aggregation as the key unifying mechanism remains poorly quantified and is rarely included in predictive soil models. Here we provide a biophysical framework for quantitative and predictive modeling of soil aggregation and its attendant soil characteristics. The framework treats aggregates as hotspots of biological, chemical and physical processes centered around roots and root residue. We keep track of the life cycle of an individual aggregate from it genesis in the rhizosphere, fueled by rhizodeposition and mediated by vigorous microbial activity, until its disappearance when the root-derived resources are depleted. The framework synthesizes current understanding of microbial life in porous media; water holding and soil binding capacity of biopolymers; and environmental controls on soil organic matter dynamics. The framework paves a way for integration of processes that are presently modeled as disparate or poorly coupled processes, including storage and protection of carbon, microbial activity, greenhouse gas fluxes, movement and storage of water, resistance of soils against erosion.

Partitioning of habitable pore space in earthworm burrows.

PubMed

Gorres, Josef H; Amador, Jose A

2010-03-01

Earthworms affect macro-pore structure of soils. However, some studies suggest that earthworm burrow walls and casts themselves differ greatly in structure from surrounding soils, potentially creating habitat for microbivorours nematodes which accelerate the decomposition and C and N mineralization. In this study aggregates were sampled from the burrow walls of the anecic earthworm Lumbricus terrestris and bulk soil (not altered by earthworms) from mesocosm incubated in the lab for 0, 1, 3, 5 and 16 weeks. Pore volumes and pore sizes were measured in triplicate with Mercury Intrusion Porosimetry (MIP). This method is well suited to establish pore size structure in the context of habitat, because it measures the stepwise intrusion of mercury from the outside of the aggregate into ever smaller pores. The progress of mercury into the aggregate interior thus resembles potential paths of a nematode into accessible habitable pore spaces residing in an aggregate. Total specific pore volume, V(s), varied between 0.13 and 0.18 mL/g and increased from 3 to 16 weeks in both burrow and bulk soil. Differences between total V(s) of bulk and burrow samples were not significant on any sampling date. However, differences were significant for pore size fractions at the scale of nematode body diameter.

Partitioning of habitable pore space in earthworm burrows

PubMed Central

Amador, Jose A.

2010-01-01

Earthworms affect macro-pore structure of soils. However, some studies suggest that earthworm burrow walls and casts themselves differ greatly in structure from surrounding soils, potentially creating habitat for microbivorours nematodes which accelerate the decomposition and C and N mineralization. In this study aggregates were sampled from the burrow walls of the anecic earthworm Lumbricus terrestris and bulk soil (not altered by earthworms) from mesocosm incubated in the lab for 0, 1, 3, 5 and 16 weeks. Pore volumes and pore sizes were measured in triplicate with Mercury Intrusion Porosimetry (MIP). This method is well suited to establish pore size structure in the context of habitat, because it measures the stepwise intrusion of mercury from the outside of the aggregate into ever smaller pores. The progress of mercury into the aggregate interior thus resembles potential paths of a nematode into accessible habitable pore spaces residing in an aggregate. Total specific pore volume, Vs, varied between 0.13 and 0.18 mL/g and increased from 3 to 16 weeks in both burrow and bulk soil. Differences between total Vs of bulk and burrow samples were not significant on any sampling date. However, differences were significant for pore size fractions at the scale of nematode body diameter. PMID:22736839

Carbon Storage in Soil Size Fractions Under Two Cacao Agroforestry Systems in Bahia, Brazil

NASA Astrophysics Data System (ADS)

Gama-Rodrigues, Emanuela F.; Ramachandran Nair, P. K.; Nair, Vimala D.; Gama-Rodrigues, Antonio C.; Baligar, Virupax C.; Machado, Regina C. R.

2010-02-01

Shaded perennial agroforestry systems contain relatively high quantities of soil carbon (C) resulting from continuous deposition of plant residues; however, the extent to which the C is sequestered in soil will depend on the extent of physical protection of soil organic C (SOC). The main objective of this study was to characterize SOC storage in relation to soil fraction-size classes in cacao ( Theobroma cacao L.) agroforestry systems (AFSs). Two shaded cacao systems and an adjacent natural forest in reddish-yellow Oxisols in Bahia, Brazil were selected. Soil samples were collected from four depth classes to 1 m depth and separated by wet-sieving into three fraction-size classes (>250 μm, 250-53 μm, and <53 μm)—corresponding to macroaggregate, microaggregate, and silt-and-clay size fractions—and analyzed for C content. The total SOC stock did not vary among systems (mean: 302 Mg/ha). On average, 72% of SOC was in macroaggregate-size, 20% in microaggregate-size, and 8% in silt-and-clay size fractions in soil. Sonication of aggregates showed that occlusion of C in soil aggregates could be a major mechanism of C protection in these soils. Considering the low level of soil disturbances in cacao AFSs, the C contained in the macroaggregate fraction might become stabilized in the soil. The study shows the role of cacao AFSs in mitigating greenhouse gas (GHG) emission through accumulation and retention of high amounts of organic C in the soils and suggests the potential benefit of this environmental service to the nearly 6 million cacao farmers worldwide.

Carbon storage in soil size fractions under two cacao agroforestry systems in Bahia, Brazil.

PubMed

Gama-Rodrigues, Emanuela F; Ramachandran Nair, P K; Nair, Vimala D; Gama-Rodrigues, Antonio C; Baligar, Virupax C; Machado, Regina C R

2010-02-01

Shaded perennial agroforestry systems contain relatively high quantities of soil carbon (C) resulting from continuous deposition of plant residues; however, the extent to which the C is sequestered in soil will depend on the extent of physical protection of soil organic C (SOC). The main objective of this study was to characterize SOC storage in relation to soil fraction-size classes in cacao (Theobroma cacao L.) agroforestry systems (AFSs). Two shaded cacao systems and an adjacent natural forest in reddish-yellow Oxisols in Bahia, Brazil were selected. Soil samples were collected from four depth classes to 1 m depth and separated by wet-sieving into three fraction-size classes (>250 microm, 250-53 microm, and <53 microm)-corresponding to macroaggregate, microaggregate, and silt-and-clay size fractions-and analyzed for C content. The total SOC stock did not vary among systems (mean: 302 Mg/ha). On average, 72% of SOC was in macroaggregate-size, 20% in microaggregate-size, and 8% in silt-and-clay size fractions in soil. Sonication of aggregates showed that occlusion of C in soil aggregates could be a major mechanism of C protection in these soils. Considering the low level of soil disturbances in cacao AFSs, the C contained in the macroaggregate fraction might become stabilized in the soil. The study shows the role of cacao AFSs in mitigating greenhouse gas (GHG) emission through accumulation and retention of high amounts of organic C in the soils and suggests the potential benefit of this environmental service to the nearly 6 million cacao farmers worldwide.

The specific role of fungal community structure on soil aggregation and carbon sequestration: results from long-term field study in a paddy soil

NASA Astrophysics Data System (ADS)

Murugan, Rajasekaran; Kumar, Sanjay

2015-04-01

Soil aggregate stability is a crucial soil property that affects soil biota, biogeochemical processes and C sequestration. The relationship between soil aggregate stability and soil C cycling is well known but the influence of specific fungal community structure on this relationship is largely unknown in paddy soils. The aim of the present study was to evaluate the long-term fertilisation (mineral fertiliser-MIN; farmyard manure-FYM; groundnut oil cake-GOC) effects on soil fungal community shifts associated with soil aggregates under rice-monoculture (RRR) and rice-legume-rice (RLR) systems. Fungal and bacterial communities were characterized using phospholipid fatty acids, and glucosamine and muramic acid were used as biomarkers for fungal and bacterial residues, respectively. Microbial biomass C and N, fungal biomass and residues were significantly higher in the organic fertiliser treatments than in the MIN treatment, for all aggregate sizes under both crop rotation systems. In general, fungal/bacterial biomass ratio and fungal residue C/bacterial residue C ratio were significantly higher in macroaggregate fractions (> 2000 and 250-2000 μm) than in microaggregate fractions (53-250 and <53 μm). In both crop rotation systems, the long-term application of FYM and GOC led to increased accumulation of saprotrophic fungi (SF) in aggregate fractions > 2000 μm. In contrast, we found that arbuscular mycorrhizal fungi (AMF) was surprisingly higher in aggregate fractions > 2000 μm than in aggregate fraction 250-2000 μm under MIN treatment. The RLR system showed significantly higher AMF biomass and fungal residue C/ bacterial residue C ratio in both macroaggregate fractions compared to the RRR system. The strong relationships between SF, AMF and water stable aggregates shows the specific contribution of fungi community on soil aggregate stability. Our results highlight the fact that changes within fungal community structure play an important role in shaping the soil aggregate stability and C sequestration in tropical agricultural ecosystems.

Modeling the transport of engineered nanoparticles in saturated porous media - an experimental setup

NASA Astrophysics Data System (ADS)

Braun, A.; Neukum, C.; Azzam, R.

2011-12-01

The accelerating production and application of engineered nanoparticles is causing concerns regarding their release and fate in the environment. For assessing the risk that is posed to drinking water resources it is important to understand the transport and retention mechanisms of engineered nanoparticles in soil and groundwater. In this study an experimental setup for analyzing the mobility of silver and titanium dioxide nanoparticles in saturated porous media is presented. Batch and column experiments with glass beads and two different soils as matrices are carried out under varied conditions to study the impact of electrolyte concentration and pore water velocities. The analysis of nanoparticles implies several challenges, such as the detection and characterization and the preparation of a well dispersed sample with defined properties, as nanoparticles tend to form agglomerates when suspended in an aqueous medium. The analytical part of the experiments is mainly undertaken with Flow Field-Flow Fractionation (FlFFF). This chromatography like technique separates a particulate sample according to size. It is coupled to a UV/Vis and a light scattering detector for analyzing concentration and size distribution of the sample. The advantage of this technique is the ability to analyze also complex environmental samples, such as the effluent of column experiments including soil components, and the gentle sample treatment. For optimization of the sample preparation and for getting a first idea of the aggregation behavior in soil solutions, in sedimentation experiments the effect of ionic strength, sample concentration and addition of a surfactant on particle or aggregate size and temporal dispersion stability was investigated. In general the samples are more stable the lower the concentration of particles is. For TiO2 nanoparticles, the addition of a surfactant yielded the most stable samples with smallest aggregate sizes. Furthermore the suspension stability is increasing with electrolyte concentration. Depending on the dispersing medium the results show that TiO2 nanoparticles tend to form aggregates between 100-200 nm in diameter while the primary particle size is given as 21 nm by the manufacturer. Aggregate sizes are increasing with time. The particle size distribution of the silver nanoparticle samples is quite uniform in each medium. The fresh samples show aggregate sizes between 40 and 45 nm while the primary particle size is 15 nm according to the manufacturer. Aggregate size is only slightly increasing with time during the sedimentation experiments. These results are used as a reference when analyzing the effluent of column experiments.

Association of Soil Aggregation with the Distribution and Quality of Organic Carbon in Soil along an Elevation Gradient on Wuyi Mountain in China.

PubMed

Li, Liguang; Vogel, Jason; He, Zhenli; Zou, Xiaoming; Ruan, Honghua; Huang, Wei; Wang, Jiashe; Bianchi, Thomas S

2016-01-01

Forest soils play a critical role in the sequestration of atmospheric CO2 and subsequent attenuation of global warming. The nature and properties of organic matter in soils have an influence on the sequestration of carbon. In this study, soils were collected from representative forestlands, including a subtropical evergreen broad-leaved forest (EBF), a coniferous forest (CF), a subalpine dwarf forest (DF), and alpine meadow (AM) along an elevation gradient on Wuyi Mountain, which is located in a subtropical area of southeastern China. These soil samples were analyzed in the laboratory to examine the distribution and speciation of organic carbon (OC) within different size fractions of water-stable soil aggregates, and subsequently to determine effects on carbon sequestration. Soil aggregation rate increased with increasing elevation. Soil aggregation rate, rather than soil temperature, moisture or clay content, showed the strongest correlation with OC in bulk soil, indicating soil structure was the critical factor in carbon sequestration of Wuyi Mountain. The content of coarse particulate organic matter fraction, rather than the silt and clay particles, represented OC stock in bulk soil and different soil aggregate fractions. With increasing soil aggregation rate, more carbon was accumulated within the macroaggregates, particularly within the coarse particulate organic matter fraction (250-2000 μm), rather than within the microaggregates (53-250μm) or silt and clay particles (< 53μm). In consideration of the high instability of macroaggregates and the liability of SOC within them, further research is needed to verify whether highly-aggregated soils at higher altitudes are more likely to lose SOC under warmer conditions.

Association of Soil Aggregation with the Distribution and Quality of Organic Carbon in Soil along an Elevation Gradient on Wuyi Mountain in China

PubMed Central

Li, Liguang; Vogel, Jason; He, Zhenli; Zou, Xiaoming; Ruan, Honghua; Huang, Wei; Wang, Jiashe; Bianchi, Thomas S.

2016-01-01

Forest soils play a critical role in the sequestration of atmospheric CO2 and subsequent attenuation of global warming. The nature and properties of organic matter in soils have an influence on the sequestration of carbon. In this study, soils were collected from representative forestlands, including a subtropical evergreen broad-leaved forest (EBF), a coniferous forest (CF), a subalpine dwarf forest (DF), and alpine meadow (AM) along an elevation gradient on Wuyi Mountain, which is located in a subtropical area of southeastern China. These soil samples were analyzed in the laboratory to examine the distribution and speciation of organic carbon (OC) within different size fractions of water-stable soil aggregates, and subsequently to determine effects on carbon sequestration. Soil aggregation rate increased with increasing elevation. Soil aggregation rate, rather than soil temperature, moisture or clay content, showed the strongest correlation with OC in bulk soil, indicating soil structure was the critical factor in carbon sequestration of Wuyi Mountain. The content of coarse particulate organic matter fraction, rather than the silt and clay particles, represented OC stock in bulk soil and different soil aggregate fractions. With increasing soil aggregation rate, more carbon was accumulated within the macroaggregates, particularly within the coarse particulate organic matter fraction (250–2000 μm), rather than within the microaggregates (53–250μm) or silt and clay particles (< 53μm). In consideration of the high instability of macroaggregates and the liability of SOC within them, further research is needed to verify whether highly-aggregated soils at higher altitudes are more likely to lose SOC under warmer conditions. PMID:26964101

The dynamics of soil aggregate breakdown in water in response to landuse as measured with laser diffraction technique

NASA Astrophysics Data System (ADS)

Oyedele, D. J.; Pini, R.; Sparvoli, E.; Scatena, M.

2012-04-01

The Mastersizer 2000G (Malvern Instruments) Diffraction Instrument was used to assess and quantify the breakdown of soil aggregates and compute wet aggregate stability indices. The study was aimed at evolving a novel rapid method of determining soil aggregate stability. Bulk surface (0-15 cm) soil samples were collected under 5 different land uses in the Teaching and Resrach Farm of Obafemi Awolowo University, Ile-Ife, Nigeria. About 0.5g of the soils aggregates (0.5 -1 mm diameter) were evaluated in the laser diffractometer with the stirrer operated at 500 rpm and the pump at 1800 rpm. The different size aggregates and particles of sand silt and clay were quantified periodically. Water stable aggregates greater than 250 µm (WSA>250), water stable aggregates less than 250 µm (WSA<250), water dispersible clay index (WDI), and mean volume diameter (MVD) among others were computed from the laser diffraction data. The values were compared with the classical Yoder wet sieving technique. The WSA>250 was significantly higher on the soils under Forest (FR), Cacao (CC), Teak (TK) and Oil Palm (OP) plantations, while it was significantly lowest under no-tillage (NT) and continuous cultivation (CT). The pasture (PD) was not significantly different from either the cultivated and the non-cultivated soils. Conversely, the WSA<250 and water dispersible clay index was highest in the cultivated soils (CT and NT) and lowest in the non-cultivated soils (FR, TK, CC and OP) while the PD was in-between. The MVD also followed a similar trend as the WSA>250. The wet sieving water stable aggregates index (WSI>250) was significantly correlated with WSA>250 (r = 0.75), MVD (r = 0.75), WDI (r = -0.68) and WSA<250 (r = - 0.73). All the laser diffraction measured aggregation indices were significantly correlated with the organic matter contents of the soils. Thus the laser diffraction promises a rapid and comprehensive method of evaluation of soil aggregate stability.

Mechanisms of Soil Aggregation: a biophysical modeling framework

NASA Astrophysics Data System (ADS)

Ghezzehei, T. A.; Or, D.

2016-12-01

Soil aggregation is one of the main crosscutting concepts in all sub-disciplines and applications of soil science from agriculture to climate regulation. The concept generally refers to adhesion of primary soil particles into distinct units that remain stable when subjected to disruptive forces. It is one of the most sensitive soil qualities that readily respond to disturbances such as cultivation, fire, drought, flooding, and changes in vegetation. These changes are commonly quantified and incorporated in soil models indirectly as alterations in carbon content and type, bulk density, aeration, permeability, as well as water retention characteristics. Soil aggregation that is primarily controlled by organic matter generally exhibits hierarchical organization of soil constituents into stable units that range in size from a few microns to centimeters. However, this conceptual model of soil aggregation as the key unifying mechanism remains poorly quantified and is rarely included in predictive soil models. Here we provide a biophysical framework for quantitative and predictive modeling of soil aggregation and its attendant soil characteristics. The framework treats aggregates as hotspots of biological, chemical and physical processes centered around roots and root residue. We keep track of the life cycle of an individual aggregate from it genesis in the rhizosphere, fueled by rhizodeposition and mediated by vigorous microbial activity, until its disappearance when the root-derived resources are depleted. The framework synthesizes current understanding of microbial life in porous media; water holding and soil binding capacity of biopolymers; and environmental controls on soil organic matter dynamics. The framework paves a way for integration of processes that are presently modeled as disparate or poorly coupled processes, including storage and protection of carbon, microbial activity, greenhouse gas fluxes, movement and storage of water, resistance of soils against erosion.

Dynamics of aggregate stability and soil organic C distribution as affected by climatic aggressiveness: a mesocosm approach

NASA Astrophysics Data System (ADS)

Pellegrini, Sergio; Elio Agnelli, Alessandro; Costanza Andrenelli, Maria; Barbetti, Roberto; Castelli, Fabio; Costantini, Edoardo A. C.; Lagomarsino, Alessandra; Pasqui, Massimiliano; Tomozeiu, Rodica; Razzaghi, Somayyeh; Vignozzi, Nadia

2014-05-01

In the framework of a research project aimed at evaluating the adaptation scenarios of the Italian agriculture to the current climate change, a mesocosm experiment under controlled conditions was set up for studying the dynamics of soil aggregate stability and organic C in different size fractions. Three alluvial loamy soils (BOV - Typic Haplustalfs coarse-loamy; CAS - Typic Haplustalfs fine-loamy; MED - Typic Hapludalfs fine-loamy) along a climatic gradient (from dryer to moister pedoclimatic conditions) in the river Po valley (northern Italy), under crop rotation for animal husbandry from more than 40 years, were selected. The Ap horizons (0-30cm) were taken and placed in 9 climatic chambers under controlled temperature and rainfall. Each soil was subjected to three different climate scenarios in terms of erosivity index obtained by combining Modified Fournier and Bagnouls-Gaussen indexes: i) typical (TYP), the median year of each site related to the 1961-1990 reference period; ii) maximum aggressive year (MAX) observed in the same period, and iii) the simulated climate (SIM), obtained by projections of climate change precipitation and temperature for the period 2021-2050 as provided by the IPCC-A1B emission scenario. In the climatic chambers the year climate was reduced to six months. The soils were analyzed for particle size distribution, aggregate stability by wet and dry sieving, and organic C content at the beginning and at the end of the trial. The soils showed different behaviour in terms of aggregate stability and dynamics of organic C in the diverse size fractions. The soils significantly differed in terms of initial mean weight diameter (MWD) (CAS>MED>BOV). A general reduction of MWD in all sites was observed at the end of the experiment, with the increase of the smallest aggregate fractions (0.250-0.05 mm). In particular, BOV showed the maximum decrease of the aggregate stability and MED the lowest. C distribution in aggregate fractions significantly changed at the end of the trial, depending of soil types. In CAS and MED a decrease of C content was observed in fractions larger than 0.250 mm, while an accumulation occurred only in CAS microaggregates. BOV showed a singular pattern, with an increase of organic C in all fractions. In this site an improvement of aggregation, involving the coarser fractions, seems to have been favoured during the experiment. Overall, the imposed climate did not affect significantly these trends, except in CAS, where TYP and SIM climates showed an increase of macroaggregates and their C concentration. Soil pedoclimatic characteristics showed to be the main factors affecting C and aggregates dynamics in this mesocosm experiment.

Scratching technique for the study and analysis of soil surface abrasion mechanism

NASA Astrophysics Data System (ADS)

Ta, Wanquan

2007-11-01

Aeolian abrasion is the most fundamental and active surface process that takes place in arid and semi-arid environments. Its nature is a wear process for wind blown grains impinging on a soil or sediment surface, which causes particles and aggregates to fracture from the soil surface through a series of plastic and brittle cracking deformation such as cutting, ploughing and brittle fracturing. Using a Universal Micro-Tribometer (UMT), a scratching test was carried out on six soil surfaces (sandy soil, sand loam, silt loam, loam, silt clay loam, and silt clay). The results indicate that traces of normal and tangential force vs. time show a jagged curve, which can reflect the plastic deformation and brittle fracturing of aggregates and particles of various sizes fractured from the soil surfaces. The jagged curve peaks, and the area enclosed underneath, may represent the bonding forces and bonding energies of some aggregates and grains on the soil surface, respectively. Connecting the scratching test with an impact abrasion experiment furthermore demonstrates that soil surface abrasion rates are proportional to the square of speeds of impacting particles and to the 2.6 power of mean soil grain size, and inversely proportional to the 1.5 power of specific surface abrasive energy or to the 1.7 power of specific surface hardness.

Carbon Structural Investigations of Concentric Layers Within Macro-aggregates From Forest and Agricultural Soils

NASA Astrophysics Data System (ADS)

Dria, K. J.; Gamblin, D. E.; Smucker, A. J.; Park, E.; Filley, T. R.

2004-12-01

Much of the current research on the potential of agricultural and forest soils to act as sinks for greenhouse gases focuses on the capacity of the systems to form long-term stabilized fractions of soil organic matter (SOM). One proposed mechanism is that carbon is sequestered within soil aggregate interiors during the aggregation process. Repeated wetting-drying cycles change internal pore geometries and associated microhabitats and create more stable macro-aggregates. Research by Smucker and coworkers (EGU Abstracts, 2004) suggest that the exterior portions of aggregates contain greater concentrations of C and N than their interiors, establishing gradients of \\ä13C values across these aggregates. We present the results of a study to test if there exists molecular evidence of such gradients. Soil samples from forest, conventional tillage (CT) and no tillage (NT) agriculture ecosystems in Hoytville and Wooster LTER sites were gently sieved into various size fractions. Soil macro-aggregates (6.3-9.5mm) were peeled, by mechanical erosion chambers, into concentric layers and separated into exterior, transitional and interior regions. Alkaline CuO oxidation was used to determine the composition of lignin, suberin, and cutin biopolymers to determine changes in source and degradative states of SOM. Preliminary results indicate that both soils show similar relative yields of lignin and hydroxyl fatty acids with a greater abundance of lignin than cutin and suberin acids. Greater abundances (per 100mg organic carbon) of CuO products were observed in the native forest than in either agricultural system. The lignin in the NT agricultural soil was least oxidized, followed by the forest soils, then the CT agricultural soils. For both soils, slight trends in biopolymer concentrations were observed between the exterior, transitional and interior regions of the aggregates from the forest and CT or NT ecosystems.

Predicting the mineral composition of dust aerosols – Part 1: Representing key processes

DOE PAGES

Perlwitz, J. P.; Perez Garcia-Pando, C.; Miller, R. L.

2015-10-21

Soil dust aerosols created by wind erosion are typically assigned globally uniform physical and chemical properties within Earth system models, despite known regional variations in the mineral content of the parent soil. Mineral composition of the aerosol particles is important to their interaction with climate, including shortwave absorption and radiative forcing, nucleation of cloud droplets and ice crystals, heterogeneous formation of sulfates and nitrates, and atmospheric processing of iron into bioavailable forms that increase the productivity of marine phytoplankton. Here, aerosol mineral composition is derived by extending a method that provides the composition of a wet-sieved soil. The extension accountsmore » for measurements showing significant differences between the mineral fractions of the wet-sieved soil and the emitted aerosol concentration. For example, some phyllosilicate aerosols are more prevalent at silt sizes, even though they are nearly absent at these diameters in a soil whose aggregates are dispersed by wet sieving. We calculate the emitted mass of each mineral with respect to size by accounting for the disintegration of soil aggregates during wet sieving. These aggregates are emitted during mobilization and fragmentation of the original undispersed soil that is subject to wind erosion. The emitted aggregates are carried far downwind from their parent soil. The soil mineral fractions used to calculate the aggregates also include larger particles that are suspended only in the vicinity of the source. We calculate the emitted size distribution of these particles using a normalized distribution derived from aerosol measurements. In addition, a method is proposed for mixing minerals with small impurities composed of iron oxides. These mixtures are important for transporting iron far from the dust source, because pure iron oxides are more dense and vulnerable to gravitational removal than most minerals comprising dust aerosols. Finally, a limited comparison to measurements from North Africa shows that the model extensions result in better agreement, consistent with a more extensive comparison to global observations as well as measurements of elemental composition downwind of the Sahara, as described in companion articles.« less

C and N Content in Density Fractions of Whole Soil and Soil Size Fraction Under Cacao Agroforestry Systems and Natural Forest in Bahia, Brazil

NASA Astrophysics Data System (ADS)

Rita, Joice Cleide O.; Gama-Rodrigues, Emanuela Forestieri; Gama-Rodrigues, Antonio Carlos; Polidoro, Jose Carlos; Machado, Regina Cele R.; Baligar, Virupax C.

2011-07-01

Agroforestry systems (AFSs) have an important role in capturing above and below ground soil carbon and play a dominant role in mitigation of atmospheric CO2. Attempts has been made here to identify soil organic matter fractions in the cacao-AFSs that have different susceptibility to microbial decomposition and further represent the basis of understanding soil C dynamics. The objective of this study was to characterize the organic matter density fractions and soil size fractions in soils of two types of cacao agroforestry systems and to compare with an adjacent natural forest in Bahia, Brazil. The land-use systems studied were: (1) a 30-year-old stand of natural forest with cacao (cacao cabruca), (2) a 30-year-old stand of cacao with Erythrina glauca as shade trees (cacao + erythrina), and (3) an adjacent natural forest without cacao. Soil samples were collected from 0-10 cm depth layer in reddish-yellow Oxisols. Soil samples was separated by wet sieving into five fraction-size classes (>2000 μm, 1000-2000 μm, 250-1000 μm, 53-250 μm, and <53 μm). C and N accumulated in to the light (free- and intra-aggregate density fractions) and heavy fractions of whole soil and soil size fraction were determined. Soil size fraction obtained in cacao AFS soils consisted mainly (65 %) of mega-aggregates (>2000 μm) mixed with macroaggregates (32-34%), and microaggregates (1-1.3%). Soil organic carbon (SOC) and total N content increased with increasing soil size fraction in all land-use systems. Organic C-to-total N ratio was higher in the macroaggregate than in the microaggregate. In general, in natural forest and cacao cabruca the contribution of C and N in the light and heavy fractions was similar. However, in cacao + erythrina the heavy fraction was the most common and contributed 67% of C and 63% of N. Finding of this study shows that the majority of C and N in all three systems studied are found in macroaggregates, particularly in the 250-1000 μm size aggregate class. The heavy fraction was the most common organic matter fraction in these soils. Thus, in mature cacao AFS on highly weathered soils the main mechanisms of C stabilization could be the physical protection within macroaggregate structures thereby minimizing the impact of conversion of forest to cacao AFS.

C and N content in density fractions of whole soil and soil size fraction under cacao agroforestry systems and natural forest in Bahia, Brazil.

PubMed

Rita, Joice Cleide O; Gama-Rodrigues, Emanuela Forestieri; Gama-Rodrigues, Antonio Carlos; Polidoro, Jose Carlos; Machado, Regina Cele R; Baligar, Virupax C

2011-07-01

Agroforestry systems (AFSs) have an important role in capturing above and below ground soil carbon and play a dominant role in mitigation of atmospheric CO(2). Attempts has been made here to identify soil organic matter fractions in the cacao-AFSs that have different susceptibility to microbial decomposition and further represent the basis of understanding soil C dynamics. The objective of this study was to characterize the organic matter density fractions and soil size fractions in soils of two types of cacao agroforestry systems and to compare with an adjacent natural forest in Bahia, Brazil. The land-use systems studied were: (1) a 30-year-old stand of natural forest with cacao (cacao cabruca), (2) a 30-year-old stand of cacao with Erythrina glauca as shade trees (cacao + erythrina), and (3) an adjacent natural forest without cacao. Soil samples were collected from 0-10 cm depth layer in reddish-yellow Oxisols. Soil samples was separated by wet sieving into five fraction-size classes (>2000 μm, 1000-2000 μm, 250-1000 μm, 53-250 μm, and <53 μm). C and N accumulated in to the light (free- and intra-aggregate density fractions) and heavy fractions of whole soil and soil size fraction were determined. Soil size fraction obtained in cacao AFS soils consisted mainly (65 %) of mega-aggregates (>2000 μm) mixed with macroaggregates (32-34%), and microaggregates (1-1.3%). Soil organic carbon (SOC) and total N content increased with increasing soil size fraction in all land-use systems. Organic C-to-total N ratio was higher in the macroaggregate than in the microaggregate. In general, in natural forest and cacao cabruca the contribution of C and N in the light and heavy fractions was similar. However, in cacao + erythrina the heavy fraction was the most common and contributed 67% of C and 63% of N. Finding of this study shows that the majority of C and N in all three systems studied are found in macroaggregates, particularly in the 250-1000 μm size aggregate class. The heavy fraction was the most common organic matter fraction in these soils. Thus, in mature cacao AFS on highly weathered soils the main mechanisms of C stabilization could be the physical protection within macroaggregate structures thereby minimizing the impact of conversion of forest to cacao AFS.

Assessing the strength of soil aggregates produced by two types of organic matter amendments using the ultrasonic energy

NASA Astrophysics Data System (ADS)

Zhu, Zhaolong; minasny, Budiman; Field, Damien; Angers, Denis

2017-04-01

The presence of organic matter (OM) is known to stimulate the formation of soil aggregates, but the aggregation strength may vary with different amount and type/quality of OM. Conventionally wet sieving method was used to assess the aggregates' strength. In this study, we wish to get insight of the effects of different types of C inputs on aggregate dynamics using quantifiable energy via ultrasonic agitation. A clay soil with an inherently low soil organic carbon (SOC) content, was amended with two different sources of organic matter (alfalfa, C:N = 16.7 and barley straw, C:N = 95.6) at different input levels (0, 10, 20, & 30 g C kg-1 soil). The soil's inherent macro aggregates were first destroyed via puddling. The soils were incubated in pots at moisture content 70% of field capacity for a period of 3 months. The pots were housed in a 1.2L sealed opaque plastic container. The CO2 generated during the incubation was captured by a vial of NaOH which was placed in each of the sealed containers and sampled per week. At 14, 28, 56, and 84 days, soil samples were collected and the change in aggregation was assessed using a combination of wet sieving and ultrasonic agitation. The relative strength of aggregates exposed to ultrasonic agitation was modelled using the aggregate disruption characteristic curve (ADCC) and soil dispersion characteristic curve (SDCC). Both residue quality and quantity of organic matter input influenced the amount of aggregates formed and their relative strength. The MWD of soils amended with alfalfa residues was greater than that of barley straw at lower input rates and early in the incubation. In the longer term, the use of ultrasonic energy revealed that barley straw resulted in stronger aggregates, especially at higher input rates despite showing similar MWD as alfalfa. The use of ultrasonic agitation, where we quantify the energy required to liberate and disperse aggregates allowed us to differentiate the effects of C inputs on the size of stable aggregates and their relative strength.

Soil aggregate mediates the impacts of land uses on organic carbon, total nitrogen, and microbial activity in a Karst ecosystem

NASA Astrophysics Data System (ADS)

Xiao, Shuangshuang; Zhang, Wei; Ye, Yingying; Zhao, Jie; Wang, Kelin

2017-02-01

Understanding the effect of land use on soil carbon, nitrogen, and microbial activity associated with aggregates is critical for thorough comprehension of the C and N dynamics of karst landscapes/ecosystems. We monitored soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), and Cmic: Corg ratio in large macro- (>2 mm), small macro- (0.25-2 mm), and micro- (0.053-0.25 mm) aggregates to determine the changes in soil properties under different land uses in the karst area of Southwest China. Five common land-use types—enclosure land (natural system, control), prescribed-burning land, fuel-wood shrubland, pasture and maize fields—were selected. Results showed that pasture and maize fields remarkably decreased the SOC and TN concentrations in aggregates. Conversion of natural system to other land uses decreased MBC (except for prescribed-burning) and increased Cmic: Corg ratios in aggregates. The extent of the response to land uses of SOC and TN concentrations was similar whereas that of MBC and Cmic: Corg ratios differed across the three aggregate sizes. Further, the SOC concentrations were significantly higher in macro-aggregates than micro-aggregates; the MBC and Cmic: Corg ratios were highest in small macro-aggregates. Therefore, small macro-aggregates might have more active C dynamics.

Soil aggregation and slope stability related to soil density, root length, and mycorrhiza

NASA Astrophysics Data System (ADS)

Graf, Frank; Frei, Martin

2013-04-01

Eco-engineering measures combine the use of living plants and inert mechanical constructions to protect slopes against erosion and shallow mass movement. Whereas in geotechnical engineering several performance standards and guidelines for structural safety and serviceability of construction exist, there is a lack of comparable tools in the field of ecological restoration. Various indicators have been proposed, including the fractal dimension of soil particle size distribution, microbiological parameters, and soil aggregate stability. We present results of an soil aggregate stability investigation and compare them with literature data of the angle of internal friction ?' which is conventionally used in slope stability analysis and soil failure calculation. Aggregate stability tests were performed with samples of differently treated moraine, including soil at low (~15.5 kN/m³) and high (~19.0 kN/m³) dry unit weight, soil planted with Alnus incana (White Alder) as well as the combination of soil planted with alder and inoculated with the mycorrhizal fungus Melanogaster variegatus s.l. After a 20 weeks growth period in a greenhouse, a total of 100 samples was tested and evaluated. Positive correlations were found between the soil aggregate stability and the three variables dry unit weight, root length per soil volume, and degree of mycorrhization. Based on robust statistics it turned out that dry unit weight and mycorrhization degree were strongest correlated with soil aggregate stability. Compared to the non-inoculated control plants, mycorrhized White Alder produced significantly more roots and higher soil aggregate stability. Furthermore, the combined biological effect of plant roots and mycorrhizal mycelia on aggregate stability on soil with low density (~15.5 kN/m³) was comparable to the compaction effect of the pure soil from 15.5 to ~19.0 kN/m³. Literature data on the effect of vegetation on the angle of internal friction ?' of the same moraine showed similar correlations, i.e. that ?' of low density soil material (~15.5 kN/m³) increased by the same amount whether by planting with White Alder or by compaction to ~19.0 kN/m³. Based on this coincidence the method to quantify soil aggregate produced satisfying results which indicate that soil aggregate stability is a potential proxy for ?' and the joint impact of mycorrhizal fungi and plant roots increase the resistance against superficial soil failure. It is concluded that soil aggregate stability mirrors biological effects on soil stability reasonably well and may be used as an indicator to quantify the effectiveness of ecological restoration and stabilisation measures.

A novel method for soil aggregate stability measurement by laser granulometry with sonication

NASA Astrophysics Data System (ADS)

Rawlins, B. G.; Lark, R. M.; Wragg, J.

2012-04-01

Regulatory authorities need to establish rapid, cost-effective methods to measure soil physical indicators - such as aggregate stability - which can be applied to large numbers of soil samples to detect changes of soil quality through monitoring. Limitations of sieve-based methods to measure the stability of soil macro-aggregates include: i) the mass of stable aggregates is measured, only for a few, discrete sieve/size fractions, ii) no account is taken of the fundamental particle size distribution of the sub-sampled material, and iii) they are labour intensive. These limitations could be overcome by measurements with a Laser Granulometer (LG) instrument, but this technology has not been widely applied to the quantification of aggregate stability of soils. We present a novel method to quantify macro-aggregate (1-2 mm) stability. We measure the difference between the mean weight diameter (MWD; μm) of aggregates that are stable in circulating water of low ionic strength, and the MWD of the fundamental particles of the soil to which these aggregates are reduced by sonication. The suspension is circulated rapidly through a LG analytical cell from a connected vessel for ten seconds; during this period hydrodynamic forces associated with the circulating water lead to the destruction of unstable aggregates. The MWD of stable aggregates is then measured by LG. In the next step, the aggregates - which are kept in the vessel at a minimal water circulation speed - are subject to sonication (18W for ten minutes) so the vast majority of the sample is broken down into its fundamental particles. The suspension is then recirculated rapidly through the LG and the MWD measured again. We refer to the difference between these two measurements as disaggregation reduction (DR) - the reduction in MWD on disaggregation by sonication. Soil types with more stable aggregates have larger values of DR. The stable aggregates - which are resistant to both slaking and mechanical breakdown by the hydrodynamic forces during circulation - are disrupted only by sonication. We used this method to compare macro-aggregate (1-2 mm) stability of air-dried agricultural topsoils under conventional tillage developed from two contrasting parent material types and compared the results with an alternative sieve-based technique. The first soil from the Midlands of England (developed from sedimentary mudstone; mean soil organic carbon (SOC) 2.5%) contained a substantially larger amount of illite/smectite (I/S) minerals compared to the second from the Wensum catchment in eastern England (developed from sands and glacial deposits; mean SOC=1.7%). The latter soils are prone to large erosive losses of fine sediment. Both sets of samples had been stored air-dried for 6 months prior to aggregate analyses. The mean values of DR (n=10 repeated subsample analyses) for the Midlands soil was 178μm; mean DR (n=10 repeat subsample analyses) for the Wensum soil was 30μm. The large difference in DR is most likely due to differences in soil mineralogy. The coefficient of variation of mean DR for duplicate analyses of sub-samples from the two topsoil types is around 10%. The majority of this variation is likely to be related to the difference in composition of the sub-samples. A standard, aggregated material could be included in further analyses to determine the relative magnitude of sub-sampling and analytical variance for this measurement technique. We then used the technique to investigate whether - as previously observed - variations (range 1000 - 4000 mg kg-1) in the quantity of amorphous (oxalate extractable) iron oxyhydroxides in a variety of soil samples (n=30) from the Wensum area (range SOC 1 - 2%) could account for differences in aggregate stability of these samples.

Carbon sequestration in soil by in situ catalyzed photo-oxidative polymerization of soil organic matter.

PubMed

Piccolo, Alessandro; Spaccini, Riccardo; Nebbioso, Antonio; Mazzei, Pierluigi

2011-08-01

Here we describe an innovative mechanism for carbon sequestration in soil by in situ photopolymerization of soil organic matter under biomimetic catalysis. Three different Mediterranean soils were added with a synthetic water-soluble iron-porphyrin, irradiated by solar light, and subjected first to 5 days incubation and, then, 15, and 30 wetting and drying (w/d) cycles. The in situ catalyst-assisted photopolymerization of soil organic carbon (SOC) increased water stability of soil aggregates both after 5 days incubation and 15 w/d cycles, but not after 30 w/d cycles. Particle-size distribution of all treated soils confirmed the induced soil physical improvement, by showing a concomitant lower yield of the clay-sized fraction and larger yields of either coarse sand- or fine sand-size fractions, depending on soil texture, though only after 5 days incubation. The gain in soil physical quality was reflected by the shift of OC content from small to large soil aggregates, thereby suggesting that photopolymerization stabilized OC by both chemical and physical processes. A further evidence of the carbon sequestration capacity of the photocatalytic treatment was provided by the significant reduction of CO(2) respired by all soils after both incubation and w/d cycles. Our findings suggest that "green" catalytic technologies may potentially be the bases for future practices to increase soil carbon stabilization and mitigate CO(2) emissions from arable soils.

Effect of biochar application and soil temperature on characteristics of organic matter associated with aggregate-size and density fractions

NASA Astrophysics Data System (ADS)

Kaiser, Michael; Grunwald, Dennis; Marhan, Sven; Poll, Christian; Bamminger, Chris; Ludwig, Bernard

2016-04-01

Potential increases in soil temperature due to climate change might result in intensified soil organic matter (SOM) decomposition and thus higher CO2 emissions. Management options to increase and stabilize SOM include the application of biochar. However, the effects of biochar amendments under elevated soil temperatures on SOM dynamics are largely unknown. The objective of this study was to analyze the effect of biochar application and elevated soil temperature on the amount and composition of OM associated with fractions of different turnover kinetics. Samples were taken from four treatments of the Hohenheim Climate Change Experiment with the factors temperature (ambient or elevated by 2.5 °C in 4 cm depth, six years before sampling) and biochar (control and 30 t / ha Miscanthus pyrolysis biochar, one year before sampling) in two depths (0 - 5 and 5 - 15 cm). Basal respiration and microbial biomass C were analyzed within an incubation experiment. Aggregate size-fractions were separated by wet-sieving and the free light, occluded light (oLF), and heavy fractions were isolated by density fractionation. All fractions were analyzed for organic C and δ13C as well as by infrared spectroscopy. Preliminary data suggest that biochar significantly increased basal respiration and that the microbial biomass C was significantly affected by elevated temperature. No biochar-C was found in the microbial biomass. Biochar and elevated temperature had only minor effects on the organic C associated with aggregate-size classes, although biochar was incorporated into all fractions already after one year of application. Biochar application significantly increased the organic C associated with oLF. In most samples affected by biochar, the proportion of C=O groups was significantly increased. The results suggest that already after one year, biochar-mineral interactions were formed leading to an aggregate occlusion of applied biochar. At least in the short-term, the effect of biochar on the amount and composition of OM associated with different aggregate-size and density fractions seem to be independent from soil temperature.

Mechanisms for increased soil C storage with increasing temporal and spatial plant diversity in Agroecosystems

NASA Astrophysics Data System (ADS)

Tiemann, L. K.; Grandy, S.; Marin-Spiotta, E.; Atkinson, E. E.

2012-12-01

Generally, there are positive relationships between plant species diversity and net primary production and other key ecosystem functions. However, the effects of aboveground diversity on soil microbial communities and ecosystem processes they mediate, such as soil C sequestration, remain unclear. In this study, we used an 11-y cropping diversity study where increases in diversity have increased crop yields. At the experimental site, temporal diversity is altered using combinations of annual crop rotations, while spatial diversity is altered using cover crop species. We used five treatments ranging in diversity from one to five species consisting of continuous corn with no cover crop or one cover crop and corn-soy-wheat rotations with no cover, one cover or two cover crop species. We collected soils from four replicate plots of each treatment and measured the distribution of mega- (>2 mm), macro- (0.25-2 mm), and micro- (0.053-0.25 mm) aggregates. Within each aggregate size class, we also measured total soil C and N, permanganate oxidizable C (POXC), extracellular enzyme activities (EEA), and microbial community structure with phospholipid fatty acid (PLFA) analysis. We use these data to address the impacts of both rotational and cover crop diversity on soil physical structure, associated microbial community structure and activity and soil C storage. As spatial diversity increased, we found concurrent increases in mega-aggregate abundance as well as increasing soil C in the mega- and micro-aggregates but not macro-aggregates. The proportion of total soil C in each aggregate size class that is relatively labile (POXC) was highest in the micro-aggregates, as was enzyme activity associated with labile C acquisition across all levels of diversity. Enzyme activity associated with more recalcitrant forms of soil C was highest in the mega-aggregate class, also across all diversity levels; however, the ratio of labile to recalcitrant EEA increased with increasing diversity in the mega- and micro-aggregates. In addition, soil N increased with diversity such that microbial C:N EEA simultaneously decreased in mega-aggregates. We also found that cropping diversity has created distinctive soil microbial communities, highlighted by variation in the abundance of gram positive bacteria and Actinomycetes. Further research will help us determine how these changes in community structure with increasing diversity are related to concomitant changes in aggregation and enzyme activities. We suggest that the additional organic matter inputs from cover crops in the high diversity treatments have increased aggregation processes and C pools. While microbial activity has also increased in association with this increased C availability, the activity of recalcitrant and N-acquiring enzymes has declined, suggesting an overall decrease in SOM mineralization with possible increased SOM stabilization. The addition of crop species in rotation (temporal diversity) had minimal influence on any of the measured parameters. We thus conclude that spatial diversity is a more important driver of soil structure and microbial activity, likely due to the high quality organic matter inputs derived from the leguminous cover crops; however, spatial diversity alone did not lead to the same level of C storage potential as mixtures of temporal and spatial diversity.

Effects of Combined Application of Biogas Slurry and Chemical Fertilizer on Soil Aggregation and C/N Distribution in an Ultisol.

PubMed

Zheng, Xuebo; Fan, Jianbo; Xu, Lei; Zhou, Jing

2017-01-01

Unreasonable use of chemical fertilizer (CF) on agricultural soil leads to massive losses of soil organic carbon (SOC) and total nitrogen (TN) in tropical and subtropical areas, where soil conditions are unfavorable for aggregate formation. This study evaluated the effects of combined application of biogas slurry (BS) plus CF on soil aggregation and aggregate-associated C/N concentration and storage in an Ultisol. Six treatments included: no fertilizer (T1), CF only (T2), partial (15% (T3), 30% (T4) and 45% (T5)) substitution of TN with BS and BS only (T6). Soil mechanical-stable aggregates (MSAs) formation and stability as well as MSAs-associated C/N concentration and storage were observed in different aggregate sizes (>5, 5-2, 2-1, 1.0-0.5, 0.50-0.25 and <0.25 mm). The proportion of MSAs >5 mm significantly increased with BS substitution (T5), while the proportions of MSAs 1.0-0.5 mm, MSAs 0.50-0.25 mm and MSAs <0.25 mm significantly decreased. Both mean weight diameter and geometric mean diameter were highest in T5, which improved soil aggregation stability as well as resulted in significantly higher SOC and TN concentrations and storage in MSAs >0.5 mm that constituted 72-82% of MSAs. Stepwise regression analysis showed that MSAs >5 mm, SOC in MSAs >5 mm and TN in MSAs >5 mm were the dominant variables affecting aggregate stability. Meanwhile SOC in MSAs <0.25 mm and TN in MSAs 2-1 mm were independent variables affecting SOC and TN concentrations in bulk soils. Therefore, certain rate of combined application of BS plus CF is an effective, eco-friendly way to improve soil quality in an Ultisol.

Effects of Land Use on Concentrations and Chemical Forms of Phosphorus in Different-Size Aggregates

NASA Astrophysics Data System (ADS)

Ahmad, E. H.; Demisie, W.; Zhang, M.

2017-12-01

Land use has been recognized as an important driver of environmental change on all spatial and temporal scales. This study was conducted to determine the effects of land uses on phosphorus concentration in bulk soil and in water-stable aggregates in different soils. The study was conducted on three soil types (Ferrosols, Cambosols, and Primosols), which were collected from three different locations from southeast China and under three land uses (Uncultivated, Vegetable and forest land) the region is characterized as a hill and plain area. Accordingly, a total of 24 soil samples were collected. The results showed that average contents of total P were 0.55-1.55 g/kg, 0.28-1.03 g/kg and 0.14-0.8 g/kg for the soils: Cambosols, Ferrosols and Primosols respectively. Vegetable and forest land led to higher total phosphorus contents in these soils than in the uncultivated land. An aggregate fraction of >2 mm under forest land made up the largest percentage (30 up to 70%), whereas the size fraction <0.106 mm made the least contribution (5 up to 20%) in all soil types. Vegetable land increased the total phosphorus, organic phosphorus and Olsen P and phosphorus forms in the soils. It implies that the conversion of natural ecosystem to vegetable land increased the phosphorus proportion in the soils, which could have negative impact on the environmental quality.

Soil organic carbon dynamics under long-term fertilization in a black soil of China: Evidence from stable C isotopes

PubMed Central

Dou, Xiaolin; He, Ping; Zhu, Ping; Zhou, Wei

2016-01-01

Effects of different fertilizers on organic carbon (C) storage and turnover of soil fractions remains unclear. We combined soil fractionation with isotope analyses to examine soil organic carbon (SOC) dynamics after 25 years of fertilization. Five types of soil samples including the initial level (CK) and four fertilization treatments (inorganic nitrogen fertilizer, N; balanced inorganic fertilizer, NPK; inorganic fertilizer plus farmyard manure, MNPK; inorganic fertilizer plus corn straw residue, SNPK) were separated into four aggregate sizes (>2000 μm, 2000–250 μm, 250–53 μm, and <53 μm), and three density fractions: free light fraction (LF), intra-aggregate particulate organic matter (iPOM), and mineral-associated organic matter (mSOM). Physical fractionation showed the iPOM fraction of aggregates dominated C storage, averaging 76.87% of SOC storage. Overall, application of N and NPK fertilizers cannot significantly increase the SOC storage but enhanced C in mSOM of aggregates, whereas MNPK fertilizer resulted in the greatest amount of SOC storage (about 5221.5 g C m2) because of the enhanced SOC in LF, iPOM and mSOM of each aggregate. The SNPK fertilizer increased SOC storage in >250 μm aggregates but reduced SOC storage in <250 μm aggregates due to SOC changes in LF and iPOM. PMID:26898121

Soil organic carbon dynamics under long-term fertilization in a black soil of China: Evidence from stable C isotopes.

PubMed

Dou, Xiaolin; He, Ping; Zhu, Ping; Zhou, Wei

2016-02-22

Effects of different fertilizers on organic carbon (C) storage and turnover of soil fractions remains unclear. We combined soil fractionation with isotope analyses to examine soil organic carbon (SOC) dynamics after 25 years of fertilization. Five types of soil samples including the initial level (CK) and four fertilization treatments (inorganic nitrogen fertilizer, N; balanced inorganic fertilizer, NPK; inorganic fertilizer plus farmyard manure, MNPK; inorganic fertilizer plus corn straw residue, SNPK) were separated into four aggregate sizes (>2000 μm, 2000-250 μm, 250-53 μm, and <53 μm), and three density fractions: free light fraction (LF), intra-aggregate particulate organic matter (iPOM), and mineral-associated organic matter (mSOM). Physical fractionation showed the iPOM fraction of aggregates dominated C storage, averaging 76.87% of SOC storage. Overall, application of N and NPK fertilizers cannot significantly increase the SOC storage but enhanced C in mSOM of aggregates, whereas MNPK fertilizer resulted in the greatest amount of SOC storage (about 5221.5 g C m(2)) because of the enhanced SOC in LF, iPOM and mSOM of each aggregate. The SNPK fertilizer increased SOC storage in >250 μm aggregates but reduced SOC storage in <250 μm aggregates due to SOC changes in LF and iPOM.

Thermal alteration of soil organic matter properties: a systematic study to infer response of Sierra Nevada climosequence soils to forest fires

NASA Astrophysics Data System (ADS)

Araya, Samuel N.; Fogel, Marilyn L.; Asefaw Berhe, Asmeret

2017-02-01

Fire is a major driver of soil organic matter (SOM) dynamics, and contemporary global climate change is changing global fire regimes. We conducted laboratory heating experiments on soils from five locations across the western Sierra Nevada climosequence to investigate thermal alteration of SOM properties and determine temperature thresholds for major shifts in SOM properties. Topsoils (0 to 5 cm depth) were exposed to a range of temperatures that are expected during prescribed and wild fires (150, 250, 350, 450, 550, and 650 °C). With increase in temperature, we found that the concentrations of carbon (C) and nitrogen (N) decreased in a similar pattern among all five soils that varied considerably in their original SOM concentrations and mineralogies. Soils were separated into discrete size classes by dry sieving. The C and N concentrations in the larger aggregate size fractions (2-0.25 mm) decreased with an increase in temperature, so that at 450 °C the remaining C and N were almost entirely associated with the smaller aggregate size fractions ( < 0.25 mm). We observed a general trend of 13C enrichment with temperature increase. There was also 15N enrichment with temperature increase, followed by 15N depletion when temperature increased beyond 350 °C. For all the measured variables, the largest physical, chemical, elemental, and isotopic changes occurred at the mid-intensity fire temperatures, i.e., 350 and 450 °C. The magnitude of the observed changes in SOM composition and distribution in three aggregate size classes, as well as the temperature thresholds for critical changes in physical and chemical properties of soils (such as specific surface area, pH, cation exchange capacity), suggest that transformation and loss of SOM are the principal responses in heated soils. Findings from this systematic investigation of soil and SOM response to heating are critical for predicting how soils are likely to be affected by future climate and fire regimes.

Pyrosequencing of microbial community of typical chernozem in contrast land use conditions

NASA Astrophysics Data System (ADS)

Ivanova, Ekaterina; Olga, Kutovaya; Azida, Tkhakakhova

2015-04-01

Chernozems are the principal soil resourse of Russia, so the sustainable use of these fertile soils in the intensive agriculturural production is of great importance, especially in terms of agro-ecological security of the country. The increase in agricultural inputs - intensive cropping, soil fallowing application accompanied with high frequency of mechanical treatment, result in decrease in soil organic matter content as well as soil structure degradation and, finally, lead to the loss of soil fertility. Soil microorganisms can serve as bioindicators of anthropogenic stress experienced by the soil during its agricultural use, so they may be universal indicators of soil quality (soil health) used for optimization and biologization of agricultural systems. The way to study the relationship between the structural status of the soil, its microbial communities and the organic matter content is the comparative analysis of soil aggregates in conditions of different land use practices. The objects of our research were soil samples of soil with permanent wheat cropping (50 years), continuous dead fallow (50 years) soil, and recovering soil (for 18 years under native steppe vegetation, fallowed in previous). The analysis of 16 S rRNA gene amplicon libraries of typical chernozem in conditions of different land use systems revealed that the way of agricultural use is a strong determinant of soil microbiome taxonomic composition. It was shown that the continuous «dead fallowing» application (for 50 years) lead to the establishment of olygothrophic components of microbial community, including spore-forming members of phylum Firmicutes. The increase of Acidobacteria lineages in this variant may be an indicator of some acidification of soil during long-time fallowing application. The variant of continuous wheat cropping lead to increasing in Proteobacteria lineages. The variant of soil under native steppe vegetation was characterized by the highest values of biodiversity indices - species richness and eveness, which can indicate the occurrence of soil recovering. This variant was also characterized by the maximum content of agricultural valuable aggregate fraction of 2-5 mm size. In soil samples from different aggregate fractions the presence of accessory components was revealed. It was determined that Actinobacteria lineages preferred microaggregates (less than 0.25 mm) rather than coarse aggregate fractions (more than 7 mm). The opposite trend was determined for Proteobacteria: the amount was maximum in aggregates more than 7 mm in diameter. The occurrence of specific components in the taxonomic structure of micro-and macro-aggregates may indicate the presence of a certain size fraction in the structure of the investigated soil. The study of soils' metagenome is promising for the development of both soil microbiology, and for the soil processes trends in soils of anthropogenic origin. The study was supported by Russian Scientific Fund (14-26-00079 and 14-26-00094)

Water stability of aggregates in subtropical and tropical soils (Georgia and China) and its relationships with the mineralogy and chemical properties

NASA Astrophysics Data System (ADS)

Alekseeva, T. V.; Sokolowska, Z.; Hajnos, M.; Alekseev, A. O.; Kalinin, P. I.

2009-04-01

Water-stable aggregates isolated from three subtropical and one tropical soil (Western Georgia and China) were studied for their organic carbon, cation exchange capacity (CEC), specific surface area, magnetic susceptibility, and total chemical elements. The soils were also studied for their particle-size distribution, mineralogy, and nonsilicate Fe and Al oxides. Describe the water stability, three indices have been used: the content of water-stable macroaggregates (>0.25 mm), the mean weighted diameter of the aggregates, and the numerical aggregation index. The yellow-cinnamonic soil (China) was neutral, and the three other soils were acid. The soils were degraded with a low content of organic matter. The yellow-cinnamonic soil was characterized by the lowest water stability due to the predominantly vermiculite composition of the clay. The high water stability of the Oxisol structure was determined by the kaolinites and high content of oxides. In three out of the four soils studied, the hierarchical levels of the soil structure organization were defined; they were identified by the content of organic matter and the Ca + Mg (in Oxisols). Iron oxides mainly participated in the formation of micro-aggregates; Al and Mn contributed to the formation of macroaggregates. The water-stable aggregates acted as sorption geochemical barriers and accumulated Pb, Zn, Cd, Cs, and other trace elements up to concentrations exceeding their levels in the soil by 5 times and more. The highest correlations were obtained with CEC, Mn, and P rather than with organic carbon and Fe.

Soil aggregate mediates the impacts of land uses on organic carbon, total nitrogen, and microbial activity in a Karst ecosystem

PubMed Central

Xiao, Shuangshuang; Zhang, Wei; Ye, Yingying; Zhao, Jie; Wang, Kelin

2017-01-01

Understanding the effect of land use on soil carbon, nitrogen, and microbial activity associated with aggregates is critical for thorough comprehension of the C and N dynamics of karst landscapes/ecosystems. We monitored soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), and Cmic: Corg ratio in large macro- (>2 mm), small macro- (0.25–2 mm), and micro- (0.053–0.25 mm) aggregates to determine the changes in soil properties under different land uses in the karst area of Southwest China. Five common land-use types—enclosure land (natural system, control), prescribed-burning land, fuel-wood shrubland, pasture and maize fields—were selected. Results showed that pasture and maize fields remarkably decreased the SOC and TN concentrations in aggregates. Conversion of natural system to other land uses decreased MBC (except for prescribed-burning) and increased Cmic: Corg ratios in aggregates. The extent of the response to land uses of SOC and TN concentrations was similar whereas that of MBC and Cmic: Corg ratios differed across the three aggregate sizes. Further, the SOC concentrations were significantly higher in macro-aggregates than micro-aggregates; the MBC and Cmic: Corg ratios were highest in small macro-aggregates. Therefore, small macro-aggregates might have more active C dynamics. PMID:28211507

Xyloglucan is released by plants and promotes soil particle aggregation.

PubMed

Galloway, Andrew F; Pedersen, Martin J; Merry, Beverley; Marcus, Susan E; Blacker, Joshua; Benning, Liane G; Field, Katie J; Knox, J Paul

2018-02-01

Soil is a crucial component of the biosphere and is a major sink for organic carbon. Plant roots are known to release a wide range of carbon-based compounds into soils, including polysaccharides, but the functions of these are not known in detail. Using a monoclonal antibody to plant cell wall xyloglucan, we show that this polysaccharide is secreted by a wide range of angiosperm roots, and relatively abundantly by grasses. It is also released from the rhizoids of liverworts, the earliest diverging lineage of land plants. Using analysis of water-stable aggregate size, dry dispersion particle analysis and scanning electron microscopy, we show that xyloglucan is effective in increasing soil particle aggregation, a key factor in the formation and function of healthy soils. To study the possible roles of xyloglucan in the formation of soils, we analysed the xyloglucan contents of mineral soils of known age exposed upon the retreat of glaciers. These glacial forefield soils had significantly higher xyloglucan contents than detected in a UK grassland soil. We propose that xyloglucan released from plant rhizoids/roots is an effective soil particle aggregator and may, in this role, have been important in the initial colonization of land. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Experimental evidence of the role of pores on movement and distribution of bacteria in soil

NASA Astrophysics Data System (ADS)

Kravchenko, Alexandra N.; Rose, Joan B.; Marsh, Terence L.; Guber, Andrey K.

2014-05-01

It has been generally recognized that micro-scale heterogeneity in soil environments can have a substantial effect on movement, fate, and survival of soil microorganisms. However, only recently the development of tools for micro-scale soil analyses, including X-ray computed micro-tomography (μ-CT), enabled quantitative analyses of these effects. The long-term goal of our work is to explore how differences in micro-scale characteristics of pore structures influence movement, spatial distribution patterns, and activities of soil microorganisms. Using X-ray μ-CT we found that differences in land use and management practices lead to development of contrasting patterns in pore size-distributions within intact soil aggregates. Then our experiments with Escherichia coli added to intact soil aggregates demonstrated that the differences in pore structures can lead to substantial differences in bacteria redistribution and movement within the aggregates. Specifically, we observed more uniform E.coli redistribution in aggregates with homogeneously spread pores, while heterogeneous pore structures resulted in heterogeneous E.coli patterns. Water flow driven by capillary forces through intact aggregate pores appeared to be the main contributor to the movement patterns of the introduced bacteria. Influence of pore structure on E.coli distribution within the aggregates further continued after the aggregates were subjected to saturated water flow. E. coli's resumed movement with saturated water flow and subsequent redistribution within the soil matrix was influenced by porosity, abundance of medium and large pores, pore tortuosity, and flow rates, indicating that greater flow accompanied by less convoluted pores facilitated E. coli transport within the intra-aggregate space. We also found that intra-aggregate heterogeneity of pore structures can have an effect on spatial distribution patterns of indigenous microbial populations. Preliminary analysis showed that in aggregates from an organic agricultural system with cover crops, characterized by greater intra-aggregate pore heterogeneity, bacteria of Actinobacteria and Firmicutes groups were more abundant in presence of large as compared to small pores. In contrast, no differences were observed in the aggregates from conventionally managed soil, overall characterized by homogeneous intra-aggregate pore patterns. Further research efforts are being directed towards quantification of the pore structure effects on activities and community composition of soil microorganisms.

Effect of different kinds of crop residues on aggregate-protected soil organic matter fractions.

NASA Astrophysics Data System (ADS)

Huisz, A.

2009-04-01

Organic matter content of soils determines many important soil properties, such as soil structure, fertility and water-management. To improve its fertility and quality, returning different kinds of organic matter to soil has a long historical tradition. Ameliorating of soil and enhancing its fertility by enhancing its carbon stock with organic matter incorporation (like farmyard manure, crop residues or green manure) are general practices, but the extent of the amelioration depends much on several factors such as quantity, quality of the used organic matters. Quality of soil organic matters is affected by their chemical build-up, which differs by their origin (i.e. plant species); and their decomposability is affected by particle-size, protection by soil aggregates and the extent of their association to mineral surfaces. In our paper we investigated the effect of three different kinds of organic matter incorporation on aggregate-protected organic matter fractions: (1) Maize stem (M), (2) Wheat straw (W), and (3) Maize stem & Wheat straw (MW). Our samples were originated from Keszthely, Western Hungary, where the texture of the investigated soil is Sandy loam, the type of soil is Eutric Cambisol (soil type FAO), or Alfisol (soil type USDA). SOM fractions might be isolated and measured by physical fractionation of soil (Cambardella and Elliott (1992), Jensen et al. (1992)). Firstly, microaggregates were separated according to their particle-size with physical fractionation (i.e. wet sieving) (Six et al. (2000a)). Each sample was pre-treated by capillary wetting and was sieved for 2 min in an analytic sieve shaker machine with the following aperture sizes: 2 mm, 250 μm, 53 μm. Therefore 4 fractions were resulted: (1) the >2000 μm large macro-, (2) the 250-2000 μm small macro-, (3) the 53-250 μm microaggregates, and (4) the

Soil aggregation and aggregate-associated carbon under four typical halophyte communities in an arid area.

PubMed

Yang, Haichang; Wang, Jingya; Zhang, Fenghua

2016-12-01

The soil microbial biomass carbon (MBC) is considered as a sensitive index of soil carbon ecosystem. The distribution of aggregate-associated MBC determines the capacity of the soil to store soil organic carbon (SOC). We compared soil aggregate-associated SOC and aggregate-associated MBC under four halophyte communities: Karelinia caspia (Pall.) Less. (Abbr. K. caspia), Bassia dasyphylla (Fisch. et C. A. Mey.) Kuntze. (Abbr. B. dasyphylla), Haloxylon ammodendron (C. A. Mey.) Bunge. (Abbr. H. ammodendron), and Tamarix ramosissima Lour (Abbr. T. ramosissima) on an alluvial fan in the Manasi River Basin, Xinjiang, China. The specific objectives of the study were to determine which aggregate size fraction was the most important for MBC and SOC retention in these soils of four halophyte communities. The results showed that the 0.053-0.25 mm fraction contained 47 to 75 % of the total soil mass. The amount of soil in the 0.053-0.25 mm fraction was significantly greater than that in the >0.25 and the <0.053 mm fractions. The >0.25 and the <0.053 mm fractions contained 7.8 to 43.0 % of the soil mass. Aggregate-associated SOC concentrations ranged from 1.70 to 13.68 g kg -1 , and the aggregate-associated SOC were the highest under the H. ammodendron and T. ramosissima communities. The aggregate-associated MBC ranged from 55.26 to 217.11 g kg -1 , and the aggregate-associated MBC were higher under the K. caspia and B. dasyphylla communities. The aggregate-associated SOC concentrations were significantly higher in the >0.25 and the <0.053 mm fractions than in the 0.053-0.25 mm fraction. The aggregate-associated MBC in the 20-40 cm depth was consistent with its law. However, in the 0-20 cm depth, the aggregate-associated MBC concentrations were significantly higher in the >0.25 mm fraction than the other two aggregate fractions, and there were no significant differences in 0.25-0.053 or <0.053 mm fraction. Correlation analyses showed that the aggregate-associated MBC positively correlated with aggregate-associated SOC in >0.25 mm fraction (P < 0.01). The microbial entropies ranged from 1.12 to 4.17 %, and the microbial entropy generally was higher in >0.25 mm fraction. Overall, the H. ammodendron community had the higher aggregate-associated SOC and aggregate-associated MBC, but the microbial entropy was low. This suggested that among the four halophyte communities in this study, the H. ammodendron community could be beneficial for soil carbon storage in arid regions.

Impact of land use change on soil organic matter dynamics in subalpine grassland

NASA Astrophysics Data System (ADS)

Meyer, Stefanie; Leifeld, Jens; Bahn, Michael; Fuhrer, Jürg

2010-05-01

Information regarding the response of soil organic matter (SOM) in soils to past and expected future land use changes in the European Alps is scarce. Understanding this response requires knowledge of size and residence times of SOM fractions with distinct stabilities. In order to quantify differences between types of land use in the amount, distribution and turnover rates of soil organic carbon (SOC) in subalpine grassland soils, we used soil aggregate and SOM density fractionation in combination with 14C dating. Samples were taken along gradients of different types of land use from meadow (M) to pasture (P) and to abandoned grassland (A) in the Stubai Valley and in the Matsch Valley. Sampling sites in both areas were located at equal altitude (1880 m and 1820 m, respectively) with the same parent material and soil type, but the Matsch Valley receives 400-500 mm less annual rainfall. SOC stocks in the top 10 cm were 2.47 ± 0.32 (M), 2.75 ± 0.32 (P), and 2.50 ± 0.31 kg C/m2 (A) in the Stubai Valley and 2.25 ± 0.14 (M), 3.45 ± 0.22 (P), 3.16 ± 0.27 kg C/m2(A) in the Matsch Valley. Three aggregate size classes were separated by wet sieving: 2 mm. The light floating fraction (wPOM, ρ >1 g/cm3) was included in the analysis. Free (f-) and occluded particulate organic matter (oPOM) were isolated from each aggregate size class (ρ >1.6 g/cm3). At both locations, more than 80% of SOC was stored in small (0.25-2 mm) and large (>2 mm) macroaggregates, but no trend in relation to the different types of land use could be detected. The fraction of C in fPOM and in oPOM in all aggregate size classes was highest for soil from abandoned grasslands. The bulk soil of the abandoned site in the Stubai Valley showed a significantly higher share of fPOM-C and oPOM-C and a higher amount of wPOM-C as compared to the soil from managed grassland, whereas in the Matsch Valley pasture soil had a significantly higher wPOM-C content. At both sites, 13C natural abundance analyses revealed a gradient in 13C between density fractions. wPOM was particularly useful to reveal differences between sampling sites. Radiocarbon values emphasized the importance of this fraction for the calculation of the turnover of bulk soil C. wPOM turned out to be the most active fraction turning over in 2-4 years. Bulk SOC turnover time was approximately 46 years for pasture soil and 78 years for meadow soil. In conclusion, density fractionation produced homogenous fractions allowing detection of differences between different land use types. However, C distribution among aggregates did not systematically differ.

Stability of aggregates in the environment: role of solid bridging

NASA Astrophysics Data System (ADS)

Seiphoori, A.; Jerolmack, D. J.; Arratia, P. E.

2017-12-01

Colloids in suspension may form larger flocs under favorable conditions, via diffusion- or reaction-limited aggregation. In addition, the process of drying colloidal suspensions drives colloids together via hydrodynamic forces to form aggregates, that may be stable or unstable when subject to re-wetting and transport. Channel banks, shorelines and hillslopes are examples where the periodic wetting and drying results in the aggregation of muds. If aggregates disperse, the mud structure is unstable to subsequent wetting or fluid shear and can easily be detached and transported to rivers and coasts. The effective friction that governs hillslope and channel-bank soil creep rates also depends on the stability of the soil aggregates. Yet, few studies probe the particle-scale assembly or stability of aggregates subject to environmental loads, and the effects of shape or size heterogeneity have not been examined in detail. Here we investigate the formation and stability of aggregates subject to passive re-wetting (by misting) and shearing using a simple Poiseuille flow in a microfluidic device. We study the kinetics of a wide range of silicate colloids of different size and surface charge properties using in situ microscopy and particle tracking. We find that negatively charged silica microspheres are dragged by the retreating edge of an evaporating drop and are resuspended easily on re-wetting, showing that aggregates are unstable. In contrast, a bi-disperse suspension created by the addition of silica nanoparticles forms stable deposits, where nanoparticles bind larger particles by bridging the interparticle space, a mechanism similar to capillary bridging that we refer to as "solid bridging." Although aggregate structure and dynamics of the bi-disperse system changes quantitatively with surface-charge of the nanoparticles, smaller particles always conferred stability on the aggregates. Investigation of other colloids, including asbestos fibers and various clays, reveals that this solid bridging effect is robust across variations in particle shape and material composition. These experiments suggest that natural mud and soil may form more stable aggregates than would naively be expected by considering the charge effects alone, because their inherent size heterogeneity is conducive to solid bridging.

Medium-term evolution of water repellency and aggregate stability in Mediterranean calcareous soils after wildfire

NASA Astrophysics Data System (ADS)

Gordillo-Rivero, Ángel; García-Moreno, Jorge; Zavala, Lorena M.; Jordán, Antonio; Granged, Arturo JP; Gil, Juan

2013-04-01

Wildfires are a common feature of Mediterranean ecosystems due to environmental factors and anthropic influence, especially in those areas where land use change and the development of touristic infrastructures are more intense. Wildfires induce a series of soil changes affecting their physical and chemical properties and the hydrological and erosive response. Two of the properties that are commonly affected by burning are soil water repellency (WR) and aggregate stability (AS). Both properties play an important role in the hydrological response of soils and other processes, and may be used as indices for assessing burn severity (Gordillo-Rivero et al., 2013). OBJECTIVES The field study was carried out between August 2006 (date of burning) and August 2011 with the following objectives: [i] to study the changes in SWR and AS immediately after fire and in the medium-term (6 years after burning) and its distribution within aggregate size fractions (<2, 1-2, 0.5-1 and 0.25-0.5 mm), [ii] to assess the relationships between postfire AS and WR, and [iii] to investigate interactions between AS and WR and different factors (site, time since burning, lithology and vegetation type) in calcareous Mediterranean soils. METHODS Five areas affected by wildfires during summer 2006 were selected for this research. Vegetation was characterized by grassland and Mediterranean shrubland. Soils were calcareous, with loam to clayey texture. As shown from adjacent areas, soils were wettable or slightly water-repellent immediately before burning. Soil WR and AS were measured in soil samples (0-15 mm deep) in fine earth (<2 mm) and aggregate sieve fractions (1-2, 0.5-1 and 0.25-0.5 mm). WR was assessed using the WDPT test, and AS was determined as the percentage of stable aggregates after laboratory rainfall simulation. RESULTS Both properties showed different tendencies in different aggregate size fractions. Results showed that soil WR was induced in wettable soils or enhanced in slightly or moderately water-repellent soils after moderate severity burning. WR increased after fire especially in the finer fractions (0.25-0.5 mm) immediately after fire, and WR from finer aggregates (0.5-1 and 0.25-0.5 mm) varied or remained stable during the studied period, but did not contribute to general soil WR assessed in the fine earth fraction. AS increased significantly after the fire and was progressively reduced during the experimental period. Both properties returned progressively to pre-fire conditions during the study period. Soil resilience to low-moderate severity burning in the study area was very high. REFERENCES Gordillo-Rivero, A.J., García-Moreno, J., Jordán, A., Zavala, L.M. 2013. Monitoring fire impacts in soil water repellency and structure stability during 6 years. FLAMMA, 4(2):71-75.

Microhabitat Effects on N2O Emissions from Floodplain Soils under Controlled Conditions

NASA Astrophysics Data System (ADS)

Ley, Martin; Lehmann, Moritz; Niklaus, Pascal; Frey, Beat; Kuhn, Thomas; Luster, Jörg

2015-04-01

Semi-terrestrial soils such as floodplain soils are considered to be potential hotspots of nitrous oxide (N2O) emissions. The quantitative assessment of N2O release from these hot spots under field conditions, and of the microbial pathways that underlie net N2O production (ammonium oxidation, nitrifier-denitrification, and denitrification) is challenging in the environment because of the high spatial and temporal variability. The production and consumption of N2O appears to be linked to the presence or absence of micro-niches, providing specific conditions that may be favorable to either of the microbial pathways that produce or consume N2O. The availability of oxygen, reactive organic carbon, and dissolved nitrogen substrates likely play key roles with regards to the net production of N2O. Previous field studies demonstrated, for example, that flooding can trigger "hot moments" of enhanced N2O emission through a close coupling of niches with high and low oxygen availabilities. Such microhabitat effects likely depend on soil aggregate formation, plant soil interactions in the rhizosphere and the degradation of organic matter accumulations. In order to assess how these factors can modulate N2O production and consumption under simulated flooding/drying conditions, we have set up a mesocosm experiment with model soils comprising various mixtures of N-rich floodplain soil aggregates (4000 - 250 µm representing large aggregates, or <250 µm representing small aggregates) and inert matrix material (glass beads of 150 - 250 µm size, or quartz sand of 2000 - 3200 µm size, respectively). Soils containing the different aggregate size groups were either planted with willow (Salix viminalis L.), mixed with leaf litter or left untreated. At several time points before, during and after a simulated flood event, we measure the net efflux rate of N2O. In addition, soil water content, redox potential as well as carbon and nitrogen substrate availability are monitored. In order to gain insight into the sources of, and biogeochemical controls on N2O production, we will measure the bulk isotopic signature of the produced N2O as well as its intramolecular 15N site preference. Changes in soil microbial communities, potentially controlling the balance between N2O production and consumption under different microhabitat conditions will be assessed using high-throughput DNA sequencing and q-PCR of key functional genes. Our study helps to increase our limited understanding of how microhabitats affect the occurrence of high N2O emissions from floodplain soils.

Linking Microbial Community Structure to β-Glucosidic Function in Soil Aggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bailey, Vanessa L.; Fansler, Sarah J.; Stegen, James C.

2013-10-01

To link microbial community 16S structure to a measured function in a natural soil we have scaled both DNA and β-glucosidase assays down to a volume of soil that may approach a unique microbial community. β-glucosidase activity was assayed in 450 individual aggregates which were then sorted into classes of high or low activities, from which groups of 10 or 11 aggregates were identified and grouped for DNA extraction and pyrosequencing. Tandem assays of ATP were conducted for each aggregate in order to normalize these small groups of aggregates for biomass size. In spite of there being no significant differencesmore » in the richness or diversity of the microbial communities associated with high β-glucosidase activities compared with the communities associated with low β-glucosidase communities, several analyses of variance clearly show that the communities of these two groups differ. The separation of these groups is partially driven by the differential abundances of members of the Chitinophagaceae family. It may be that observed functional differences in otherwise similar soil aggregates can be largely attributed to differences in resource availability, rather than to presence or absence of particular taxonomic groups.« less

Scale Model of a Soil Aggregate and Associated Organisms: A Teaching Tool for Soil Ecology

ERIC Educational Resources Information Center

Bruns, Mary Ann; Byrne, Loren B.

2004-01-01

Soil is a complex habitat for diverse biota. A significant challenge in teaching soil ecology is our inability to observe organisms as they live and interact in the soil. The objective of this article is to describe an interactive class project to help students visualize the sizes of different groups of soil organisms and to relate these to soil…

Influence of tillage practices and straw incorporation on soil aggregates, organic carbon, and crop yields in a rice-wheat rotation system

PubMed Central

Song, Ke; Yang, Jianjun; Xue, Yong; Lv, Weiguang; Zheng, Xianqing; Pan, Jianjun

2016-01-01

In this study, a fixed-site field experiment was conducted to study the influence of different combinations of tillage and straw incorporation management on carbon storage in different-sized soil aggregates and on crop yield after three years of rice-wheat rotation. Compared to conventional tillage, the percentages of >2 mm macroaggregates and water-stable macroaggregates in rice-wheat double-conservation tillage (zero-tillage and straw incorporation) were increased 17.22% and 36.38% in the 0–15 cm soil layer and 28.93% and 66.34% in the 15–30 cm soil layer, respectively. Zero tillage and straw incorporation also increased the mean weight diameter and stability of the soil aggregates. In surface soil (0–15 cm), the maximum proportion of total aggregated carbon was retained with 0.25–0.106 mm aggregates, and rice-wheat double-conservation tillage had the greatest ability to hold the organic carbon (33.64 g kg−1). However, different forms occurred at higher levels in the 15–30 cm soil layer under the conventional tillage. In terms of crop yield, the rice grown under conventional tillage and the wheat under zero tillage showed improved equivalent rice yields of 8.77% and 6.17% compared to rice-wheat double-cropping under zero tillage or conventional tillage, respectively. PMID:27812038

Physico-chemical protection, rather than biochemical composition, governs the responses of soil organic carbon decomposition to nitrogen addition in a temperate agroecosystem.

PubMed

Tan, Wenbing; Wang, Guoan; Huang, Caihong; Gao, Rutai; Xi, Beidou; Zhu, Biao

2017-11-15

The heterogeneous responses of soil organic carbon (SOC) decomposition in different soil fractions to nitrogen (N) addition remain elusive. In this study, turnover rates of SOC in different aggregate fractions were quantified based on changes in δ 13 C following the conversion of C 3 to C 4 vegetation in a temperate agroecosystem. The turnover of both total organic matter and specific organic compound classes within each aggregate fraction was inhibited by N addition. Moreover, the intensity of inhibition increases with decreasing aggregate size and increasing N addition level, but does not vary among chemical compound classes within each aggregate fraction. Overall, the response of SOC decomposition to N addition is dependent on the physico-chemical protection of SOC by aggregates and minerals, rather than the biochemical composition of organic substrates. The results of this study could help to understand the fate of SOC in the context of increasing N deposition. Copyright © 2017 Elsevier B.V. All rights reserved.

Turnover of intra- and extra-aggregate organic matter at the silt-size scale

Treesearch

I. Virto; C. Moni; C. Swanston; C. Chenu

2010-01-01

Temperate silty soils are especially sensitive to organic matter losses associated to some agricultural management systems. Long-term preservation of organic C in these soils has been demonstrated to occur mainly in the silt- and clay-size fractions, although our knowledge about the mechanisms through which it happens remains unclear. Although organic matter in such...

Stability of Soil Carbon Fractions - from molecules to aggregates

NASA Astrophysics Data System (ADS)

Mueller, C. W.; Mueller, K. E.; Freeman, K. H.; Eissenstat, D.; Kögel-Knabner, I.

2009-12-01

The turnover of soil organic matter (SOM) is controlled both by its chemical composition, its spatial bioavailability and the association with the mineral phase. Separation by physical fractionation of bulk soils and subsequent chemical analysis of these fractions should give insights to how compositional differences in SOM drive turnover rates of different size-defined carbon pools. The main objective of the study was to elucidate the relative abundance and recalcitrance of lignin and plant lipids (e.g. cutin and suberin) in the course of SOM decomposition within aggregated bulk soils and SOM fractions. By the parallel incubation of physically-separated size fractions and bulk soils of the Ah horizon from a forested soil (Picea abies L.Karst) over a period of 400 days, a unique set of samples was created to study SOM dynamics. We used solid-state 13C-CPMAS NMR spectroscopy and GC-MS (after copper oxide oxidation and solvent extraction) to analyze the composition of the incubated samples. The abundance and isotopic composition (including 13C and 14C) of respired CO2 further enabled us to monitor the dynamics of SOM mineralization. This approach allowed for differentiating between C stabilization of soil fractions due to accessibility/aggregation and to recalcitrance at different scales of resolution (GC-MS, NMR). A relative enrichment of alkyl C and decreasing lignin contents in the order of sand < silt < clay were observed by 13C-NMR and GC-MS within soils and fractions before the incubation, resulting in increased lipid to lignin ratios with decreasing particle size. A relative enrichment of lignin in the incubated fractions compared to the incubated bulk soils clearly indicated the preferential mineralization of less recalcitrant C compounds that were spatially inaccessible in aggregates of the bulk soil. Differences in the abundance of various lignin, cutin, and suberin monomers measured by GC-MS before and after the incubation indicate selective degradation and preservation patterns at the molecular scale that are rarely observed and are unresolved by NMR analyses. We suggest that the monomer-specific patterns of lignin, cutin, and suberin decomposition facilitate better understanding and modelling of SOM dynamics by providing a tool to potentially separate the influence of input rates from selective preservation on the abundance of these bipolymers in soil.

Field sampling of loose erodible material: A new method to consider the full particle-size range

NASA Astrophysics Data System (ADS)

Klose, Martina; Gill, Thomas E.

2017-04-01

The aerodynamic entrainment of sand and dust is determined by the atmospheric forces exerted onto the soil surface and by the soil-surface condition. If aerodynamic forces are strong enough to generate sand and dust lifting, the entrained sediment amount still critically depends on the supply of loose particles readily available for lifting. This loose erodible material (LEM) is sometimes defined as the thin layer of loose particles on top of a crusted surface. Here, we more generally define LEM as loose particles or particle aggregates available for entrainment, which may or may not overlay a soil crust. Field sampling of LEM is difficult and only few attempts have been made. Motivated by saltation as the most efficient process to generate dust emission, methods have focused on capturing LEM in the sand-size range or on determining the potential of a soil surface to be eroded by aerodynamic forces and particle impacts. Here, our focus is to capture the full particle-size distribution of LEM in situ, including the dust and sand-size range, to investigate the potential and likelihood of dust emission mechanisms (aerodynamic entrainment, saltation bombardment, aggregate disintegration) to occur. A new vacuum method is introduced and its capability to sample LEM without significant alteration of the LEM particle-size distribution is investigated.

Soil wind erodibility based on dry aggregate-size distribution in the Tarim Basin

USDA-ARS?s Scientific Manuscript database

The Tarim Basin is an important source of airborne particulate matter that contributes to poor air quality in China. However, little attention has been given to estimating wind erodibility of soils in the region. The objective of this study was to determine the soil wind erodibility for six land use...

Numerical modeling of sorption kinetics of organic compounds to soil and sediment particles

NASA Astrophysics Data System (ADS)

Wu, Shian-chee; Gschwend, Phillip M.

1988-08-01

A numerical model is developed to simulate hydrophobic organic compound sorption kinetics, based on a retarded intraaggregate diffusion conceptualization of this solid-water exchange process. This model was used to ascertain the sensitivity of the sorption process for various sorbates to nonsteady solution concentrations and to polydisperse soil or sediment aggregate particle size distributions. Common approaches to modeling sorption kinetics amount to simplifications of our model and appear justified only when (1) the concentration fluctuations occur on a time scale which matches the sorption timescale of interest and (2) the particle size distribution is relatively narrow. Finally, a means is provided to estimate the extent of approach of a sorbing system to equilibrium as a function of aggregate size, chemical diffusivity and hydrophobicity, and system solids concentration.

Organomineral Interactions and Herbicide Sorption in Brazilian Tropical and Subtropical Oxisols under No-Tillage.

PubMed

Bonfleur, Eloana J; Kookana, Rai S; Tornisielo, Valdemar L; Regitano, Jussara B

2016-05-25

We evaluated the effects of the soil organic matter (SOM) composition, distribution between soil aggregates size, and their interactions with the mineral phase on herbicide sorption (alachlor, bentazon, and imazethapyr) in tropical and subtropical Oxisols under no-till systems (NT). Using soil physical fractionation approach, sorption experiments were performed on whole soils and their aggregates. SOM chemistry was assessed by CP/MAS (13)C NMR. The lower sorption observed in tropical soils was attributed to the greater blockage of SOM sorption sites than in subtropical soils. When these sites were exposed upon physical fractionation, sorption of the three herbicides in tropical soils increased, especially for imazethapyr. High amounts of poorly crystallized sesquioxides in these soils may have contributed to masking of sorption sites, indicating that organomineral interactions may lead to blockage of sorption sites on SOM in tropical soils.

Distribution of light and heavy fractions of soil organic carbon as related to land use and tillage practice

USGS Publications Warehouse

Tan, Zhengxi; Lal, R.; Owens, L.; Izaurralde, R. C.

2007-01-01

Mass distributions of different soil organic carbon (SOC) fractions are influenced by land use and management. Concentrations of C and N in light- and heavy fractions of bulk soils and aggregates in 0–20 cm were determined to evaluate the role of aggregation in SOC sequestration under conventional tillage (CT), no-till (NT), and forest treatments. Light- and heavy fractions of SOC were separated using 1.85 g mL−1 sodium polytungstate solution. Soils under forest and NT preserved, respectively, 167% and 94% more light fraction than those under CT. The mass of light fraction decreased with an increase in soil depth, but significantly increased with an increase in aggregate size. C concentrations of light fraction in all aggregate classes were significantly higher under NT and forest than under CT. C concentrations in heavy fraction averaged 20, 10, and 8 g kg−1 under forest, NT, and CT, respectively. Of the total SOC pool, heavy fraction C accounted for 76% in CT soils and 63% in forest and NT soils. These data suggest that there is a greater protection of SOC by aggregates in the light fraction of minimally disturbed soils than that of disturbed soil, and the SOC loss following conversion from forest to agriculture is attributed to reduction in C concentrations in both heavy and light fractions. In contrast, the SOC gain upon conversion from CT to NT is primarily attributed to an increase in C concentration in the light fraction.

Effects of Combined Application of Biogas Slurry and Chemical Fertilizer on Soil Aggregation and C/N Distribution in an Ultisol

PubMed Central

Zheng, Xuebo; Fan, Jianbo; Xu, Lei; Zhou, Jing

2017-01-01

Unreasonable use of chemical fertilizer (CF) on agricultural soil leads to massive losses of soil organic carbon (SOC) and total nitrogen (TN) in tropical and subtropical areas, where soil conditions are unfavorable for aggregate formation. This study evaluated the effects of combined application of biogas slurry (BS) plus CF on soil aggregation and aggregate—associated C/N concentration and storage in an Ultisol. Six treatments included: no fertilizer (T1), CF only (T2), partial (15% (T3), 30% (T4) and 45% (T5)) substitution of TN with BS and BS only (T6). Soil mechanical—stable aggregates (MSAs) formation and stability as well as MSAs—associated C/N concentration and storage were observed in different aggregate sizes (>5, 5–2, 2–1, 1.0–0.5, 0.50–0.25 and <0.25 mm). The proportion of MSAs >5 mm significantly increased with BS substitution (T5), while the proportions of MSAs 1.0–0.5 mm, MSAs 0.50–0.25 mm and MSAs <0.25 mm significantly decreased. Both mean weight diameter and geometric mean diameter were highest in T5, which improved soil aggregation stability as well as resulted in significantly higher SOC and TN concentrations and storage in MSAs >0.5 mm that constituted 72–82% of MSAs. Stepwise regression analysis showed that MSAs >5 mm, SOC in MSAs >5 mm and TN in MSAs >5 mm were the dominant variables affecting aggregate stability. Meanwhile SOC in MSAs <0.25 mm and TN in MSAs 2–1 mm were independent variables affecting SOC and TN concentrations in bulk soils. Therefore, certain rate of combined application of BS plus CF is an effective, eco—friendly way to improve soil quality in an Ultisol. PMID:28125647

Clay minerals, metallic oxides and oxy-hydroxides and soil organic carbon distribution within soil aggregates in temperate forest soils

NASA Astrophysics Data System (ADS)

Gartzia-Bengoetxea, Nahia; Fernández-Ugalde, Oihane; Virto, Iñigo; Arias-González, Ander

2017-04-01

Soil mineralogy is of primary importance for key environmental services provided by soils like carbon sequestration. However, current knowledge on the effects of clay mineralogy on soil organic carbon (SOC) stabilization is based on limited and conflicting data. In this study, we investigated the relationship between clay minerals, metallic oxides and oxy-hydroxides and SOC distribution within soil aggregates in mature Pinus radiata D.Don forest plantations. Nine forest stands located in the same geographical area of the Basque Country (North of Spain) were selected. These stands were planted on different parent material (3 on each of the following: sandstone, basalt and trachyte). There were no significant differences in climate and forest management among them. Moreover, soils under these plantations presented similar content of clay particles. We determined bulk SOC storage, clay mineralogy, the content of Fe-Si-Al-oxides and oxyhydroxides and the distribution of organic C in different soil aggregate sizes at different soil depths (0-5 cm and 5-20 cm). The relationship between SOC and abiotic factors was investigated using a factor analysis (PCA) followed by stepwise regression analysis. Soils developed on sandstone showed significantly lower concentration of SOC (29 g C kg-1) than soils developed on basalts (97 g C kg-1) and trachytes (119 g C kg-1). The soils on sandstone presented a mixed clay mineralogy dominated by illite, with lesser amounts of hydroxivermiculite, hydrobiotite and kaolinite, and a total absence of interstratified chlorite/vermiculite. In contrast, the major crystalline clay mineral identified in the soils developed on volcanic rocks was interstratified chlorite/vermiculite. Nevertheless, no major differences were observed between basaltic and trachytic soils in the clay mineralogy. The selective extraction of Fe showed that the oxalate extractable iron was significantly lower in soils on sandstone (3.7%) than on basalts (11.2%) and trachytes (8.2%) with no significant differences between the last two. On the other hand, ditionithe extractable iron was significantly different among all soils with the following content: sandstone (13%) < trachytes (23%) < basalts (27%). Short-range order inorganic phases of Al and Fe were significantly higher in soils developed on volcanic parent materials. The distribution of organic C in soil aggregates revealed that as much as 50% of the organic C was concentrated in mega (20-10 mm and 10-5 mm) and large-(5-2 mm) aggregates in soils developed in sandstones, while 25% and 36% of the total organic C was found in theses aggregates in basaltic and trachytic soils respectively. Basaltic soils showed significantly higher proportion of organic C (>20%) in microaggregates (0.25-0.053 mm) and silt+clay size aggregates (< 0.053 mm) than the other two soils (<10%). The regression analysis revealed that short-range order minerals influence the amount of SOC via microaggregation and that chlorite-vermiculite mixed layer minerals had a significant influence on the amount of SOC relating this stabilization mechanism to macroagregation. This study highlights that dynamic models of SOC turnover in acid soils from temperate forest should include proxies for clay mineralogy and for the content of Fe and Al oxides and oxy-hydro-oxides.

Influence of 20–Year Organic and Inorganic Fertilization on Organic Carbon Accumulation and Microbial Community Structure of Aggregates in an Intensively Cultivated Sandy Loam Soil

PubMed Central

Zhang, Huanjun; Ding, Weixin; He, Xinhua; Yu, Hongyan; Fan, Jianling; Liu, Deyan

2014-01-01

To evaluate the long–term effect of compost (CM) and inorganic fertilizer (NPK) application on microbial community structure and organic carbon (OC) accumulation at aggregate scale, soils from plots amended with CM, NPK and no fertilizer (control) for 20 years (1989–2009) were collected. Soil was separated into large macroaggregate (>2,000 μm), small macroaggregate (250–2,000 μm), microaggregate (53–250 μm), silt (2–53 μm) and clay fraction (<2 μm) by wet-sieving, and their OC concentration and phospholipid fatty acids (PLFA) were measured. The 20-year application of compost significantly (P<0.05) increased OC by 123–134% and accelerated the formation of macroaggregates, but decreased soil oxygen diffusion coefficient. NPK mainly increased OC in macroaggregates and displayed weaker influence on aggregation. Bacteria distributed in all aggregates, while fungi and actinobacteria were mainly in macroaggregates and microaggregates. The ratio of monounsaturated to branched (M/B) PLFAs, as an indicator for the ratio of aerobic to anaerobic microorganisms, increased inversely with aggregate size. Both NPK and especially CM significantly (P<0.05) decreased M/B ratios in all aggregates except the silt fraction compared with the control. The increased organic C in aggregates significantly (P<0.05) negatively correlated with M/B ratios under CM and NPK. Our study suggested that more efficient OC accumulations in aggregates under CM–treated than under NPK–treated soil was not only due to a more effective decrease of actinobacteria, but also a decrease of monounsaturated PLFAs and an increase of branched PLFAs. Aggregations under CM appear to alter micro-habitats to those more suitable for anaerobes, which in turn boosts OC accumulation. PMID:24667543

Synchrotron-based micro and nanotomographic investigations of soil aggregate microbial and pore structure

NASA Astrophysics Data System (ADS)

Kemner, K. M.; O'Brien, S.; Whiteside, M. D.; Sholto-Douglas, D.; Antipova, O.; Bailey, V.; Boyanov, M.; Dohnalkova, A.; Gursoy, D.; Kovarik, L.; Lai, B.; Roehrig, C.; Vogt, S.

2017-12-01

Soil is a highly complex network of pore spaces, minerals, and organic matter (e.g., roots, fungi, and bacteria), making it physically heterogeneous over nano- to macro-scales. Such complexity arises from feedbacks between physical processes and biological activity that generate a dynamic, self-organizing 3D complex. Since we first demonstrated the utility of synchrotron-based transmission tomography to image internal soil aggregate structure [Kemner et al., 1998], we and many other researchers have made use of and have advanced the application of this technique. However, our understanding of how microbes and microbial metabolism are distributed throughout soil aggregates is limited, because no technique is available to image the soil pore network and the life that inhabits it. X-ray transmission microtomography can provide highly detailed 3D renderings of soil structure but cannot distinguish cells from other electron-light material such as air or water. However, the use of CdSe quantum dots (QDs) as a reporter of bacterial presence enables us to overcome this constraint, instilling bacterial cells with enough contrast to detect them and their metabolic functions in their opaque soil habitat, with hard x-rays capable of penetrating 3D soil structures at high resolution. Previous transmission tomographic imaging of soil aggregates with high energy synchrotron x-rays has demonstrated 700 nm3 voxel spatial resolution. These and recent results from nanotomographic x-ray transmission imaging of soil aggregates with 30 nm3 voxel resolution will be presented. In addition, results of submicron voxel-sized x-ray fluorescence 3D imaging to determine microbial distributions within soil aggregates and the critical role to be played by the upgrade of the Advanced Photon Source for 100-1000X increases in hard x-ray brilliance will also be presented. *Kemner, et al., SPIE 3449, 45-53, 1998

Soil carbon storage in silvopasture and related land-use systems in the brazilian cerrado.

PubMed

Tonucci, Rafael G; Nair, P K Ramachandran; Nair, Vimala D; Garcia, Rasmo; Bernardino, Fernando S

2011-01-01

Silvopastoral management of fast-growing tree plantations is becoming popular in the Brazilian Cerrado (savanna). To understand the influence of such systems on soil carbon (C) storage, we studied C content in three aggregate size classes in six land-use systems (LUS) on Oxisols in Minas Gerais, Brazil. The systems were a native forest, a treeless pasture, 24- and 4-yr-old eucalyptus ( sp.) plantations, and 15- and 4-yr-old silvopastures of fodder grass plus animals under eucalyptus. From each system, replicated soil samples were collected from four depths (0-10, 10-20, 20-50, and 50-100 cm), fractionated into 2000- to 250-, 250- to 53-, and <53-μm size classes representing macroaggregates, microaggregates, and silt + clay, respectively, and their C contents determined. Macroaggregate was the predominant size fraction under all LUS, especially in the surface soil layers of tree-based systems. In general, C concentrations (g kg soil) in the different aggregate size fractions did not vary within the same depth. The soil organic carbon (SOC) stock (Mg C ha) to 1-m depth was highest under pasture compared with other LUS owing to its higher soil bulk density. The soils under all LUS had higher C stock compared with other reported values for managed tropical ecosystems: down to 1 m, total SOC stock values ranged from 461 Mg ha under pasture to 393 Mg ha under old eucalyptus. Considering the possibility for formation and retention of microaggregates within macroggregates in low management-intensive systems such as silvopasture, the macroaggregate dynamics in the soil seem to be a good indicator of its C storage potential. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Effects of long-term fertilisation on aggregates and dynamics of soil organic carbon in a semi-arid agro-ecosystem in China

PubMed Central

Zhang, Jiaoyang; Sun, Caili; Xue, Sha

2018-01-01

Background Long-term fertilisation has a large influence on soil physical and chemical properties in agro-ecosystems. The effects on the distribution of aggregates, however, are not fully understood. We determined the dynamic change of the distribution of aggregates and soil organic carbon (SOC) content over time in a long-term field experiment established in 1998 on the Loess Plateau of China and illustrated the relationship between them. Methods We determined SOC content and the distribution of aggregates in nine fertiliser treatments: manure (M); nitrogen (N); phosphorus (P); M and N; M, N, and P; M and P; N and P; bare land; and an unfertilised control. These parameters were then used for a path analysis and to analyse the fractal dimension (Dv). Results The organic fertiliser increased SOC content. The proportions of 0.1–0.25 mm microaggregates and 0.25–0.5 mm macroaggregates were higher and the proportion of the 0.01–0.05 mm size class of the silt + clay fraction was lower in the treatments receiving organic fertiliser (M, MN, MNP, and MP) than that in the control, indicating that the addition of organic fertiliser promoted aggregation. The distribution of aggregates characterised by their fractal dimension (Dv), however, did not differ among the treatments. Discussion Dv was strongly correlated with the proportion of the <0.002 mm size class of the silt + clay fraction that did not differ significantly among the treatments. The change in the distribution of aggregates was strongly correlated with SOC content, which could produce organic polymer binding agents to increase the proportion of larger particles. Long-term application of organic fertiliser is thus necessary for the improvement and maintenance of soil quality in semi-arid agricultural land when residues are removed. PMID:29844955

Does Aggregation Affect the Redistribution and Quality of Eroded SOC?

NASA Astrophysics Data System (ADS)

Hu, Yaxian; Kuhn, Nikolaus

2015-04-01

A substantial amount of literature has discussed the impacts of soil erosion on global carbon cycling. However, numerous gaps in our knowledge remain unaddressed, for instance, the biogeochemical fate of displaced SOC during transport being one of them. The transport distance and the quality of eroded SOC are the two major factors that determine its fate. Previous laboratory-based research had demonstrated that the effects of aggregation can potentially shorten the transport distance of eroded SOC. The mineralization potential of SOC also differs in sediment fractions of different likely transport distances. It is therefore essential to examine the transport distance and quality of eroded SOC under field conditions with natural rainfall as the agent of erosion. Soil samples from a silty clay soil from Switzerland and a sandy soil from Denmark, were collected in the field this summer after natural rainfall events. The soil from Switzerland was sampled from a field of maize in St. Ursanne (47°20' N 7°09' E) on August 6th, 2014 after a natural rainfall event. A depositional fan consisting of aggregated sediment was formed outside the lower edge of the field. The sandy soil from Denmark was sampled from a farm in Foulum (56°30' N, 9°35' W) on September 4, 2014, after a series of natural rainfall events. Soil samples were collected at different topographic positions along the two slopes. All the soil samples from the two farms were fractionated by a settling tube. Bulk soil from Switzerland and Denmark was also dispersed by ultrasound. The SOC contents of all bulk soils and associated fractions were determined using a carbon analyzer Leco 612 at 1000°C. The quality of SOC in different settling fractions collected from various topographic positions were also determined by stable isotopes of C and N (13C and 15N). Our results show that 1) the aggregate specific SOC distribution evidently differs from the mineral particle specific SOC distribution, indicating that re-distribution of eroded SOC is determined by actual aggregate size distribution rather than mineral particle size distribution. 2) The aggregate specific distributions of SOC content from different positions along hillslopes demonstrate that preferential deposition of SOC-enrich sediment along hillslopes is much more pronounced than the mineral particle specific SOC would suggest. 3) The quality of SOC differs significantly in various settling fractions. The fast settling fractions consist of more of labile SOC, and thus is very likely to be mineralized during transport across landscapes, thereby likely contributing as a source of atmospheric CO2. Overall, effects of aggregation can potentially change the transport distance of eroded SOC and thus skew its redistribution towards the terrestrial deposition.

The effects of arbuscular mycorrhizal fungi on glomalin-related soil protein distribution, aggregate stability and their relationships with soil properties at different soil depths in lead-zinc contaminated area

PubMed Central

Huang, Li; Ban, Yihui; Tang, Ming

2017-01-01

Glomalin-related soil protein (GRSP), a widespread glycoprotein produced by arbuscular mycorrhizal fungi (AMF), is crucial for ecosystem functioning and ecological restoration. In the present study, an investigation was conducted to comprehensively analyze the effects of heavy metal (HM) contamination on AMF status, soil properties, aggregate distribution and stability, and their correlations at different soil depths (0–10, 10–20, 20–30, 30–40 cm). Our results showed that the mycorrhizal colonization (MC), hyphal length density (HLD), GRSP, soil organic matter (SOM) and soil organic carbon (SOC) were significantly inhibited by Pb compared to Zn at 0–20 cm soil depth, indicating that HM had significant inhibitory effects on AMF growth and soil properties, and that Pb exhibited greater toxicity than Zn at shallow layer of soil. Both the proportion of soil large macroaggregates (>2000 μm) and mean weight diameter (MWD) were positively correlated with GRSP, SOM and SOC at 0–20 cm soil depth (P < 0.05), proving the important contributions of GRSP, SOM and SOC for binding soil particles together into large macroaggregates and improving aggregate stability. Furthermore, MC and HLD had significantly positive correlation with GRSP, SOM and SOC, suggesting that AMF played an essential role in GRSP, SOM and SOC accumulation and subsequently influencing aggregate formation and particle-size distribution in HM polluted soils. Our study highlighted that the introduction of indigenous plant associated with AMF might be a successful biotechnological tool to assist the recovery of HM polluted soils, and that proper management practices should be developed to guarantee maximum benefits from plant-AMF symbiosis during ecological restoration. PMID:28771531

The effects of arbuscular mycorrhizal fungi on glomalin-related soil protein distribution, aggregate stability and their relationships with soil properties at different soil depths in lead-zinc contaminated area.

PubMed

Yang, Yurong; He, Chuangjun; Huang, Li; Ban, Yihui; Tang, Ming

2017-01-01

Glomalin-related soil protein (GRSP), a widespread glycoprotein produced by arbuscular mycorrhizal fungi (AMF), is crucial for ecosystem functioning and ecological restoration. In the present study, an investigation was conducted to comprehensively analyze the effects of heavy metal (HM) contamination on AMF status, soil properties, aggregate distribution and stability, and their correlations at different soil depths (0-10, 10-20, 20-30, 30-40 cm). Our results showed that the mycorrhizal colonization (MC), hyphal length density (HLD), GRSP, soil organic matter (SOM) and soil organic carbon (SOC) were significantly inhibited by Pb compared to Zn at 0-20 cm soil depth, indicating that HM had significant inhibitory effects on AMF growth and soil properties, and that Pb exhibited greater toxicity than Zn at shallow layer of soil. Both the proportion of soil large macroaggregates (>2000 μm) and mean weight diameter (MWD) were positively correlated with GRSP, SOM and SOC at 0-20 cm soil depth (P < 0.05), proving the important contributions of GRSP, SOM and SOC for binding soil particles together into large macroaggregates and improving aggregate stability. Furthermore, MC and HLD had significantly positive correlation with GRSP, SOM and SOC, suggesting that AMF played an essential role in GRSP, SOM and SOC accumulation and subsequently influencing aggregate formation and particle-size distribution in HM polluted soils. Our study highlighted that the introduction of indigenous plant associated with AMF might be a successful biotechnological tool to assist the recovery of HM polluted soils, and that proper management practices should be developed to guarantee maximum benefits from plant-AMF symbiosis during ecological restoration.

Accumulation of organic C components in soil and aggregates

PubMed Central

Yu, Hongyan; Ding, Weixin; Chen, Zengming; Zhang, Huanjun; Luo, Jiafa; Bolan, Nanthi

2015-01-01

To explore soil organic carbon (SOC) accumulation mechanisms, the dynamics of C functional groups and macroaggregation were studied synchronously through aggregate fractionation and 13C NMR spectroscopy in sandy loam soil following an 18-year application of compost and fertilizer in China. Compared with no fertilizer control, both compost and fertilizer improved SOC content, while the application of compost increased macroaggregation. Fertilizer application mainly increased the levels of recalcitrant organic C components characterized by methoxyl/N-alkyl C and alkyl C, whereas compost application mainly promoted the accumulation of methoxyl/N-alkyl C, phenolic C, carboxyl C, O-alkyl C and di-O-alkyl C in bulk soil. The preferential accumulation of organic C functional groups in aggregates depended on aggregate size rather than nutrient amendments. These groups were characterized by phenolic C and di-O-alkyl C in the silt + clay fraction, carboxyl C in microaggregates and phenolic C, carboxyl C and methoxyl/N-alkyl C in macroaggregates. Thus, the differences in accumulated organic C components in compost- and fertilizer-amended soils were primarily attributable to macroaggregation. The accumulation of methoxyl/N-alkyl C in microaggregates effectively promoted macroaggregation. Our results suggest that organic amendment rich in methoxyl/N-alkyl C effectively improved SOC content and accelerated macroaggregation in the test soil. PMID:26358660

[Characteristics of soil organic carbon and enzyme activities in soil aggregates under different vegetation zones on the Loess Plateau].

PubMed

Li, Xin; Ma, Rui-ping; An, Shao-shan; Zeng, Quan-chao; Li, Ya-yun

2015-08-01

In order to explore the distribution characteristics of organic carbon of different forms and the active enzymes in soil aggregates with different particle sizes, soil samples were chosen from forest zone, forest-grass zone and grass zone in the Yanhe watershed of Loess Plateau to study the content of organic carbon, easily oxidized carbon, and humus carbon, and the activities of cellulase, β-D-glucosidase, sucrose, urease and peroxidase, as well as the relations between the soil aggregates carbon and its components with the active soil enzymes were also analyzed. It was showed that the content of organic carbon and its components were in order of forest zone > grass zone > forest-grass zone, and the contents of three forms of organic carbon were the highest in the diameter group of 0.25-2 mm. The content of organic carbon and its components, as well as the activities of soil enzymes were higher in the soil layer of 0-10 cm than those in the 10-20 cm soil layer of different vegetation zones. The activities of cellulase, β-D-glucosidase, sucrose and urease were in order of forest zone > grass zone > forest-grass zone. The peroxidase activity was in order of forest zone > forest-grass zone > grass zone. The activities of various soil enzymes increased with the decreasing soil particle diameter in the three vegetation zones. The activities of cellulose, peroxidase, sucrose and urease had significant positive correlations with the contents of various forms of organic carbon in the soil aggregates.

Carbon and nitrogen mineralization and enzyme activities in soil aggregate-size classes: Effects of biochar, oyster shells, and polymers.

PubMed

Awad, Yasser Mahmoud; Lee, Sang Soo; Kim, Ki-Hyun; Ok, Yong Sik; Kuzyakov, Yakov

2018-05-01

Biochar (BC) and polymers are cost-effective additives for soil quality improvement and long-term sustainability. The additional use of the oyster shells (OS) powder in BC- or polymer-treated soils is recommended as a nutrient source, to enhance aggregation and to increase enzyme activities. The effects of soil treatments (i.e., BC (5 Mg ha -1 ) and polymers (biopolymer at 0.4 Mg ha -1 or polyacrylamide at 0.4 Mg ha -1 ) with or without the OS (1%)) on the short-term changes were evaluated based on a 30-day incubation experiment with respect to several variables (e.g., CO 2 release, NH 4 + and NO 3 - concentrations, aggregate-size classes, and enzyme activities in an agricultural Luvisol). The BC and BP with the addition of OS increased the portion of microaggregates (<0.25 mm) relative to the control soil without any additions, while PAM alone increased the portion of large macroaggregates (1-2 mm). Concentrations of NO 3 - also increased in soils treated with OS, OS + BC, and OS + BP as result of the increased chitinase and leucine aminopeptidase activities. The BC and BP when treated with the additional OS had significant short-term impacts on N mineralization without affecting C mineralization in soil. Consequently, the combination of BC or BP with OS was seen to accelerate N turnover without affecting C turnover (and related C losses) from soil. As such, the addition of these additives contributed considerably to the improvement of soil fertility and C sequestration. Copyright © 2018 Elsevier Ltd. All rights reserved.

Glyphosate and AMPA content in the PM10 emitted by a soil of the central semiarid region of Argentine (CSRA)

NASA Astrophysics Data System (ADS)

Mendez, Mariano; Aimar, Silvia; Aparicio, Virginia; Buschiazzo, Daniel; De Geronimo, Eduardo; Costa, Jose Luis

2017-04-01

Particle matter with aerodynamic diameter lesser than 10 um (PM10) has shown adverse effects on health even at low concentrations. Entic Haplustoll dominates central semiarid region of Argentine (CSRA) and PM10 are emitted from the soil by tillage and wind erosion. The aim of study was measure glyphosate concentration in the PM10 emitted by a soil fine-sandy loam Entic Haplustoll. The study was carried in Santa Rosa La Pampa (S36° 46´; W64° 16´; 210 m a.s.l.) in a plot where 3.7 kg ha-1 active ingredient of glyphosate was used in the last two year and glyphosate was not used in the last 12 months. Soil samples were air dried and sieved with a rotary sieve to separate the following aggregate fractions: <0.42 mm, 0.42 to 0.84 mm, 0.84 to 2 mm, 2 to 6.4 mm, 6.4 to 19.2 mm, and > 19.2 mm. The Easy Dust Generator (EDG) was used to generate dust from the soil and its aggregate fractions. The PM10 emitted by EDG was collected using an electrostatic precipitator (C&L model number GH-939). The following determinations were carried out in the soil, aggregates and PM10 emitted by them: organic matter contents (OM) (Walkley & Black, 1934), particle size composition (Malvern martersizer2000) and the Glyphosate and AMPA content. Results showed that mean geometric diameter (MGD) of the material collected in the electrostatic precipitator and emitted by the aggregate fraction and the soil was between 4.6 and 5.3 µm. OM content in the aggregates fraction and soil ranged between 1.4% and 2.9% while than in the PM10 emitted by them ranged between 3.5% and 3.7 %. Clay content in aggregates and soil ranged between 6.5% and 8.5% while than in PM10 emitted by them ranged between 17.5% and 19.0%. Glyphosate content in aggregates fraction and soil ranged between 1 and 3 ppb. Glyphosate in PM10 emitted by aggregates and soil did not show differences in despite of it ranged between 11.0 ppb and 19.5 ppb. OM and clay in aggregate fractions and PM10 do not explained glyphosate content in PM10. AMPA concentration in aggregates and soil ranged between 80 ppb and 150 ppb, while than in PM10 emitted by them ranged between 520 ppb and 750 ppb. The enrichment ratio (ER, quotient between concentration or content in PM10 and aggregates) of glyphosate and AMPA (between 4 and 17) were higher than ER of clay and OM (between 1 and 3). ERglyphosate and ERAMPA were different among aggregate fractions (p< 0.05) and the highest ER was found in the fraction >19.2 (ERglyphosate = 17 and ERAMPA = 10). Our results showed contents variable of glyphosate and AMPA in the soil and its aggregate fractions after 12 month from the last glyphosate application in a haplustoll soil of the CSRA. High glyphosate content were also found in PM10 emitted by the soil and its aggregate fractions. More studies are necessary to evaluate the glyphosate content in PM10 and its potential impact in the heath.

Root exudate as major player on soil-water retention dynamics

NASA Astrophysics Data System (ADS)

Albalasmeh, A. A.; Sweet, J. R.; Gebrenegus, T. B.; Ghezzehei, T. A.

2012-12-01

Plant roots and soil microbes release 5-60% of the entirety of photosynthetically fixed carbon in to the soil as exudates to adapt to their surrounding. There is indirect evidence suggesting that these exudates play a major role in altering the of the soil water retention properties. In this study, we used a uniformly sized (40 μm) glass beads and various concentrations (0, 2, 10, 20 and 29 g/L) of polygalacutronic acid (PGA) to mimic sandy soil and the organic exudates from plant roots, respectively. The samples were subjected to periods of drying and subsequent equilibration. At each stage, the water potential was measured using WP4C Dewpoint PotentiaMeter. The effect of root exudates on soil water retention can be attributed t at least two factors. The most widely speculated effect is through enhanced of soil aggregation. This effect is primarily due to capillary adhesion in fine pores within aggregates and is consistent was visual observation of pronounced aggregation in many rhizosphere soils. The second factor is related to osmotic effect of the exudate solution. Our observations show that the capillary effect is mostly to higher water potential regime (> -1 bar suction). Whereas the osmotic effect dominates in <- 1 bar suction. These results will provide direct quantitative evidence of how rhizosphere organic matter helps plant-soil relations.

A Conceptual Approach to Assimilating Remote Sensing Data to Improve Soil Moisture Profile Estimates in a Surface Flux/Hydrology Model. 2; Aggregation

NASA Technical Reports Server (NTRS)

Schamschula, Marius; Crosson, William L.; Inguva, Ramarao; Yates, Thomas; Laymen, Charles A.; Caulfield, John

1998-01-01

This is a follow up on the preceding presentation by Crosson. The grid size for remote microwave measurements is much coarser than the hydrological model computational grids. To validate the hydrological models with measurements we propose mechanisms to aggregate the hydrological model outputs for soil moisture to allow comparison with measurements. Weighted neighborhood averaging methods are proposed to facilitate the comparison. We will also discuss such complications as misalignment, rotation and other distortions introduced by a generalized sensor image.

Nitrite-Oxidizing Bacteria Community Composition and Diversity Are Influenced by Fertilizer Regimes, but Are Independent of the Soil Aggregate in Acidic Subtropical Red Soil.

PubMed

Han, Shun; Li, Xiang; Luo, Xuesong; Wen, Shilin; Chen, Wenli; Huang, Qiaoyun

2018-01-01

Nitrification is the two-step aerobic oxidation of ammonia to nitrate via nitrite in the nitrogen-cycle on earth. However, very limited information is available on how fertilizer regimes affect the distribution of nitrite oxidizers, which are involved in the second step of nitrification, across aggregate size classes in soil. In this study, the community compositions of nitrite oxidizers ( Nitrobacter and Nitrospira ) were characterized from a red soil amended with four types of fertilizer regimes over a 26-year fertilization experiment, including control without fertilizer (CK), swine manure (M), chemical fertilization (NPK), and chemical/organic combined fertilization (MNPK). Our results showed that the addition of M and NPK significantly decreased Nitrobacter Shannon and Chao1 index, while M and MNPK remarkably increased Nitrospira Shannon and Chao1 index, and NPK considerably decreased Nitrospira Shannon and Chao1 index, with the greatest diversity achieved in soils amended with MNPK. However, the soil aggregate fractions had no impact on that alpha-diversity of Nitrobacter and Nitrospira under the fertilizer treatment. Soil carbon, nitrogen and phosphorus in the soil had a significant correlation with Nitrospira Shannon and Chao1 diversity index, while total potassium only had a significant correlation with Nitrospira Shannon diversity index. However, all of them had no significant correlation with Nitrobacter Shannon and Chao1 diversity index. The resistance indices for alpha-diversity indexes (Shannon and Chao1) of Nitrobacter were higher than those of Nitrospira in response to the fertilization regimes. Manure fertilizer is important in enhancing the Nitrospira Shannon and Chao1 index resistance. Principal co-ordinate analysis revealed that Nitrobacter - and Nitrospira -like NOB communities under four fertilizer regimes were differentiated from each other, but soil aggregate fractions had less effect on the nitrite oxidizers community. Redundancy analysis and Mantel test indicated that soil nitrogen, carbon, phosphorus, and available potassium content were important environmental attributes that control the Nitrobacter - and Nitrospira -like NOB community structure across different fertilization treatments under aggregate levels in the red soil. In general, nitrite-oxidizing bacteria community composition and alpha-diversity are depending on fertilizer regimes, but independent of the soil aggregate.

Effect of cover crops management in aggregate stability of a vineyard in Central Spain.

NASA Astrophysics Data System (ADS)

Ruiz-Colmenero, Marta; Bienes, Ramon; Marques, Maria-Jose

2010-05-01

Our research focuses in cover crop treatments used to avoid soil degradation in hillsides. The soil-plant interaction can influence the soil structure. In this study we pay special attention to the soil aggregates in a hillside vineyard (average slope of 14%), under Mediterranean semiarid climatic conditions (average annual temperature 14°C, annual rainfall around 400 mm), in the South East of Madrid located at an altitude of 800 masl. The soil classification according to USDA (2006) is Calcic Haploxeralf. Its particle size yields 58% sand, 18% silt and 24% clay, so that according to USDA classification it is a sandy clay loam soil. The bulk density of the first 10 cm of topsoil is 1.2 g cm-3 and its real density is 2.4 g cm-3. It has low organic matter content: 1.3 ± 0.1% (Walkley and Black, 1934). Three treatments were tested: i) traditional tillage ii) soil covered by Brachypodium distachyon allowing self-sowing, and iii) soil covered by Secale cereale, mown in early spring. In each treatment the aggregate stability was measured. These cover crops were established in a 2m wide strip at the center of the rows. We have collected samples of soil for each treatment along 2 years and we analyzed the aggregates, trying to find changes in their stability. Aggregates of 4 to 4.75 mm diameter were selected by dry sieving. The stability was measured with Drop-test: CND and TDI (Imeson and Vis, 1984). An improvement in the stability of aggregates was observed after two years of cover crop treatment. There are significant differences among the treatments analyzed with Kolmogorov-Smirnov test, being Brachypodium distachyon the treatment with more stable aggregates, it is necessary a mean higher than 8 drops to disintegrate every aggregate completely. Organic carbon was also measured by Loss on Ignition method (Schulte and Hopkins, 1996). This method can lead to an overestimation of the organic matter in soil samples but is considered suitable for aggregates. Again, those aggregates from treatments with cover crops had more organic carbon than the aggregates from traditional tillage treatment (Brachypodium distachyon 26.35, Secale cereale 18.83 and traditional tillage 17.04 g Kg-1). Lastly, the oxidable soil organic matter was also analyzed (Walkley-Black, 1934) and these results also indicated an increase in cover crop treatments, especially after the second year of treatment when the percentage of oxidable organic matter in the treatments with vegetable covers is approximately 1.5 times higher than this content in tillage treatment (1.015 %). The results support the conclusion that treatments with cover crops increased or at least maintained the stability of aggregates which is linked to the organic matter in the aggregates, on the contrary, the traditional tillage treatment showed less stable aggregates along the time. Keywords: aggregates stability, LOI, organic matter, vineyard, vegetable cover Aknowledgements: Projects FP06-DR3 IMIDRA, RTA2007-0086 INIA. Predoctoral INIA. Bodegas-Viñedos Gosálbez-Ortí.

Fate of lignin, cutin and suberin in soil organic matter fractions - an incubation experiment

NASA Astrophysics Data System (ADS)

Mueller, Carsten W.; Mueller, Kevin E.; Freeman, Katherine H.; Ingrid, Kögel-Knabner

2010-05-01

The turnover of soil organic matter (SOM) is controlled by its chemical composition, its spatial accessibility and the association with the mineral phase. Separation of bulk soils by physical fractionation and subsequent chemical analysis of these fractions should give insights to how compositional differences in SOM drive turnover rates of different size-defined carbon pools. The main objective of this study was to elucidate the relative abundance and recalcitrance of lignin, cutin and suberin in aggregated bulk soils and SOM fractions in the course of SOM decomposition. Bulk soils and physically-separated size fractions (sand, silt and clay) of the Ah horizon of a forest soil (under Picea abies L.Karst) were parallel incubated over a period of one year. In order to differentiate between particulate OM (POM) and mineral-associated SOM the particle size fractions were additionally separated by density after the incubation experiment. We used solid-state 13C-CPMAS NMR spectroscopy and GC-MS (after copper oxide oxidation and solvent extraction) to analyze the composition of the incubated samples. The abundance and isotopic composition (including 13C and 14C) of the respired CO2 further enabled us to monitor the dynamics of SOM mineralization. This approach allowed for differentiating between C stabilization of soil fractions due to accessibility/aggregation and to biochemical recalcitrance at different scales of resolution (GC-MS, NMR). We found a relative enrichment of alkyl C and decreasing lignin contents in the order of sand < silt < clay by 13C-NMR spectroscopy and GC-MS within soils and fractions before the incubation, resulting in increased lipid to lignin ratios with decreasing particle size. An accumulation of aliphatic C compounds was especially found for the small silt and clay sized particulate OM (POM). For the fresh particulate OM (POM) of the sand fraction a clear decay of lignin was observed in the course of the incubation experiment, indicated by decreasing C/V and increasing ac/alV ratios. A relative decrease of aliphatic C in the incubated fractions compared to the incubated bulk soils showed the preferential mineralization of less recalcitrant C compounds that were spatially inaccessible in aggregates of the bulk soil. Differences in the abundance of lignin monomers, hydroxyl acids, n-alkanols and n-fatty acid methyl esters measured by GC MS before and after the incubation indicated selective degradation and preservation patterns at the molecular scale.

Soil aggregate stability within the morphologically diverse area

NASA Astrophysics Data System (ADS)

Jaksik, Ondrej; Kodesova, Radka; Kubis, Adam; Klement, Ales; Fer, Miroslav

2013-04-01

This study evaluates the effect of soil erosion on properties of topsoil especially on soil aggregate stability. Study was performed on morphologically diverse study site (6 ha area) in loess region of Southern Moravia, Czech Republic. The region has been under uninterrupted agricultural use since the middle of the Holocene. Haplic Chernozem is an original dominant soil unit in the area, nowadays progressively transformed into different soil units along with intensive soil erosion. There are eroded phases of Chernozem, Regosol (the steepest and heavily eroded parts of the study area), colluvial Chernozem and Colluvial soil (base slope). Sampling spots were selected in order to represent diverse soil units and morphological units. Soil samples were taken from the topsoil, carefully transported to the laboratory and consequently air dried. Following soil properties were measured: pH_KCl, pH_CaCl2, soil organic matter content (SOM), carbonate content (CO3), content of iron and manganese (in ammonium oxalate extract, Feo and Mn_o, and dithionite-citrate extract, Fed and Mn_d), and stability of soil aggregates using two different methods. The indexes of water stable aggregates (WSA) were determined using the procedure presented by Nimmo and Perkins (2002). The three methods proposed by Le Bissonnais (1996) were also used to study various destruction mechanisms. The fast wetting test (KV1) was applied to study aggregate slaking due to the compression of the entrapped air (mechanism similar to the WSA test). The slow wetting test (KV2) was used to evaluate aggregate disintegration caused by the micro cracking due to the different swelling, and physico-chemical dispersion due to the osmotic stress. The shaking after prewetting test (KV3) was utilized to study the mechanical aggregate breakdown. Terrain attributes were evaluated from digital terrain model. In general the lowest soil aggregate stability was observed on steep slopes, which were highly impacted by soil erosion. The highest aggregate stability was measured on soils sampled at relatively flat upper parts, which were only slightly influenced by erosion processes. Higher stability was also obtained on base slope, where the sedimentation of previously eroded soil material occurred. Following correlations were obtained between different test results: R=0.911 for WSA and KV1, R=0.481 for WSA and KV2, R=0.700 for WSA and KV3. The statistical significant correlation was found between WSA index and SOM (R=0.403), WSA and pH_CaCl2 (R=-0.360), WSA and Mnd (R=0.408), WSA and Mno (R=0.355), KV1 and SOM (R=-0.377), KV1 and pH_CaCl2 (R=0.352), KV2 and CO3 (R=0.379), KV3 and pH_CaCl2 (R=0.376). We also found statistical significant correlation between WSA index and two terrain attributes (plan curvature R=-0.490, and total curvature R=-0.501). Acknowledgment: Authors acknowledge the financial support of the Ministry of Agriculture of the Czech Republic (QJ1230319). References Le Bissonnais Y. 1996. Aggregate stability and assessment of soil crustability and erodibility: Theory and methodology. Eur. J. Soil Sci. 47: 425-437. Nimmo J.R., Perkins K.S. 2002. Aggregate stability and size distribution, pp. 317-328. In: Dane J. H. & Topp G.C. (eds), Methods of Soil Analysis, Part 4 - Physical Methods. Soil Science Society of America, Inc. Madison, USA.

Aggregation and C dynamics along an elevation gradient in carbonate-containing grassland soils of the Alps

NASA Astrophysics Data System (ADS)

Garcia-Franco, Noelia; Wiesmeier, Martin; Kiese, Ralf; Dannenmann, Michael; Wolf, Benjamin; Zistl-Schlingmann, Marcus; Kögel-Knabner, Ingrid

2017-04-01

C sequestration in mountainous grassland soils is regulated by physical, chemical and biological soil process. An improved knowledge of the relationship between these stabilization mechanisms is decisive to recommend the best management practices for climate change mitigation. In this regard, the identification of a successful indicator of soil structural improvement and C sequestration in mountainous grassland soils is necessary. Alpine and pre-alpine grassland soils in Bavaria represent a good example for mountainous grassland soils faced with climate change. We sampled grassland soils of the northern limestone alps in Bavaria along an elevation gradient from 550 to 1300 m above sea level. We analyzed C dynamics by a comparative analysis of the distribution of C according to aggregate size classes: large-macroaggregates (> 2000 µm), small-macroaggregates (250-2000 µm), microaggregates (63-250 µm), silt plus clay particles (<63 µm) and bulk soil. Our preliminary results showed higher C content and changed water-stable aggregate distribution in the high elevation sites compared to lower elevations. Magnesium carbonate seem to play an important role in stabilizing macroaggregates formed from fresh OM. In addition, the isolation of occluded microaggregates within macroaggregates will help us to improve our understanding on the effects of climate change on soil structure and on the sensitivity of different C stabilization mechanisms present in mountainous soils.

Microhabitat Effects on N2O Emissions from Floodplain Soils under Controlled Conditions

NASA Astrophysics Data System (ADS)

Ley, Martin; Lehmann, Moritz F.; Niklaus, Pascal A.; Kuhn, Thomas; Luster, Jörg

2016-04-01

Semi-terrestrial soils such as floodplain soils are considered to be potential hotspots of nitrous oxide (N2O) emissions. The quantitative assessment of N2O release from these hotspots under field conditions, and of the microbial pathways that underlie net N2O production (ammonium oxidation, nitrifier-denitrification, and denitrification) is challenging because of their high spatial and temporal variability. The production and consumption of N2O appears to be linked to the presence or absence of micro-niches, providing specific conditions that may be favorable to either of the relevant microbial pathways. Flood events have been shown to trigger moments of enhanced N2O emission through a close coupling of niches with high and low oxygen availabilities. This coupling might be modulated by microhabitat effects related to soil aggregate formation, root soil interactions and the degradation of organic matter accumulations. In order to assess how these factors can modulate N2O production and consumption under simulated flooding/drying conditions, we have set up a mesocosm experiment with N-rich floodplain soils comprising different combinations of soil aggregate size classes and inert matrix material. These model soils were either planted with basket willow (Salix viminalis L.), mixed with leaf litter, or left untreated. Throughout a simulated flood event, we repeatedly measured the net N2O production rate. In addition, soil water content, redox potential, as well as C and N substrate availability were monitored. In order to gain insight into the sources of, and biogeochemical controls on N2O production, we also measured the bulk δ15N signature of the produced N2O, as well as its intramolecular 15N site preference (SP). In this presentation we focus on a period of enhanced N2O emission during the drying phase after 48 hrs of flooding. We will discuss the observed emission patterns in the context of possible treatment effects. Soils with large aggregates showed a tendency to emit more N2O than small-aggregate soils. Salix viminalis strongly suppressed the N2O emissions, fully compensating for any aggregate effects. Litter accumulation on the other hand enhanced N2O emission from well-aggregated soils, but showed only a small effect in combination with small aggregates. In moments of highest emission rates, the measured δ15Nbulk of headspace N2O was considerably lower relative to atmospheric N2O (δ15N between -20 ‰ and -25 ‰) in the amended treatments, suggesting N2O production by denitrification or by nitrifier-denitrification. Untreated mesocosms produced an even lower δ15Nbulk (-40‰). Similarly, aggregate formation/size seemed to affect the N2O δ15Nbulk values, suggesting different net N2O production dynamics under different microhabitat conditions, which will be elucidated further, using 15N site preference SP data. Combining stable isotope techniques with quantitative flux data from a mesoscale laboratory experiment, our data highlight the importance of microhabitat effects in modulating N2O emission from floodplain soils. It also underscores their influence on the N2O production pathways involved in the occurrence of N2O emission hot spots and moments.

How the Assumed Size Distribution of Dust Minerals Affects the Predicted Ice Forming Nuclei

NASA Technical Reports Server (NTRS)

Perlwitz, Jan P.; Fridlind, Ann M.; Garcia-Pando, Carlos Perez; Miller, Ron L.; Knopf, Daniel A.

2015-01-01

The formation of ice in clouds depends on the availability of ice forming nuclei (IFN). Dust aerosol particles are considered the most important source of IFN at a global scale. Recent laboratory studies have demonstrated that the mineral feldspar provides the most efficient dust IFN for immersion freezing and together with kaolinite for deposition ice nucleation, and that the phyllosilicates illite and montmorillonite (a member of the smectite group) are of secondary importance.A few studies have applied global models that simulate mineral specific dust to predict the number and geographical distribution of IFN. These studies have been based on the simple assumption that the mineral composition of soil as provided in data sets from the literature translates directly into the mineral composition of the dust aerosols. However, these tables are based on measurements of wet-sieved soil where dust aggregates are destroyed to a large degree. In consequence, the size distribution of dust is shifted to smaller sizes, and phyllosilicates like illite, kaolinite, and smectite are only found in the size range 2 m. In contrast, in measurements of the mineral composition of dust aerosols, the largest mass fraction of these phyllosilicates is found in the size range 2 m as part of dust aggregates. Conversely, the mass fraction of feldspar is smaller in this size range, varying with the geographical location. This may have a significant effect on the predicted IFN number and its geographical distribution.An improved mineral specific dust aerosol module has been recently implemented in the NASA GISS Earth System ModelE2. The dust module takes into consideration the disaggregated state of wet-sieved soil, on which the tables of soil mineral fractions are based. To simulate the atmospheric cycle of the minerals, the mass size distribution of each mineral in aggregates that are emitted from undispersed parent soil is reconstructed. In the current study, we test the null-hypothesis that simulating the presence of a large mass fraction of phyllosilicates in dust aerosols in the size range 2 m, in comparison to a simple model assumption where this is neglected, does not yield a significant effect on the magnitude and geographical distribution of the predicted IFN number. Results from sensitivity experiments are presented as well.

[Aluminum dissolution and changes of pH in soil solution during sorption of copper by aggregates of paddy soil].

PubMed

Xu, Hai-Bo; Zhao, Dao-Yuan; Qin, Chao; Li, Yu-Jiao; Dong, Chang-Xun

2014-01-01

Size fractions of soil aggregates in Lake Tai region were collected by the low-energy ultrasonic dispersion and the freeze-desiccation methods. The dissolution of aluminum and changes of pH in soil solution during sorption of Cu2+ and changes of the dissolution of aluminum at different pH in the solution of Cu2+ by aggregates were studied by the equilibrium sorption method. The results showed that in the process of Cu2+ sorption by aggregates, the aluminum was dissoluted and the pH decreased. The elution amount of aluminum and the decrease of pH changed with the sorption of Cu2+, both increasing with the increase of Cu2+ sorption. Under the same conditions, the dissolution of aluminum and the decrease of pH were in the order of coarse silt fraction > silt fraction > sand fraction > clay fraction, which was negatively correlated with the amount of iron oxide, aluminum and organic matter. It suggested that iron oxide, aluminum and organic matters had inhibitory and buffering effect on the aluminum dissolution and the decrease of pH during the sorption of Cu2+.

Flocculation characteristics of freshly eroded aggregates

NASA Astrophysics Data System (ADS)

Manning, Andrew; Wendling, Valentin; Gratiot, Nicolas; Legout, Cedric; Michallet, Herve

2014-05-01

In Europe, 260,000 square kms of soils already suffer erosion by water. This worrying level of land degradation is expected to increase in the context of climate change, with situations particularly critical in mountainous environments. This study aims at improving sediment transport parameterisation, by examining the kinetics of fine soil aggregates (size D, settling velocity Ws, density), once immersed in a turbulent flow. Thus observing the changing state, as soil aggregates become suspended sediment floc/aggregates. Particle properties of two Mediterranean materials (black marl and molasse, both sampled in badlands) were tested in grid stirred experiments. Hydrodynamic properties were monitored with ADV and turbidity sensors. For each soil, three suspended sediment concentration (SSC) loads (1.5; 5; 10 g/l) representative of flood conditions were tested. Aggregate properties were obtained at four depths above the grid, using the video LabSFLOC technique and laser techniques. These acquisition heights are associated with the corresponding turbulence dissipation rates G of 1.5, 3, 7 and 19 s^-1. Once particles were injected in the tank, a quasi-equilibrium state was rapidly reached, after one to two minutes. The floc/aggregate properties did not vary with sediment load. The median diameter D_50 was measured to be around 60 microns for the clay loam soil and around 15 microns for the two badlands materials. Examining the molasse samples, we see that the SSC at 1, 5, 10, 20 and 40 minute intervals were all +12 g/l at distances 10 cm and 15 cm above the nominal vertical mid-stroke grid position for the experimental SSC ranges. At the less turbulent zone, a 2 g/l base SSC reduced by 80% and at a nominal 10 g/l the SSC dipped by two orders of magnitude from the base concentration. If we consider the population distribution for molasse at a base SSC of 10 g/l sampled 15cm above the grid after 40 minutes, D ranged from 39 - 273 microns. A small microfloc cluster only had Ws of 0.4-0.5 mm/s, an order of magnitude slower than the peak sample Ws of 5.8 mm/s. These fast settling aggregates spanned the macrofloc (> 160 microns) and microfloc transition from 100-220 microns, representing over half the SSC. The majority of the microflocs (< 160 microns) exhibited effective densities between 160-1600 kg/m^-3, which suggests that some degree of flocculation has occurred. Furthermore, there are highly porous macroflocs demonstrating effective densities < 40 kg/m^-3; these flocs fell at a Ws of about 1 mm/s and represented ~4% of the total SSC. A key fundamental research question to be addressed in this study was: do aggregates rapidly turn into flocs? The initial results indicate that aggregates do not easily/rapidly turn into flocs. However, despite their poor kinetics, particles were undoubtedly aggregated. The aggregation index was measured to be of 50% for badlands materials. The behaviour of the soils differ significantly from those observed for estuarine muds, floc size and settling velocity increases with suspended sediment concentration, where as the soils tested did not.

Methane Emissions from Natural Gas Vehicles in Beijing, Baoding, and Shijiazhuang, China during CAREBEIJING Field Campaign

NASA Astrophysics Data System (ADS)

Pérez García-Pando, C.; Miller, R. L.; Perlwitz, J. P.; Kok, J. F.; Scanza, R.; Mahowald, N. M.

2014-12-01

Mineral dust created by wind erosion of soil particles is the dominant aerosol by mass in the atmosphere. It exerts significant effects on radiative fluxes, clouds, ocean biogeochemistry, and human health. Models that predict the lifecycle of mineral dust aerosols generally assume a globally uniform mineral composition. However, this simplification limits our understanding of the role of dust in the Earth system, since the effects of dust strongly depend on the particles' physical and chemical properties, which vary with their mineral composition. Hence, not only a detailed understanding of the processes determining the dust emission flux is needed, but also information about its size dependent mineral composition. Determining the mineral composition of dust aerosols is complicated. The largest uncertainty derives from the current atlases of soil mineral composition. These atlases provide global estimates of soil mineral fractions, but they are based upon massive extrapolation of a limited number of soil samples assuming that mineral composition is related to soil type. This disregards the potentially large variability of soil properties within each defined soil type. In addition, the analysis of these soil samples is based on wet sieving, a technique that breaks the aggregates found in the undisturbed parent soil. During wind erosion, these aggregates are subject to partial fragmentation, which generates differences on the size distribution and composition between the undisturbed parent soil and the emitted dust aerosols. We review recent progress on the representation of the mineral and chemical composition of dust in climate models. We discuss extensions of brittle fragmentation theory to prescribe the emitted size-resolved dust composition, and we identify key processes and uncertainties based upon model simulations and an unprecedented compilation of observations.

Dust Composition in Climate Models: Current Status and Prospects

NASA Astrophysics Data System (ADS)

Pérez García-Pando, C.; Miller, R. L.; Perlwitz, J. P.; Kok, J. F.; Scanza, R.; Mahowald, N. M.

2015-12-01

Mineral dust created by wind erosion of soil particles is the dominant aerosol by mass in the atmosphere. It exerts significant effects on radiative fluxes, clouds, ocean biogeochemistry, and human health. Models that predict the lifecycle of mineral dust aerosols generally assume a globally uniform mineral composition. However, this simplification limits our understanding of the role of dust in the Earth system, since the effects of dust strongly depend on the particles' physical and chemical properties, which vary with their mineral composition. Hence, not only a detailed understanding of the processes determining the dust emission flux is needed, but also information about its size dependent mineral composition. Determining the mineral composition of dust aerosols is complicated. The largest uncertainty derives from the current atlases of soil mineral composition. These atlases provide global estimates of soil mineral fractions, but they are based upon massive extrapolation of a limited number of soil samples assuming that mineral composition is related to soil type. This disregards the potentially large variability of soil properties within each defined soil type. In addition, the analysis of these soil samples is based on wet sieving, a technique that breaks the aggregates found in the undisturbed parent soil. During wind erosion, these aggregates are subject to partial fragmentation, which generates differences on the size distribution and composition between the undisturbed parent soil and the emitted dust aerosols. We review recent progress on the representation of the mineral and chemical composition of dust in climate models. We discuss extensions of brittle fragmentation theory to prescribe the emitted size-resolved dust composition, and we identify key processes and uncertainties based upon model simulations and an unprecedented compilation of observations.

Predicting the Mineral Composition of Dust Aerosols. Part 2; Model Evaluation and Identification of Key Processes with Observations

NASA Technical Reports Server (NTRS)

Perlwitz, J. P.; Garcia-Pando, C. Perez; Miller, R. L.

2015-01-01

A global compilation of nearly sixty measurement studies is used to evaluate two methods of simulating the mineral composition of dust aerosols in an Earth system model. Both methods are based upon a Mean Mineralogical Table (MMT) that relates the soil mineral fractions to a global atlas of arid soil type. The Soil Mineral Fraction (SMF) method assumes that the aerosol mineral fractions match the fractions of the soil. The MMT is based upon soil measurements after wet sieving, a process that destroys aggregates of soil particles that would have been emitted from the original, undisturbed soil. The second method approximately reconstructs the emitted aggregates. This model is referred to as the Aerosol Mineral Fraction (AMF) method because the mineral fractions of the aerosols differ from those of the wet-sieved parent soil, partly due to reaggregation. The AMF method remedies some of the deficiencies of the SMF method in comparison to observations. Only the AMF method exhibits phyllosilicate mass at silt sizes, where they are abundant according to observations. In addition, the AMF quartz fraction of silt particles is in better agreement with measured values, in contrast to the overestimated SMF fraction. Measurements at distinct clay and silt particle sizes are shown to be more useful for evaluation of the models, in contrast to the sum over all particles sizes that is susceptible to compensating errors, as illustrated by the SMF experiment. Model errors suggest that allocation of the emitted silt fraction of each mineral into the corresponding transported size categories is an important remaining source of uncertainty. Evaluation of both models and the MMT is hindered by the limited number of size-resolved measurements of mineral content that sparsely sample aerosols from the major dust sources. The importance of climate processes dependent upon aerosol mineral composition shows the need for global and routine mineral measurements.

Predicting the mineral composition of dust aerosols – Part 2: Model evaluation and identification of key processes with observations

DOE PAGES

Perlwitz, J. P.; Perez Garcia-Pando, C.; Miller, R. L.

2015-10-21

A global compilation of nearly sixty measurement studies is used to evaluate two methods of simulating the mineral composition of dust aerosols in an Earth system model. Both methods are based upon a Mean Mineralogical Table (MMT) that relates the soil mineral fractions to a global atlas of arid soil type. The Soil Mineral Fraction (SMF) method assumes that the aerosol mineral fractions match the fractions of the soil. The MMT is based upon soil measurements after wet sieving, a process that destroys aggregates of soil particles that would have been emitted from the original, undisturbed soil. The second methodmore » approximately reconstructs the emitted aggregates. This model is referred to as the Aerosol Mineral Fraction (AMF) method because the mineral fractions of the aerosols differ from those of the wet-sieved parent soil, partly due to reaggregation. The AMF method remedies some of the deficiencies of the SMF method in comparison to observations. Only the AMF method exhibits phyllosilicate mass at silt sizes, where they are abundant according to observations. In addition, the AMF quartz fraction of silt particles is in better agreement with measured values, in contrast to the overestimated SMF fraction. Measurements at distinct clay and silt particle sizes are shown to be more useful for evaluation of the models, in contrast to the sum over all particles sizes that is susceptible to compensating errors, as illustrated by the SMF experiment. Model errors suggest that allocation of the emitted silt fraction of each mineral into the corresponding transported size categories is an important remaining source of uncertainty. Evaluation of both models and the MMT is hindered by the limited number of size-resolved measurements of mineral content that sparsely sample aerosols from the major dust sources. In conclusion, the importance of climate processes dependent upon aerosol mineral composition shows the need for global and routine mineral measurements.« less

Chemical Composition of Soil Horizons and Aggregate Size Fractions Under the Hawaiian Fern Dicranopteris and Angiosperm Cheirodendrom

NASA Astrophysics Data System (ADS)

Stewart, C. E.; Amatangelo, K.; Neff, J.

2007-12-01

Soil organic matter (SOM) inherits much of its chemical nature from the dominant vegetation, including phenolic (lignin-derived), aromatic, and aliphatic (cutin and wax-derived) compounds. However, relatively stable recalcitrant compounds may also be formed as a result of condensation and complexation reactions through decomposition and protected with association with mineral particles. The Hawaiian fern species Dicranopteris decomposes more slowly than the angiosperm, Cheirodendrom due to high concentrations of recalcitrant C compounds. These aliphatic fern leaf waxes are well-preserved and may comprise a large portion of the recalcitrant organic matter in these soils. Our objective was to determine the chemical composition of the SOM under the O- (litter-dominated) and the A- (mineral) horizons formed under fern and angiosperm vegetation. To determine the effect of mineral-association, we fractioned the soil into four size classes; 850-590 μm, 590-180 μm, 180-53 μm and <53 μm and characterized the SOM via pyrolysis-gas chromatography-mass spectrometry (py-GC/MS). As the soils developed from the O- to the A-horizon, there was a decrease of lignin-derived phenolic compounds and an increase in more recalcitrant, aromatic and aliphatic C. Soils under ferns had greater relative concentrations of phenolic compounds, while the angiosperms had greater concentrations of fatty-acid methyl esters and furans (some polysaccharide-derived). Differences between size fractions were most evident in the O-horizon of both species. Recalcitrant fern-derived cutin and leaf waxes (alkene and alkanes structures) occurred in the 180-53 μm fraction, which has been shown to be the most stable of the aggregate-size fractions. Soils developed under fern versus angiosperm vegetation have distinct chemical signatures, which likely determine the recalcitrance of the SOM.

Soil aggregate stability as an indicator for eco-engineering effectiveness?

NASA Astrophysics Data System (ADS)

Graf, Frank

2015-04-01

Eco-engineering aims at stabilising soil and slopes by applying technical and biological measures. Engineering structures are commonly well defined, immediately usable and operative, and their stability effects quantifiable and verifiable. Differently, the use of plants requires more restrictive boundary conditions and the protection potential is rarely easily calculable and develop-ing as a function of growth rate. Although the use of vegetation is widely appreciated and their stabilising effect recognised, there is an increasing demand on sound facts on its efficiency, in particular, in relation to time. Conclusively, a certain necessity has been recognised to monitor, assess and quantify the effectiveness of ecological restora-tion measures in order to facilitate the transfer of technology and knowledge. Recent theoretical models emphasize the im-portance of taking an integrated monitoring approach that considers multiple variables. However, limited financial and time resources often prevent such comprehensive assessments. A solution to this problem may be to use integrated indicators that reflect multiple aspects and, therefore, allow extensive information on ecosystem status to be gathered in a relatively short time. Among various other indicators, such as fractal dimension of soil particle size distribution or microbiological parameters, soil aggregate stability seems the most appropriate indicator with regard to protecting slopes from superficial soil failure as it is critical to both plant growth and soil structure. Soil aggregation processes play a crucial role in re-establishing soil structure and function and, conclusively, for successful and sustainable re-colonisation. Whereas the key role of soil aggregate stability in ecosystem functioning is well known concerning water, gas, and nutrient fluxes, only limited information is available with regard to soil mechanical and geotechnical aspects. Correspondingly, in the last couple of years several studies have been performed in order to bridge this gap addressing partic-ularly the influence of root growth and mycorrhizal fungi on the resistance of soil aggregates against disintegration and linking it to slope stability. As superficial soil failure is often related to heavy rainstorms and, in this regard, mainly due to water satura-tion, recent investigations focused on the pore water pressure, too. Summarising main results of the different studies a positive relationship between soil aggregate stability and traditional soil mechanical shear strength parameters was found, e.g. given certain soil conditions, an increase in aggregate stability may be equated to an increase of the angle of internal friction Φ' and/or cohesion c'. In addition, almost all investigations showed a strong positive correlation between root length per soil volume and soil aggregate stability. In respect of mycorrhizal fungi, results are not yet as clear. On the one hand it was found that the use of unspecific (commercial) inoculum had no or even a negative effect on root growth within the first vegetation period and, correspondingly, on soil aggregate stability. However, the use of specific plant fungi combinations almost ever resulted in an obvious acceleration of root growth immediately with con-comitant gain of soil stability. As far as pore water pressure is concerned we did not yet find an interpretation that is fairly straightforward and not overly prone to controversy. It looks like soil aggregated by mycorrhized plants does have a higher capacity for building up pressure than such permeated by non-mycorrhized roots. Within this scope results of several studies showing these (inter-) relationships and correlations are presented and differences as well as unexpected results discussed.

Response of Microbial Soil Carbon Mineralization Rates to Oxygen Limitations

NASA Astrophysics Data System (ADS)

Keiluweit, M.; Denney, A.; Nico, P. S.; Fendorf, S. E.

2014-12-01

The rate of soil organic matter (SOM) mineralization is known to be controlled by climatic factors as well as molecular structure, mineral-organic associations, and physical protection. What remains elusive is to what extent oxygen (O2) limitations impact overall rates of microbial SOM mineralization (oxidation) in soils. Even within upland soils that are aerobic in bulk, factors limiting O2 diffusion such as texture and soil moisture can result in an abundance of anaerobic microsites in the interior of soil aggregates. Variation in ensuing anaerobic respiration pathways can further impact SOM mineralization rates. Using a combination of (first) aggregate model systems and (second) manipulations of intact field samples, we show how limitations on diffusion and carbon bioavailability interact to impose anaerobic conditions and associated respiration constraints on SOM mineralization rates. In model aggregates, we examined how particle size (soil texture) and amount of dissolved organic carbon (bioavailable carbon) affect O2 availability and distribution. Monitoring electron acceptor profiles (O2, NO3-, Mn and Fe) and SOM transformations (dissolved, particulate, mineral-associated pools) across the resulting redox gradients, we then determined the distribution of operative microbial metabolisms and their cumulative impact on SOM mineralization rates. Our results show that anaerobic conditions decrease SOM mineralization rates overall, but those are partially offset by the concurrent increases in SOM bioavailability due to transformations of protective mineral phases. In intact soil aggregates collected from soils varying in texture and SOM content, we mapped the spatial distribution of anaerobic microsites. Optode imaging, microsensor profiling and 3D tomography revealed that soil texture regulates overall O2 availability in aggregate interiors, while particulate SOM in biopores appears to control the fine-scale distribution of anaerobic microsites. Collectively, our results suggest that texture and particulate organic matter content are useful predictors for the impact of O2 limitations on SOM mineralization rates.

Deep horizons: Soil Carbon sequestration and storage potential in grassland soils

NASA Astrophysics Data System (ADS)

Torres-Sallan, Gemma; Schulte, Rogier; Lanigan, Gary J.; Byrne, Kenneth A.; Reidy, Brian; Creamer, Rachel

2016-04-01

Soil Organic Carbon (SOC) enhances soil fertility, holding nutrients in a plant-available form. It also improves aeration and water infiltration. Soils are considered a vital pool for C (Carbon) sequestration, as they are the largest pool of C after the oceans, and contain 3.5 more C than the atmosphere. SOC models and inventories tend to focus on the top 30 cm of soils, only analysing total SOC values. Association of C with microaggregates (53-250 μm) and silt and clay (<53 μm) is considered C sequestration as these fractions offer the greatest protection against mineralization. This study assessed the role of aggregation in C sequestration throughout the profile, down to 1 m depth, of 30 grassland sites divided in 6 soil types. One kg sample was collected for each horizon, sieved at 8 mm and dried at 40 °C. Through a wet sieving procedure, four aggregate sizes were isolated: large macroaggregates (>2000 μm); macroaggregates (250-2000 μm); microaggregates and silt & clay. Organic C associated to each aggregate fraction was analysed on a LECO combustion analyser. Sand-free C was calculated for each aggregate size. For all soil types, 84% of the SOC located in the first 30 cm was contained inside macroaggregates and large macroaggregates. Given that this fraction has a turnover time of 1 to 10 years, sampling at that depth only provides information on the labile fraction in soil, and does not consider the longer term C sequestration potential. Only when looking at the whole profile, two clear trends could be observed: 1) soils with a clay increase at depth had most of their C located in the silt and clay fractions, which indicate their enhanced C sequestration capacity, 2) free-draining soils had a bigger part of their SOC located in the macroaggregate fractions. These results indicate that current C inventories and models that focus on the top 30 cm, do not accurately measure soil C sequestration potential in soils, but rather the more labile fraction. However, at depth soil forming processes have been identified as a major factor influencing C sequestration potential in soils. This has a major impact in further quantifying and sustaining C sequestration into the future. Soils with a high sequestration potential at depth need to be managed to enhance the residence time to contribute to future off-setting of greenhouse gas emissions.

Soils as sediment: does aggregation skew slope scale SOC balances?

NASA Astrophysics Data System (ADS)

Hu, Yaxian; Fister, Wolfgang; Kuhn, Nikolaus

2014-05-01

The net effect of soil erosion as a source or sink of CO2 in global carbon cycling has been the subject of a heated debate. On one hand, erosion exposes the previously encapsulated soil organic carbon (SOC), which may accelerate the mineralization of eroded SOC. On the other hand, deposition limits the decomposition of SOC upon burial, while incorporation of biomass at eroding sites replaces the lost SOC. So far, effects of erosion on CO2 emissions have largely been assessed by comparing SOC stocks at eroding and depositional sites. The underlying assumption for this approach is a non-selective transport of eroded SOC across a landscape. However, several recent publications showed both an at least temporary on-site enrichment of SOC in sediment as well as a preferential deposition of sediment particles with SOC concentrations that differed from the soil SOC. As a consequence, balances between eroding and depositional sites may over- or underestimate mineralization of eroded SOC during transport. Two Luvisols, from the villages of Möhlin and Movelier in northwest Switzerland, were used in this study. They have different mineral grain size distribution, organic carbon concentration and aggregate stability. Based on the concept of Equivalent Quartz Size (EQS), the eroded sediments were fractionated by a settling tube apparatus into six different size classes, according to their settling velocities and likely transport distances. According to the model developed by Starr et al., 2000, the likely transport distances of six EQS classes were grouped into three likely fates: deposited across landscapes, possibly transferred into rivers, and likely transferred into rivers. Respiration rates of the fractionated sediments were measured by gas chromatograph for 50 days. Our results show that 1) due to aggregation, 60% of the Möhlin eroded fractions and 82% of the Movelier fractions would be re-deposited in the terrestrial system, which strongly contrasts with their grain size distribution; 2) 63% of eroded SOC for the Möhlin soil and 83% for the Movelier soil would be re-deposited in the terrestrial system rather than transferred into the aquatic system. This is much greater than the high concentration of SOC in grain size fraction <32 µm would suggest; 3) the SOC re-deposited in the terrestrial system is more likely to be mineralized than the SOC in fine particles which would be transferred into the aquatic system. Our observations indicate that 1) aggregation reduces the likely transport distances of eroded SOC, and thus decreases the likelihood of eroded SOC to be transferred from eroding hill-slopes to the aquatic system; 2) the re-deposited SOC in the terrestrial system is more likely to be mineralized than the SOC in fine particles that could be transferred into the aquatic system. These findings highlight a potentially higher contribution of erosion to atmospheric CO2 than anticipated by estimating source for sink transfer without considering the effects of aggregation.

Direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability in rhizosphere of trifoliate orange.

PubMed

Wu, Qiang-Sheng; Cao, Ming-Qin; Zou, Ying-Ning; He, Xin-hua

2014-07-25

To test direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability, perspex pots separated by 37-μm nylon mesh in the middle were used to form root-free hyphae and root/hyphae chambers, where trifoliate orange (Poncirus trifoliata) seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in the root/hyphae chamber. Both fungal species induced significantly higher plant growth, root total length, easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP), and mean weight diameter (an aggregate stability indicator). The Pearson correlation showed that root colonization or soil hyphal length significantly positively correlated with EE-GRSP, difficultly-extractable GRSP (DE-GRSP), T-GRSP, and water-stable aggregates in 2.00-4.00, 0.50-1.00, and 0.25-0.50 mm size fractions. The path analysis indicated that in the root/hyphae chamber, aggregate stability derived from a direct effect of root colonization, EE-GRSP or DE-GRSP. Meanwhile, the direct effect was stronger by EE-GRSP or DE-GRSP than by mycorrhizal colonization. In the root-free hyphae chamber, mycorrhizal-mediated aggregate stability was due to total effect but not direct effect of soil hyphal length, EE-GRSP and T-GRSP. Our results suggest that GRSP among these tested factors may be the primary contributor to aggregate stability in the citrus rhizosphere.

Does thermophoresis reduce aggregate stability?

NASA Astrophysics Data System (ADS)

Sachs, Eyal; Sarah, Pariente

2017-04-01

Thermophoresis is mass flow driven by a thermal gradient. As a result of Seebeck effect and Soret effect, colloids can move from the hot to the cold region or vice versa, depending on the electrolyte composition and on the particle size. This migration of colloids can weaken aggregates. The effect of raindrop temperatures on runoff generation and erosion on clayey soil was investigated in sprinkling experiments with a laboratory rotating disk rain simulator. The experiments were applied to Rhodoxeralt (Terra Rossa) soil with two pre-prepared moisture contents: hygroscopic and field capacity. For each moisture content three rainfall temperatures were applied: 2, 20, and 35°C. Erosion was generally lower in the pre-wetted soil than in the dry soil (12.5 and 24.4 g m-2 per 40 mm of rain,respectively). Whereas there was no significant effect of raindrop temperature on the dry soil the soil that was pre-moistened to field capacity was affected by rainwater temperature: runoff and erosion were high when the temperature difference between rainfall and soil surface was high, sediment yields were 13.9, 5.2, and 18.3 g m-2 per 40 mm of rain, for rain temperature of 2, 20, and 35 °C, respectively. It is reasonable to conclude that thermophoresis caused by thermal gradients within the soil solution reduces the stability of aggregates and then increase the soil losses.

Improving the Representation of Soluble Iron in Climate Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perez Garcia-Pando, Carlos

2016-03-13

Mineral dust produced in the arid and semi-arid regions of the world is the dominant source of iron (Fe) in atmospheric aerosol inputs to the open ocean. The bioavailable Fe fraction of atmospheric dust is thought to regulate and occasionally limit the primary productivity in large oceanic regions, which influences the CO2 uptake from the atmosphere affecting the Earth’s climate. Because Fe bioavailability cannot be directly measured, it is assumed that the dissolved Fe or highly reactive Fe in the dust is bioavailable. The fraction of soluble Fe in dust is mainly controlled by: (1) the mineral composition of themore » soils and the emitted dust from the source areas; (2) the atmospheric processing that converts the Fe in Fe-bearing minerals into highly soluble forms of Fe. The project has mainly focused on constraining the mineral composition of dust aerosols (1), a previously neglected, yet a key issue to constrain the deposition of soluble iron. Deriving aerosol mineral composition requires global knowledge of the soil mineral content, which is available from poorly constrained global atlases. In addition, the mineral content of the emitted aerosol differs from that of the parent soil. Measurements of soil mineral fractions are based upon wet sedimentation (or ’wet sieving’) techniques that disturb the soil sample, breaking aggregates that are found in the original, undispersed soil that is subject to wind erosion. Wet sieving alters the soil size distribution, replacing aggregates that are potentially mobilized as aerosols with a collection of smaller particles. A major challenge is to derive the size-distributed mineral fractions of the emitted dust based upon their fractions measured from wet-sieved soils. Finally, representations of dust mineral composition need to account for mixtures of minerals. Examination of individual particles shows that iron, an element that is central to many climate processes, is often found as trace impurities of iron oxide attached to aggregates of other minerals. This is another challenge that has been tackled by the project. The project has produced a major step forward on our understanding of the key processes needed to predict the mineral composition of dust aerosols by connecting theory, modeling and observations. The project has produced novel semi-empirical and theoretical methods to estimate the emitted size distribution and mineral composition of dust aerosols. These methods account for soil aggregates that are potentially emitted from the original undisturbed soil but are destroyed during wet sieving. The methods construct the emitted size distribution of individual minerals building upon brittle fragmentation theory, reconstructions of wet-sieved soil mineral size distributions, and/or characteristic mineral size distributions estimated from observations at times of high concentration. Based on an unprecedented evaluation with a new global compilation of observations produced with the project support, we showed that the new methods remedy some key deficiencies compared to the previous state-of-the-art. This includes the correct representation of Fe-bearing phyllosilicates at silt sizes, where they are abundant according to observations. In addition, the quartz fraction of silt particles is in better agreement with measured values. In addition, we represent an additional class of iron oxide aerosol that is a small impurity embedded within other minerals, allowing it to travel farther than in its pure crystalline state. We assume that these impurities are least frequent in soils rich in iron oxides (as a result of the assumed effect of weathering that creates pure iron oxide crystals). The mineral composition of dust is also important to other interaction with climate - through shortwave absorption and radiative forcing, nucleation of cloud droplets and ice crystals, and the heterogeneous formation of sulfates and nitrates - and to its impacts upon human health. Despite the importance of mineral composition, models have typically assumed that soil dust aerosols have globally uniform composition. The results of this project will allow an improved estimation of the dust effects upon climate and health.« less

Global distribution of clay-size minerals on land surface for biogeochemical and climatological studies

PubMed Central

Ito, Akihiko; Wagai, Rota

2017-01-01

Clay-size minerals play important roles in terrestrial biogeochemistry and atmospheric physics, but their data have been only partially compiled at global scale. We present a global dataset of clay-size minerals in the topsoil and subsoil at different spatial resolutions. The data of soil clay and its mineralogical composition were gathered through a literature survey and aggregated by soil orders of the Soil Taxonomy for each of the ten groups: gibbsite, kaolinite, illite/mica, smectite, vermiculite, chlorite, iron oxide, quartz, non-crystalline, and others. Using a global soil map, a global dataset of soil clay-size mineral distribution was developed at resolutions of 2' to 2° grid cells. The data uncertainty associated with data variability and assumption was evaluated using a Monte Carlo method, and validity of the clay-size mineral distribution obtained in this study was examined by comparing with other datasets. The global soil clay data offer spatially explicit studies on terrestrial biogeochemical cycles, dust emission to the atmosphere, and other interdisciplinary earth sciences. PMID:28829435

Size- and composition-dependent toxicity of synthetic and soil-derived Fe oxide colloids for the nematode Caenorhabditis elegans.

PubMed

Höss, Sebastian; Fritzsche, Andreas; Meyer, Carolin; Bosch, Julian; Meckenstock, Rainer U; Totsche, Kai Uwe

2015-01-06

Colloidal iron oxides (FeOx) are increasingly released to the environment due to their use in environmental remediation and biomedical applications, potentially harming living organisms. Size and composition could affect the bioavailability and toxicity of such colloids. Therefore, we investigated the toxicity of selected FeOx with variable aggregate size and variably composed FeOx-associated organic matter (OM) toward the nematode Caenorhabditis elegans. Ferrihydrite colloids containing citrate were taken up by C. elegans with the food and accumulated inside their body. The toxicity of ferrihydrite, goethite, and akaganeite was dependent on aggregate size and specific surface area, with EC50 values for reproduction ranging from 4 to 29 mg Fe L(-1). Experiments with mutant strains lacking mitochondrial superoxide dismutase (sod-2) showed oxidative stress for two FeOx and Fe(3+)-ions, however, revealed that it was not the predominant mechanism of toxicity. The OM composition determined the toxicity of mixed OM-FeOx phases on C. elegans. FeOx associated with humic acids or citrate were less toxic than OM-free FeOx. In contrast, soil-derived ferrihydrite, containing proteins and polysaccharides from mobile OM, was even more toxic than OM-free Fh of similar aggregate size. Consequently, the careful choice of the type of FeOx and the type of associated OM may help in reducing the ecological risks if actively applied to the subsurface.

Impact of monovalent cations on soil structure. Part I. Results of an Iranian soil

NASA Astrophysics Data System (ADS)

Farahani, Elham; Emami, Hojat; Keller, Thomas; Fotovat, Amir; Khorassani, Reza

2018-01-01

This study investigated the impact of monovalent cations on clay dispersion, aggregate stability, soil pore size distribution, and saturated hydraulic conductivity on agricultural soil in Iran. The soil was incubated with treatment solutions containing different concentrations (0-54.4 mmol l-1) of potassium and sodium cations. The treatment solutions included two levels of electrical conductivity (EC=3 or 6 dS m-1) and six K:Na ratios per electrical conductivity level. At both electrical conductivity levels, spontaneously dispersible clay increased with increasing K concentration, and with increasing K:Na ratio. A negative linear relationship between percentage of water-stable aggregates and spontaneously dispersible clay was observed. Clay dispersion generally reduced the mean pore size, presumably due to clogging of pores, resulting in increased water retention. At both electrical conductivity levels, hydraulic conductivity increased with increasing exchangeable potassium percentage at low exchangeable potassium percentage values, but decreased with further increases in exchangeable potassium percentage at higher exchangeable potassium percentage. This is in agreement with earlier studies, but seems in conflict with our data showing increasing spontaneously dispersible clay with increasing exchangeable potassium percentage. Our findings show that clay dispersion increased with increasing K concentration and increasing K:Na ratio, demonstrating that K can have negative impacts on soil structure.

Enrichment Ratio and Aggregate Stability Dynamics in Intensely Managed Landscapes

NASA Astrophysics Data System (ADS)

Wacha, K.; Papanicolaou, T.; Filley, T. R.; Hou, T.; Abban, B. K.; Wilson, C. G.; Boys, J.

2015-12-01

Challenges in understanding the soil carbon dynamics within intensely managed landscapes (IMLs), found throughout much the US Midwest, is highly complex due to the presence of heterogeneous landscape features and properties, as well as a mosaic of physical and biogeochemical processes occurring at different time scales. In addition, rainfall events exacerbate the effects of tillage by the impact of raindrops, which break down aggregates that encase carbon and dislodge and entrain soil particles and aggregates along the downslope. The redistribution of soil and carbon can have huge implications on biogeochemical cycling and overall carbon budgeting. In this study, we provide some rare field data on the mechanisms impacting aggregate stability, enrichment ratio values to estimate fluxes of carbon, as well as lignin chemistry to see influences on oxidation/mineralization rates. Rainfall simulation experiments were conducted within agricultural fields. Experiments were performed on the midslope (eroding) and toeslope (depositional) sections of representative hillslopes, under a variety of land managements, including row crop (conventional and conservation) and restored grasslands. Sensors were utilized to capture the evolution of soil moisture, temperature, microbial respiration pulses, and discharge rates to identify pseudo-steady state conditions. Samples collected at the weir outlet were tested for sediment concentrations and size fractions, as well as carbon and lignin fluxes. Preliminary findings show that conservation management practices have higher aggregate stability and decreased mass fluxes of carbon in the downslope than conventional tillage techniques.

Soil aggregate stability and rainfall-induced sediment transport on field plots as affected by amendment with organic matter inputs

NASA Astrophysics Data System (ADS)

Shi, Pu; Arter, Christian; Liu, Xingyu; Keller, Martin; Schulin, Rainer

2017-04-01

Aggregate stability is an important factor in soil resistance against erosion, and, by influencing the extent of sediment transport associated with surface runoff, it is thus also one of the key factors which determine on- and off-site effects of water erosion. As it strongly depends on soil organic matter, many studies have explored how aggregate stability can be improved by organic matter inputs into the soil. However, the focus of these studies has been on the relationship between aggregate stability and soil organic matter dynamics. How the effects of organic matter inputs on aggregate stability translate into soil erodibility under rainfall impacts has received much less attention. In this study, we performed field plot experiments to examine how organic matter inputs affect aggregate breakdown and surface sediment transport under field conditions in artificial rainfall events. Three pairs of plots were prepared by adding a mixture of grass and wheat straw to one of plots in each pair but not to the other, while all plots were treated in the same way otherwise. The rainfall events were applied some weeks later so that the applied organic residues had sufficient time for decomposition and incorporation into the soil. Surface runoff rate and sediment concentration showed substantial differences between the treatments with and without organic matter inputs. The plots with organic inputs had coarser and more stable aggregates and a rougher surface than the control plots without organic inputs, resulting in a higher infiltration rate and lower transport capacity of the surface runoff. Consequently, sediments exported from the amended plots were less concentrated but more enriched in suspended particles (<20 µm) than from the un-amended plots, indicating a more size-selective sediment transport. In contrast to the amended plots, there was an increase in the coarse particle fraction (> 250 µm) in the runoff from the plots with no organic matter inputs towards the end of the rainfall events due to emerging bed-load transport. The results show that a single application of organic matter can already cause a large difference in aggregate breakdown, surface sealing, and lateral sediment-associated matter transfer under rainfall impact. Furthermore, we will present terrestrial laser scanning data showing the treatment effects on soil surface structure, as well as data on carbon, phosphorus and heavy metal export associated with the translocation of the sediments.

[Effect of mineral N fertilizer reduction and organic fertilizer substitution on soil biological properties and aggregate characteristics in drip-irrigated cotton field.

PubMed

Li, Rui; Tai, Rui; Wang, Dan; Chu, Gui-Xin

2017-10-01

A four year field study was conducted to determine how soil biological properties and soil aggregate stability changed when organic fertilizer and biofertilizer were used to reduce chemical fertilizer application to a drip irrigated cotton field. The study consisted of six fertilization treatments: unfertilized (CK); chemical fertilizer (CF, 300 kg N·hm -2 ; 90 kg P2O5 · hm -2 , 60 kg K2 O·hm -2 ); 80% CF plus 3000 kg·hm -2 organic fertilizer (80%CF+OF); 60% CF plus 6000 kg·hm -2 organic fertilizer (60%CF+OF); 80% CF plus 3000 kg·hm -2 biofertilizer (80%CF+BF); and 60% CF plus 6000 kg·hm -2 biofertilizer (60%CF+BF). The relationships among soil organic C, soil biological properties, and soil aggregate size distribution were determined. The results showed that organic fertilizer and biofertilizer both significantly increased soil enzyme activities. Compared with CF, the biofertilizer treatments increased urease activity by 55.6%-84.0%, alkaline phosphatise activity by 53.1%-74.0%, invertase activity by 15.1%-38.0%, β-glucosidase activity by 38.2%-68.0%, polyphenoloxidase activity by 29.6%-52.0%, and arylsulfatase activity by 35.4%-58.9%. Soil enzyme activity increased as the amount of organic fertilizer and biofertilizer increased (i.e., 60%CF+OF > 80%CF+OF, 60%CF+BF > 80%CF+BF). Soil basal respiration decreased significantly in the order BF > OF > CF > CK. Soil microbial biomass C and N were 22.3% and 43.5% greater, respectively, in 60%CF+BF than in CF. The microbial biomass C:N was significantly lower in 60%CF+BF than in CF. The organic fertilizer and the biofertilizer both improved soil aggregate structure. Soil mass in the >0.25 mm fraction was 7.1% greater in 80%CF+OF and 8.0% greater in (60%CF+OF) than in CF. The geometric mean diameter was 9.2% greater in 80%CF+BF than in 80%CF+OF. Redundancy analysis and cluster analysis both demonstrated that soil aggregate structure and biological activities increased when organic fertilizer and biofertilizer were used to reduce chemical fertilizer application. In conclusion, the organic fertilizer and the biofertilizer significantly increased SOC, soil enzyme activity, and soil microbial biomass C and N. The organic fertilizers also improved soil aggregation. Therefore, soil quality could be improved by using these fertilizers to reduce chemical fertilizer application, especially under drip-irrigation.

Patterns in woody vegetation structure across African savannas

NASA Astrophysics Data System (ADS)

Axelsson, Christoffer R.; Hanan, Niall P.

2017-07-01

Vegetation structure in water-limited systems is to a large degree controlled by ecohydrological processes, including mean annual precipitation (MAP) modulated by the characteristics of precipitation and geomorphology that collectively determine how rainfall is distributed vertically into soils or horizontally in the landscape. We anticipate that woody canopy cover, crown density, crown size, and the level of spatial aggregation among woody plants in the landscape will vary across environmental gradients. A high level of woody plant aggregation is most distinct in periodic vegetation patterns (PVPs), which emerge as a result of ecohydrological processes such as runoff generation and increased infiltration close to plants. Similar, albeit weaker, forces may influence the spatial distribution of woody plants elsewhere in savannas. Exploring these trends can extend our knowledge of how semi-arid vegetation structure is constrained by rainfall regime, soil type, topography, and disturbance processes such as fire. Using high-spatial-resolution imagery, a flexible classification framework, and a crown delineation method, we extracted woody vegetation properties from 876 sites spread over African savannas. At each site, we estimated woody cover, mean crown size, crown density, and the degree of aggregation among woody plants. This enabled us to elucidate the effects of rainfall regimes (MAP and seasonality), soil texture, slope, and fire frequency on woody vegetation properties. We found that previously documented increases in woody cover with rainfall is more consistently a result of increasing crown size than increasing density of woody plants. Along a gradient of mean annual precipitation from the driest (< 200 mm yr-1) to the wettest (1200-1400 mm yr-1) end, mean estimates of crown size, crown density, and woody cover increased by 233, 73, and 491 % respectively. We also found a unimodal relationship between mean crown size and sand content suggesting that maximal savanna tree sizes do not occur in either coarse sands or heavy clays. When examining the occurrence of PVPs, we found that the same factors that contribute to the formation of PVPs also correlate with higher levels of woody plant aggregation elsewhere in savannas and that rainfall seasonality plays a key role for the underlying processes.

Characteristics of organic matter fractions separated by wet-sieving and differences in density from five soils of different pedogenesis under mature beech forest.

NASA Astrophysics Data System (ADS)

Vormstein, Svendja; Kaiser, Michael; Ludwig, Bernard

2017-04-01

Forest top- and subsoil account for approximately 70 % of the organic C (OC) globally stored in soil reasoning their large importance for terrestrial ecosystem services such as the mitigation of climate change. In contrast to forest topsoil, there is much less information about the decomposition and stabilization of organic matter (OM) in subsoil. Therefore, we sampled the pedogenetic horizons of five soils under mature beech forest developed on different parent material (i.e. Tertiary Sand, Loess, Basalt, Lime Stone, Red Sandstone) down to the bedrock. The bulk soil samples were characterized for texture, oxalate and dithionite soluble Fe and Al, pH, OC, microbial biomass C and basal respiration (cumulative CO2 emission after 7 and 14 days). Furthermore, we analyzed aggregate size fractions separated by wet-sieving (i.e. >1000 µm, 1000-250 µm, 250-53 µm, <53 µm) and density fractions separated using NaPT (i.e. light, occluded light, and heavy fraction) from the soil horizon specific samples. The OC of the topsoil (Ah horizon) on Lime Stone and Red Sandstone was predominately stored in the larger macro-aggregates (>1000 µm). In contrast, the major part of the topsoil OC on Basalt and Tertiary Sand was found in the smaller macro-aggregates (1000-250 µm). For the topsoil samples, we found that the basal respiration as well as the microbial biomass C were positively correlated (p ≤0.05) with the OC amounts associated with the free and occluded light fraction and with the macro-aggregates (1000-250 µm) and micro-aggregates (250-53 µm) suggesting these fractions to store the major part of the easily decomposable OM. The OC amount associated with the heavy fraction and the fraction <53 µm was correlated with the contents of oxalate and dithionite soluble Fe and Al suggesting interactions between organic compounds and Fe- and Al-oxides to be highly important for the OM stabilization in forest topsoil. In the subsoil (horizons below the Ah), the contribution of the OC associated with the aggregate size fractions <250 µm to the OC stored in the subsoil increased with depth. The OC contents associated with the free and occluded light as well as the heavy fraction and with the aggregate size fractions >53 µm were positively correlated with basal respiration and the microbial biomass C. This suggests, in contrast to the topsoil, the easily decomposable OM to be distributed more homogeneously among fractions. Only the OC content of the <53 µm fraction showed positive correlations to soil mineral characteristics such as the contents of clay oxalate and dithionite soluble Fe or Al and no relationship to the basal respiration and microbial biomass C. This indicates the OM associated with this fraction to be most diagnostic for the amount of OC stabilized against microbial decay in the subsoil and interactions between OM and oxides as well as layer silicates to be relevant stabilization mechanisms. The results point toward similar OM stabilization mechanisms in the analysed forest top- and subsoils but revealed differences in the distribution of easily decomposable OM within the soil matrix.

Nitrite-Oxidizing Bacteria Community Composition and Diversity Are Influenced by Fertilizer Regimes, but Are Independent of the Soil Aggregate in Acidic Subtropical Red Soil

PubMed Central

Han, Shun; Li, Xiang; Luo, Xuesong; Wen, Shilin; Chen, Wenli; Huang, Qiaoyun

2018-01-01

Nitrification is the two-step aerobic oxidation of ammonia to nitrate via nitrite in the nitrogen-cycle on earth. However, very limited information is available on how fertilizer regimes affect the distribution of nitrite oxidizers, which are involved in the second step of nitrification, across aggregate size classes in soil. In this study, the community compositions of nitrite oxidizers (Nitrobacter and Nitrospira) were characterized from a red soil amended with four types of fertilizer regimes over a 26-year fertilization experiment, including control without fertilizer (CK), swine manure (M), chemical fertilization (NPK), and chemical/organic combined fertilization (MNPK). Our results showed that the addition of M and NPK significantly decreased Nitrobacter Shannon and Chao1 index, while M and MNPK remarkably increased Nitrospira Shannon and Chao1 index, and NPK considerably decreased Nitrospira Shannon and Chao1 index, with the greatest diversity achieved in soils amended with MNPK. However, the soil aggregate fractions had no impact on that alpha-diversity of Nitrobacter and Nitrospira under the fertilizer treatment. Soil carbon, nitrogen and phosphorus in the soil had a significant correlation with Nitrospira Shannon and Chao1 diversity index, while total potassium only had a significant correlation with Nitrospira Shannon diversity index. However, all of them had no significant correlation with Nitrobacter Shannon and Chao1 diversity index. The resistance indices for alpha-diversity indexes (Shannon and Chao1) of Nitrobacter were higher than those of Nitrospira in response to the fertilization regimes. Manure fertilizer is important in enhancing the Nitrospira Shannon and Chao1 index resistance. Principal co-ordinate analysis revealed that Nitrobacter- and Nitrospira-like NOB communities under four fertilizer regimes were differentiated from each other, but soil aggregate fractions had less effect on the nitrite oxidizers community. Redundancy analysis and Mantel test indicated that soil nitrogen, carbon, phosphorus, and available potassium content were important environmental attributes that control the Nitrobacter- and Nitrospira-like NOB community structure across different fertilization treatments under aggregate levels in the red soil. In general, nitrite-oxidizing bacteria community composition and alpha-diversity are depending on fertilizer regimes, but independent of the soil aggregate. PMID:29867799

Soil pH Errors Propagation from Measurements to Spatial Predictions - Cost Benefit Analysis and Risk Assessment Implications for Practitioners and Modelers

NASA Astrophysics Data System (ADS)

Owens, P. R.; Libohova, Z.; Seybold, C. A.; Wills, S. A.; Peaslee, S.; Beaudette, D.; Lindbo, D. L.

2017-12-01

The measurement errors and spatial prediction uncertainties of soil properties in the modeling community are usually assessed against measured values when available. However, of equal importance is the assessment of errors and uncertainty impacts on cost benefit analysis and risk assessments. Soil pH was selected as one of the most commonly measured soil properties used for liming recommendations. The objective of this study was to assess the error size from different sources and their implications with respect to management decisions. Error sources include measurement methods, laboratory sources, pedotransfer functions, database transections, spatial aggregations, etc. Several databases of measured and predicted soil pH were used for this study including the United States National Cooperative Soil Survey Characterization Database (NCSS-SCDB), the US Soil Survey Geographic (SSURGO) Database. The distribution of errors among different sources from measurement methods to spatial aggregation showed a wide range of values. The greatest RMSE of 0.79 pH units was from spatial aggregation (SSURGO vs Kriging), while the measurement methods had the lowest RMSE of 0.06 pH units. Assuming the order of data acquisition based on the transaction distance i.e. from measurement method to spatial aggregation the RMSE increased from 0.06 to 0.8 pH units suggesting an "error propagation". This has major implications for practitioners and modeling community. Most soil liming rate recommendations are based on 0.1 pH unit increments, while the desired soil pH level increments are based on 0.4 to 0.5 pH units. Thus, even when the measured and desired target soil pH are the same most guidelines recommend 1 ton ha-1 lime, which translates in 111 ha-1 that the farmer has to factor in the cost-benefit analysis. However, this analysis need to be based on uncertainty predictions (0.5-1.0 pH units) rather than measurement errors (0.1 pH units) which would translate in 555-1,111 investment that need to be assessed against the risk. The modeling community can benefit from such analysis, however, error size and spatial distribution for global and regional predictions need to be assessed against the variability of other drivers and impact on management decisions.

New approach to measure soil particulate organic matter in intact samples using X-ray computed micro-tomography

NASA Astrophysics Data System (ADS)

Kravchenko, Alexandra; Negassa, Wakene; Guber, Andrey; Schmidt, Sonja

2014-05-01

Particulate soil organic matter (POM) is biologically and chemically active fraction of soil organic matter. It is a source of many agricultural and ecological benefits, among which are POM's contribution to C sequestration. Most of conventional research methods for studying organic matter dynamics involve measurements conducted on pre-processed i.e., ground and sieved soil samples. Unfortunately, grinding and sieving completely destroys soil structure, the component crucial for soil functioning and C protection. Importance of a better understanding of the role of soil structure and of the physical protection that it provides to soil C cannot be overstated; and analysis of quantities, characteristics, and decomposition rates of POM in soil samples with intact structure is among the key elements of gaining such understanding. However, a marked difficulty hindering the progress in such analyses is a lack of tools for identification and quantitative analysis of POM in intact soil samples. Recent advancement in applications of X-ray computed micro-tomography (μ-CT) to soil science has given an opportunity to conduct such analyses. The objective of the current study is to develop a procedure for identification and quantitative characterization of POM within intact soil samples using X-ray μ-CT images and to test performance of the proposed procedure on a set of multiple intact soil macro-aggregates. We used 16 4-6 mm soil aggregates collected at 0-15 cm depth from a Typic Hapludalf soil at multiple field sites with diverse agricultural management history. The aggregates have been scanned at SIMBIOS Centre, Dundee, Scotland at 10 micron resolution. POM was determined from the aggregate images using the developed procedure. The procedure was based on combining image pre-processing steps with discriminant analysis classification. The first component of the procedure consisted of image pre-processing steps based on the range of gray values (GV) along with shape and size of POM pieces. That was followed by discriminant analysis conducted using statistical and geostatistical characteristics of POM pieces. POM identified in the intact individual soil aggregates using the proposed procedure was in good agreement with POM measured in the studied aggregates using conventional lab method (R2=0.75). Of particular importance for accurate identification of POM in the images was the information on spatial characteristics of POM's GVs. Since this is the first attempt of POM determination, future work will be needed to explore how the proposed procedure performs under a variety of potentially influential factors, such as POM's origin and decomposition stage, X-ray scanning settings, image filtering and segmentation methods.

Soil aggregate stability and size-selective sediment transport with surface runoff as affected by organic residue amendment.

PubMed

Shi, Pu; Arter, Christian; Liu, Xingyu; Keller, Martin; Schulin, Rainer

2017-12-31

Aggregate breakdown influences the availability of soil particles for size-selective sediment transport with surface runoff during erosive rainfall events. Organic matter management is known to affect aggregate stability against breakdown, but little is known about how this translates into rainfall-induced aggregate fragmentation and sediment transport under field conditions. In this study, we performed field experiments in which artificial rainfall was applied after pre-wetting on three pairs of arable soil plots (1.5×0.75m) six weeks after incorporating a mixture of grass and wheat straw into the topsoil of one plot in each pair (OI treatment) but not on the other plot (NI treatment). Artificial rainfall was applied for approximately 2h on each pair at an intensity of 49.1mmh -1 . In both treatments, discharge and sediment concentration in the discharge were correlated and followed a similar temporal pattern after the onset of surface runoff: After a sharp increase at the beginning both approached a steady state. But the onset of runoff was more delayed on the OI plots, and the discharge and sediment concentration were in average only roughly half as high on the OI as on the NI plots. With increasing discharge the fraction of coarse sediment increased. This relationship did not differ between the two treatments. Thus, due to the lower discharge, the fraction of fine particles in the exported sediment was larger in the runoff from the OI plots than from the NI plots. The later runoff onset and lower discharge rate was related to a higher initial aggregate stability on the OI plots. Terrestrial laser scanning proved to be a very valuable method to map changes in the micro-topography of the soil surfaces. It revealed a much less profound decrease in surface roughness on the OI than on the NI plots. Copyright © 2017 Elsevier B.V. All rights reserved.

Sensitivity Analysis of the USLE Soil Erodibility Factor to Its Determining Parameters

NASA Astrophysics Data System (ADS)

Mitova, Milena; Rousseva, Svetla

2014-05-01

Soil erosion is recognized as one of the most serious soil threats worldwide. Soil erosion prediction is the first step in soil conservation planning. The Universal Soil Loss Equation (USLE) is one of the most widely used models for soil erosion predictions. One of the five USLE predictors is the soil erodibility factor (K-factor), which evaluates the impact of soil characteristics on soil erosion rates. Soil erodibility nomograph defines K-factor depending on soil characteristics, such as: particle size distribution (fractions finer that 0.002 mm and from 0.1 to 0.002 mm), organic matter content, soil structure and soil profile water permeability. Identifying the soil characteristics, which mostly influence the K-factor would give an opportunity to control the soil loss through erosion by controlling the parameters, which reduce the K-factor value. The aim of the report is to present the results of analysis of the relative weight of these soil characteristics in the K-factor values. The relative impact of the soil characteristics on K-factor was studied through a series of statistical analyses of data from the geographic database for soil erosion risk assessments in Bulgaria. Degree of correlation between K-factor values and the parameters that determine it was studied by correlation analysis. The sensitivity of the K-factor was determined by studying the variance of each parameter within the range between minimum and maximum possible values considering average value of the other factors. Normalizing transformation of data sets was applied because of the different dimensions and the orders of variation of the values of the various parameters. The results show that the content of particles finer than 0.002 mm has the most significant relative impact on the soil erodibility, followed by the content of particles with size from 0.1 mm to 0.002 mm, the class of the water permeability of the soil profile, the content of organic matter and the aggregation class. The relationships of the K-factor with the relative content of particle size from 0.1 to 0.002 mm and the class of aggregation are linear, directly proportional. When the content of particles sized from 0.1 to 0.002 mm increases with one relative unit, the K-factor increases with 0.0091 t ha h / ha MJ mm, while the same relative increase of the class of aggregation, results to an increase of the K-factor by 0.0034 t ha h / ha MJ mm. On the other side, the relationships between the K-factor values and the contents of clay and organic matter, and the class of profile water permeability, are linear, inversely proportional. When the clay content increases with one relative unit, the K-factor value decreases by 0.0099 t ha h / ha MJ mm. The same relative increases in the content of soil organic matter and the class of soil profile water permeability, result to a decrease of the values of K-factor respectively by 0.0042 and 0.0045 t ha h / ha MJ mm.

Experimental Studies on Geocells and Mat Systems for Stabilization of Unpaved Shoulders and Temporary Roads

NASA Astrophysics Data System (ADS)

Guo, Jun

Geosynthetics have been used to improve the performance of geomaterials, especially when weak soil exists in roadway applications. In this study, two types of geosynthetic materials, geocell and a mat system, were studied for their applications for unpaved roads and shoulders. The study of geocell was focused on its application for unpaved shoulders. The ability of geocell to improve different geomaterials over intermediate strength subgrade and its possible effect on vegetation were investigated. The study of the mat system was focused on investigating the performance of the mat system over soft and intermediate subgrade with different strengths under cyclic loading to simulate temporary roadway conditions. In the study of geocell for the application for unpaved shoulders, six large scale plate loading tests were conducted on a single type of geocell on target 5% CBR subgrade to investigate the benefits of geocell reinforcement on different base course and topsoil combinations. Different base course and topsoil combinations were investigated including: 200-mm thick unreinforced aggregate, 200-mm thick soil-aggregate mixture (50% aggregate and 50% top soil) with and without geocell reinforcement, 200-mm thick geocell-reinforced topsoil, 50-mm thick aggregate over 150-mm soil-aggregate mixture (50% aggregate and 50% top soil), and 50-mm thick top soil over 150-mm thick geocell-reinforced soil-aggregate mixture (50% aggregate and 50% top soil). Earth pressure cells were install at the interface between subgrade and base course to monitor the load distribution. The cyclic plate loading tests showed that geocell effectively reduced the permanent deformation and the geocell-reinforced soil-aggregate mixture slightly outperformed the unreinforced aggregate at the same thickness. The plate loading tests also suggested the topsoil cover resulted in large permanent deformations. A one-year long outdoor field vegetation test was conducted on base courses with different combinations of aggregate and topsoil including: 200-mm thick unreinforced topsoil, 200-mm thick soil-aggregate mixture (50% aggregate and 50% topsoil), 50-mm thick aggregate over 150-mm soil-aggregate mixture (50% aggregate and 50% topsoil), and 50-mm thick topsoil over 150-mm reinforced soil-aggregate mixture (50% aggregate and 50% topsoil) to investigate the possible effect of geocell on shoulder vegetation established mainly by tall fescue grass and perennial ryegrass. One control (unreinforced) section and one geocell-reinforced section were prepared for each base course combination with a surface area of 1.5 m by 1.5 m. During the one-year test period, soil moisture temperature and volumetric moisture content were monitored. Weather data, such as precipitation and air temperature, were obtain from the nearby weather station at the Lawrence airport. Vegetation growth was evaluated by grass leaf blade length, root length, and grass density. Vegetation biomass was obtained at the end of the test. The test results showed no definite evidence of geocell influencing the vegetation in unpaved shoulders. In the study of the mat system, six large-scale cyclic plate loading tests were conducted on a single type of polyethylene mat system with anchorage to study its performance over soft and intermediate subgrade with the CBR ranging from 1% to 4%. For the comparison purposes, test sections with and without the mat system were prepared and evaluated. For the test section with 1% CBR subgrade, an aggregate base course was used for the test section without the mat system to enable the cyclic plate loading test. The size of the mat system under the investigation was 1.92 m by 1.92 m. A cyclic load at the magnitude of 40 kN was applied through a 300 mm diameter loading plate with a thin rubber pad to simulate a vehicle tire. Earth pressure cells were installed at the interface between the mat system and the subgrade to monitor the load distribution. Loading plate displacements were measured by the displacement transducer inside the actuator. Test results concluded that the mat system was more effective over the intermediate subgrade than the soft subgrade and when large permanent deformations were allowed.

[Composition and stability of soil aggregates in hedgerow-crop slope land].

PubMed

Pu, Yu-Lin; Lin, Chao-Wen; Xie, De-Ti; Wei, Chao-Fu; Ni, Jiu-Pai

2013-01-01

Based on a long-term experiment of using hedgerow to control soil and water loss, this paper studied the composition and stability of soil aggregates in a hedgerow-crop slope land. Compared with those under routine contour cropping, the contents of > 0.25 mm soil mechanical-stable and water-stable aggregates under the complex mode hedgerow-crop increased significantly by 13.3%-16.1% and 37.8% -55.6%, respectively. Under the complex mode, the contents of > 0.25 mm soil water-stable aggregates on each slope position increased obviously, and the status of > 0.25 mm soil water-stable aggregates being relatively rich at low slope and poor at top slope was improved. Planting hedgerow could significantly increase the mean mass diameter and geometric mean diameter of soil aggregates, decrease the fractal dimension of soil aggregates and the destruction rate of > 0.25 mm soil aggregates, and thus, increase the stability and erosion-resistance of soil aggregates in slope cropland. No significant effects of slope and hedgerow types were observed on the composition, stability and distribution of soil aggregates.

Quantification of soil structure based on Minkowski functions

NASA Astrophysics Data System (ADS)

Vogel, H.-J.; Weller, U.; Schlüter, S.

2010-10-01

The structure of soils and other geologic media is a complex three-dimensional object. Most of the physical material properties including mechanical and hydraulic characteristics are immediately linked to the structure given by the pore space and its spatial distribution. It is an old dream and still a formidable challenge to relate structural features of porous media to their functional properties. Using tomographic techniques, soil structure can be directly observed at a range of spatial scales. In this paper we present a scale-invariant concept to quantify complex structures based on a limited set of meaningful morphological functions. They are based on d+1 Minkowski functionals as defined for d-dimensional bodies. These basic quantities are determined as a function of pore size or aggregate size obtained by filter procedures using mathematical morphology. The resulting Minkowski functions provide valuable information on the size of pores and aggregates, the pore surface area and the pore topology having the potential to be linked to physical properties. The theoretical background and the related algorithms are presented and the approach is demonstrated for the pore structure of an arable soil and the pore structure of a sand both obtained by X-ray micro-tomography. We also analyze the fundamental problem of limited resolution which is critical for any attempt to quantify structural features at any scale using samples of different size recorded at different resolutions. The results demonstrate that objects smaller than 5 voxels are critical for quantitative analysis.

Direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability in rhizosphere of trifoliate orange

PubMed Central

Wu, Qiang-Sheng; Cao, Ming-Qin; Zou, Ying-Ning; He, Xin-hua

2014-01-01

To test direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability, perspex pots separated by 37-μm nylon mesh in the middle were used to form root-free hyphae and root/hyphae chambers, where trifoliate orange (Poncirus trifoliata) seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in the root/hyphae chamber. Both fungal species induced significantly higher plant growth, root total length, easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP), and mean weight diameter (an aggregate stability indicator). The Pearson correlation showed that root colonization or soil hyphal length significantly positively correlated with EE-GRSP, difficultly-extractable GRSP (DE-GRSP), T-GRSP, and water-stable aggregates in 2.00–4.00, 0.50–1.00, and 0.25–0.50 mm size fractions. The path analysis indicated that in the root/hyphae chamber, aggregate stability derived from a direct effect of root colonization, EE-GRSP or DE-GRSP. Meanwhile, the direct effect was stronger by EE-GRSP or DE-GRSP than by mycorrhizal colonization. In the root-free hyphae chamber, mycorrhizal-mediated aggregate stability was due to total effect but not direct effect of soil hyphal length, EE-GRSP and T-GRSP. Our results suggest that GRSP among these tested factors may be the primary contributor to aggregate stability in the citrus rhizosphere. PMID:25059396

Effects of earthworms and plants on the soil structure, the physical stabilization of soil organic matter and the microbial abundance and diversity in soil aggregates in a long term study

NASA Astrophysics Data System (ADS)

Zangerlé, Anne; Hissler, Christophe; Lavelle, Patrick

2014-05-01

Earthworms and plant roots, as ecosystem engineers, have large effects on biotic and abiotic properties of the soil system. They create biogenic soil macroaggregates (i.e. earthworm casts and root macroaggregates) with specific physical, chemical and microbiological properties. Research to date has mainly considered their impacts in isolation thereby ignoring potential interactions between these organisms. On the other hand, most of the existing studies focused on short to midterm time scale. We propose in this study to consider effect of earthworms and plants on aggregate dynamics at long time scale. A 24 months macrocosm experiment, under semi-controlled conditions, was conducted to assess the impacts of corn and endogeic plus anecic earthworms (Apporectodea caliginosa and Lumbricus terrestris) on soil structure, C stabilization and microbial abundance and biodiversity. Aggregate stability was assessed by wet-sieving. Macroaggregates (>2 mm) were also visually separated according to their biological origin (e.g., earthworms, roots). Total C and N contents were measured in aggregates of all size classes and origins. Natural abundances of 13C of corn, a C4 plant, were used as a supplemental marker of OM incorporation in aggregates. The genetic structure and the abundance of the bacterial and fungal communities were characterized by using respectively the B- and F-ARISA fingerprinting approach and quantitative PCR bacteria (341F/515R) and fungi (FF330/FR1). They significantly impacted the soil physical properties in comparison to the other treatments: lower bulk density in the first 10cm of the soil with 0.95 g/cm3 in absence of corn plants and 0.88 g/cm3 in presence of corn plants compared to control soil (1.21g/cm3). The presence of earthworms increased aggregate stability (mean weight diameter) by 7.6 %, while plants alone had no simple impacts on aggregation. A significant interaction revealed that earthworms increased aggregate stability in the presence of roots by 2.4% when compared to macrocosms without plants. Additionally, the presence of roots increased the total C and N concentration in earthworm casts, while earthworms increased C storage in microaggregates within root-derived aggregates. Analyses of 13C abundances revealed that OM had been incorporated in earthworm casts from the fifth month of the experiment. Earthworms showed an impact on bacterial abundance of 26.7% of increase in single species macroaggregates and 35.5% in mixt species macroaggregates after the first harvest of corn plants. Trends however changed on the long term since bacterial abundances decreased dramatically (67.1% in single species treatments and 59.3% in mixed species treatments) during the second year and fungal abundances, stable during the first 5 months of the experiment, later increased 80% and 73.2% in earthworm and mixed species macroaggregates. This experiment showed how interactions between plants and earthworms can influence the soil structure and the soil aggregates dynamics by cooperating in macroaggregate formation. Both organisms need to be considered simultaneously for proper management of soils.

Process-oriented modelling to identify main drivers of erosion-induced carbon fluxes

NASA Astrophysics Data System (ADS)

Wilken, Florian; Sommer, Michael; Van Oost, Kristof; Bens, Oliver; Fiener, Peter

2017-05-01

Coupled modelling of soil erosion, carbon redistribution, and turnover has received great attention over the last decades due to large uncertainties regarding erosion-induced carbon fluxes. For a process-oriented representation of event dynamics, coupled soil-carbon erosion models have been developed. However, there are currently few models that represent tillage erosion, preferential water erosion, and transport of different carbon fractions (e.g. mineral bound carbon, carbon encapsulated by soil aggregates). We couple a process-oriented multi-class sediment transport model with a carbon turnover model (MCST-C) to identify relevant redistribution processes for carbon dynamics. The model is applied for two arable catchments (3.7 and 7.8 ha) located in the Tertiary Hills about 40 km north of Munich, Germany. Our findings indicate the following: (i) redistribution by tillage has a large effect on erosion-induced vertical carbon fluxes and has a large carbon sequestration potential; (ii) water erosion has a minor effect on vertical fluxes, but episodic soil organic carbon (SOC) delivery controls the long-term erosion-induced carbon balance; (iii) delivered sediments are highly enriched in SOC compared to the parent soil, and sediment delivery is driven by event size and catchment connectivity; and (iv) soil aggregation enhances SOC deposition due to the transformation of highly mobile carbon-rich fine primary particles into rather immobile soil aggregates.

Factors controlling threshold friction velocity in semiarid and arid areas of the United States

USGS Publications Warehouse

Marticorena, Beatrice; Bergametti, G.; Belnap, Jayne

1997-01-01

A physical model was developed to explain threshold friction velocities u*t for particles of the size 60a??120 I?m lying on a rough surface in loose soils for semiarid and arid parts of the United States. The model corrected for the effect of momentum absorption by the nonerodible roughness. For loose or disturbed soils the most important parameter that controls u*t is the aerodynamic roughness height z 0. For physical crusts damaged by wind the size of erodible crust pieces is important along with the roughness. The presence of cyanobacteriallichen soil crusts roughens the surface, and the biological fibrous growth aggregates soil particles. Only undisturbed sandy soils and disturbed soils of all types would be expected to be erodible in normal wind storms. Therefore disturbance of soils by both cattle and humans is very important in predicting wind erosion as confirmed by our measurements.

Synchrotron microtomographic quantification of geometrical soil pore characteristics affected by compaction

NASA Astrophysics Data System (ADS)

Udawatta, Ranjith P.; Gantzer, Clark J.; Anderson, Stephen H.; Assouline, Shmuel

2016-05-01

Soil compaction degrades soil structure and affects water, heat, and gas exchange as well as root penetration and crop production. The objective of this study was to use X-ray computed microtomography (CMT) techniques to compare differences in geometrical soil pore parameters as influenced by compaction of two different aggregate size classes. Sieved (diameter < 2 mm and < 0.5 mm) and repacked (1.51 and 1.72 Mg m-3) Hamra soil cores of 5 by 5 mm (average porosities were 0.44 and 0.35) were imaged at 9.6 μm resolution at the Argonne Advanced Photon Source (synchrotron facility) using X-ray CMT. Images of 58.9 mm3 volume were analyzed using 3-Dimensional Medial Axis (3-DMA) software. Geometrical characteristics of the spatial distributions of pore structures (pore radii, volume, connectivity, path length, and tortuosity) were numerically investigated. Results show that the coordination number (CN) distribution and path length (PL) measured from the medial axis were reasonably fit by exponential relationships P(CN) = 10-CN/Co and P(PL) = 10-PL/PLo, respectively, where Co and PLo are the corresponding characteristic constants. Compaction reduced porosity, average pore size, number of pores, and characteristic constants. The average pore radii (63.7 and 61 µm; p < 0.04), largest pore volume (1.58 and 0.58 mm3; p = 0.06), number of pores (55 and 50; p = 0.09), and characteristic coordination number (3.74 and 3.94; p = 0.02) were significantly different between the low-density than the high-density treatment. Aggregate size also influenced measured geometrical pore parameters. This analytical technique provides a tool for assessing changes in soil pores that affect hydraulic properties and thereby provides information to assist in assessment of soil management systems.

Wettability, soil organic matter and structure-properties of typical chernozems under the forest and under the arable land

NASA Astrophysics Data System (ADS)

Bykova, Galina; Umarova, Aminat; Tyugai, Zemfira; Milanovskiy, Evgeny; Shein, Evgeny

2017-04-01

Intensive tillage affects the properties of soil: decrease in content of soil organic matter and in hydrophobicity of the soil's solid phase, the reduction of amount of water stable aggregates - all this leads to deterioration of the structure of the soil and affects the process of movement of moisture in the soil profile. One of the hypotheses of soil's structure formation ascribes the formation of water stable aggregates with the presence of hydrophobic organic substances on the surface of the soil's solid phase. The aim of this work is to study the effect of tillage on properties of typical chernozems (pachic Voronic Chernozems, Haplic Chernozems) (Russia, Kursk region), located under the forest and under the arable land. The determination of soil-water contact angle was performed by a Drop Shape Analyzer DSA100 (Krüss GmbH, Germany) by the static sessile drop method. For all samples the content of total and organic carbon by dry combustion in oxygen flow and the particle size distribution by the laser diffraction method on the device Analysette 22 comfort, FRITCH, Germany were determined. The estimation of aggregate composition was performed by dry sieving (AS 200, Retsch, Germany), the content of water stable aggregates was estimated by the Savvinov method. There was a positive correlation between the content of organic matter and soil's wettability in studied soils, a growth of contact angle with the increasing the content of organic matter. Under the forest the content of soil organic matter was changed from 6,41% on the surface up to 1,9% at the depth of 100 cm. In the Chernozem under the arable land the organic carbon content in arable horizon is almost two times less. The maximum of hydrophobicity (78.1o) was observed at the depth of 5 cm under the forest. In the profile under the arable land the contact angle value at the same depth was 50o. The results of the structure analysis has shown a decrease in the content of agronomically valuable and water stable aggregates in the profile under arable land. These data indicate the correlation between the wettability of soils with the content of organic matter and their influence on the formation of water stable structure, as well as the negative impact of tillage on the analyzed characteristics.

Pore-scale water dynamics during drying and the impacts of structure and surface wettability

NASA Astrophysics Data System (ADS)

Cruz, Brian C.; Furrer, Jessica M.; Guo, Yi-Syuan; Dougherty, Daniel; Hinestroza, Hector F.; Hernandez, Jhoan S.; Gage, Daniel J.; Cho, Yong Ku; Shor, Leslie M.

2017-07-01

Plants and microbes secrete mucilage into soil during dry conditions, which can alter soil structure and increase contact angle. Structured soils exhibit a broad pore size distribution with many small and many large pores, and strong capillary forces in narrow pores can retain moisture in soil aggregates. Meanwhile, contact angle determines the water repellency of soils, which can result in suppressed evaporation rates. Although they are often studied independently, both structure and contact angle influence water movement, distribution, and retention in soils. Here drying experiments were conducted using soil micromodels patterned to emulate different aggregation states of a sandy loam soil. Micromodels were treated to exhibit contact angles representative of those in bulk soil (8.4° ± 1.9°) and the rhizosphere (65° ± 9.2°). Drying was simulated using a lattice Boltzmann single-component, multiphase model. In our experiments, micromodels with higher contact angle surfaces took 4 times longer to completely dry versus micromodels with lower contact angle surfaces. Microstructure influenced drying rate as a function of saturation and controlled the spatial distribution of moisture within micromodels. Lattice Boltzmann simulations accurately predicted pore-scale moisture retention patterns within micromodels with different structures and contact angles.

Long term management practices influenced soil aggregation and carbon dynamics

USDA-ARS?s Scientific Manuscript database

Soil aggregation protects soil organic C (SOC) against rapid decomposition, improves soil quality, and reduces soil erosion potential. The objectives of this study are to evaluate the effects of long-term (21 yrs.) management practices on SOC, water stable aggregate (WSA), and aggregate-associated ...

Changes in SOC stocks and fractions after natural afforestation of alpine grasslands

NASA Astrophysics Data System (ADS)

Guidi, Claudia; Rodeghiero, Mirco; Vesterdal, Lars; Gianelle, Damiano

2013-04-01

Land use changes are considered one of the major driving forces of global carbon fluxes and can induce significant alterations of soil organic carbon stocks. In the European Alps, the dominant form of land use change is represented by the abandonment of marginal mountain grasslands and their invasion by tree species, i.e. a transition from grassland to forest. While an increase in live and dead aboveground biomass is commonly reported, the impact on soil organic carbon (SOC) is still unclear. The main objective of the current study was to quantify the effect of abandonment and forest regrowth of mountain grassland on SOC, considering both SOC stocks and its physically separated fractions. The study area is located in a pre-alpine area of the Trentino region (Italy), with an elevation of about 1150 m. We compared four land uses representing a transition from grassland to forest: I) managed grassland; II) grassland abandoned 10 years ago; III) natural afforested grassland abandoned after 1973; IV) reference forest, already present in 1861. The afforested area and the reference forest are both dominated by Norway spruce (Picea abies) and beech (Fagus sylvatica). For each land use intensity three sampling areas were selected. In each area we collected eight soil cores to a depth of 30 cm, dividing the soil core in 4 depth increments. To assess changes in SOC stocks, we measured bulk density, stoniness, root biomass and organic carbon content. Mineral SOC stocks were calculated using both an equivalent depth and an equivalent mass approach. Changes in SOC fractions were assessed using aggregate size fractionation (Cambardella and Elliott, 1993) and size-density fractionation procedures. Preliminary results show higher soil C concentrations in forest sites compared to grassland. This can be attributed to higher C inputs and lower mineralization rates due to a higher degree of soil aggregation and protection of soil organic matter, but also to the higher stoniness registered in forest sites which can lead to a concentration of C inputs in a smaller volume of soil. If C stocks are computed using an equivalent soil depth approach, mineral SOC stocks are lower in forest land uses compared to grassland while no significant difference emerges if an equivalent soil mass approach is used. The aggregate size fractionation highlighted an increase in C stored in large macroaggregates following afforestation and a decrease in silt and clay size fraction (<53 μm). The strongest change shown through the size-density fractionation procedure is a three-fold increase in C stored in free organic matter (POM) from grassland to forest. Intriguingly, we found a decreasing trend in the microaggregate (53-250 μm) fraction as well as for the mineral-associated heavy fraction following afforestation, suggesting a decrease in the more stable SOC fraction, while the labile fractions increased.

The SAWO (Small And Well Organized) avatar teaches the importance of the aggregates on the soil system and how to determine their stability

NASA Astrophysics Data System (ADS)

Mataix-Solera, Jorge; Cerdà, Artemi; Jordán, Antonio; Úbeda, Xavier; Pereira, Paulo

2015-04-01

Soil structure is the key factor that determine the soil quality as control the organic matter turnnover, soil biology and soil erodibility (Cerdà, 1996; 1998; Wick et al., 2014; Gelaw, 2015). There is a need to understand better the factors and the processes that act on the soil aggregation and the dynamics of the soil aggregation, which will make easier to understand the soil system functioning (Jordán et al., 2011; Jordán et al., 2012; Pulido Moncada et al., 2013). Fire, mines, grazing and agricultura (Cerdà, 2000; Mataix Solera et al., 2011; Cerdà et al., 2012; Hallett et al., 2014; Lozano et al., 2013) determines how the soil structure is highly affected by the humankind. And this determines the sustainability of the land managements (García Orenes et al., 2012; K¨ropfl et al., 2013; Mekuria and Aynekulu, 2013; Taguas et al., 2013; Zhao et al., 2013). Aggregates are Small And Well Organized (SAWO) structures that allow the water to flow, the air fill the porous and the life to be diverse and abundant in the soil. The SAWO avatar will teach the importance of the functions and the services of the aggregates to students and other scientists, but also to any audience. This means that the experiments and the vocabulary to be used by SAWO will be very wide and rich. The Avatar SAWO will use different strategies and skills to teach the soil aggregation properties and characteristics. And also, how to measure. Easy to carry out experiments will be shown by SAWO to measure the aggregate stability in the field and in the laboratory, and the soil sampling in the field. The SAWO avatar will play a special attention to the impact of forest fires on aggregate stability changes and how to measure. The SAWO avatar will teach how to take samples in the field, how to transport and manage in the laboratory, and finally which measurements and test can be done to determine the aggregate stability. Acknowledgements To the "Ministerio de Economía and Competitividad" of Spanish Government for finance the POSTFIRE project (CGL2013- 47862-C2-1-R). The research projects GL2008-02879/BTE, LEDDRA 243857 and PREVENTING AND REMEDIATING DEGRADATION OF SOILS IN EUROPE THROUGH LAND CARE (RECARE)FP7-ENV-2013- supported this research. References Cerdà, A. 1996. Soil aggregate stability in three mediterranean environments. Soil Technology, 9, 129-133. Cerdà, A. 1998. Soil aggregate stability under different Mediterranean vegetation types. Catena, 32, 73-86. Cerdà, A. 2000. Aggregate stability against water forces under different climates on agriculture land and scrubland in southern Bolivia. Soil and Tillage Research, 36, 1- 8. Cerdà, A., Mataix-Solera, J., Arcenegui, V. (2012, April). Aggregate stability in citrus plantations. The impact of drip irrigation. In EGU General Assembly Conference Abstracts (Vol. 14, p. 3772). García-Orenes, F., Roldán, A., Mataix-Solera, J., Cerdà, A., Campoy, M., Arcenegui, V., Caravaca, F. 2012. Soil structural stability and erosion rates influenced by agricultural management practices in a semi-arid Mediterranean agro-ecosystem. Soil Use and Management 28(4): 571-579. DOI: 10.1111/j.1475-2743.2012.00451.x Gelaw, A. M., Singh, B. R., Lal, R. 2015. Organic carbon and nitrogen associated with soil aggregates and particle sizes under different land uses in Tigray, northern Ethiopia. Land Degradation & Development.DOI: 10.1002/ldr.2261 Hallett, P., Ogden, M., Karim, K., Schmidt, S., Yoshida, S. (2014, May). Beneath aggregate stability-quantifying thermodynamic properties that drive soil structure dynamics. In EGU General Assembly Conference Abstracts (Vol. 16, p. 10792). Jordán, A., Zavala, L. M., Mataix-Solera, J., Nava, A. L., Alanís, N. (2011). Effect of fire severity on water repellency and aggregate stability on Mexican volcanic soils. Catena, 84(3), 136-147. Jordan, M., Garcia-Orenes, F., Mataix-Solera, J., Garcia-Sanchez, E. (2012, April). Evaluation of the physical properties, bulk density and aggregate stability of potential substrates in quarry restoration. In EGU General Assembly Conference Abstracts (Vol. 14, p. 1110). Kröpfl, A. I., Cecchi, G. A., Villasuso, N. M., Distel, R. A. 2013. Degradation and recovery processes in Semi-Arid patchy rangelands of northern Patagonia, Argentina. Land Degradation & Development, 24: 393- 399. DOI 10.1002/ldr.1145 Lozano, E., Temporal, B., Oltra, Á., Mataix-Solera, J., Arcenegui, V., García-Orenes, F. (2013, April). Effect of freeze-thawing on aggregate stability in a calcareous Mediterranean soil. In EGU General Assembly Conference Abstracts (Vol. 15, p. 1483). Mataix-Solera, J., Cerdà, A., Arcenegui, V., Jordán, A., Zavala, L.M. 2011 Fire effects on soil aggregation: a review. Earth-Science Reviews 109: 44-60 http://dx.doi.org/10.1016/j.earscirev.2011.08.002 Mekuria, W., Aynekulu, E. 2013. Exclosure land management for restoration of the soils in degrade communal grazing lands in Northern Ethiopia. Land Degradation & Development, 24: 528- 538. DOI 10.1002/ldr.1146 Pulido Moncada, M., Gabriels, D., Cornelis, W., Lobo, D. 2013. Comparing aggregate stability tests for soil physical quality indicators. Land Degradation & Development.| DOI: 10.1002/ldr.2225 Taguas, E. V., Carpintero, E., and Ayuso, J. L. 2013. Assessing land degradation risk through the long-term analysis of erosivity: a case study in Southern Spain. Land Degradation & Development, 24: 179- 187. DOI 10.1002/ldr.1119 Wick, A.F., Daniels, W.L. Nash, W.L. a Burger, J.A. 2014. Aggregate recovery in reclaimed coal mine soils of SW Virginia. Land Degradation and Development. 2014. DOI: 10.1002/ldr.2309S Zhao, G., Mu, X., Wen, Z., Wang, F., and Gao, P. 2013. Soil erosion, conservation, and Eco-environment changes in the Loess Plateau of China. Land Degradation & Development, 24: 499- 510. DOI 10.1002/ldr.2246

Plant litter chemistry alters the content and composition of organic carbon associated with soil mineral and aggregate fractions in invaded ecosystems.

PubMed

Tamura, Mioko; Suseela, Vidya; Simpson, Myrna; Powell, Brian; Tharayil, Nishanth

2017-10-01

Through the input of disproportionate quantities of chemically distinct litter, invasive plants may potentially influence the fate of organic matter associated with soil mineral and aggregate fractions in some of the ecosystems they invade. Although context dependent, these native ecosystems subjected to prolonged invasion by exotic plants may be instrumental in distinguishing the role of plant-microbe-mineral interactions from the broader edaphic and climatic influences on the formation of soil organic matter (SOM). We hypothesized that the soils subjected to prolonged invasion by an exotic plant that input recalcitrant litter (Japanese knotweed, Polygonum cuspidatum) would have a greater proportion of plant-derived carbon (C) in the aggregate fractions, as compared with that in adjacent soil inhabited by native vegetation that input labile litter, whereas the soils under an invader that input labile litter (kudzu, Pueraria lobata) would have a greater proportion of microbial-derived C in the silt-clay fraction, as compared with that in adjacent soils that receive recalcitrant litter. At the knotweed site, the higher C content in soils under P. cuspidatum, compared with noninvaded soils inhabited by grasses and forbs, was limited to the macroaggregate fraction, which was abundant in plant biomarkers. The noninvaded soils at this site had a higher abundance of lignins in mineral and microaggregate fractions and suberin in the macroaggregate fraction, partly because of the greater root density of the native species, which might have had an overriding influence on the chemistry of the above-ground litter input. At the kudzu site, soils under P. lobata had lower C content across all size fractions at a 0-5 cm soil depth despite receiving similar amounts of Pinus litter. Contrary to our prediction, the noninvaded soils receiving recalcitrant Pinus litter had a similar abundance of plant biomarkers across both mineral and aggregate fractions, potentially because of the higher surface area of soil minerals at this site. The plant biomarkers were lower in the aggregate fractions of the P. lobata-invaded soils, compared with noninvaded pine stands, potentially suggesting a microbial co-metabolism of pine-derived compounds. These results highlight the complex interactions among litter chemistry, soil biota, and minerals in mediating soil C storage in unmanaged ecosystems; these interactions are particularly important under global changes that may alter plant species composition and hence the quantity and chemistry of litter inputs in terrestrial ecosystems. © 2017 John Wiley & Sons Ltd.

Characterization of wet aggregate stability of soils by ¹H-NMR relaxometry.

PubMed

Buchmann, C; Meyer, M; Schaumann, G E

2015-09-01

For the assessment of soil structural stability against hydraulic stress, wet sieving or constant head permeability tests are typically used but rather limited in their intrinsic information value. The multiple applications of several tests is the only possibility to assess important processes and mechanisms during soil aggregate breakdown, e.g. the influences of soil fragment release or differential swelling on the porous systems of soils or soil aggregate columns. Consequently, the development of new techniques for a faster and more detailed wet aggregate stability assessment is required. (1)H nuclear magnetic resonance relaxometry ((1)H-NMR relaxometry) might provide these requirements because it has already been successfully applied on soils. We evaluated the potential of (1)H-NMR relaxometry for the assessment of wet aggregate stability of soils, with more detailed information on occurring mechanisms at the same time. Therefore, we conducted single wet sieving and constant head permeability tests on untreated and 1% polyacrylic acid-treated soil aggregates of different textures and organic matter contents, subsequently measured by (1)H-NMR relaxometry after percolation. The stability of the soil aggregates were mainly depending on their organic matter contents and the type of aggregate stabilization, whereby additional effects of clay swelling on the measured wet aggregate stability were identified by the transverse relaxation time (T2) distributions. Regression analyses showed that only the percentage of water stable aggregates could be determined accurately from percolated soil aggregate columns by (1)H-NMR relaxometry measurements. (1)H-NMR relaxometry seems a promising technique for wet aggregate stability measurements but should be further developed for nonpercolated aggregate columns and real soil samples. Copyright © 2014 John Wiley & Sons, Ltd.

Aggregate Stability and Erodibility of Purple Soil on Sloping Farmland as affected by different Soil Thickness

NASA Astrophysics Data System (ADS)

Huang, Xinjun; Zhang, Qingwen; Chen, Shanghong; Dong, Yuequn; Xiao, Meijia; Hamed, Lamy Mamdoh Mohamed

2017-04-01

Soil thickness is basic limiting condition for purple soil, not only due to its effect on crop production, but also its effect on soil structure. Steady-state of soil thickness will be achieved over time, as result the soil aggregate which the key factor of soil erodibility can be enhanced as well. However, the effect of soil thickness on aggregates stability and the characteristics of soil erodibility in sloping land have not yet fully understood.A field survey was conducted in hilly area of Sichuan region located in southeast China to study the relationship between soil aggregate stability and soil erodibility on sloping farmland under different four thickness (100cm, 80cm, 60cm, 30cm) of purple soil. Based on two different sieving methods (Dry and Wet sieving), we analyzed soil aggregate stability and its effect on soil erodibility within depth of 0-30cm soil layers. The results indicated that: Water stable aggregate on sloping farmland was ranged between 37.9% to 58.6%, where it increased with increasing the soil thickness. Moreover, fractal dimension calculated from dry-sieving and wet-sieving was 2.06-2.49 and 2.70-2.85 respectively, where it decreased with decreasing the soil thickness. The overall soil erodibility was 0.05-1.00 and a negative significant correlation was found between soil aggregate stability and erodibility(P<0.01). Moreover, farmland with thick soil profile tended to be high in soil erodibility within the top soil layer (0-30cm). The results reveal that soil thickness can affect soil aggregate stability as well as erodibility. As soil thickness increased, the top soil became more stable and less erodible. Keywords：purple soil; soil thickness; soil aggregate；soil erodibility

Dry heat effects on survival of indigenous soil particle microflora and particle viability studies of Kennedy Space Center soil

NASA Technical Reports Server (NTRS)

Ruschmeyer, O. R.; Pflug, I. J.; Gove, R.; Heisserer, Y.

1975-01-01

Research efforts were concentrated on attempts to obtain data concerning the dry heat resistance of particle microflora in Kennedy Space Center soil samples. The in situ dry heat resistance profiles at selected temperatures for the aggregate microflora on soil particles of certain size ranges were determined. Viability profiles of older soil samples were compared with more recently stored soil samples. The effect of increased particle numbers on viability profiles after dry heat treatment was investigated. These soil particle viability data for various temperatures and times provide information on the soil microflora response to heat treatment and are useful in making selections for spacecraft sterilization cycles.

An analysis of carbon and radiocarbon profiles across a range ecosystems types

NASA Astrophysics Data System (ADS)

Heckman, K. A.; Gallo, A.; Hatten, J. A.; Swanston, C.; Strahm, B. D.; Sanclements, M.

2016-12-01

Soil carbon stocks have become recognized as increasingly important in the context of climate change and global C cycle modeling. As modelers seek to identify key parameters affecting the size and stability of belowground C stocks, attention has been drawn to the mineral matrix and the soil physiochemical factors influenced by it. Though clay content has often been utilized as a convenient and key explanatory variable for soil C dynamics, its utility has recently come under scrutiny as new paradigms of soil organic matter stabilization have been developed. We utilized soil cores from a range of National Ecological Observatory Network (NEON) experimental plots to examine the influence of mineralogical parameters on soil C stocks and turnover and their relative importance in comparison to climatic variables. Results are presented for a total of 11 NEON sites, spanning Alfisols, Entisols, Mollisols and Spodosols. Soils were sampled by genetic horizon, density separated according to density fractionation: light fractions (particulate organics neither occluded within aggregates nor associated with mineral surfaces), occluded fractions (particulate organics occluded within aggregates), and heavy fractions (organics associated with mineral surfaces). Bulk soils and density fractions were measured for % C and radiocarbon abundance (as a measure of C stability). Carbon and radiocarbon abundances were examined among fractions and in the context of climatic variables (temperature, precipitation, elevation) and soil physiochemical variables (% clay and pH). No direct relationships between temperature and soil C or radiocarbon abundances were found. As a whole, soil radiocarbon abundance in density fractions decreased in the order of light>heavy>occluded, highlighting the importance of both surface sorption and aggregation to the preservation of organics. Radiocarbon concentrations of the heavy fraction (mineral adsorbed) were significantly, though weakly, correlated with pH (r2 = 0.35, p = 0.02), though C concentrations were not. Data suggest an important role for both aggregation and soil chemistry in regulating soil C cycling across a diversity of soil orders. The current presented results serve as a preliminary report on a project spanning 40 NEON sites and a range of physiochemical analyses.

Feasibility of digital imaging to characterize earth materials : part 2.

DOT National Transportation Integrated Search

2012-06-06

This study demonstrated the feasibility of digital imaging to characterize earth materials. Two rapid, relatively low cost image-based methods were developed for determining the grain size distribution of soils and aggregates. The first method, calle...

Feasibility of digital imaging to characterize earth materials : part 6.

DOT National Transportation Integrated Search

2012-06-06

This study demonstrated the feasibility of digital imaging to characterize earth materials. Two rapid, relatively low cost image-based methods were developed for determining the grain size distribution of soils and aggregates. The first method, calle...

Feasibility of digital imaging to characterize earth materials : part 3.

DOT National Transportation Integrated Search

2012-06-06

This study demonstrated the feasibility of digital imaging to characterize earth materials. Two rapid, relatively low cost image-based methods were developed for determining the grain size distribution of soils and aggregates. The first method, calle...

Feasibility of digital imaging to characterize earth materials : part 1.

DOT National Transportation Integrated Search

2012-06-06

This study demonstrated the feasibility of digital imaging to characterize earth materials. Two rapid, relatively low cost image-based methods were developed for determining the grain size distribution of soils and aggregates. The first method, calle...

Feasibility of digital imaging to characterize earth materials : part 4.

DOT National Transportation Integrated Search

2012-06-06

This study demonstrated the feasibility of digital imaging to characterize earth materials. Two rapid, relatively low cost image-based methods were developed for determining the grain size distribution of soils and aggregates. The first method, calle...

Feasibility of digital imaging to characterize earth materials : part 5.

DOT National Transportation Integrated Search

2012-05-06

This study demonstrated the feasibility of digital imaging to characterize earth materials. Two rapid, relatively low cost image-based methods were developed for determining the grain size distribution of soils and aggregates. The first method, calle...

Radical change of Zn speciation in pig slurry amended soil: Key role of nano-sized sulfide particles.

PubMed

Formentini, Thiago Augusto; Legros, Samuel; Fernandes, Cristovão Vicente Scapulatempo; Pinheiro, Adilson; Le Bars, Maureen; Levard, Clément; Mallmann, Fábio Joel Kochem; da Veiga, Milton; Doelsch, Emmanuel

2017-03-01

Spreading livestock manure as fertilizer on farmlands is a widespread practice. It represents the major source of heavy metal(loid)s (HM) input in agricultural soils. Since zinc (Zn) is present at high concentrations in manure, it poses special environmental concerns related to phytotoxicity, groundwater contamination, and introduction in the food chain. Therefore, investigations on the fate and behavior of manure-borne Zn, when it enters the soil environment, are necessary to predict the environmental effects. Nevertheless, long-term field studies assessing Zn speciation in the organic waste matrix, as well as within the soil after manure application, are lacking. This study was designed to fill this gap. Using SEM-EDS and XAS analysis, we reported the following new results: (i) ZnS made up 100% of the Zn speciation in the pig slurry (the highest proportion of ZnS ever observed in organic waste); and (ii) ZnS aggregates were about 1-μm diameter (the smallest particle size ever reported in pig slurry). Moreover, the pig slurry containing ZnS was spread on the soil over an 11-year period, totaling 22 applications, and the resulting Zn speciation within the amended soil was analyzed. Surprisingly, ZnS, i.e. the only species responsible for a nearly 2-fold increase in the Zn concentration within the amended soil, was not detected in this soil. Based on SEM-EDS and XAS observations, we put forward the hypothesis that Zn in the pig slurry consisted of nano-sized ZnS crystallites that further aggregated. The low stability of ZnS nanoparticles within oxic and complex environments such as the studied soil was the key explanation for the radical change in pig slurry-borne Zn speciation after long-term amendments. Copyright © 2016 Elsevier Ltd. All rights reserved.

Imaging of pore networks and related interfaces in soil systems by using high resolution X-ray micro-CT

NASA Astrophysics Data System (ADS)

Zacher, Gerhard; Eickhorst, Thilo; Schmidt, Hannes; Halisch, Matthias

2016-04-01

Today's high-resolution X-ray CT with its powerful tubes and great detail detectability lends itself naturally to geological and pedological applications. Those include the non-destructive interior examination and textural analysis of rock and soil samples and their permeability and porosity - to name only a few. Especially spatial distribution and geometry of pores, mineral phases and fractures are important for the evaluation of hydrologic and aeration properties in soils as well as for root development in the soil matrix. The possibility to visualize a whole soil aggregate or root tissue in a non-destructive way is undoubtedly the most valuable feature of this type of analysis and is a new area for routine application of high resolution X-ray micro-CT. The paper outlines recent developments in hard- and software requirements for high resolution CT. It highlights several pedological applications which were performed with the phoenix nanotom m, the first 180 kV nanofocus CT system tailored specifically for extremely high-resolution scans of variable sized samples with voxel-resolutions down to < 300 nm. In addition very good contrast resolution can be obtained as well which is necessary to distinguish biogenic material in soil aggregates amongst others. We will address visualization and quantification of porous networks in 3D in different environmental samples ranging from clastic sedimentary rock to soil cores and individual soil aggregates. As several processes and habitat functions are related to various pore sizes imaging of the intact soil matrix will be presented on different scales of interest - from the mm-scale representing the connectivity of macro-pores down to the micro-scale representing the space of microbial habitats. Therefore, soils were impregnated with resin and scanned via X-ray CT. Scans at higher resolution were obtained from sub-volumes cut from the entire resin impregnated block and from crop roots surrounded by rhizosphere soil. Within the scanned structures we will highlight interfaces i.e. pore-solid interface and soil-root interface. The latter will be linked to examples of fluorescent microscopy and scanning electron microscopy obtained from 2D sections revealing additional biological and chemical information in the respective microenvironment. Based on the combination of all 3D and 2D imaging data habitat features of soils can be characterized and combined with studies analyzing microbial rhizosphere colonization.

Microbial Ecology of Soil Aggregation in Agroecosystems

NASA Astrophysics Data System (ADS)

Hofmockel, K. S.; Bell, S.; Tfailly, M.; Thompson, A.; Callister, S.

2017-12-01

Crop selection and soil texture influence the physicochemical attributes of the soil, which structures microbial communities and influences soil C cycling storage. At the molecular scale, microbial metabolites and necromass alter the soil environment, which creates feedbacks that influence ecosystem functions, including soil C accumulation. By integrating lab to field studies we aim to identify the molecules, organisms and metabolic pathways that control carbon cycling and stabilization in bioenergy soils. We investigated the relative influence of plants, microbes, and minerals on soil aggregate ecology at the Great Lakes Bioenergy Research experiment. Sites in WI and MI, USA have been in corn and switchgrass cropping systems for a decade. By comparing soil aggregate ecology across sites and cropping systems we are able to test the relative importance of plant, microbe, mineral influences on soil aggregate dynamics. Soil microbial communities (16S) differ in diversity and phylogeny among sites and cropping systems. FT-ICR MS revealed differences in the molecular composition of water-soluble fraction of soil organic matter for cropping systems and soil origin for both relative abundance of assigned formulas and biogeochemical classes of compounds. We found the degree of aggregation, measured by mean weighted diameter of aggregate fractions, is influenced by plant-soil interactions. Similarly, the proportion of soil aggregate fractions varied by both soil and plant factors. Differences in aggregation were reflected in differences in bacterial, but not fungal community composition across aggregate fractions, within each soil. Scanning electron microscopy revealed stark differences in mineral-organic interactions that influence the microbial niche and the accessibility of substrates within the soil. The clay soils show greater surface heterogeneity, enabling interactions with organic fraction of the soil. This is consistent with molecular data that reveal differences in the abundance of chemical classes in clay loams compared to sandy loams. Together our data demonstrate that the potential for aggregation and C storage is strongly influenced by soil mineralogy with important implications for plant-microbe interactions that mediate C biogeochemistry.

Impact of Amendments on the Physical Properties of Soil under Tropical Long-Term No Till Conditions.

PubMed

Carmeis Filho, Antonio C A; Crusciol, Carlos A C; Guimarães, Tiara M; Calonego, Juliano C; Mooney, Sacha J

2016-01-01

Tropical regions have been considered the world's primary agricultural frontier; however, some physico-chemical deficiencies, such as low soil organic matter content, poor soil structure, high erodibility, soil acidity, and aluminum toxicity, have affected their productive capacity. Lime and gypsum are commonly used to improve soil chemical fertility, but no information exists about the long-term effects of these products on the physical attributes and C protection mechanisms of highly weathered Oxisols. A field trial was conducted in a sandy clay loam (kaolinitic, thermic Typic Haplorthox) under a no-tillage system for 12 years. The trial consisted of four treatments: a control with no soil amendment application, the application of 2.1 Mg ha-1 phosphogypsum, the application of 2.0 Mg ha-1 lime, and the application of lime + phosphogypsum (2.0 + 2.1 Mg ha-1, respectively). Since the experiment was established in 2002, the rates have been applied three times (2002, 2004, and 2010). Surface liming effectively increased water-stable aggregates > 2.0 mm at a depth of up to 0.2 m; however, the association with phosphogypsum was considered a good strategy to improve the macroaggregate stability in subsoil layers (0.20 to 0.40 m). Consequently, both soil amendments applied together increased the mean weight diameter (MWD) and geometric mean diameter (GMD) in all soil layers, with increases of up to 118 and 89%, respectively, according to the soil layer. The formation and stabilization of larger aggregates contributed to a higher accumulation of total organic carbon (TOC) on these structures. In addition to TOC, the MWD and aggregate stability index were positively correlated with Ca2+ and Mg2+ levels and base saturation. Consequently, the increase observed in the aggregate size class resulted in a better organization of soil particles, increasing the macroporosity and reducing the soil bulk density and penetration resistance. Therefore, adequate soil chemical management plays a fundamental role in improving the soil's physical attributes in tropical areas under conservative management and highly affected by compaction caused by intensive farming.

[Impact of Land Utilization Pattern on Distributing Characters of Labile Organic Carbon in Soil Aggregates in Jinyun Mountain].

PubMed

Li, Rui; Jiang, Chang-sheng; Hao, Qing-ju

2015-09-01

Four land utilization patterns were selected for this study in Jinyun mountain, including subtropical evergreen broad-leaved forest (abbreviation: forest), sloping farmland, orchard and abandoned land. Soil samples were taken every 10 cm in the depth of 60 cm soil and proportions of large macroaggregates (> 2 mm), small macroaggregates (0. 25-2 mm), microaggregates (0. 053 - 0. 25 mm) and silt + clay (<0. 053 mm) were obtained by wet sieving method to measure the content of organic carbon and labile organic carbon in each aggregate fraction and analyze impacts of land uses on organic carbon and labile organic carbon of soil aggregates. LOC content of four soil aggregates were significantly reduced with the increase of soil depth; in layers of 0-60 cm soil depth, our results showed that LOC contents of forest and abandoned land were higher than orchard and sloping farmland. Reserves of labile organic carbon were estimated by the same soil quality, it revealed that forest (3. 68 Mg.hm-2) > abandoned land (1. 73 Mg.hm-2) > orchard (1. 43 Mg.hm-2) >sloping farmland (0.54 Mg.hm-2) in large macroaggregates, abandoned land (7.77, 5. 01 Mg.hm-2) > forest (4. 96, 2.71 Mg.hm-2) > orchard (3. 33, 21. 10 Mg.hm-2) > sloping farmland (1. 68, 1. 35 Mg.hm-2) in small macroaggregates and microaggregates, and abandoned land(4. 32 Mg.hm-2) > orchard(4. 00 Mg.hm-2) > forest(3. 22 Mg.hm-2) > sloping farmland (2.37 Mg.hm-2) in silt + clay, forest and abandoned land were higher than orchard and sloping farmland in other three soil aggregates except silt + clay. It was observed that the level of organic carbon and labile organic carbon were decreased when bringing forest under cultivation to orchard or farmland, and augments on organic carbon and labile organic carbon were found after exchanging farmland to abandoned land. The most reverses of forest and abandoned land emerged in small macroaggregates, orchard and sloping farmland were in microaggregates. That was, during the transformations of land utilization pattern, soil aggregates with bigger size were easier to accumulate or lose labile organic carbon. Allocation ratios of labile organic carbon to soil organic carbon under four land uses were decreased as the soil depth added. Allocation ratios of orchard and sloping farmland were a bit higher than forest and abandoned land, which indicated that organic carbon of forest and abandoned land were more steady and available for soil as a carbon sink, meanwhile, the forest and abandoned land would avoid more CO2 diffusing to the atmosphere from the decomposition of soil organic carbon.

Contribution of ants in modifying of soil acidity and particle size distribution

NASA Astrophysics Data System (ADS)

Morgun, Alexandra; Golichenkov, Maxim

2015-04-01

Being a natural body, formed by the influence of biota on the upper layers of the Earth's crust, the soil is the most striking example of biogenic-abiogenic interactions in the biosphere. Invertebrates (especially ants that build soil nests) are important agents that change soil properties in well developed terrestrial ecosystems. Impact of soil microorganisms on soil properties is particularly described in numerous literature and concerns mainly chemical properties and general indicators of soil biological activity. Influence of ants (as representatives of the soil mesofauna) mostly appears as mechanical movement of soil particles and aggregates, and chemical effects caused by concentration of organic matter within the ant's nest. The aim of this research was to evaluate the effect of ants on physical and chemical soil attributes such as particle size distribution and soil acidity. The samples were taken from aerial parts of Lasius niger nests, selected on different elements of the relief (summit position, slope, terrace and floodplain) in the Arkhangelsk region (north of the European part of Russia) and compared with the specimens of the upper horizons of the reference soils. Particle size distribution was determined by laser diffraction method using laser diffraction particle size analyzer «Analysette 22 comfort» (FRITSCH, Germany). The acidity (pH) was determined by potentiometry in water suspension. Particle size distribution of the samples from the nests is more variable as compared to the control samples. For example, the content of 5-10 μm fraction ranges from 9% to 12% in reference soils, while in the anthill samples the variation is from 8% to 15%. Similarly, for 50-250 μm fraction - it ranges from 15% to 18% in reference soils, whereas in anthills - from 6% to 29%. The results of particle size analysis showed that the reference sample on the terrace has silty loam texture and nests soil L. niger are medium loam. The reference soil on the slope is characterized as medium loam, and ant's nest material has silty loam texture. The control samples of soil and ants nests on the summit position are similar and have medium loam texture. Generally we outline that the particle size distribution of anthill samples shows more variability. We assume that ants operate with small soil aggregates, in which fine fractions may link together coarser particles. pH measurements show that the reference soils have a strongly acidic reaction on the summit position (pH 4.6), slightly acidic on the slope (pH 5.5) and neutral on the terrace and on the floodplain (pH 7.2). While the material of the anthills tends to be slightly alkalinized on the summit (pH 4.8) and alkalinized on the slope (pH 7.2), but acidified to neutral on the floodplain and terrace (pH 6.4 and 5.7). Therefore, the ants form specific physico-chemical conditions that are different from the surrounding (native) soil, significantly increasing the complexity of soil cover structure. This is a clear example of ecosystem engineering functions of ants in nature. Increased complexity of soil pattern is the result of variations in pH and particle size distribution. Both cause the preconditions for the formation of new environmental niches and enhance biodiversity in natural ecosystems.

Effects of Inter- and Intra-aggregate Pore Space on the Soil-Gas Diffusivity Behavior in Unsaturated, Undisturbed Volcanic Ash Soils

NASA Astrophysics Data System (ADS)

Resurreccion, A. C.; Kawamoto, K.; Komatsu, T.; Moldrup, P.

2006-12-01

Volcanic ash soils (Andisols) have a unique dual porosity structure that results in good drainage and high soil- water retention. Despite of the complicated and highly developed soil structure, recent studies have reported a simple, highly linear relation between the soil-gas diffusion coefficient, Dp, and the soil-air content, ɛ, for several Japanese Andisols. In this study, we explain the linear Dp(ɛ) behavior from the effects of the inter- and intra-aggregate pore-size distributions. We couple the bimodal van Genuchten soil-water retention model with a general Dp(ɛ) model, ɛ^{X}, allowing the tortuosity- connectivity factor X to vary with pF (= log(-ψ; the soil-water matric potential in cm H2O)). Measured data suggest that the tortuosity-connectivity parameter X is at the minimum at pF 3 (where X ~ 2, following Buckingham, 1904), equal to the water retention point where a separation of inter- and intra-aggregate effects on Dp is observed. At pF < 3, the X values increased as pF decreased because of inactive/remote air-filled pore space entrapped by the inter-connected water films between inter-aggregate pore spaces. At pF > 3, X increased to a high value at very dry conditions due to remote air-filled space inside the intra-aggregate pores. By combining the complex dual porosity soil-water retention model with the power- law gas diffusivity model using a parabolic X(pF) function, the surprisingly simple linear behavior of Dp with ɛ was captured while the variation of Dp with pF followed a dual s-shaped curve similar to the water retention curve. A simple linear model to predict Dp(ɛ) is suggested, with slope C and threshold soil-air content, ɛth, calculated from the power-law model ɛ^{X} at pF 2 (near field capacity) and at pF 4.1 (near wilting point) using the same X value (= 2.3) at both pF in agreement with measured data. This linear Dp(ɛ) model performed better, especially at dry conditions, compared to the traditionally-used predictive models when tested against several independent Andisol datasets from literature.

Using Color, Texture and Object-Based Image Analysis of Multi-Temporal Camera Data to Monitor Soil Aggregate Breakdown

PubMed Central

Ymeti, Irena; van der Werff, Harald; Shrestha, Dhruba Pikha; Jetten, Victor G.; Lievens, Caroline; van der Meer, Freek

2017-01-01

Remote sensing has shown its potential to assess soil properties and is a fast and non-destructive method for monitoring soil surface changes. In this paper, we monitor soil aggregate breakdown under natural conditions. From November 2014 to February 2015, images and weather data were collected on a daily basis from five soils susceptible to detachment (Silty Loam with various organic matter content, Loam and Sandy Loam). Three techniques that vary in image processing complexity and user interaction were tested for the ability of monitoring aggregate breakdown. Considering that the soil surface roughness causes shadow cast, the blue/red band ratio is utilized to observe the soil aggregate changes. Dealing with images with high spatial resolution, image texture entropy, which reflects the process of soil aggregate breakdown, is used. In addition, the Huang thresholding technique, which allows estimation of the image area occupied by soil aggregate, is performed. Our results show that all three techniques indicate soil aggregate breakdown over time. The shadow ratio shows a gradual change over time with no details related to weather conditions. Both the entropy and the Huang thresholding technique show variations of soil aggregate breakdown responding to weather conditions. Using data obtained with a regular camera, we found that freezing–thawing cycles are the cause of soil aggregate breakdown. PMID:28556803

Using Color, Texture and Object-Based Image Analysis of Multi-Temporal Camera Data to Monitor Soil Aggregate Breakdown.

PubMed

Ymeti, Irena; van der Werff, Harald; Shrestha, Dhruba Pikha; Jetten, Victor G; Lievens, Caroline; van der Meer, Freek

2017-05-30

Remote sensing has shown its potential to assess soil properties and is a fast and non-destructive method for monitoring soil surface changes. In this paper, we monitor soil aggregate breakdown under natural conditions. From November 2014 to February 2015, images and weather data were collected on a daily basis from five soils susceptible to detachment (Silty Loam with various organic matter content, Loam and Sandy Loam). Three techniques that vary in image processing complexity and user interaction were tested for the ability of monitoring aggregate breakdown. Considering that the soil surface roughness causes shadow cast, the blue/red band ratio is utilized to observe the soil aggregate changes. Dealing with images with high spatial resolution, image texture entropy, which reflects the process of soil aggregate breakdown, is used. In addition, the Huang thresholding technique, which allows estimation of the image area occupied by soil aggregate, is performed. Our results show that all three techniques indicate soil aggregate breakdown over time. The shadow ratio shows a gradual change over time with no details related to weather conditions. Both the entropy and the Huang thresholding technique show variations of soil aggregate breakdown responding to weather conditions. Using data obtained with a regular camera, we found that freezing-thawing cycles are the cause of soil aggregate breakdown.

Soil aggregation and aggregating agents as affected by long term contrasting management of an Anthrosol

NASA Astrophysics Data System (ADS)

Zhang, Shulan; Wang, Renjie; Yang, Xueyun; Sun, Benhua; Li, Qinghui

2016-12-01

Soil aggregation was studied in a 21-year experiment conducted on an Anthrosol. The soil management regimes consisted of cropland abandonment, bare fallow without vegetation and cropping system. The cropping system was combined with the following nutrient management treatments: control (CONTROL, no nutrient input); nitrogen, phosphorus and potassium (NPK); straw plus NPK (SNPK); and manure (M) plus NPK (MNPK). Compared with the CONTROL treatment, the abandonment treatment significantly increased the formation of large soil macroaggregates (>2 mm) and consequently improved the stability of aggregates in the surface soil layer due to enhancement of hyphal length and of soil organic matter content. However, in response to long-term bare fallow treatment aggregate stability was low, as were the levels of aggregating agents. Long term fertilization significantly redistributed macroaggregates; this could be mainly ascribed to soil organic matter contributing to the formation of 0.5-2 mm classes of aggregates and a decrease in the formation of the >2 mm class of aggregates, especially in the MNPK treatment. Overall, hyphae represented a major aggregating agent in both of the systems tested, while soil organic compounds played significantly different roles in stabilizing aggregates in Anthrosol when the cropping system and the soil management regimes were compared.

Soil aggregation and aggregating agents as affected by long term contrasting management of an Anthrosol

PubMed Central

Zhang, Shulan; Wang, Renjie; Yang, Xueyun; Sun, Benhua; Li, Qinghui

2016-01-01

Soil aggregation was studied in a 21-year experiment conducted on an Anthrosol. The soil management regimes consisted of cropland abandonment, bare fallow without vegetation and cropping system. The cropping system was combined with the following nutrient management treatments: control (CONTROL, no nutrient input); nitrogen, phosphorus and potassium (NPK); straw plus NPK (SNPK); and manure (M) plus NPK (MNPK). Compared with the CONTROL treatment, the abandonment treatment significantly increased the formation of large soil macroaggregates (>2 mm) and consequently improved the stability of aggregates in the surface soil layer due to enhancement of hyphal length and of soil organic matter content. However, in response to long-term bare fallow treatment aggregate stability was low, as were the levels of aggregating agents. Long term fertilization significantly redistributed macroaggregates; this could be mainly ascribed to soil organic matter contributing to the formation of 0.5–2 mm classes of aggregates and a decrease in the formation of the >2 mm class of aggregates, especially in the MNPK treatment. Overall, hyphae represented a major aggregating agent in both of the systems tested, while soil organic compounds played significantly different roles in stabilizing aggregates in Anthrosol when the cropping system and the soil management regimes were compared. PMID:27958366

Soil aggregation, erodibility, and erosion rates in mountain soils (NW Alps, Italy)

NASA Astrophysics Data System (ADS)

Stanchi, S.; Falsone, G.; Bonifacio, E.

2015-04-01

Erosion is a relevant soil degradation factor in mountain agrosilvopastoral ecosystems that can be enhanced by the abandonment of agricultural land and pastures left to natural evolution. The on-site and off-site consequences of soil erosion at the catchment and landscape scale are particularly relevant and may affect settlements at the interface with mountain ecosystems. RUSLE (Revised Universal Soil Loss Equation) estimates of soil erosion consider, among others, the soil erodibility factor (K), which depends on properties involved in structure and aggregation. A relationship between soil erodibility and aggregation should therefore be expected. However, erosion may limit the development of soil structure; hence aggregates should not only be related to erodibility but also partially mirror soil erosion rates. The aim of the research was to evaluate the agreement between aggregate stability and erosion-related variables and to discuss the possible reasons for discrepancies in the two kinds of land use considered (forest and pasture). Topsoil horizons were sampled in a mountain catchment under two vegetation covers (pasture vs. forest) and analyzed for total organic carbon, total extractable carbon, pH, and texture. Soil erodibility was computed, RUSLE erosion rate was estimated, and aggregate stability was determined by wet sieving. Aggregation and RUSLE-related parameters for the two vegetation covers were investigated through statistical tests such as ANOVA, correlation, and regression. Soil erodibility was in agreement with the aggregate stability parameters; i.e., the most erodible soils in terms of K values also displayed weaker aggregation. Despite this general observation, when estimating K from aggregate losses the ANOVA conducted on the regression residuals showed land-use-dependent trends (negative average residuals for forest soils, positive for pastures). Therefore, soil aggregation seemed to mirror the actual topsoil conditions better than soil erodibility. Several hypotheses for this behavior were discussed. A relevant effect of the physical protection of the organic matter by the aggregates that cannot be considered in K computation was finally hypothesized in the case of pastures, while in forests soil erodibility seemed to keep trace of past erosion and depletion of finer particles. A good relationship between RUSLE soil erosion rates and aggregate stability occurred in pastures, while no relationship was visible in forests. Therefore, soil aggregation seemed to capture aspects of actual vulnerability that are not visible through the erodibility estimate. Considering the relevance and extension of agrosilvopastoral ecosystems partly left to natural colonization, further studies on litter and humus protective action might improve the understanding of the relationship among erosion, erodibility, and structure.

[Effects of tillage rotation and fertilization on soil aggregates and organic carbon content in corn field in Weibei Highland].

PubMed

Wang, Li; Li, Jun; Li, Juan; Bai, Wei-Xia

2014-03-01

A field experiment on effects of tillage rotation and fertilization on corn continuous cropping-practiced lands was carried out in Heyang of Shaanxi in 2007-2012. The tillage types included annual rotation of no-tillage and subsoiling (NT-ST), subsoiling and conventional tillage (ST-CT), or conventional tillage and no-tillage (CT-NT), and yearly practice of no tillage (NT-NT), subsoiling (ST-ST) or conventional tillage (CT-CT). The fertilization treatments included balanced fertilization, low-rate fertilization and conventional fertilization, which were separately practiced against the different tillage types. The experiment investigated compositions, mean mass diameters (MWD), geometrical mean diameters (GMD) and fraction dimension numbers (D) of soil aggregates in 0-40 cm soil and contents of organic carbon in 0-60 cm soil. The results indicated that: 1) The increased tillage intensity caused the reduced mechanical stability and content of soil aggregates and increased soil organic carbon loss. No-tillage or tillage rotation increased the MWD, GMD and contents of soil organic carbon and soil aggregates with diameters of more than 0.25 mm, but decreased D. Under the same fertilization treatment, the contents of soil aggregates with diameters of more than 0.25 mm were ranked in the order of NT-NT>NT-ST>NT-CT>ST-ST>CT-ST>CT-CT, and under the same tillage rotations, the soil aggregates were more stable with the balanced or low- rate fertilization than with the conventional fertilization. 2) Mathematical fractal dimension fitting of soil aggregates indicated that the fractal dimension numbers of soil aggregates ranged within 2.247-2.681 by dry sieving and 2.897-2.976 by wet sieving. In 0-30 cm soil, the fractal dimension numbers of soil aggregates were significantly lower under no-tillage or tillage rotation than under conventional tillage, and in 0-40 cm soil, the fractal dimensions of soil aggregates increased with soil depth, and tended to stabilize at the soil depth of 40 cm. 3) The different fertilization treatments exerted significantly different influences on the contents of soil organic carbon (P < 0.05), which tended to decline with soil depth. Compared to the conventional fertilization, the balanced fertilization increased the content of soil organic carbon by 6.9%, and the contents of soil organic carbon increased as the diameters of soil aggregates increased. The correlation analysis showed that the contents of soil aggregates with diameters of 0.25-2 mm significantly affected the content of soil organic carbon, with the coefficient of determination being 0.848 (P < 0.01).

Impact of Amendments on the Physical Properties of Soil under Tropical Long-Term No Till Conditions

PubMed Central

Mooney, Sacha J.

2016-01-01

Tropical regions have been considered the world’s primary agricultural frontier; however, some physico-chemical deficiencies, such as low soil organic matter content, poor soil structure, high erodibility, soil acidity, and aluminum toxicity, have affected their productive capacity. Lime and gypsum are commonly used to improve soil chemical fertility, but no information exists about the long-term effects of these products on the physical attributes and C protection mechanisms of highly weathered Oxisols. A field trial was conducted in a sandy clay loam (kaolinitic, thermic Typic Haplorthox) under a no-tillage system for 12 years. The trial consisted of four treatments: a control with no soil amendment application, the application of 2.1 Mg ha-1 phosphogypsum, the application of 2.0 Mg ha-1 lime, and the application of lime + phosphogypsum (2.0 + 2.1 Mg ha-1, respectively). Since the experiment was established in 2002, the rates have been applied three times (2002, 2004, and 2010). Surface liming effectively increased water-stable aggregates > 2.0 mm at a depth of up to 0.2 m; however, the association with phosphogypsum was considered a good strategy to improve the macroaggregate stability in subsoil layers (0.20 to 0.40 m). Consequently, both soil amendments applied together increased the mean weight diameter (MWD) and geometric mean diameter (GMD) in all soil layers, with increases of up to 118 and 89%, respectively, according to the soil layer. The formation and stabilization of larger aggregates contributed to a higher accumulation of total organic carbon (TOC) on these structures. In addition to TOC, the MWD and aggregate stability index were positively correlated with Ca2+ and Mg2+ levels and base saturation. Consequently, the increase observed in the aggregate size class resulted in a better organization of soil particles, increasing the macroporosity and reducing the soil bulk density and penetration resistance. Therefore, adequate soil chemical management plays a fundamental role in improving the soil’s physical attributes in tropical areas under conservative management and highly affected by compaction caused by intensive farming. PMID:27959897

Carbon availability structures microbial community composition and function in soil aggregate fractions

NASA Astrophysics Data System (ADS)

Hofmockel, K. S.; Bach, E.; Williams, R.; Howe, A.

2014-12-01

Identifying the microbial metabolic pathways that most strongly influence ecosystem carbon (C) cycling requires a deeper understanding of the availability and accessibility of microbial substrates. A first step towards this goal is characterizing the relationships between microbial community function and soil C chemistry in a field context. For this perspective, soil aggregate fractions can be used as model systems that scale between microbe-substrate interactions and ecosystem C cycling and storage. The present study addresses how physicochemical variation among soil aggregate fractions influences the composition and functional potential of C cycling microbial communities. We report variation across soil aggregates using plot scale biological replicates from biofuel agroecosystems (fertilized, reconstructed, tallgrass prairie). Our results suggest that C and nitrogen (N) chemistry significantly differ among aggregate fractions. This leads to variation in microbial community composition, which was better characterized among aggregates than by using the whole soil. In fact by considering soil aggregation, we were able to characterize almost 2000 more taxa than whole soil alone, resulting in 65% greater community richness. Availability of C and N strongly influenced the composition of microbial communities among soil aggregate fractions. The normalized abundance of microbial functional guilds among aggregate fractions correlated with C and N chemistry, as did functional potential, measured by extracellular enzyme activity. Metagenomic results suggest that soil aggregate fractions select for functionally distinct microbial communities, which may significantly influence decomposition and soil C storage. Our study provides support for the premise that integration of soil aggregate chemistry, especially microaggregates that have greater microbial richness and occur at spatial scales relevant to microbial community functioning, may be necessary to understand the role of microbial communities on terrestrial C and N cycling.

Does Diffusion Sequester Heavy Metals in Old Contamination Soils?

NASA Astrophysics Data System (ADS)

Ma, J.; Jennings, A. A.

2002-12-01

Old soil contamination refers to soil contamination that has aged over a long period of time. For example, at some brownfields, the soil heavy metal contamination can be one hundred or more years old. When contamination is young, the heavy metals are bound relatively weakly to the soil. However, the speciation and/or mechanisms of association evolve with aging into much more stable forms. It also appears that the metals migrate deeper into the bulk soil matrix where they are less available to participate in surface-related phenomena. Previous research showed elevated heavy metal extraction result after the soil was pulverized, with all other experiment conditions remaining unchanged. This indicates the presence of sequestered heavy metal contamination within the large soil particles (aggregate). The mechanisms of sequestering are uncertain, but diffusion appears to be a major factor. There are two possible pathways of diffusion that can account for heavy metal sequestering: solid-state diffusion through the bulk aggregate or liquid-phase diffusion through micro-pores within the aggregate structure. The second diffusion mechanism can be coupled with sorption (or other surface-related phenomena) on the pore walls. The remediation of sequestered heavy metals is also impacted by diffusion. Grinding a soil significantly reduces its average particle size. This exposes more of its internal bulk volume to extraction and results in much shorter diffusion pathway for the sequestered heavy metals to be released. Evidence has illustrated that this both improves remediation efficiency and provides a method by which the degree of sequestering can be quantified. This paper will present the results of ongoing research that is developing methods to identify the mechanisms of, quantify the magnitude of and determine the relative importance of (i.e. risk analysis) heavy metals sequestered in old contamination soils.

Long-term manure amendments reduced soil aggregate stability via redistribution of the glomalin-related soil protein in macroaggregates

PubMed Central

Xie, Hongtu; Li, Jianwei; Zhang, Bin; Wang, Lianfeng; Wang, Jingkuan; He, Hongbo; Zhang, Xudong

2015-01-01

Glomalin-related soil protein (GRSP) contributes to the formation and maintenance of soil aggregates, it is however remains unclear whether long-term intensive manure amendments alter soil aggregates stability and whether GRSP regulates these changes. Based on a three-decade long fertilization experiment in northeast China, this study examined the impact of long-term manure input on soil organic carbon (SOC), total and easily extractable GRSP (GRSPt and GRSPe) and their respective allocations in four soil aggregates (>2000 μm; 2000–250 μm; 250–53 μm; and <53 μm). The treatments include no fertilization (CK), low and high manure amendment (M1, M2), chemical nitrogen, phosphorus and potassium fertilizers (NPK), and combined manure and chemical fertilizers (NPKM1, NPKM2). Though SOC, GRSPe and GRSPt in soil and SOC in each aggregate generally increased with increasing manure input, GRSPt and GRSPe in each aggregate showed varying changes with manure input. Both GRSP in macroaggregates (2000–250 μm) were significantly higher under low manure input, a pattern consistent with changes in soil aggregate stability. Constituting 38~49% of soil mass, macroaggregates likely contributed to the nonlinear changes of aggregate stability under manure amendments. The regulatory process of GRSP allocations in soil aggregates has important implications for manure management under intensive agriculture. PMID:26423355

Plant-soil-microbe interactions regulating soil C storage

NASA Astrophysics Data System (ADS)

Hofmockel, K. S.; Bach, E.; Williams, R.

2016-12-01

Integration across disciplines is required to identify the emergent microbial scale properties that regulate the release or occlusion of plant inputs in soil organic matter. To investigate how micro-scale processes influence soil carbon cycling, we measured microbial community composition and activity within soil aggregates monthly over two growing seasons of a long-term bioenergy field experiment. Using a biologically sensitive sieving technique, soil aggregates were isolated and microbial community activity and composition were measured. This aggregate approach revealed biogeochemical processes regulating C cycling that are not detected using whole soil approaches. Soil aggregation influenced microbe-substrate interactions, where diversified perennial grassland systems supported greater aggregation and reduced severity of aggregate turnover compared to corn systems. Aggregate turnover and concurrent increases in activity resulted in greater microbial biomass and physical protection of soil organic matter in prairie systems, especially fertilized prairies. Fertilized prairie enhanced microbial biomass, enzyme activity, and soil aggregation despite greater root biomass in unfertilized prairie. Independent of ecosystem or sampling date, N-acetyl-glucosaminidase activity and Nitrospirae abundance was greatest in large macroaggregates (>2000 µm), which harbored the highest C:N; cellobiohydrolase activity and Acidobacteria abundance was greatest in microaggregates (<250 µm) which had the lowest C:N. Aggregate fractions differed in microbial community composition (bacteria, archaea, and fungi) and potential enzyme activity, independent of cropping system. Microaggregates harbored significantly greater microbial diversity and richness across all bioenergy cropping systems. Together these results suggest that by mediating access to substrates, soil structure (aggregates) can influence the microbial community composition and extracellular enzyme activity to regulate ecosystem scale decomposition of soil organic matter.

Metal-based nanoparticles in soil: fate, behavior, and effects on soil invertebrates.

PubMed

Tourinho, Paula S; van Gestel, Cornelis A M; Lofts, Stephen; Svendsen, Claus; Soares, Amadeu M V M; Loureiro, Susana

2012-08-01

Metal-based nanoparticles (NPs) (e.g., silver, zinc oxide, titanium dioxide, iron oxide) are being widely used in the nanotechnology industry. Because of the release of particles from NP-containing products, it is likely that NPs will enter the soil compartment, especially through land application of sewage sludge derived from wastewater treatment. This review presents an overview of the literature dealing with the fate and effects of metal-based NPs in soil. In the environment, the characteristics of NPs (e.g., size, shape, surface charge) and soil (e.g., pH, ionic strength, organic matter, and clay content) will affect physical and chemical processes, resulting in NP dissolution, agglomeration, and aggregation. The behavior of NPs in soil will control their mobility and their bioavailability to soil organisms. Consequently, exposure characterization in ecotoxicological studies should obtain as much information as possible about dissolution, agglomeration, and aggregation processes. Comparing existing studies is a challenging task, because no standards exist for toxicity tests with NPs. In many cases, the reporting of associated characterization data is sparse, or missing, making it impossible to interpret and explain observed differences in results among studies. Copyright © 2012 SETAC.

3D soil structure characterization of Biological Soil Crusts from Alpine Tarfala Valley

NASA Astrophysics Data System (ADS)

Mele, Giacomo; Gargiulo, Laura; Zucconi, Laura; D'Acqui, Luigi; Ventura, Stefano

2017-04-01

Cyanobacteria filaments, microfungal hyphae, lichen rhizinae and anchoring rhizoids of bryophytes all together contribute to induce formation of structure in the thin soil layer beneath the Biological Soil Crusts (BSCs). Quantitative assessment of the soil structure beneath the BSCs is primarily hindered by the fragile nature of the crusts. Therefore, the role of BSCs in affecting such soil physical property has been rarely addressed using direct measurements. In this work we applied non-destructive X-ray microtomography imaging on five different samples of BSCs collected in the Alpine Tarfala Valley (northern Sweden), which have already been characterized in terms of fungal biodiversity in a previous work. We obtained images of the 3D spatial organization of the soil underneath the BSCs and characterized its structure by applying procedures of image analysis allowing to determine pore size distribution, pore connectivity and aggregate size distribution. Results has then been correlated with the different fungal assemblages of the samples.

Multiscale variability of soil aggregate stability: implications for rangeland hydrology and erosion

USDA-ARS?s Scientific Manuscript database

Conservation of soil and water resources in rangelands is a crucial step in stopping desertification processes. The formation of water-stable soil aggregates reduces soil erodibility and can increase infiltration capacity in many soils. Soil aggregate stability is highly variable at scales ranging f...

Soil biochar amendments: type and dose effects

NASA Astrophysics Data System (ADS)

Ojeda, G.; Domene, X.; Mattana, S.; Sousa, J. P.; Ortiz, O.; Andres, P.; Alcañiz, J. M.

2012-04-01

Biochar is an organic material produced via the pyrolysis of C-based biomass, which is increasingly being recognized by scientists and policy makers for its potential role in carbon sequestration, reducing greenhouse gas emissions, waste mitigation, and as a soil amendment. Recent studies indicated that biochar improves soil fertility through its positive influence on physical-chemical properties, since not only improves water retention, aggregation and permeability, but its high charge density can also hold large amounts of nutrients, increasing crop production. However, it was observed that combustion temperature could affects the degree of aromaticity and the size of aromatic sheets, which in turns determine short-term mineralization rates. To reconcile the different decompasibility observations of biochar, it has sugested that physical protection and interactions with soil minerals play a significant part in biochar stability. In this context, it has initiated one pilot studies which aims to assess the effects of biochar application on physical and chemical properties of agricultural soil under Mediterranean conditions, such as changes in aggregate formation, intra-aggregate carbon sequestration and chemistry of soil water. In the present study, different clases of biochar produced from fast, slow and gasification pyrolisis of vegetal (pine, poplar) and dried sludge biomass, were applied at 1% of biochar-C to mesocosmos of an agricultural soil. Preliminary, it must be pointed out that slow and gasification pyrolisis changes the proportion of particles < 2 mm in diameter, from 10% (original materials) to almost 100%. In contrast, slow pyrolisis not modifies significantly biochar granulometry. As a consequence, bulk density of poplar and pine splinters decreases after fast pyrolisis. Regarding to organic carbon contents of biochar, all biochars obtained from plant biomass presented percentagens of total organic carbon (TOC) between 70 - 90%, while biochar obtained from dried sludge by slow pyrolisis has a TOC around of 22%. On the other hand, pH values of biochar depends of the type of pyrolisis as observed in the biochar obtained from poplar biomass, where pH of slow pyrolisis < fast pyrolisis < gasification pyrolisis. When soil aggregate stability was tested, it was observed that biochars from pine biomass obtained by slow and fast pyrolisis trend to increase the water-stable soil aggregates, while the biochars from poplar and thermally-dreid sludge obtained by slow pyrolisis and from pine biomass obtained by gasification trend to the contrary. These differences were not explained by TOC contents or bulk density of bichars, probably because specific resistence to slaking and wettability of each biochar. At least, when measuring pH values of water where soil aggregates were immersed during soil aggregate stability test, it was observed that biochars from thermally-dried sludge obtained by slow pyrolisis and from pine biomass obtained by gasification pyrolisis increased water pH, which corresponded with high pH values of both biochars. In general, increases in the percentage of water-stable soil aggregates corresponded with increases in water pH values, except in the case of biochar from pine biomass obtained by slow pyrolisis.

Variations in organic carbon, aggregation, and enzyme activities of gangue-fly ash-reconstructed soils with sludge and arbuscular mycorrhizal fungi during 6-year reclamation.

PubMed

Yin, Ningning; Zhang, Zhen; Wang, Liping; Qian, Kuimei

2016-09-01

Mining activities can cause drastic disturbances in soil properties, which adversely affect the nutrient cycling and soil environment. As a result, many efforts have been made to explore suitable reclamation strategies that can be applied to accelerate ecology restoration. In this study, we reconstructed mine soils with fly ash, gangue, sludge, planted ryegrass, and inoculated arbuscular mycorrhizal fungi (AMF) in Pangzhuang mine of Xuzhou during 2009 to 2015. The soil aggregation process, enzyme activities (i.e., invertase, urease and acid phosphatase activities), soil organic carbon (SOC) as well as other soil nutrients such as nitrogen, phosphorus, and potassium contents of the reconstructed mine soils were monitored during 6-year reclamation. The integrated application of sludge and AMF led to a promising reclamation performance of mining areas, in which soil aggregate stability, enzyme activities, SOC, and ryegrass biomass were effectively enhanced. The micro-aggregates (< 0.25 mm) decreased with the increase of macro-aggregates (> 0.25 mm) during the reclamation, indicating that macro-aggregates were gradually formed from micro-aggregates during the pedogenesis of reconstructed mine soils. The correlation analysis shows that SOC contents in aggregate fraction of 0.25∼0.5 mm were correlated with aggregate distribution and enzyme activities. Enzyme activities, however, were not significantly correlated with aggregate distribution. The outcomes from the present study could enrich our understanding on soil property changes in pedogenesis process of reconstructed mine soils, and meanwhile, the employment of sludge combined with AMF is suggested to be an effective alternative for the mine soil reclamation.

Particle size, charge and colloidal stability of humic acids coprecipitated with Ferrihydrite.

PubMed

Angelico, Ruggero; Ceglie, Andrea; He, Ji-Zheng; Liu, Yu-Rong; Palumbo, Giuseppe; Colombo, Claudio

2014-03-01

Humic acids (HA) have a colloidal character whose size and negative charge are strictly dependent on surface functional groups. They are able to complex large amount of poorly ordered iron (hydr)oxides in soil as a function of pH and other environmental conditions. Accordingly, with the present study we intend to assess the colloidal properties of Fe(II) coprecipitated with humic acids (HA) and their effect on Fe hydroxide crystallinity under abiotic oxidation and order of addition of both Fe(II) and HA. TEM, XRD and DRS experiments showed that Fe-HA consisted of Ferrihydrite with important structural variations. DLS data of Fe-HA at acidic pH showed a bimodal size distribution, while at very low pH a slow aggregation process was observed. Electrophoretic zeta-potential measurements revealed a negative surface charge for Fe-HA macromolecules, providing a strong electrostatic barrier against aggregation. Under alkaline conditions HA chains swelled, which resulted in an enhanced stabilization of the colloid particles. The increasing of zeta potential and size of the Fe-HA macromolecules, reflects a linear dependence of both with pH. The increase in the size and negative charge of the Fe-HA precipitate seems to be more affected by the ionization of the phenolic acid groups, than by the carboxylic acid groups. The main cause of negative charge generation of Fe/HA is due to increased dissociation of phenolic groups in more expanded structure. The increased net negative surface potential induced by coprecipitation with Ferrihydrite and the correspondent changes in configuration of the HA could trigger the inter-particle aggregation with the formation of new negative surface. The Fe-HA coprecipitation can reduce electrosteric repulsive forces, which in turn may inhibit the aggregation process at different pH. Therefore, coprecipitation of Ferrihydrite would be expected to play an important role in the carbon stabilization and persistence not only in organic soils, but also in waters containing dissolved organic matter. Copyright © 2013 Elsevier Ltd. All rights reserved.

Assessing Soil Organic C Stability at the Continental Scale: An Analysis of Soil C and Radiocarbon Profiles Across the NEON Sites

NASA Astrophysics Data System (ADS)

Heckman, K. A.; Gallo, A.; Hatten, J. A.; Swanston, C.; McKnight, D. M.; Strahm, B. D.; Sanclements, M.

2017-12-01

Soil carbon stocks have become recognized as increasingly important in the context of climate change and global C cycle modeling. As modelers seek to identify key parameters affecting the size and stability of belowground C stocks, attention has been drawn to the mineral matrix and the soil physiochemical factors influenced by it. Though clay content has often been utilized as a convenient and key explanatory variable for soil C dynamics, its utility has recently come under scrutiny as new paradigms of soil organic matter stabilization have been developed. We utilized soil cores from a range of National Ecological Observatory Network (NEON) experimental plots to examine the influence of physicochemical parameters on soil C stocks and turnover, and their relative importance in comparison to climatic variables. Soils were cored at NEON sites, sampled by genetic horizon, and density separated into light fractions (particulate organics neither occluded within aggregates nor associated with mineral surfaces), occluded fractions (particulate organics occluded within aggregates), and heavy fractions (organics associated with mineral surfaces). Bulk soils and density fractions were measured for % C and radiocarbon abundance (as a measure of C stability). Carbon and radiocarbon abundances were examined among fractions and in the context of climatic variables (temperature, precipitation, elevation) and soil physiochemical variables (% clay and pH). No direct relationships between temperature and soil C or radiocarbon abundances were found. As a whole, soil radiocarbon abundance in density fractions decreased in the order of light>heavy>occluded, highlighting the importance of both surface sorption and aggregation to the preservation of organics. Radiocarbon abundance was correlated with pH, with variance also grouping by dominate vegetation type. Soil order was also identified as an important proxy variable for C and radiocarbon abundance. Preliminary results suggest that both integrative proxies as well as physicochemical properties may be needed to account for variation in soil C abundance and stability at the continental scale.

Surface roughness and runoff

NASA Astrophysics Data System (ADS)

Szabó, Judit Alexandra; Szabó, Boglárka; Centeri, Csaba; Józsa, Sándor; Szalai, Zoltán; Jakab, Gergely

2017-04-01

Soil surface conditions changes dynamically during a precipitation event. The changes involve compaction, aggregate detachment and of course transportation by runoff or drop erosion. Those processes together have an effect on the transport process of the soil particles and aggregates, and influences the roughness of the soil surface as well. How does surface roughness have an effect on the aggregate and particle size distribution of the sediment? How does the sediment connectivity change from precipitation event to precipitation event? Beside the previous questions on of the main aim of the present research is to apply rainfall simulators for the built-up of a complex approach, rather than to concentrate only on one of two factors. Hence four types of sample were collected during the simulation experiment sequences: 1) photos were taken about the surface before and after the rain, in order to build digital surface models; 2) all the runoff and eroded sediment was collected; 3) soil loss due to drop erosion was also sampled separately; and 4) undisturbed crust samples were collected for thin section analyses. Though the runoff ratio was smaller than what, the preliminary results suggest that the sediment connectivity covered bigger area on crusty surface, than on a rough one. These ambiguous data may be connected to the soil crust development. J. A. Szabó wish to acknowledge the support of NTP-NFTÖ-16-0203. G. Jakab wish to acknowledge the support of János Bolyai Fellowship.

Linking plants, fungi and soil mechanics

NASA Astrophysics Data System (ADS)

Yildiz, Anil; Graf, Frank

2017-04-01

Plants provide important functions in respect soil strength and are increasingly considered for slope stabilisation within eco-engineering methods, particularly to prevent superficial soil failure. The protective functions include hydrological regulation through interception and evapo-transpiration as well as mechanical stabilisation through root reinforcement and, to a certain extent, chemical stabilisation through sticky metabolites. The ever-growing application of plants in slope stabilisation demanded more precise information of the vegetation effects and, concomitant, led the models for quantifying the reinforcement shoot up like mushrooms. However, so far, the framework and interrelationships for both the role of plants and the quantification concepts have not been thoroughly analysed and comprehensively considered, respectively, often resulting in unsatisfactory results. Although it seems obvious and is implicitly presupposed that the plant specific functions related to slope stability require growth and development, this is anything but given, particularly under the often hostile conditions dominating on bare and steep slopes. There, the superficial soil layer is often characterised by a lack of fines and missing medium-sized and fine pores due to an unstable soil matrix, predominantly formed by coarse grains. Low water retention capacity and substantial leaching of nutrients are the adverse consequences. Given this general set-up, sustainable plant growth and, particularly, root development is virtually unachievable. At exactly this point mycorrhizal fungi, the symbiotic partners of almost all plants used in eco-engineering, come into play. Though, they are probably well-known within the eco-engineering community, mycorrhizal fungi lead a humble existence. This is in spite of the fact that they supply their hosts with water and nutrients, improving the plant's ability to master otherwise unbridgeable environmental conditions. However, in order to support their plant partners, the fungi themselves need to have access to water and nutrients. For this purpose, a resilient soil matrix consisting of stable micro- and macro-aggregates is an indispensable prerequisite. Luckily, the fungi are among the pioneers in assembling stable aggregates. The fungal hyphae intensively penetrate the unstructured soil body, enmeshing small organic and inorganic soil particles and form and cement them to micro- and macro-aggregates. On the one hand, growing hyphae are able to align primary particles and, on the other hand, exert pressure on surrounding particles and compounds forcing them together, such as clay and organic matter. Under physiological (or neutral) pH values, the fungal mycelia have a net negative charge. It is suggested that negatively charged fungal polysaccharides are bound to negatively charged clay minerals by bridges of polyvalent cations which have been proven to be stronger than some direct bonds between clay and organic matter. The formation of aggregates up to a size of 2 mm is associated with hyphal length of fungi. With regard to the assemblage of aggregates >2 mm both fungal mycelia and roots are involved. Indirectly, the mycorrhizal fungi affect the aggregate establishment through their host plants, particularly by accelerating the development of their root network and by serving as a distribution vector for associated micro-organisms, mainly bacteria and archaea, additionally contributing to cementation. Therefore, root-reinforcement as addressed for quantification of vegetation effects on slope stability almost ever is a combined contribution of fungal mycelia and root networks. With soil aggregates as the "bricks" for building a stable soil matrix and pore structure, root-reinforcement strongly depends on aggregate strength controlling potential, efficiency, and sustainability of growth and development of the protective vegetation. From a geotechnical point of view, aggregation of fines may be such pronounced that characteristics of coarse-grained soils are adopted, often mirrored by higher values of the shear strength parameters, particularly the angle of internal friction Φ'. Consequently, neither the positive relationship between the strength of soil aggregates and slope stability is astonishing nor is the positive correlation between root characteristics - architecture represented by 3D-complexity, specific length and its density - and factor of safety calculations related to superficial soil failure. As far as the latter is concerned, however, so far almost exclusively the common shear strength parameters have been considered, namely angle of internal friction Φ' and root cohesion c'. However, similarly to the way fungi were ignored in biological slope stabilisation, the soil mechanically relevant parameter dilatancy (Ψ) was not in the concepts and modelling approaches for quantifying root-reinforcement. Nevertheless, dilatancy (Ψ) is an important mechanism and a contributing factor to the shearing behaviour of root-permeated soil that definitively cannot be ignored. Such evidence is soundly based on the fact that specific root characteristics combined with the maximum dilatancy angle (Ψmax) can explain the most variation in peak shear strength parameters. Therefore, a combined approach including soil, fungi, and roots under consideration of dilatancy is a promising way towards better understanding and more reliably quantifying the shear strength of root-permeated soil. Since sound quantification of biological stabilisation effects is the key for both sustainable slope stabilisation and wide acceptance of eco-engineering measures within the scope of risk and hazard prevention.

[Fractal features of soil aggregate structure in slope farmland with different de-farming patterns in South Sichuan Province of China].

PubMed

Wang, Jing-Yan; Hu, Ting-Xing; Gong, Wei; Gong, Yuan-Bo; Luo, Cheng-De

2010-06-01

By using fractal model, this paper studied the fractal dimension of soil aggregate structure (D) in the slope farmland (CK), its 5-year de-farmed Neosinocalamus affinis plantation (NAP), Bambusa pervariabilis x Dendrocalamopsis oldhami plantation (BDP), Alnus crenastogyne + Neosinocalamus affinis plantation (ANP), and abandoned farmland (AFL) in south Sichuan Province of China, and analyzed the relationships between the D and soil physical and chemical properties. In the de-farmed plantations and abandoned farmland, the contents of > 0.25 mm soil aggregates and water-stable aggregates were increased significantly, compared with those in the slope farmland. The D was 1.377-2.826, being in the order of NAP < BDP < ANP < AFL < CK, and decreased with the increasing contents of > 0.25 mm soil aggregates and water-stable aggregates. Comparing with CK, de-farming increased the soil natural water content, capillary porosity, and contents of soil organic matter, total N, alkali-hydrolysable N, total P, and total K, and decreased soil bulk density, non-capillary porosity, and aeration porosity. There were close relationships between the fractal dimension of soil aggregate structure and the soil physical and chemical properties. All the results suggested that the de-farming of slope farmland was beneficial to the increase of the contents of > 0.25 mm soil aggregates and water-stable aggregates, and the enhancement of soil structure stability. The D could be used as an ideal index to evaluate soil fertility, and planting Neosinocalamus affinis on the de-farming slope farmland was a good measure for the improvement of soil fertility in the research area.

Method for analyzing soil structure according to the size of structural elements

NASA Astrophysics Data System (ADS)

Wieland, Ralf; Rogasik, Helmut

2015-02-01

The soil structure in situ is the result of cropping history and soil development over time. It can be assessed by the size distribution of soil structural elements such as air-filled macro-pores, aggregates and stones, which are responsible for important water and solute transport processes, gas exchange, and the stability of the soil against compacting and shearing forces exerted by agricultural machinery. A method was developed to detect structural elements of the soil in selected horizontal slices of soil core samples with different soil structures in order for them to be implemented accordingly. In the second step, a fitting tool (Eureqa) based on artificial programming was used to find a general function to describe ordered sets of detected structural elements. It was shown that all the samples obey a hyperbolic function: Y(k) = A /(B + k) , k ∈ { 0 , 1 , 2 , … }. This general behavior can be used to develop a classification method based on parameters {A and B}. An open source software program in Python was developed, which can be downloaded together with a selection of soil samples.

The effect of operating conditions on the performance of soil slurry-SBRs.

PubMed

Cassidy, D P; Irvine, R L

2001-01-01

Biological treatment of a silty clay loam with aged diesel fuel contamination was conducted in 8 L Soil Slurry-Sequencing Batch Reactors (SS-SBRs). The purpose was to monitor slurry conditions and evaluate reactor performance for varying solids concentration (5%, 25%, 40%, 50%), mixing speed (300 rpm, 700 rpm, 1200 rpm), retention time (8 d, 10 d, 20 d), and volume replaced per cycle (10%, 50%, 90%). Diesel fuel was measured in slurry and in filtered aqueous samples. Oxygen uptake rate (OUR) was monitored. Aggregate size was measured with sieve analyses. Biosurfactant production was quantified with surface tension measurements. Increasing solids concentration and decreasing mixing speed resulted in increased aggregate size, which in turn increased effluent diesel fuel concentrations. Diesel fuel removal was unaffected by retention time and volume replaced per cycle. Biosurfactant production occurred with all operating strategies. Foam thickness was related to surfactant concentration and mixing speed. OUR, surfactant concentration, and foam thickness increased with increasing diesel fuel added per cycle.

Effect of sulfate and carbonate minerals on particle-size distributions in arid soils

USGS Publications Warehouse

Goossens, Dirk; Buck, Brenda J.; Teng, Yuazxin; Robins, Colin; Goldstein, Harland L.

2014-01-01

Arid soils pose unique problems during measurement and interpretation of particle-size distributions (PSDs) because they often contain high concentrations of water-soluble salts. This study investigates the effects of sulfate and carbonate minerals on grain-size analysis by comparing analyses in water, in which the minerals dissolve, and isopropanol (IPA), in which they do not. The presence of gypsum, in particular, substantially affects particle-size analysis once the concentration of gypsum in the sample exceeds the mineral’s solubility threshold. For smaller concentrations particle-size results are unaffected. This is because at concentrations above the solubility threshold fine particles cement together or bind to coarser particles or aggregates already present in the sample, or soluble mineral coatings enlarge grains. Formation of discrete crystallites exacerbates the problem. When soluble minerals are dissolved the original, insoluble grains will become partly or entirely liberated. Thus, removing soluble minerals will result in an increase in measured fine particles. Distortion of particle-size analysis is larger for sulfate minerals than for carbonate minerals because of the much higher solubility in water of the former. When possible, arid soils should be analyzed using a liquid in which the mineral grains do not dissolve, such as IPA, because the results will more accurately reflect the PSD under most arid soil field conditions. This is especially important when interpreting soil and environmental processes affected by particle size.

Influence of the individual or combined application of biochar and slurry on soil macro-aggregate formation under varying moisture conditions

NASA Astrophysics Data System (ADS)

Kaiser, Michael; Grunwald, Dennis; Koch, Heinz-Josef; Rauber, Rolf; Ludwig, Bernard

2017-04-01

The formation of aggregates is of large importance for the structure and the storage of organic matter (OM) in soil. Although positive effects of organic soil additives on the formation of macro-aggregates (> 250 µm) have been reported, the influence of biochar especially applied in combination with other organic amendments remains unclear. Furthermore, studies on the effect of varying soil moisture conditions in form of drying-rewetting cycles on soil aggregate dynamics in the presence of biochar are almost missing. The objectives of this study were to analyze the effects of biochar and slurry applied to the soil individually or in combination on the formation of macro-aggregates under constant and under varying moisture conditions. We sampled four silty loam soils, carefully crushed the soil macro-aggregates, and incubated the soil at 15 °C for 60 days with the following additions: (i) none (control), (ii) biochar (12 % of dry soil mass), (iii) slurry (150 kg N ha-1), (iv) biochar (6 %) + slurry (75 kg N ha-1), (v) biochar (12 %) + slurry (75 kg N ha-1), (vi) biochar (6 %) + slurry (150 kg N ha-1) and (vii) biochar (12 %) + slurry (150 kg N ha-1). The samples were further subdivided into two groups that were incubated under conditions of constant soil moisture and of three drying-rewetting cycles. The CO2 fluxes were continuously measured during the incubation period and the samples were analyzed for microbial biomass C, macro-aggregate yields and macro-aggregate-associated C after finishing the experiment. We found the application of biochar to result in lower macro-aggregate yields with or without slurry compared to the control or the individual slurry application. In contrast, similar or higher C contents in the macro-aggregate fraction of the biochar treatments as compared to the control or slurry treatments were found indicating an occlusion of biochar in macro-aggregates. Due to the sorption characteristics of biochar, we assume the aggregate formation to be partially abiotic with direct interactions between biochar, (adsorbed) slurry, and the mineral phase of the soil. Therefore, in the presence of slurry, a prolonged period of microbial processing does not seem to be necessary to render the biochar suitable to form aggregates. Drying and rewetting of the samples resulted in significantly lower aggregate yields especially for the biochar/slurry mixtures. The drying of slurry as thought to be the most important macro-aggregate binding agent in these treatments might irreversibly disrupt large amounts of the macro-aggregates formed. Additionally, the general lower microbial biomass C and CO2 emissions for the samples experiencing drying-rewetting cycles compared to the constantly moist soils point toward less microbial activity under varying moisture conditions. This might have led to less microbial derived aggregate binding agents contributing to the lower aggregate yields found for the samples from the drying-rewetting treatments. Beside the amount and type of binding agents derived from organic soil additives, the formation and stability of soil macro-aggregate seem also to be controlled by climatically controlled soil moisture conditions.

[Effects of different tillage patterns on soil properties, maize yield and water use efficiency in Weibei Highland, China.

PubMed

Liu, Dan; Zhang, Xia; Li, Jun; Wang, Xu-Dong

2018-02-01

An eight-year field experiment of straw returning was conducted on dark loessial soil in Weibei Highland to investigate the effects of tillage patterns on soil aggregate, soil organic carbon (SOC), corn yield and soil water use efficiency (WUE). There were six tillage patterns, including conventional tillage (CT/CT), no-tillage (NT/NT), subsoiling tillage (ST/ST), no-tillage/subsoiling tillage (NT/ST), conventional tillage/no-tillage (CT/NT) and conventional tillage/subsoiling tillage (CT/ST). The results showed that compared with CT/CT, the patterns of NT/NT, ST/ST and the rotational tillage patterns (NT/ST, CT/NT and CT/ST) decreased the mean mass diameter of soil mechanical stable aggregate. The patterns of NT/NT, ST/ST and NT/ST increased the content of soil water-stable aggregate with the particle size >0.25 mm (WR 0.25 ) and their mean mass diameter, especially in the depth of 20-50 cm. These patterns reduced the proportion of aggregate destruction (PAD). Compared with CT/CT, the patterns of NT/ST, CT/NT, NT/NT and ST/ST increased the content of SOC in 0-10 cm soil layer. The content of SOC decreased as the increases of soil depth for all tillage patterns, but the decrease in SOC of three single tillage patterns (ST/ST, NT/NT and CT/CT) was larger than that of three rotational tillage patterns. Compared with CT/CT, the other five tillage patterns increased soil water storage in 0-200 cm soil profile, crop yield and WUE in maize. The yield and WUE in NT/ST pattern were significantly increased by 15.1% and 27.5%, respectively. Both corn yield and WUE were significantly and positively correlated with soil water storage in 0-200 cm soil profile in field during the cropping and fallow periods. Moreover, soil water storage during the cropping period was positively correlated with WR 0.25 , but negatively correlated with PAD in 0-50 cm soil layer. Particularly, maize yield, WUE and soil water storage during the cropping period were closely related to WR 0.25 in 20-50 cm soil layer and PAD. Both WUE and soil water storage during the cropping period was correlated with the SOC content in 0-10 cm soil layer. With respect to the soil properties, crop yield and WUE, the tillage pattern of NT/ST was the best stratety in dark loessial soil for spring maize growth in Weibei Highland.

Morphological classification of bioaerosols from composting using scanning electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamer Vestlund, A.; FIRA International Ltd., Maxwell Road, Stevenage, Herts SG1 2EW; Al-Ashaab, R.

2014-07-15

Highlights: • Bioaerosols were captured using the filter method. • Bioaerosols were analysed using scanning electron microscope. • Bioaerosols were classified on the basis of morphology. • Single small cells were found more frequently than aggregates and larger cells. • Smaller cells may disperse further than heavier aggregate structures. - Abstract: This research classifies the physical morphology (form and structure) of bioaerosols emitted from open windrow composting. Aggregation state, shape and size of the particles captured are reported alongside the implications for bioaerosol dispersal after release. Bioaerosol sampling took place at a composting facility using personal air filter samplers. Samplesmore » were analysed using scanning electron microscopy. Particles were released mainly as small (<1 μm) single, spherical cells, followed by larger (>1 μm) single cells, with aggregates occurring in smaller proportions. Most aggregates consisted of clusters of 2–3 particles as opposed to chains, and were <10 μm in size. No cells were attached to soil debris or wood particles. These small single cells or small aggregates are more likely to disperse further downwind from source, and cell viability may be reduced due to increased exposure to environmental factors.« less

Synchrotron Microtomographic Quantification of Geometrical Soil Pore Characteristics Affected by Compaction

NASA Astrophysics Data System (ADS)

Udawatta, Ranjith; Gantzer, Clark; Anderson, Stephen; Assouline, Shmuel

2015-04-01

Soil compaction degrades soil structure and affects water, heat, and gas exchange as well as root penetration and crop production. The objective of this study was to use X-ray computed microtomography (CMT) techniques to compare differences in geometrical soil pore parameters as influenced by compaction of two different aggregate size classes. Sieved (diam. < 2mm and < 0.5mm) and repacked (1.51 and 1.72 Mg m-3) Hamra soil cores of 5- by 5-mm (average porosities were 0.44 and 0.35) were imaged at 9.6-micrometer resolution at the Argonne Advanced Photon Source (synchrotron facility) using X-ray computed microtomography. Images of 58.9 mm3 volume were analyzed using 3-Dimensional Medial Axis (3DMA) software. Geometrical characteristics of the spatial distributions of pore structures (pore radii, volume, connectivity, path length, and tortuosity) were numerically investigated. Results show that the coordination number (CN) distribution and path length (PL) measured from the medial axis were reasonably fit by exponential relationships P(CN)=10-CN/Co and P(PL)=10-PL/PLo, respectively, where Co and PLo are the corresponding characteristic constants. Compaction reduced porosity, average pore size, number of pores, and characteristic constants. The average pore radii (64 and 61 μm; p<0.04), largest pore volume (1.6 and 0.6 mm3; p=0.06), number of pores (55 and 50; p=0.09), characteristic coordination number (6.3 and 6.0; p=0.09), and characteristic path length number (116 and 105; p=0.001) were significantly greater in the low density than the high density treatment. Aggregate size also influenced measured geometrical pore parameters. This analytical technique provides a tool for assessing changes in soil pores that affect hydraulic properties and thereby provides information to assist in assessment of soil management systems.

Synchrotron microtomographic quantification of geometrical soil pore characteristics affected by compaction

NASA Astrophysics Data System (ADS)

Udawatta, R. P.; Gantzer, C. J.; Anderson, S. H.; Assouline, S.

2015-07-01

Soil compaction degrades soil structure and affects water, heat, and gas exchange as well as root penetration and crop production. The objective of this study was to use X-ray computed microtomography (CMT) techniques to compare differences in geometrical soil pore parameters as influenced by compaction of two different aggregate size classes. Sieved (diam. < 2 mm and < 0.5 mm) and repacked (1.51 and 1.72 Mg m-3) Hamra soil cores of 5- by 5 mm (average porosities were 0.44 and 0.35) were imaged at 9.6-micrometer resolution at the Argonne Advanced Photon Source (synchrotron facility) using X-ray computed microtomography. Images of 58.9 mm3 volume were analyzed using 3-Dimensional Medial Axis (3DMA) software. Geometrical characteristics of the spatial distributions of pore structures (pore radii, volume, connectivity, path length, and tortuosity) were numerically investigated. Results show that the coordination number (CN) distribution and path length (PL) measured from the medial axis were reasonably fit by exponential relationships P(CN) = 10-CN/Co and P(PL) = 10-PL/PLo, respectively, where Co and PLo are the corresponding characteristic constants. Compaction reduced porosity, average pore size, number of pores, and characteristic constants. The average pore radii (63.7 and 61 μm; p < 0.04), largest pore volume (1.58 and 0.58 mm3; p = 0.06), number of pores (55 and 50; p = 0.09), characteristic coordination number (6.32 and 5.94; p = 0.09), and characteristic path length number (116 and 105; p = 0.001) were significantly greater in the low density than the high density treatment. Aggregate size also influenced measured geometrical pore parameters. This analytical technique provides a tool for assessing changes in soil pores that affect hydraulic properties and thereby provides information to assist in assessment of soil management systems.

The potential of arbuscular mycorrhizal fungi application on aggregrate stability in alfisol soil

NASA Astrophysics Data System (ADS)

Syamsiyah, J.; Herawati, A.; Mujiyo

2018-03-01

The aim of this study was to determine the soil aggregate stability and its relationship with another variable in alfisol. The research used completely randomized design with four treatments: two sterilization levels (no sterilization and with sterilization) and two levels of mycorrhizal inoculation (no mycorrhizal and with mycorrhizal). Mycorrhizal (5 grams/pot) was inoculated before planting rice seeds. The soil aggregate stability was measured by wet-sieving and turbidimetric measurements. The results showed that soil aggregate stability was higher in mycorrhizal inoculated than non-mycorrhizal inoculated treatment, by 5% in sterilization soil and 3.2% in non-sterilization soil. The correlation analysis indicated that soil aggregate stability has a tight relationship with spore population, total glomalin, available glomalin, dry weight, tiller number of plant, and soil organic C. Inoculation of mycorrhizal contributed to stabilize soil aggregates in alfisol

Seasonal variability of soil aggregate stability

NASA Astrophysics Data System (ADS)

Rohoskova, M.; Kodesova, R.; Jirku, V.; Zigova, A.; Kozak, J.

2009-04-01

Seasonal variability of soil properties measured in surface horizons of three soil types (Haplic Luvisol, Greyic Phaeozem, Haplic Cambisol) was studied in years 2007 and 2008. Undisturbed and disturbed soil samples were taken every month to evaluate field water content, bulk density, porosity, ration of gravitational and capillary pores, pHKCl and pHH2O, organic matter content and its quality, aggregate stability using WSA index. In addition, micromorphological features of soil aggregates were studied in thin soil sections that were made from undisturbed large soil aggregates. Results showed that soil aggregate stability depended on stage of the root zone development, soil management and climatic conditions. Larger aggregate stabilities and also larger ranges of measure values were obtained in the year 2007 then those measured in 2008. This was probably caused by lower precipitations and consequently lower soil water contents observed in 2007 than those measured in 2008. The highest aggregate stability was measured at the end of April in the years 2007 and 2008 in Haplic Luvisol and Greyic Phaeozem, and at the end of June in the year 2007 and at the beginning of June in 2008 in Haplic Cambisol. In all cases aggregate stability increased during the root growth and then gradually decreased due to summer rainfall events. Aggregate stability reflected aggregate structure and soil pore system development, which was documented on micromorphological images and evaluated using the ration of gravitational and capillary pores measured on the undisturbed sol samples. Acknowledgement: Authors acknowledge the financial support of the Grant Agency of the Czech Republic grant No. 526/08/0434, and the Ministry of Education, Youth and Sports grant No. MSM 6046070901.

Infiltration Variability in Agricultural Soil Aggregates Caused by Air Slaking

NASA Astrophysics Data System (ADS)

Korenkova, L.; Urik, M.

2018-04-01

This article reports on variation in infiltration rates of soil aggregates as a result of phenomenon known as air slaking. Air slaking is caused by the compression and subsequent escape of air captured inside soil aggregates during water saturation. Although it has been generally assumed that it occurs mostly when dry aggregates are rapidly wetted, the measurements used for this paper have proved that it takes place even if the wetting is gradual, not just immediate. It is a phenomenon that contributes to an infiltration variability of soils. In measuring the course of water flow through the soil, several small aggregates of five agricultural soils were exposed to distilled water at zero tension in order to characterize their hydraulic properties. Infiltration curves obtained for these aggregates demonstrate the effect of entrapped air on the increase and decrease of infiltration rates. The measurements were performed under various moisture conditions of the A-horizon aggregates using a simple device.

Geotechnical Characteristics and Stability Analysis of Rock-Soil Aggregate Slope at the Gushui Hydropower Station, Southwest China

PubMed Central

Shi, Chong; Xu, Fu-gang

2013-01-01

Two important features of the high slopes at Gushui Hydropower Station are layered accumulations (rock-soil aggregate) and multilevel toppling failures of plate rock masses; the Gendakan slope is selected for case study in this paper. Geological processes of the layered accumulation of rock and soil particles are carried out by the movement of water flow; the main reasons for the toppling failure of plate rock masses are the increasing weight of the upper rock-soil aggregate and mountain erosion by river water. Indoor triaxial compression test results show that, the cohesion and friction angle of the rock-soil aggregate decreased with the increasing water content; the cohesion and the friction angle for natural rock-soil aggregate are 57.7 kPa and 31.3° and 26.1 kPa and 29.1° for saturated rock-soil aggregate, respectively. The deformation and failure mechanism of the rock-soil aggregate slope is a progressive process, and local landslides will occur step by step. Three-dimensional limit equilibrium analysis results show that the minimum safety factor of Gendakan slope is 0.953 when the rock-soil aggregate is saturated, and small scale of landslide will happen at the lower slope. PMID:24082854

Geotechnical characteristics and stability analysis of rock-soil aggregate slope at the Gushui Hydropower Station, southwest China.

PubMed

Zhou, Jia-wen; Shi, Chong; Xu, Fu-gang

2013-01-01

Two important features of the high slopes at Gushui Hydropower Station are layered accumulations (rock-soil aggregate) and multilevel toppling failures of plate rock masses; the Gendakan slope is selected for case study in this paper. Geological processes of the layered accumulation of rock and soil particles are carried out by the movement of water flow; the main reasons for the toppling failure of plate rock masses are the increasing weight of the upper rock-soil aggregate and mountain erosion by river water. Indoor triaxial compression test results show that, the cohesion and friction angle of the rock-soil aggregate decreased with the increasing water content; the cohesion and the friction angle for natural rock-soil aggregate are 57.7 kPa and 31.3° and 26.1 kPa and 29.1° for saturated rock-soil aggregate, respectively. The deformation and failure mechanism of the rock-soil aggregate slope is a progressive process, and local landslides will occur step by step. Three-dimensional limit equilibrium analysis results show that the minimum safety factor of Gendakan slope is 0.953 when the rock-soil aggregate is saturated, and small scale of landslide will happen at the lower slope.

Intra-aggregate CO2 enrichment: a modelling approach for aerobic soils

NASA Astrophysics Data System (ADS)

Schlotter, D.; Schack-Kirchner, H.

2013-02-01

CO2 concentration gradients inside soil aggregates, caused by the respiration of soil microorganisms and fungal hyphae, might lead to variations in the soil solution chemistry on a mm-scale, and to an underestimation of the CO2 storage. But, up to now, there seems to be no feasible method for measuring CO2 inside natural aggregates with sufficient spatial resolution. We combined a one-dimensional model for gas diffusion in the inter-aggregate pore space with a cylinder diffusion model, simulating the consumption/production and diffusion of O2 and CO2 inside soil aggregates with air- and water-filled pores. Our model predicts that for aerobic respiration (respiratory quotient = 1) the intra-aggregate increase in the CO2 partial pressure can never be higher than 0.9 kPa for siliceous, and 0.1 kPa for calcaric aggregates, independent of the level of water-saturation. This suggests that only for siliceous aggregates CO2 produced by aerobic respiration might cause a high small-scale spatial variability in the soil solution chemistry. In calcaric aggregates, however, the contribution of carbonate species to the CO2 transport should lead to secondary carbonates on the aggregate surfaces. As regards the total CO2 storage in aerobic soils, both siliceous and calcaric, the effect of intra-aggregate CO2 gradients seems to be negligible. To assess the effect of anaerobic respiration on the intra-aggregate CO2 gradients, the development of a device for measuring CO2 on a mm-scale in soils is indispensable.

Simulating root-induced rhizosphere deformation and its effect on water flow

NASA Astrophysics Data System (ADS)

Aravena, J. E.; Ruiz, S.; Mandava, A.; Regentova, E. E.; Ghezzehei, T.; Berli, M.; Tyler, S. W.

2011-12-01

Soil structure in the rhizosphere is influenced by root activities, such as mucilage production, microbial activity and root growth. Root growth alters soil structure by moving and deforming soil aggregates, affecting water and nutrient flow from the bulk soil to the root surface. In this study, we utilized synchrotron X-ray micro-tomography (XMT) and finite element analysis to quantify the effect of root-induced compaction on water flow through the rhizosphere to the root surface. In a first step, finite element meshes of structured soil around the root were created by processing rhizosphere XMT images. Then, soil deformation by root expansion was simulated using COMSOL Multiphysics° (Version 4.2) considering the soil an elasto-plastic porous material. Finally, fluid flow simulations were carried out on the deformed mesh to quantify the effect of root-induced compaction on water flow to the root surface. We found a 31% increase in water flow from the bulk soil to the root due to a 56% increase in root diameter. Simulations also show that the increase of root-soil contact area was the dominating factor with respect to the calculated increase in water flow. Increase of inter-aggregate contacts in size and number were observed within a couple of root diameters away from the root surface. But their influence on water flow was, in this case, rather limited compared to the immediate soil-root contact.

Texture-contrast profile development across the prairie-forest ecotone in northern Minnesota, USA, and its relation to soil aggregation and clay dispersion.

NASA Astrophysics Data System (ADS)

Kasmerchak, C. S.; Mason, J. A.

2016-12-01

Along the prairie-forest ecotone, Alfisols with distinct clay-enriched B horizons are found under forest, established only within the past 4 ka, including outlying patches of prairie groves surrounded by prairie. Grassland soils only 5-10 km away from the vegetation boundary show much weaker texture-contrast. In order for clay to be dispersed it must first be released from aggregates upper horizons, which occurs when exposed top soil undergoes wetting and mechanical stress. The relationship between physiochemical soil characteristics and soil aggregation/clay dispersion is of particular interest in explaining texture-contrast development under forest. Soil samples were collected along a transect in northern Minnesota on gentle slopes in similar glacial sediment. Aggregate stability experiments show Mollisol A and B horizons have the most stable aggregates, while Alfisol E horizons have the weakest aggregates and disintegrate rapidly. This demonstrates the strong influence of OM and exchange chemistry on aggregation. Analysis of other physiochemical soil characteristics such as base saturation and pH follow a gradual decreasing eastward trend across the study sites, and do not abruptly change at the prairie-forest boundary like soil morphology does. Linear models show the strongest relationship between rapid aggregate disintegration and ECEC, although they only explain 47-50% of the variance. Higher surface charge enhances aggregation by allowing for greater potential of cation bridging between OM and clay particles. ECEC also represents multiple soil characteristics such as OC, clay, mineralogy, and carbonate presence, suggesting the relationship between aggregation stability and soil characteristics is not simple. Given the parent material consists of calcareous glacial sediment, abundant Ca2+ and Mg2+ from carbonates weathering also contributes to enhanced aggregation in upper horizons. Differences in the rates of bioturbation, most likely also contribute differences in soil morphology, although this was not explored in this research.

Self-organizing biochemical cycle in dynamic feedback with soil structure

NASA Astrophysics Data System (ADS)

Vasilyeva, Nadezda; Vladimirov, Artem; Smirnov, Alexander; Matveev, Sergey; Tyrtyshnikov, Evgeniy; Yudina, Anna; Milanovskiy, Evgeniy; Shein, Evgeniy

2016-04-01

In the present study we perform bifurcation analysis of a physically-based mathematical model of self-organized structures in soil (Vasilyeva et al., 2015). The state variables in this model included microbial biomass, two organic matter types, oxygen, carbon dioxide, water content and capillary pore size. According to our previous experimental studies, organic matter affinity to water is an important property affecting soil structure. Therefore, organic matter wettability was taken as principle distinction between organic matter types in this model. It considers general known biological feedbacks with soil physical properties formulated as a system of parabolic type non-linear partial differential equations with elements of discrete modeling for water and pore formation. The model shows complex behavior, involving emergence of temporal and spatial irregular auto-oscillations from initially homogeneous distributions. The energy of external impact on a system was defined by a constant oxygen level on the boundary. Non-linear as opposed to linear oxygen diffusion gives possibility of modeling anaerobic micro-zones formation (organic matter conservation mechanism). For the current study we also introduced population competition of three different types of microorganisms according to their mobility/feeding (diffusive, moving and fungal growth). The strongly non-linear system was solved and parameterized by time-optimized algorithm combining explicit and implicit (matrix form of Thomas algorithm) methods considering the time for execution of the evaluated time-step according to accuracy control. The integral flux of the CO2 state variable was used as a macroscopic parameter to describe system as a whole and validation was carried out on temperature series of moisture dependence for soil heterotrophic respiration data. Thus, soil heterotrophic respiration can be naturally modeled as an integral result of complex dynamics on microscale, arising from biological processes formulated as a sum of state variables products, with no need to introduce any saturation functions, such as Mikhaelis-Menten type kinetics, inside the model. Analyzed dynamic soil model is being further developed to describe soil structure formation and its effect on organic matter decomposition at macro-scale, to predict changes with external perturbations. To link micro- and macro-scales we additionally model soil particles aggregation process. The results from local biochemical soil organic matter cycle serve as inputs to aggregation process, while the output aggregate size distributions define physical properties in the soil profile, these in turn serve as dynamic parameters in local biochemical cycles. The additional formulation is a system of non-linear ordinary differential equations, including Smoluchowski-type equations for aggregation and reaction kinetics equations for coagulation/adsorption/adhesion processes. Vasilyeva N.A., Ingtem J.G., Silaev D.A. Nonlinear dynamical model of microbial growth in soil medium. Computational Mathematics and Modeling, vol. 49, p.31-44, 2015 (in Russian). English version is expected in corresponding vol.27, issue 2, 2016.

Changes of Soil Aggregate C Isotopes in No-Till Corn Following Bromegrass.

NASA Astrophysics Data System (ADS)

Follett, R. F.; Varvel, G.; Vogel, K. P.

2007-12-01

This field study is near Ithaca, Nebraska, USA (lat. 41.151, long. 96.401) on a Filbert silt loam (fine, smectitic, mesic Vertic Argialboll). The site was in bromegrass since 1986. Corn was no-till seeded into the bromegrass sod in spring 1999. A randomized complete block design with three replicates was used. No-till corn was the main treatment with nitrogen (N) as subplots. N was broadcast at the start of each growing season at 60 or 120 kg N/ha as NH4NO3. Total biomass was measured by weighing 4.4 m of row in each plot. Soil samples were obtained in May 1999 (baseline sampling), Sept 1999, June 2000, Oct 2000, Sept 2001, Nov 2002, Sept 2003, and Oct 2005 from pre-selected areas by removal of plant material from the soil surface and removing the 0-5, 5- 10, and at 4 of the 8 harvests also sampling the 10-30 cm depths with a flat-bladed shovel. Soil bulk densities were determined on clods from each layer. The moist soil was passed through an 8 mm sieve before air drying and storing. Aggregate size fractions were obtained with a Yoder wet-aggregate method. Soil size fractions obtained were > 2, 1, 0.5, 0.25, 0.125, 0.045 and < 0.045 mm. Detritus was floated to the surface and skimmed off for transfer to a separate container. Aggregates were dried at 55°C, weighed, ground, and analyzed for total C and N and 13C:12C isotope ratio. Because soil organic carbon (SOC) was labeled with the bromegrass (C3 plant) isotope signature, then during the 77 months of this experiment the re-labeling of each fraction and the total SOC with the corn (C4 plant) isotope signature and the amounts of SOC lost from aggregate size fractions with conversion of the bromegrass sod to no-till corn was measured. During 6.5 years, total SOC decreased from 21.1, 17.0, and 55.8 t/ha in the 0-5, 5-10, and 10-30 cm depths to 20.1, 16.7, and 55.5 t/ha, respectively. However the SOC in the < 2, 0.5-2, and < 0.5 mm fractions of the 0 - 5 cm depth changed from 62, 21, and 16 % of the total SOC at the studies beginning to 31, 40, and 29 %, respectively, by the end of 77 months. Weight of SOC from C4 plants was 34.8, 49.8, and 73.2 % of total SOC in the 0-5, 5-10, and 0-30 cm depths, respectively at the beginning of the study, but after 77 months of no-till corn was 47.3, 59.0, and 71.8 % of total SOC for these same depths. In summary, it is important to evaluate losses or gains of SOC under cultivation. Use of the 13C:12C ratios, as influenced by reversing the growing sequence of C3 vs. C4 plants, allows losses of older SOC from C3 plants (bromegrass) vs. that added by growing C4 plants (corn) to be determined over time and allows rates of change of the SOC associated with various soil fractions to be evaluated.

Impact of reduced tillage and organic inputs on aggregate stability and earthworm community in a Breton context in France

NASA Astrophysics Data System (ADS)

Paillat, Louise; Menasseri, Safya; Busnot, Sylvain; Roucaute, Marc; Benard, Yannick; Morvan, Thierry; Pérès, Guénola

2017-04-01

Soil aggregate stability, which refers to the ability of soil aggregates to resist breakdown when disruptive forces are applied (water, wind), is a good indicator of the sensitivity of soil to crusting and erosion and is a relevant indicator for soil stability. Within soil parameters which affect soil stability, organic matter is one of the main important by functioning as bonding agent between mineral soil particles, but soil organisms such as microorganisms and earthworms are also recognized as efficient agents. However the relationship between earthworms, fungal hyphae and aggregation is still unclear. In order to assess the influence of these biological agents on aggregate dynamics, we have combined a field study and a laboratory experiment. On a long term experiment trial in Brittany, SOERE PRO-EFELE, we have studied the effect of reduced tillage (vs. conventional tillage) combined to organic inputs (vs. mineral inputs) on earthworm community and soil stability. Aggregate stability was measured at different perturbations intensities: fast wetting (FW), slow wetting (SW) and mechanical breakdown (MB). This study showed that after 4 years of experiments, reduced tillage and organic inputs enhanced aggregate stability. Earthworms modulated aggregation process: endogeics reduced FW stability (mechanical binding by hyphae) and anecics increased SW stability (aggregate interparticular cohesion and hydrophobicity). Some precisions were provided by the laboratory experiment, using microcosms, which compared casts of the endogeic Aporectodea c. caliginosa (NCCT) and the anecic Lumbricus terrestris (LT). The presumed hyphae fragmentation by endogeics could not be highlight in NCCT casts. Nevertheless, hyphae were more abundant and C content and aggregate stability were higher in LT casts corroborating the positive contribution of anecics to aggregate stability.

Effect of long term organic amendments and vegetation of vineyard soils on the microscale distribution and biogeochemistry of copper.

PubMed

Navel, Aline; Martins, Jean M F

2014-01-01

In this study we evaluated the effect of the long term organic management of a vineyard-soil on the biogeochemistry of copper at the micro-aggregate scale. The model vineyard-soil (Mâcon-France) experienced a long-term field-experiment that consisted in amendments and vegetations with various materials and plants. We studied specifically the effect of Straw (S) and Conifer Compost (CC) organic amendments and Clover (Cl) and Fescue (F) vegetation on the fate of copper (fungicide) in the surface layer of this loamy soil, through a comparison with the Non Amended soil (NA). After collection the five soils were immediately physically fractionated in order to obtain 5 granulometric size-fractions. All soils and size-fractions were quantitatively characterized in terms of granulometry, chemical content and copper distribution, speciation and bioavailability to bacteria and plants. The results showed strong increases of soil-constituents aggregation for all treatments (Cl>CC>S>F>NA), in relation with the increased cementation of soil-constituents by organic matter (OM). The distribution patterns of all major elements and organic carbon were found highly variable within the soil sub-fractions and also between the 5 treatments. Due to their specific inorganic and organic composition, soil sub-fractions can thus be considered as a specific microbial habitat. Added OM accumulated preferentially in the 20-2 μm and in the >250 μm of the 5 soils. The distribution patterns of copper as well as its speciation and bioavailability to bacteria in the soil sub-fractions were shown to be strongly different among the five soils, in relation with OM distribution. Our results also suggest that Cu-bioavailability to plants is controlled by soil-rhizosphere structure. Altogether our results permitted to show that long-term organic management of a vineyard soil induced stable modifications of soil physical and chemical properties at both macro and micro-scales. These modifications affected in turn the micro-scale biogeochemistry of copper, and especially its bioavailability to bacteria and plants. © 2013.

Direct Visualization of Aggregate Morphology and Dynamics in a Model Soil Organic–Mineral System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hufschmid, Ryan; Newcomb, Christina J.; Grate, Jay W.

Interactions between mineral surfaces and organic matter are ubiquitous in soils and the environment. Through both physical and chemical mechanisms, organic-mineral assemblages prevent decomposition of soil organic matter by limiting accessibility or reducing efficacy of enzymes and microbes. To understand the mechanisms underlying organic-mineral interactions, researchers have begun to interrogate these systems at smaller length scales. Current techniques that maintain a hydrated state and allow researchers to characterize nanometer length scales are limited. Here we chose a model organic-mineral system and performed complementary imaging techniques that enable direct nanoscale observations in environmentally relevant conditions: cryogenic TEM and in-situ liquid cellmore » TEM. We observed a three-fold increase in aggregate size of goethite nanoparticles upon addition of a model organic phosphate ligand and quantification of nanoparticle orientation reveals a preference for side-to-side interactions independent of the addition of an organic ligand. Additionally, in-situ liquid cell TEM experiments provides a dynamic view of the interactions allowing us to report velocities of mineral assemblages during aggregation and disaggregation, which could potentially provide binding energetics and kinetic parameters about organic-mineral and mineral-mineral systems.« less

Impact of Spatial Soil and Climate Input Data Aggregation on Regional Yield Simulations

PubMed Central

Hoffmann, Holger; Zhao, Gang; Asseng, Senthold; Bindi, Marco; Biernath, Christian; Constantin, Julie; Coucheney, Elsa; Dechow, Rene; Doro, Luca; Eckersten, Henrik; Gaiser, Thomas; Grosz, Balázs; Heinlein, Florian; Kassie, Belay T.; Kersebaum, Kurt-Christian; Klein, Christian; Kuhnert, Matthias; Lewan, Elisabet; Moriondo, Marco; Nendel, Claas; Priesack, Eckart; Raynal, Helene; Roggero, Pier P.; Rötter, Reimund P.; Siebert, Stefan; Specka, Xenia; Tao, Fulu; Teixeira, Edmar; Trombi, Giacomo; Wallach, Daniel; Weihermüller, Lutz; Yeluripati, Jagadeesh; Ewert, Frank

2016-01-01

We show the error in water-limited yields simulated by crop models which is associated with spatially aggregated soil and climate input data. Crop simulations at large scales (regional, national, continental) frequently use input data of low resolution. Therefore, climate and soil data are often generated via averaging and sampling by area majority. This may bias simulated yields at large scales, varying largely across models. Thus, we evaluated the error associated with spatially aggregated soil and climate data for 14 crop models. Yields of winter wheat and silage maize were simulated under water-limited production conditions. We calculated this error from crop yields simulated at spatial resolutions from 1 to 100 km for the state of North Rhine-Westphalia, Germany. Most models showed yields biased by <15% when aggregating only soil data. The relative mean absolute error (rMAE) of most models using aggregated soil data was in the range or larger than the inter-annual or inter-model variability in yields. This error increased further when both climate and soil data were aggregated. Distinct error patterns indicate that the rMAE may be estimated from few soil variables. Illustrating the range of these aggregation effects across models, this study is a first step towards an ex-ante assessment of aggregation errors in large-scale simulations. PMID:27055028

Impact of Spatial Soil and Climate Input Data Aggregation on Regional Yield Simulations.

PubMed

Hoffmann, Holger; Zhao, Gang; Asseng, Senthold; Bindi, Marco; Biernath, Christian; Constantin, Julie; Coucheney, Elsa; Dechow, Rene; Doro, Luca; Eckersten, Henrik; Gaiser, Thomas; Grosz, Balázs; Heinlein, Florian; Kassie, Belay T; Kersebaum, Kurt-Christian; Klein, Christian; Kuhnert, Matthias; Lewan, Elisabet; Moriondo, Marco; Nendel, Claas; Priesack, Eckart; Raynal, Helene; Roggero, Pier P; Rötter, Reimund P; Siebert, Stefan; Specka, Xenia; Tao, Fulu; Teixeira, Edmar; Trombi, Giacomo; Wallach, Daniel; Weihermüller, Lutz; Yeluripati, Jagadeesh; Ewert, Frank

2016-01-01

We show the error in water-limited yields simulated by crop models which is associated with spatially aggregated soil and climate input data. Crop simulations at large scales (regional, national, continental) frequently use input data of low resolution. Therefore, climate and soil data are often generated via averaging and sampling by area majority. This may bias simulated yields at large scales, varying largely across models. Thus, we evaluated the error associated with spatially aggregated soil and climate data for 14 crop models. Yields of winter wheat and silage maize were simulated under water-limited production conditions. We calculated this error from crop yields simulated at spatial resolutions from 1 to 100 km for the state of North Rhine-Westphalia, Germany. Most models showed yields biased by <15% when aggregating only soil data. The relative mean absolute error (rMAE) of most models using aggregated soil data was in the range or larger than the inter-annual or inter-model variability in yields. This error increased further when both climate and soil data were aggregated. Distinct error patterns indicate that the rMAE may be estimated from few soil variables. Illustrating the range of these aggregation effects across models, this study is a first step towards an ex-ante assessment of aggregation errors in large-scale simulations.

Impacts of corn residue grazing and baling on wind erosion potential in a semiarid environment

USDA-ARS?s Scientific Manuscript database

Implications of corn (Zea mays L.) residue grazing and baling on wind erosion in integrated crop-livestock systems are not well understood. We studied: 1) soil properties affecting wind erosion potential including dry aggregate-size distribution, geometric mean diameter (GMDA), geometric standard de...

Changes in soil aggregate dynamics following 18 years of experimentally increased precipitation in a cold desert ecosystem

NASA Astrophysics Data System (ADS)

De Graaff, M.; vanderVeen, J.; Germino, M. J.

2011-12-01

Climate change is expected to alter the amount and timing of precipitation in semiarid ecosystems of the intermountain west, which can alter soil carbon dynamics. Specifically, an increase in precipitation in arid ecosystems promotes microbial activity, which can increase soil aggregate formation and enhance sequestration of soil organic carbon within stable aggregates. This study was conducted to assess: (1) how precipitation shifts affect soil aggregate formation and associated soil organic carbon contents in semi arid ecosystems, and (2) how plants mediate precipitation impacts on soil aggregate dynamics. Soil samples were collected from a long-term ecohydrology study located in the cold desert of the Idaho National Lab, USA. Precipitation treatments delivered during the previous 18 years consist of three regimes: (1) a control (ambient precipitation), (2) 200 mm irrigation added during the growing season, and (3) 200 mm irrigation added during the cold dormant season. Experimental plots were planted with a diverse native mix of big sagebrush (Artemisia tridentate) and associated shrubs, grasses, and forbs, but had also become invaded by crested wheatgrass (Agropyron cristatum). Soils were collected in February (2011) with a 4.8 cm diameter soil corer to a depth of 15 cm. Across all precipitation treatments we sampled both directly beneath sagebrush and crested wheatgrass and from relatively bare plant-interspaces. Subsamples (100 g) were sieved (4.75 mm) and air dried. Then, the soils were fractionated into (1) macro aggregates (> 250 μm), (2) free micro aggregates (53-250 μm) and (3) free silt and clay fractions (<53 μm), using a wet sieving protocol. Further, macro aggregates were separated into particulate organic matter (POM), micro aggregates and silt and clay fractions using a micro aggregate isolator. Soil fractions were analyzed for soil organic carbon contents after removal of soil carbonates using sulfurous acid. Our preliminary results indicate that supplemental precipitation enhanced macro aggregate formation by 20% under plants and by 70% in plant interspaces. In contrast, free silt and clay fractions decreased in response to supplemental precipitation. These preliminary findings suggest that increased precipitation in a cold desert ecosystem may significantly enhance soil structure, particularly in the interspaces separating plants where surface crusting, poor infiltration and reduced fertility otherwise prevail.

Aspects of spatial and temporal aggregation in estimating regional carbon dioxide fluxes from temperate forest soils

NASA Technical Reports Server (NTRS)

Kicklighter, David W.; Melillo, Jerry M.; Peterjohn, William T.; Rastetter, Edward B.; Mcguire, A. David; Steudler, Paul A.; Aber, John D.

1994-01-01

We examine the influence of aggregation errors on developing estimates of regional soil-CO2 flux from temperate forests. We find daily soil-CO2 fluxes to be more sensitive to changes in soil temperatures (Q(sub 10) = 3.08) than air temperatures (Q(sub 10) = 1.99). The direct use of mean monthly air temperatures with a daily flux model underestimates regional fluxes by approximately 4%. Temporal aggregation error varies with spatial resolution. Overall, our calibrated modeling approach reduces spatial aggregation error by 9.3% and temporal aggregation error by 15.5%. After minimizing spatial and temporal aggregation errors, mature temperate forest soils are estimated to contribute 12.9 Pg C/yr to the atmosphere as carbon dioxide. Georeferenced model estimates agree well with annual soil-CO2 fluxes measured during chamber studies in mature temperate forest stands around the globe.

Aggregation protects flexible-shelled reptile eggs from severe hydric stress.

PubMed

Marco, Adolfo; Díaz-Paniagua, Carmen

2008-03-01

Many reptiles lay eggs with flexible shells that can progressively lose water until lethal dehydration under dry soil conditions. The number of eggs that develop together may influence the water exchange in the nest. We hypothesise that egg aggregation could reduce water lost under dry conditions. We exposed aggregated and isolated eggs to severe hydric stress followed by a period of rehydration. Hydric stress caused a general loss of water in common chameleon eggs. Initial egg mass did not affect survival but eggs that had lost more water had higher mortality and produced smaller hatchlings. Mass loss was higher and even lethal for isolated Chamaeleo chameleon eggs. However, aggregated eggs lost less water and most survived this period. After hydric stress, all surviving eggs gained mass via water absorption, and aggregation negatively affected water uptake. Isolated eggs hatched at smaller sizes than aggregated eggs. Aggregation also favoured hatching synchrony. Large clutches may favour hatching success of terrestrial flexible-shelled eggs incubated under severe drought conditions.

Modification of the USLE K factor for soil erodibility assessment on calcareous soils in Iran

NASA Astrophysics Data System (ADS)

Ostovari, Yaser; Ghorbani-Dashtaki, Shoja; Bahrami, Hossein-Ali; Naderi, Mehdi; Dematte, Jose Alexandre M.; Kerry, Ruth

2016-11-01

The measurement of soil erodibility (K) in the field is tedious, time-consuming and expensive; therefore, its prediction through pedotransfer functions (PTFs) could be far less costly and time-consuming. The aim of this study was to develop new PTFs to estimate the K factor using multiple linear regression, Mamdani fuzzy inference systems, and artificial neural networks. For this purpose, K was measured in 40 erosion plots with natural rainfall. Various soil properties including the soil particle size distribution, calcium carbonate equivalent, organic matter, permeability, and wet-aggregate stability were measured. The results showed that the mean measured K was 0.014 t h MJ- 1 mm- 1 and 2.08 times less than the estimated mean K (0.030 t h MJ- 1 mm- 1) using the USLE model. Permeability, wet-aggregate stability, very fine sand, and calcium carbonate were selected as independent variables by forward stepwise regression in order to assess the ability of multiple linear regression, Mamdani fuzzy inference systems and artificial neural networks to predict K. The calcium carbonate equivalent, which is not accounted for in the USLE model, had a significant impact on K in multiple linear regression due to its strong influence on the stability of aggregates and soil permeability. Statistical indices in validation and calibration datasets determined that the artificial neural networks method with the highest R2, lowest RMSE, and lowest ME was the best model for estimating the K factor. A strong correlation (R2 = 0.81, n = 40, p < 0.05) between the estimated K from multiple linear regression and measured K indicates that the use of calcium carbonate equivalent as a predictor variable gives a better estimation of K in areas with calcareous soils.

Micro-scale heterogeneity of soil phosphorus depends on soil substrate and depth

DOE PAGES

Werner, Florian; Mueller, Carsten W.; Thieme, Jurgen; ...

2017-06-09

Soils comprise various heterogeneously distributed pools of lithogenic, free organic, occluded, adsorbed, and precipitated phosphorus (P) forms, which differ depending on soil forming factors. Small-scale heterogeneity of element distributions recently has received increased attention in soil science due to its influence on soil functions and soil fertility. We investigated the micro-scale distribution of total P and different specific P binding forms in aggregates taken from a high-P clay-rich soil and a low-P sandy soil by combining advanced spectrometric and spectroscopic techniques to introduce new insights on P accessibility and availability in soils. Here we show that soil substrate and soilmore » depth determine micro-scale P heterogeneity in soil aggregates. In P-rich areas of all investigated soil aggregates, P was predominantly co-located with aluminium and iron oxides and hydroxides, which are known to strongly adsorb P. Clay minerals were co-located with P only to a lesser extent. In the low-P topsoil aggregate, the majority of the P was bound organically. Aluminium and iron phosphate predominated in the quartz-rich low-P subsoil aggregate. Sorbed and mineral P phases determined P speciation in the high-P top- and subsoil, and apatite was only detected in the high-P subsoil aggregate. Lastly, our results indicate that micro-scale spatial and chemical heterogeneity of P influences P accessibility and bioavailability.« less

Micro-scale heterogeneity of soil phosphorus depends on soil substrate and depth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Werner, Florian; Mueller, Carsten W.; Thieme, Jurgen

Soils comprise various heterogeneously distributed pools of lithogenic, free organic, occluded, adsorbed, and precipitated phosphorus (P) forms, which differ depending on soil forming factors. Small-scale heterogeneity of element distributions recently has received increased attention in soil science due to its influence on soil functions and soil fertility. We investigated the micro-scale distribution of total P and different specific P binding forms in aggregates taken from a high-P clay-rich soil and a low-P sandy soil by combining advanced spectrometric and spectroscopic techniques to introduce new insights on P accessibility and availability in soils. Here we show that soil substrate and soilmore » depth determine micro-scale P heterogeneity in soil aggregates. In P-rich areas of all investigated soil aggregates, P was predominantly co-located with aluminium and iron oxides and hydroxides, which are known to strongly adsorb P. Clay minerals were co-located with P only to a lesser extent. In the low-P topsoil aggregate, the majority of the P was bound organically. Aluminium and iron phosphate predominated in the quartz-rich low-P subsoil aggregate. Sorbed and mineral P phases determined P speciation in the high-P top- and subsoil, and apatite was only detected in the high-P subsoil aggregate. Lastly, our results indicate that micro-scale spatial and chemical heterogeneity of P influences P accessibility and bioavailability.« less

Quantitative characterization of non-classic polarization of cations on clay aggregate stability.

PubMed

Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

2015-01-01

Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10-5 to 10-1 mol L-1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation-surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability.

Quantitative Characterization of Non-Classic Polarization of Cations on Clay Aggregate Stability

PubMed Central

Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

2015-01-01

Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10−5 to 10−1 mol L−1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation–surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability. PMID:25874864

A Novel Method to Quantify Soil Aggregate Stability by Measuring Aggregate Bond Energies

NASA Astrophysics Data System (ADS)

Efrat, Rachel; Rawlins, Barry G.; Quinton, John N.; Watts, Chris W.; Whitmore, Andy P.

2016-04-01

Soil aggregate stability is a key indicator of soil quality because it controls physical, biological and chemical functions important in cultivated soils. Micro-aggregates are responsible for the long term sequestration of carbon in soil, therefore determine soils role in the carbon cycle. It is thus vital that techniques to measure aggregate stability are accurate, consistent and reliable, in order to appropriately manage and monitor soil quality, and to develop our understanding and estimates of soil as a carbon store to appropriately incorporate in carbon cycle models. Practices used to assess the stability of aggregates vary in sample preparation, operational technique and unit of results. They use proxies and lack quantification. Conflicting results are therefore drawn between projects that do not provide methodological or resultant comparability. Typical modern stability tests suspend aggregates in water and monitor fragmentation upon exposure to an un-quantified amount of ultrasonic energy, utilising a laser granulometer to measure the change in mean weight diameter. In this project a novel approach has been developed based on that of Zhu et al., (2009), to accurately quantify the stability of aggregates by specifically measuring their bond energies. The bond energies are measured operating a combination of calorimetry and a high powered ultrasonic probe, with computable output function. Temperature change during sonication is monitored by an array of probes which enables calculation of the energy spent heating the system (Ph). Our novel technique suspends aggregates in heavy liquid lithium heteropolytungstate, as opposed to water, to avoid exposing aggregates to an immeasurable disruptive energy source, due to cavitation, collisions and clay swelling. Mean weight diameter is measured by a laser granulometer to monitor aggregate breakdown after successive periods of calculated ultrasonic energy input (Pi), until complete dispersion is achieved and bond energy (Pb; input energy used in aggregate breakdown) can be calculated by the following equation: ΣPi - Ph = Pb The novel technique was tested by comparing the bond energies measured from a series of soil aggregates sampled from different land management histories, to the samples corresponding stability measurement obtained from standard modern stability tests. The effectiveness of the heavy liquid as a suspension (as opposed to water) was evaluated by comparing the bond energies of samples measured in both suspensions. Our results determine i) how disruptive water is in aggregate stability tests, ii) how accurate and representative standard aggregate stability tests are, and iii) how bond strength varies depending on land use. Keywords: Aggregate; Bond; Fragmentation; Soil; Sonication; Stability References: Zhu, Z. L., Minasny, B. & Field D. J. 2009. Measurement of aggregate bond energy using ultrasonic dispersion. European Journal of Soil Science, 60, 695-705

Direct observation and determination of the mechanisms governing mobility of asbestos in porous media

NASA Astrophysics Data System (ADS)

Seiphoori, A.; Ortiz, C. P.; Jerolmack, D. J.

2017-12-01

Transport of asbestos through soil by groundwater is typically considered to be negligible. There are indications, however, that under some conditions of pore-water/soil chemistry asbestos may become mobile, implying that buried contaminants could migrate from a disposal site and surface elsewhere. Shape, size and surface charge may influence the physical and chemical interactions of colloids with the soil matrix, and asbestos consists of elongated particles with different size and unique surface charge properties. Although chemical factors such as pH and ionic strength of pore water may affect the transport properties, the presence of dissolved organic carbon (DOC) has been identified to remarkably enhance the mobility of colloids including asbestos. To date, there is no explanation for how the presence of DOC may facilitate the mobilization of asbestos in soil - mainly because the soil medium has been treated as a black box without the possibility of observing particles within the matrix. Here, we investigated the mobility of chrysotile asbestos particles ( 10 um long) in porous media by developing a flow cell with an optically-transparent porous medium composed of granules of a refractive-index matched material. This enabled us to observe and track the particles within the water-saturated porous medium using in situ microscopy. The aqueous suspension of asbestos fibers was passed through this artificial soil, while the physical and chemical interaction of asbestos particles with the medium and their pore-scale distribution were analyzed. We studied the effects of changing solution chemistry (e.g., ionic strength, pH, and DOC content) on transport, attachment and aggregation of chrysotile particles. Experiments revealed a novel mechanism where the DOC-associated nanoparticles attach to chrysotile fibers by an electrostatic attraction, which facilitates their mobilization through the porous medium while modulating aggregation among fibers. Although pH and ionic strength also influenced aggregation and the attachment rate of particles to the substrate, the effect of DOC was more pronounced. This work may lead to enhanced predictions for the fate and transport of asbestos (as well as other contaminants) in the environment, and has implications for the mobility of asbestos particles in the human body.

Impact of soil structure heterogeneity on the degradation of organic pollutants at the centimeter scale : 3D Modeling using graph based method

NASA Astrophysics Data System (ADS)

Sinclair Yemini, Francis; Chenu, Claire; Monga, Olivier; Vieuble Gonond, Laure; Juarez, Sabrina; Pihneiro, Marc; otten, Wilfred; Garnier, Patricia

2014-05-01

Contaminant degradation by microorganisms is very variable in soils because of the very heterogeneous spatial relationship of contaminant/degraders. Repacked Soil columns were carried out to study the degradation of 2,4D pesticide labelled with C14 for different scenarios of microorganisms and pesticide initial location. Measurements of global C14-CO2 emission and C14 distribution in the soil column showed that the initial location play a crucial rule on the dissipation of the pollutant. Experiments were simulated using a 3D model able to model microbial degradation and substrate diffusion between aggregates by considering explicitly the 3D structure of soil from CT images. The initial version of the model (Monga et al., 2008) was improved in order to simulate diffusion in samples of large size. Partial differential equations were implemented using freefem++ solver. The model simulates properly the dynamics of 2,4D in the column for the different initial situations. CT images of the same soil but using undisturbed structure instead of repacked aggregates were also carried out. Significant differences of the simulated results were observed between the repacked and the undisturbed soil. The conclusion of our work is that the heterogeneity of the soil structure and location of pollutants and decomposers has a very strong influence on the dissipation of pollutants.

Greatest soil microbial diversity found in micro-habitats

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bach, Elizabeth M.; Williams, Ryan J.; Hargreaves, Sarah K.

Microbial interactions occur in habitats much smaller than typically considered in classic ecological studies. This study uses soil aggregates to examine soil microbial community composition and structure of both bacteria and fungi at a microbially relevant scale. Aggregates were isolated from three land management systems in central Iowa, USA to test if aggregate-level microbial responses were sensitive to large-scale shifts in plant community and management practices. Bacteria and fungi exhibited similar patterns of community structure and diversity among soil aggregates, regardless of land management. Microaggregates supported more diverse microbial communities, both taxonomically and functionally. Calculation of a weighted proportional wholemore » soil diversity, which accounted for microbes found in aggregate fractions, resulted in 65% greater bacterial richness and 100% greater fungal richness over independently sampled whole soil. Our results show microaggregates support a previously unrecognized diverse microbial community that likely effects microbial access and metabolism of soil substrates.« less

Do chemical gradients within soil aggregates reflect plant/soil interactions?

NASA Astrophysics Data System (ADS)

Krüger, Jaane; Hallas, Till; Kinsch, Lena; Stahr, Simon; Prietzel, Jörg; Lang, Friederike

2016-04-01

As roots and hyphae often accumulate at the surface of soil aggregates, their formation and turnover might be related to the bioavailability especially of immobile nutrients like phosphorus. Several methods have been developed to obtain specific samples from aggregate surfaces and aggregate cores and thus to investigate differences between aggregate shell and core. However, these methods are often complex and time-consuming; therefore most common methods of soil analysis neglect the distribution of nutrients within aggregates and yield bulk soil concentrations. We developed a new sequential aggregate peeling method to analyze the distribution of different nutrients within soil aggregates (4-20 mm) from four forest sites (Germany) differing in concentrations of easily available mineral P. Aggregates from three soil depths (Ah, BwAh, Bw) were isolated, air-dried, and peeled with a sieving machine performing four sieving levels with increasing sieving intensity. This procedure was repeated in quadruplicate, and fractions of the same sample and sieving level were pooled. Carbon and N concentration, citric acid-extractable PO4 and P, as well as total element concentrations (P, K, Mg, Ca, Al, Fe) were analyzed. Additionally, synchrotron-based P K-edge XANES spectroscopy was applied on selected samples to detect P speciation changes within the aggregates. The results reveal for most samples a significantly higher C and N concentration at the surface compared to the interior of the aggregates. Carbon and N gradients get more pronounced with increasing soil depth and decreasing P status of study sites. This might be explained by lower aggregate turnover rates of subsoil horizons and intense bioturbation on P-rich sites. This assumption is also confirmed by concentrations of citric acid-extractable PO4 and P: gradients within aggregates are getting more pronounced with increasing soil depth and decreasing P status. However, the direction of these gradients is site-specific: On P-rich study sites the results reveal a significant depletion of citric acid-extractable PO4 and P on aggregate surfaces in subsoil horizons, while at the other study sites a slight enrichment at the aggregate surfaces could be observed. Total P concentrations show no distinct gradients within topsoil aggregates, but a slight P enrichment at the surface of subsoil aggregates at the P-rich site. A strong correlation with the total Al concentrations may indicate a P speciation change within aggregates (e.g., due to acidification processes). These results were also confirmed by P K-edge XANES spectra of aggregate core and shell samples of the P-rich site: In the aggregate shells of topsoil as well as subsoil aggregates, organic P forms are most dominant (82 and 80 %, respectively) than in the aggregate interior (54 and 66%, respectively). Moreover, P in the shell seems to be completely associated to Al, whereas some of the P in the aggregate interior is bound to Fe and/or Ca. Overall, our results show that plant/soil interactions impact on small-scale distribution and bioavailability of nutrients by root uptake and root-induced aggregate engineering.

Visual assessment of soil structure quality in an agroextractivist system in Southeastern Amazonia

NASA Astrophysics Data System (ADS)

Fernanda Simões da Silva, Laura; Stuchi Boschi, Raquel; Ortega Gomes, Matheus; Cooper, Miguel

2016-04-01

Soil structure is considered a key factor in the functioning of soil, affecting its ability to support plant and animal life, and moderate environmental quality. Numerous methods are available to evaluate soil structure based on physical, chemical and biological indicators. Among the physical indicators, the attributes most commonly used are soil bulk density, porosity, soil resistance to penetration, tensile strength of aggregates, soil water infiltration, and available water. However, these methods are expensive and generally time costly for sampling and laboratorial procedures. Recently, evaluations using qualitative and semi-quantitative indicators of soil structure quality have gained importance. Among these methods, the method known as Visual Evaluation of Soil Structure (VESS) (Ball et al., 2007; Guimarães et al., 2011) can supply this necessity in temperate and tropical regions. The study area is located in the Piranheira Praialta Agroextrativist Settlement Project in the county of Nova Ipixuna, Pará, Brazil. Two toposequences were chosen, one under native forest and the other under pasture. Pits were opened in different landscape positions (upslope, midslope and downslope) for soil morphological, micromorphological and physical characterization. The use of the soil visual evaluation method (SVE) consisted in collecting an undisturbed soil sample of approximately 25 cm in length, 20 cm in width and 10 cm in depth. 12 soil samples were taken for each land use. The samples were manually fragmented, respecting the fracture planes between the aggregates. The SVE was done comparing the fragmented sample with a visual chart and scores were given to the soil structure. The categories that define the soil structure quality (Qe) vary from 1 to 5. Lower scores mean better soil structure. The final score calculation was done using the classification key of Ball et al. (2007) adapted by Guimarães (2011). A change in soil structure was observed between forest and pasture. The presence of layers of different depths, and size and shape of aggregates resulted in a lower Qe in the forest soils (Qe= 2,04 ±0,4), followed by the pasture (Qe= 3,09 ± 1,3). These results indicate certain degradation in the soil structure in the pasture. The variability of the soil structure in the forest samples was lower. The pasture samples presented a worse soil structure when compared to the forest, although their Qe values can be considered good.

Elemental and isotopic imaging to study biogeochemical functioning of intact soil micro-environments

NASA Astrophysics Data System (ADS)

Mueller, Carsten W.

2017-04-01

The complexity of soils extends from the ecosystem-scale to individual micro-aggregates, where nano-scale interactions between biota, organic matter (OM) and mineral particles are thought to control the long-term fate of soil carbon and nitrogen. It is known that such biogeochemical processes show disproportionally high reaction rates within nano- to micro-meter sized isolated zones ('hot spots') in comparison to surrounding areas. However, the majority of soil research is conducted on large bulk (> 1 g) samples, which are often significantly altered prior to analysis and analysed destructively. Thus it has previously been impossible to study elemental flows (e.g. C and N) between plants, microbes and soil in complex environments at the necessary spatial resolution within an intact soil system. By using nano-scale secondary ion mass spectrometry (NanoSIMS) in concert with other imaging techniques (e.g. scanning electron microscopy (SEM) and micro computed tomography (µCT)), classic analyses (isotopic and elemental analysis) and biochemical methods (e.g. GC-MS) it is possible to exhibit a more complete picture of soil processes at the micro-scale. I will present exemplarily results about the fate and distribution of organic C and N in complex micro-scale soil structures for a range of intact soil systems. Elemental imaging was used to study initial soil formation as an increase in the structural connectivity of micro-aggregates. Element distribution will be presented as a key to detect functional spatial patterns and biogeochemical hot spots in macro-aggregate functioning and development. In addition isotopic imaging will be demonstrated as a key to trace the fate of plant derived OM in the intact rhizosphere from the root to microbiota and mineral soil particles. Especially the use of stable isotope enrichment (e.g. 13CO2, 15NH4+) in conjunction with NanoSIMS allows to directly trace the fate of OM or nutrients in soils at the relevant scale (e.g. assimilate C / inorganic N in the rhizosphere). However, especially the elemental mapping requires more sophisticated computational approaches to evaluate (and quantify) the spatial heterogeneities of biogeochemical properties in intact soil systems.

An ecosystem approach to assess soil quality in organically and conventionally managed farms in Iceland and Austria

NASA Astrophysics Data System (ADS)

van Leeuwen, J. P.; Lehtinen, T.; Lair, G. J.; Bloem, J.; Hemerik, L.; Ragnarsdóttir, K. V.; Gísladóttir, G.; Newton, J. S.; de Ruiter, P. C.

2015-01-01

Intensive agricultural production can be an important driver for the loss of long-term soil quality. For this reason, the European Critical Zone Observatory (CZO) network adopted four pairs of agricultural CZO sites that differ in their management: conventional or organic. The CZO sites include two pairs of grassland farms in Iceland and two pairs of arable farms in Austria. Conventional fields differed from the organic fields in the use of artificial fertilisers and pesticides. Soils of these eight farms were analysed in terms of their physical, chemical, and biological properties, including soil aggregate size distribution, soil organic matter contents, abundance of soil microbes and soil fauna, and taxonomic diversity of soil microarthropods. In Icelandic grasslands, organically farmed soils had larger mean weight diameters of soil aggregates than the conventional farms, while there were no differences on the Austrian farms. Organic farming did not systematically influence organic matter contents or composition, nor soil carbon and nitrogen contents. Also, soil food web structures, in terms of presence of trophic groups of soil organisms, were highly similar among all farms, indicating a low sensitivity of trophic structure to land use or climate. However, soil organism biomass, especially of bacteria and nematodes, was consistently higher on organic farms than on conventional farms. Within the microarthropods, taxonomic diversity was systematically higher in the organic farms compared to the conventional farms. This difference was found across countries and farm, crop, and soil types. The results do not show systematic differences in physical and chemical properties between organic and conventional farms, but confirm that organic farming can enhance soil biomass and that microarthropod diversity is a sensitive and consistent indicator for land management.

[Impact of land use type on stability and organic carbon of soil aggregates in Jinyun Mountain].

PubMed

Li, Jian-Lin; Jiang, Chang-Sheng; Hao, Qing-Ju

2014-12-01

Soil aggregates have the important effect on soil fertility, soil quality and the sustainable utilization of soil, and they are the mass bases of water and fertilizer retention ability of soil and the supply or release of soil nutrients. In this paper, in order to study the impact of land use type on stability and organic carbon of soil aggregates in Jinyun Mountain, we separated four land use types of soil, which are woodland, abandoned land, orchard and sloping farmland by wet sieving method, then we got the proportion of large macroaggregates (> 2 mm), small macroaggregates (0.25-2 mm), microaggregates (53 μm-0.25 mm) and silt + clay (< 53 μm) and measured the content of organic carbon in each aggregate fraction in soil depth of 0-60 cm and calculated the total content of organic carbon of all aggregates fraction in each soil. The results showed that reclamation of woodland will lead to fragmentation of macroaggregates and deterioration of soil structure, and the proportion of macroaggrgates (> 0.25 mm) were 44.62% and 32.28% respectively in the soils of orchard and sloping farmland, which reduced 38.58% (P < 0.05) and 91.52% (P < 0.05) compared with woodland. While after changing the sloping farmland to abandoned land, which lead to the conversion of soil fraction from silt + clay to large macroaggregates and small macroaggregates, so it will improve the soil structure. MWD (mean weight diameter) and GMD (geometric mean diameter) are important indicators of evaluating the stability of soil aggregates. We found the MWD and GWD in soil depth of 0-60 cm in orchards and sloping farmland were significantly lower than those in woodland (P < 0.05), while after changing the sloping farmland to abandoned land, the MWD and GWD increased significantly (P < 0.05), which indicated that reclamation of woodland will lead to the decrease of stability of soil aggregates, and they will be separated more easily by water. However, after changing the sloping farmland to abandoned land will enhance the stability of soil aggregates, and improve the ability of soil to resist external damage. The organic carbon content in each soil aggregate of four land use types decreased with the increase of soil depth. In soil depth of 0-60 cm, the storage of organic carbon of large macroaggregates in each soil are in orders of woodland (14.98 Mg x hm(-2)) > abandoned land (8.71 Mg x hm(-2)) > orchard (5.82 Mg x hm(-2)) > sloping farmland (2.13 Mg x hm(-2)), and abandoned land (35.61 Mg x hm(-2)) > woodland (20.38 Mg x hm-(-2)) > orchard (13.83 Mg x hm(-2)) > sloping farmland (6.77 Mg x hm(-2)) in small macroaggregates, and abandoned land (22.44 Mg x hm(-2)) > woodland (10.20 Mg x hm(-2)) > orchard (6.80 Mg x hm(-2)) > sloping farmland (5. 60 Mg x hm(-2)) in microaggregates, and abandoned land (22.21 Mg x hm(-2)) > woodland (17.01 Mg x hm(-2)) > orchard (16.70 Mg x hm(-2)) > sloping farmland (9.85 Mg x hm(-2)) in silt and clay fraction. Storage of organic carbon in each aggregate in the soils of woodland and abandoned land were higher than those in the soils of orchard and sloping farmland, which indicated that reclamation of woodland will lead to a loss of organic carbon in each soil aggregate fraction, while after changing the sloping farmland to abandoned land will contribute to restore and sequestrate the soil organic carbon. In addition, it showed that most organic carbon accumulated in small macroaggregate in soils of woodland and abandoned land, while they are in silt and clay in soils of orchard and sloping farmland, indicating that organic carbon in larger aggregates is unstable and is easier to convert during the land use change.

Soil compaction: Evaluation of stress transmission and resulting soil structure

NASA Astrophysics Data System (ADS)

Naveed, Muhammad; Schjønning, Per; Keller, Thomas; Lamande, Mathieu

2016-04-01

Accurate estimation of stress transmission and resultant deformation in soil profiles is a prerequisite for the development of predictive models and decision support tools for preventing soil compaction. Numerous studies have been carried out on the effects of soil compaction, whilst relatively few studies have focused on the cause (mode of stress transmission in the soil). We have coupled both cause and effects together in the present study by carrying out partially confined compression tests on (1) wet aggregates, (2) air dry aggregates, and (3) intact soils to quantify stress transmission and compaction-resulted soil structure at the same time. Stress transmission was quantified using both X-ray CT and Tactilus sensor mat, and soil-pore structure was quantified using X-ray CT. Our results imply that stress transmission through soil highly depends on the magnitude of applied load and aggregate strength. As soon as the applied load is lower than the aggregate strength, the mode of stress transmission is discrete as stresses were mainly transmitted through chain of aggregates. With increasing applied load soil aggregates start deforming that transformed heterogeneous soil into homogenous, as a result stress transmission mode was shifted from discrete towards more like a continuum. Continuum-like stress transmission mode was better simulated with Boussinesq (1885) model based on theory of elasticity compared to discrete. The soil-pore structure was greatly affected by increasing applied stresses. Total porosity was reduced 5-16% and macroporosity 50-85% at 620 kPa applied stress for the intact soils. Similarly, significant changes in the morphological indices of the macropore space were also observed with increasing applied stresses.

Dissolved Organic Matter Assisted Transport of Hormones Through An Agricultural Soil

NASA Astrophysics Data System (ADS)

Jann, S.; Totsche, K. U.; Koegel-Knabner, I.; Schiffer, B.; Meyer, H. H. D.

In the last years the disrupting activity of steroidal sex hormones like estrogens has been discussed for various ecosystems and even for human fertility. Once released into the environment, steroids pose a severe risk to fauna and man. After excretion of the relevant compounds or their metabolites by the target animals, the transition of biologically active substances via dung or manure onto soils and into the groundwa- ter cannot be excluded. Yet there is only little knowledge on the stability, degradation and transport pathways of steroids in soils. Just as little is known about the fate of anabolic steroids which are licensed as growth promotants for farm animals in many meat-exporting countries outside the EU (e.g. USA, Australia). We therefore studied the transport of Trenbolone-17 and Melengestrolacetate (MGA) with col- umn experiments employing aggregated agricultural field soil materials (Luvisol E and Bt horizons). The columns (14.6 cm in height, 4.7 cm in diameter) were perco- lated from bottom to top using a peristaltic pump. The mean volumetric flow rate was kept constant throughout the experiments at 20 ml h-1. Chloride was used as nonreac- tive tracer. The flow regime is controlled by two flow regions reflecting the dual mode pore size distribution of the aggregated soil material. Our results show that although the very high KOC values U Trenbolone: 24311 within the E-horizon; 21622 within the Bt-horizon and MGA: 16708 within the E-horizon; 59459 within the Bt horizon - we observe a quick breakthrough of low concentrations of the hormones simultaneous with the non-reactive tracer chloride. This points to the fact that within aggregated field soil, the risk for deep seepage of low concentrations of hormones is high.

Applicability of recycled aggregates in concrete piles for soft soil improvement.

PubMed

Medeiros-Junior, Ronaldo A; Balestra, Carlos Et; Lima, Maryangela G

2017-01-01

The expressive generation of construction and demolition waste is stimulating several studies for reusing this material. The improvement of soft soils by concrete compaction piles has been widely applied for 40 years in some Brazilian cities. This technique is used to improve the bearing capacity of soft soils, allowing executing shallow foundations instead of deep foundations. The compaction piles use a high volume of material. This article explored the possibility of using recycled aggregates from construction waste to replace the natural aggregates in order to improve the bearing capacity of the soft soil, regarding its compressive strength. Construction wastes from different stages of a construction were used in order to make samples of concrete with recycled aggregates. The strength of concretes with natural aggregates was compared with the strength of concretes with recycled (fine and coarse) aggregates. Results show that all samples met the minimum compressive strength specified for compaction piles used to improve the bearing capacity of soft soils. The concrete with recycled aggregate from the structural stage had even higher resistances than the concrete with natural aggregates. This behaviour was attributed to the large amount of cementitious materials in the composition of this type of concrete. It was also observed that concrete with recycled fine aggregate has a superior resistance to concrete with recycled coarse aggregate.

Adsorption and desorption of Cu2+ on paddy soil aggregates pretreated with different levels of phosphate.

PubMed

Dai, Jun; Wang, Wenqin; Wu, Wenchen; Gao, Jianbo; Dong, Changxun

2017-05-01

Interactions between anions and cations are important for understanding the behaviors of chemical pollutants and their potential risks in the environment. Here we prepared soil aggregates of a yellow paddy soil from the Taihu Lake region, and investigated the effects of phosphate (P) pretreatment on adsorption-desorption of Cu 2+ of soil aggregates, free iron oxyhydrates-removed soil aggregates, goethite, and kaolinite with batch adsorption method. The results showed that Cu 2+ adsorption was reduced on the aggregates pretreated with low concentrations of P, and promoted with high concentrations of P, showing a V-shaped change. Compared with the untreated aggregates, the adsorption capacity of Cu 2+ was reduced when P application rates were lower than 260, 220, 130 and 110mg/kg for coarse, clay, silt and fine sand fractions, respectively. On the contrary, the adsorption capacity of Cu 2+ was higher on P-pretreated soil aggregates than on the control ones when P application rates were greater than those values. However, the desorption of Cu 2+ was enhanced at low levels of P, but suppressed at high levels of P, displaying an inverted V-shaped change over P adsorption. The Cu 2+ adsorption by the aggregate particles with and without P pretreatments was well described by the Freundlich equation. Similar results were obtained on P-pretreated goethite. However, such P effects on Cu 2+ adsorption-desorption were not observed on kaolinite and free iron oxyhydrates-removed soil aggregates. The present results indicate that goethite is one of the main soil substances responsible for the P-induced promotion and inhibition of Cu 2+ adsorption. Copyright © 2016. Published by Elsevier B.V.

Dynamics and mechanisms of asbestos-fiber aggregate growth in water

NASA Astrophysics Data System (ADS)

Wu, L.; Ortiz, C. P.; Jerolmack, D. J.

2015-12-01

Most colloidal particles including asbestos fibers form aggregates in water, when solution chemistry provides favorable conditions. To date, the growth of colloidal aggregates has been observed in many model systems under optical and scanning electron microscopy; however, all of these studies have used near-spherical particles. The highly elongated nature of asbestos fibers may cause anomalous aggregate growth and morphology, but this has never been examined. Although the exposure pathway of concern for asbestos is through the air, asbestos particles typically reside in soil that is at least partially saturated, and aggregates formed in the aqueous phase may influence the mobility of particles in the environment. Here we study solution-phase aggregation kinetics of asbestos fibers using a liquid-cell by in situ microscopy, over micron to centimeter length scales and from a tenth of a second to hours. We employ an elliptical particle tracking technique to determine particle trajectories and to quantify diffusivity. Experiments reveal that diffusing fibers join by cross linking, but that such linking is sometimes reversible. The resulting aggregates are very sparse and non-compact, with a fractal dimension that is lower than any previously reported value. Their morphology, growth rate and particle size distribution exhibit non-classical behavior that deviates significantly from observations of aggregates composed of near-spherical particles. We also perform experiments using synthetic colloidal particles, and compare these to asbestos in order to separate the controls of particle shape vs. material properties. This direct method for quantitatively observing aggregate growth is a first step toward predicting asbestos fiber aggregate size distributions in the environment. Moreover, many emerging environmental contaminants - such as carbon nanotubes - are elongated colloids, and our work suggests that theories for aggregate growth may need to be modified in order to model these particles.

Forty years experience in developing and using rainfall simulators under tropical and Mediterranean conditions

NASA Astrophysics Data System (ADS)

Pla-Sentís, Ildefonso; Nacci, Silvana

2010-05-01

Rainfall simulation has been used as a practical tool for evaluating the interaction of falling water drops on the soil surface, to measure both stability of soil aggregates to drop impact and water infiltration rates. In both cases it is tried to simulate the effects of natural rainfall, which usually occurs at very different, variable and erratic rates and intensities. One of the main arguments against the use of rainfall simulators is the difficulty to reproduce the size, final velocity and kinetic energy of the drops in natural rainfall. Since the early 70´s we have been developing and using different kinds of rainfall simulators, both at laboratory and field levels, and under tropical and Mediterranean soil and climate conditions, in flat and sloping lands. They have been mainly used to evaluate the relative effects of different land use and management, including different cropping systems, tillage practices, surface soil conditioning, surface covers, etc. on soil water infiltration, on runoff and on erosion. Our experience is that in any case it is impossible to reproduce the variable size distribution and terminal velocity of raindrops, and the variable changes in intensity of natural storms, under a particular climate condition. In spite of this, with the use of rainfall simulators it is possible to obtain very good information, which if it is properly interpreted in relation to each particular condition (land and crop management, rainfall characteristics, measurement conditions, etc.) may be used as one of the parameters for deducing and modelling soil water balance and soil moisture regime under different land use and management and variable climate conditions. Due to the possibility for a better control of the intensity of simulated rainfall and of the size of water drops, and the possibility to make more repeated measurements under very variable soil and land conditions, both in the laboratory and specially in the field, the better results have been obtained with small size 500-1000 cm2, easily dismantled, drop former simulators, than with larger, nozzle, or more sophisticated equipments. In this contribution there are presented some of the rainfall simulators developed and used by the main author, and some of the results obtained in different studies of practical problems under tropical and Mediterranean conditions. References Pla, I.,G.Campero, y R.Useche.1974.Physical degradación of agricultural soils in the Western Plains of Venezuela. "Trans.10th Int.Cong.Soil.Sci.Soc". 1:231-240. .Moscú Pla, I. 1975.Effects of bitumen emulsion and polyacrilamide on some physical properties of Venezuelan soils. En "Soil Sci. Soc. Am. Special Publication"• 7. 35-46. Madison. Wisconsin . (USA). Pla, I. 1977.Aggregate size and erosion control on sloping land treated with hydrophobic bitumen emulsion."Soil Conservation and Management in the Humid Tropics".109-115. John Wiley & Sons. Pla, I.1981.Simuladores de lluvia para el estudio de relaciones suelo-agua bajo agricultura de secano en los trópicos. Rev. Fac. Agron. XII(1-2):81-93.Maracay (Venezuela) Pla, I. 1986.A routine laboratory index to predict the effects of soil sealing on soil and water conservation. En "Assesment of Soil Surface Sealing and Crusting". 154-162.State Univ. of Ghent.Gante (Bélgica Pla, I., M.C. Ramos, S. Nacci, F. Fonseca y X. Abreu. 2005. Soil moisture regime in dryland vineyards of Catalunya (Spain) as influenced by climate, soil and land management. "Integrated Soil and Water Management for Orchard Development". FAO Land and Water Bulletin 10. 41-49. Roma (Italia).

Biological and physical factors controlling aggregate stability under different climatic conditions in Southern Spain.

NASA Astrophysics Data System (ADS)

Ángel Gabarrón-Galeote, Miguel; Damián Ruiz-Sinoga, Jose; Francisco Martinez-Murillo, Juan; Lavee, Hanoch

2013-04-01

Soil aggregation is a key factor determining the soil structure. The presence of stable aggregates is essential to maintain a good soil structure, that in turn plays an important role in sustaining agricultural productivity and preserving environmental quality. A wide range of physical and biological soil components are involved in the aggregate formation and stabilization, namely clay mineral content; the quantity and quality of organic matter, that can be derived from plants, fungal hyphae, microorganism and soil animals; and the soil water content. Climatic conditions, through their effect on soil water content, vegetation cover and organic matter content, are supposed to affect soil aggregation. Thus the main objective of this research is to analyse the effect of organic matter, clay content and soil water content on aggregate stability along a climatic transect in Southern Spain. This study was conducted in four catchments along a pluviometric gradient in the South of Spain (rainfall depth decreases from west to east from more than 1000 mm year-1 to less than 300 mm year-1) and was based on a methodology approximating the climatic gradient in Mediterranean conditions. The selected sites shared similar conditions of geology, topography and soil use, which allowed making comparisons among them and relating the differences to the pluviometric conditions. In February 2007, 250 disturbed and undisturbed samples from the first 5cm of the soil were collected along the transect. We measured the aggregate stability, organic matter, clay content and bulk density of every sample. In the field we measured rainfall, air temperature, relative humidity, wind speed, wind direction, solar radiation, potential evapotranspiration, soil water content, vegetation cover and presence of litter. Our results suggest that aggregate stability is a property determined by a great number of highly variable factors, which can make extremely difficult to predict its behavior taking in account only a few of them. The climate exerted a great influence in aggregate stability and could determine by itself the soil structure along the climate transect. As a result, properties unrelated in a specific point of the climate transect became highly associated if we took it into account completely. Along the climate transect analyzed could be defined two areas, separated by a threshold located between 573.6 mm y-1 and 335.9 mm y-1. In the wettest part soil structure was mainly determined by biotic factors and in the driest part was highly probable that abiotic factors play a key role determining aggregate stability.

Symbiosis of Arbuscular Mycorrhizal Fungi and Robinia pseudoacacia L. Improves Root Tensile Strength and Soil Aggregate Stability

PubMed Central

Zhang, Haoqiang; Liu, Zhenkun; Chen, Hui; Tang, Ming

2016-01-01

Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention. PMID:27064570

Symbiosis of Arbuscular Mycorrhizal Fungi and Robinia pseudoacacia L. Improves Root Tensile Strength and Soil Aggregate Stability.

PubMed

Zhang, Haoqiang; Liu, Zhenkun; Chen, Hui; Tang, Ming

2016-01-01

Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention.

Roles of biology, chemistry, and physics in soil macroaggregate formation and stabilization

USDA-ARS?s Scientific Manuscript database

Soil functions or ecosystem services depend on the distribution of macro- (= 0.25 mm) and micro- (< 0.25 mm) aggregates and open space between aggregates. It is the arrangement of the aggregates and pore space which allows air and water movement in and out of soil; reduces compaction; and stimulates...

WSA index as an indicator of soil degradation due to erosion

NASA Astrophysics Data System (ADS)

Jaksik, Ondrej; Kodesova, Radka; Schmidtova, Zuzana; Kubis, Adam; Fer, Miroslav; Klement, Ales; Nikodem, Antonin

2014-05-01

Knowledge of spatial distribution of soil aggregate stability as an indicator of soil degradation vulnerability is required for many scientific and practical environmental studies. The goal of our study was to assess predisposition of different soil types to change aggregate stability due to erosion. Five agriculture arable lands with different soil types were chosen. The common feature of these sites is relatively large slope and thus soils are impacted by water erosion. The first studied area was in Brumovice. The original soil type was Haplic Chernozem on loess, which was due to erosion changed into Regosol (steep parts) and Colluvial soil (base slope and the tributary valley). A similar process has been described at other four locations Vidim, Sedlcany, Zelezna and Hostoun, where the original soil types were Haplic Luvisol on loess and Haplic Cambisol on gneiss, Haplic Cambisol on shales, and Calcaric Cambisol on marlstone, respectively. The regular and semi-regular soil sampling grids were set at all five sites. The basic soil properties were measured and stability of soil aggregates (WSA index) was evaluated. In all cases, the higher aggregates stability was observed in soils, which were not (or only slightly) affected by water erosion and at base slope and the tributary valley (eroded soil particle accumulation). The lowest aggregate stability was measured at the steepest parts. When comparing individual sites, the highest WSA index, e.g. aggregate stability, was found in Sedlcany (Cambisol). Lower WSA indexes were measured on aggregates from Hostoun (Cambisol), Zelezna (Cambisol), Vidim (Luvisol) and the lowest values were obtained in Brumovice (Chernozem). The largest WSA indexes for Cambisols in comparison to Luvisols and Chernozem could be attributed to higher organic matter content and presence of iron oxides. Slightly higher aggregate stability of Luvisols in comparison to Chernozem, could be explained by the positive influence of clay (especially in form of clay coatings) and organic matter, and negative impact of pH. The largest range of WSA values were found for Sedlcany (WSA = 0.41 to 0.93), followed by Vidim (WSA = 0.32 to 0.78) and Brumovice (0.20 to 0.67), Zelezna (WSA = 0.35 to 0.78) and Hostoun (WSA = 0.53 to 0.85). This indicates that the largest impact of erosion on aggregate stability was measured for Cambisol in Sedlcany. Similar impact of soil erosion was observed for both soils on loess and Cambisol in Zelezna. The lowest impact of erosion on aggregate stability was measured for Cambisol in Hostoun. Acknowledgement: Authors acknowledge the financial support of the Ministry of Agriculture of the Czech Republic No. QJ1230319

New Model for Agglutinitic Glass Formation from LSCC Data

NASA Technical Reports Server (NTRS)

Pieters, C. M.; Taylor, L. A.

2003-01-01

Since the return of the first lunar samples it has been well known that glass-welded aggregates (agglutinates) accumulate in lunar soil as the result of multiple processes, many of which are driven by micrometeorite impacts. The proportion of agglutinates increases with increasing exposure to the space environment, and for an individual soil the proportion of agglutinates also increases with decreasing particle size. Detailed chemical and petrographic analyses of a suite of mare soils and their agglutinate constituents prepared by the Lunar Soil Characterization Consortium appeared to confirm the "Fusion of the Finest Fraction" model for agglutinate formation (or F3) proposed by Papike et al. However, recent LSCC data for highland soils are not consistent with the F3 model and alternate models for agglutinate formation must be revisited. Instead, we suggest differential melting of soil species may be more consistent with the full range of soil data to date.

Stabilities of ant nests and their adjacent soils

NASA Astrophysics Data System (ADS)

Echezona, B. C.; Igwe, C. A.

2012-10-01

Nests habour ants and termites and protect them from harsh environmental conditions. The structural stabilities of nests were studied to ascertain their relative vulnerability to environmental stresses. Arboreal-ant nests were pried from different trees, while epigeous-termite nests were excavated from soil surface within the sample area. Soils without any visible sign of ant or termite activity were also sampled 6 m away from the nests as control. Laboratory analysis result showed that irrespective of the tree hosts, the aggregate stabilities of the ant nests were lower than those of the ground termite, with nests formed on Cola nitida significantly showing lower aggregate stability (19.7%) than other antnest structures. Clay dispersion ratio, moisture content, water stable aggregate class <0.25mm and sand mass were each negatively correlated with aggregate stability, while water stable aggregate class1.00-0.50 mm gave a positive correlation. Nest structures were dominated more by water stable aggregate class >2.00 mm but path analysis demonstrated that water stable aggregate class <0.25 mm contributed most to the higher aggregate stability of the termite nest than the other nest. Nest aggregates had greater structural stability compared to the control soil. The higher structural stability of termite nests over other nest and soil was considered a better adaptive mechanism against body desiccation.

Soil aggregates, organic matter turnover and carbon balance in a Mediterranean eroded vineyard

NASA Astrophysics Data System (ADS)

Novara, Agata; Lo Papa, Giuseppe; Dazzi, Carmelo; Gristina, Luciano; Cerdà, Artemi

2014-05-01

The carbon cycle is being affected by the human impacts (Novara et al., 2011; Yan-Gui et al., 2013), and one of those is the intensification in the soil erosion in agriculture land (Cerdà et al., 2009; García Orenes et al., 2009). Vineyards also are affected by the human activities (Fernández Calviño, 2012). Vineyards in Sicily are cultivated on 110.000 ha, 10% of which on >10% slope. Deficiencies of soil organic matter are typical of the semi arid Mediterranean environment especially where traditional intensive cropping practices are adopted (Novara et al., 2012; 2013). These practices in vineyards could lead soil to intensive erosion processes (Novara et al., 2011). The fate of SOC under erosion processes is difficult to understand because of the influence of the erosion impact on SOC pathway, which depends on the different features of the process involved (detachment, transport and/or deposition). Soil erosion must be considered a net C source (Lal, 2003), as eroded soils have lower net primary productivity (NPP) (Dick and Gregorich, 2004) caused by reduction in the effective rooting depth and all in all determining decline in soil quality. Breakdown of aggregates and soil dispersion expose SOM to microbial/enzymatic processes and chemical soil properties (Dimoyiannis, 2012; Kocyigit and Demirci, 2012). Moreover the light fraction, transported by runoff, is labile and easily mineralized determining CO2 emission in the atmosphere (Jacinthe and Lal, 2004). Therefore, the carbon pool is lower in eroded than in un-eroded soil scapes and the rate of mineralization of soil organic matter is higher in sediments than in original soil. In this survey we show a research conducted on a slope sequence of three soil profiles in an irrigated vineyard located in Sambuca di Sicilia, Italy (UTM33-WGS84: 4169367N; 325011E). The SOC content was measured at depth intervals of 10 cm up to a depth of 60 cm in each pedon. Wet aggregate-size fractions with no prior chemical dispersion, were isolated by mechanical shaking of 100 g, air-dried fine earth on a column with sieves of 250 and 63 μm using a Shaker AS 200 Sieve (RETSCH analytical, Haan, Germany) (200-mm sieves, amplitude of 2 cm, frequency of 1.6 Hz and a water flux of 2 litres minute-1). After the physical fractionation, we discriminate three main aggregate-size fractions: >250, 63-250 and <63 μm. Three replicate samples of 5 g of the soil material that we prepared for the fractionation from three different pedons along the slope gradient were incubated at two different depth intervals (Topsoil: 0-15 cm; Subsoil: 35-50 cm). Respiration was monitored during a period of 50 days keeping moisture and temperature constant. Both in topsoil and subsoil layers, particle size distribution in the depositional area shows a decrease of the finest size (<63 μm) respect to the soil in the detachment area. A SOC increase was observed due to depositional processes. Mean Residence Time of SOC strongly decreased in the subsoil particularly in the depositional area corroborating that erosion processes could be a SOC sink. Anyway we should also stress that, considering the estimated "off farm" erosion processes, the carbon budget resulted highly negative. References Barbera, V., Poma, I., Gristina, L., Novara, A., Egli, M. 2013. Long-term cropping systems and tillage management effects on soil organic carbon stock and steady state level of C sequestration rates in a semiarid environment. Land Degradation & Development, 23: 82- 91. DOI 10.1002/ldr.1055 Cerdà, A., Giménez-Morera, A.G., Bodí, M.B. 2009b. Soil and water losses from new citrus orchards growing on sloped soils in the western Mediterranean basin. Earth Surface Processes and Landforms 34, 1822-1830. Dick, W.A., Gregorich, E.G. 2004. Developing and maintaining soil organic matter levels. In: Schjonning, P., Elmholt,S., Christensen, B.T. (Eds.), Managing Soil Quality: Challenges in Modern Agriculture. CAB International, Wallingford, UK, pp. 103-120. Dimoyiannis, D. 2012. Wet aggregate stability as affected by excess carbonate and other soil properties. Land Degradation & Development, 23: 450- 455. DOI 10.1002/ldr.1085 Fernández-Calviño, D., Garrido-Rodríguez, B., López-Periago, J. E., Paradelo, M., and Arias-Estévez, M. 2013. Spatial distribution of copper fractions in a vineyard soil. Land Degradation & Development, 24: 556- 563. DOI 10.1002/ldr.1150 García-Orenes, F., Cerdà, A., Mataix-Solera, J., Guerrero, C., Bodí, M.B., Arcenegui, V., Zornoza, R. & Sempere, J.G. 2009. Effects of agricultural management on surface soil properties and soil-water losses in eastern Spain. Soil and Tillage Research 106, 117-123. 10.1016/j.still.2009.06.002 Jacinthe, P.A., R. Lal, L.B. Owens, and D.L. Hothem. (2004) Transport of labile carbon in runoff as affected by land use and rainfall characteristics. Soil and Tillage Research 77: 111-123 Kocyigit, R., Demirci, S. 2012. Long-term changes of aggregate-associated and labile soil organic carbon and nitrogen after conversion from forest to grassland and cropland in northern Turkey. Land Degradation & Development, 23: 475- 482. DOI 10.1002/ldr.1092 Lal, R., 2003. Soil erosion and the global carbon budget. Environment International 29, 437-450 Novara, A., Gristina, L., Bodì, M.B., Cerdà, A. 2011. The impact of fire on redistribution of soil organic matter on a Mediterranean hillslope under maquia vegetation type. Land Degradation and Development, 2: 530 - 536. DOI: 10.1002/ldr.1027 Novara, A., Gristina, L., Kuzyakov, Y., Schillaci, C., Laudicina, V.A., La Mantia, T., 2013. Turnover and availability of soil organic carbon under different Mediterranean land use as estimated by 13C natural abundance. European Journal ofSoil science, 64, 466-475. DOI: 10.1111/ejss.12038 Novara, A., Gristina, L., Saladino, S., Santoro, A., Cerda, A. 2011. Soil erosion assessment on tillage and alternative soil managements in a Sicilian vineyard. Soil & Tillage Research 117:140-147. Novara, A., La Mantia, T., Barbera V., Gristina, L. 2012. Paired-site approach for studying soil organic carbon dynamics in a Mediterranean semiarid environment. Catena, 89 (1): 1-7, doi.org/10.1016/j.catena.2011.09.008 Yan-Gui, S., Xin-Rong, L., Ying-Wu, C., Zhi-Shan, Z., and Yan, L. 2013. Carbon fixaton of cyanobacterial-algal crusts after desert fixation and its implication to soil organic matter accumulation in Desert. Land Degradation & Development, 24: 342- 349. DOI 10.1002/ldr.1131

Modeling Bacteria-Water Interactions in Soil: EPS Dynamics Under Evaporative Conditions

NASA Astrophysics Data System (ADS)

Furrer, J.; Hinestroza, H. F.; Guo, Y. S.; Gage, D. J.; Cho, Y. K.; Shor, L. M.

2017-12-01

The soil habitat represents a major linkage between the water and carbon cycles: the ability of soils to sequester or release carbon is determined primarily by soil moisture. Water retention and distribution in soils controls the abundance and activity of soil microbes. Microbes in turn impact water retention by creating biofilms, composed of extracellular polymeric substances (EPS). We model the effects of bacterial EPS on water retention at the pore scale. We use the lattice Boltzmann method (LBM), a well-established fluid dynamics modeling platform, and modify it to include the effects of water uptake and release by the swelling/shrinking EPS phase. The LB model is implemented in 2-D, with a non-ideal gas equation of state that allows condensation and evaporation of fluid in pore spaces. Soil particles are modeled according to experimentally determined particle size distributions and include realistic pore geometries, in contrast to many soil models which use spherical soil particles for simplicity. Model results are compared with evaporation experiments in soil micromodels and other simpler experimental systems, and model parameters are tuned to match experimental results. Drying behavior and solid-gel contact angle of EPS produced by the soil bacteria Sinorhizobium meliloti has been characterized and compared to the behavior of deionized water under the same conditions. The difference in behavior between the fluids is used to parameterize the model. The model shows excellent qualitative agreement for soil micromodels with both aggregated and non-aggregated particle arrangements under no-EPS conditions, and reproduces realistic drying behavior for EPS. This work represents a multi-disciplinary approach to understanding microbe-soil interactions at the pore scale.

Interrelationships between soil biota and soil physical properties in forest areas of the Pieniny National Park (Poland)

NASA Astrophysics Data System (ADS)

Józefowska, Agnieszka; Zaleski, Tomasz; Sokołowska, Justyna; Dzierwa, Agata

2017-04-01

The study area was located in the Pieniny National Park (PNP) in the Carpathian Mountain (Southern Poland). Investigated soil belonged to Eutric Cambisols and had silt or silt loam texture. The purpose of this research was to investigated relationship between soil biota, such as microbial activity, soil Oligochaeta (Lumbricidae and Enchytraeidae) and soil physical properties, such as water retention or aggregates stability. This research was conducted at six forest monitoring areas of the PNP. Sampling was collected in the September 2016. For each of the 6 places, undisturbed and disturbed soil samples were taken from the 0-15-cm and 15-30-cm layer in 3 to 5 replicates. Undisturbed soil was taken: i) into Kopecky cylinders to determined soil physical properties; ii) a soil cores to determined enchytraeids and fine roots biomass (RB). Disturbed soil was collected in 3 reps and homogenized. Next such soil samples were divided into three parts: i) fresh one to determined dehydrogenase activity (ADh), microbial carbon biomass (MC) and labile carbon (LC); ii) air-dried, passed through a sieve (2-mm mesh size) and used for analysis: pH, organic carbon and bulk density; iii) last part air dried was used to determined stability of different size aggregates. In field, earthworms were collected in 3 reps using hand sorting method. Investigated soils were strongly acidic to neutral (pH 4.8-6.8). Organic carbon (Corg) content was varied from 0.8% to 4.5% and was higher in 0-15-cm layers than in 15-30-cm layers. Higher Corgcontent was connected with lower bulk density. Enchytraeids density was ranged from 1807 ind. m-2 to 88855 ind. m-2 and was correlated with microbial activity (ADh and MB) and RB. Earthworms density (ED) was ranged from 7 ind. m-2to 507 ind. m-2. In investigated soil was 6 genus and 7 species (Octolasion lacteum, Aporrectodea caliginosa, Aporrectodea rosea, Aporrectodea jassyensis, Lumbricus rubellus, Eisenia lucens, and Fitzingeria platyura depressa). ED was closely related with soil moisture and water field capacity. This Research was financed by the Ministry of Science and Higher Education of the Republic of Poland, No. BM - 4175/16

Soil aggregation and glomalin in a soil quality management study in a cold, semi-arid region

USDA-ARS?s Scientific Manuscript database

Global food insecurity and rapidly diminishing water, soil, and energy resources are putting pressure on agroecosystems to efficiently produce more food while maintaining or enhancing soil quality, particularly soil aggregation. A field study established in 1993 near Mandan, ND sought to evaluate im...

Long-term tillage and cropping effects on biological properties associated with soil aggregation in semi-arid eastern Montana, USA

USDA-ARS?s Scientific Manuscript database

Long-term tillage and cropping may influence biological attributes responsible for semi-arid soil aggregation in Montana, USA. Aggregate stability, glomalin, basidiomycete fungi, uronic acids, total organic C (TOC) and total N (TN) at 0-5 cm soil depth from 1991 to 2003 were evaluated in different a...

Afforestation impacts microbial biomass and its natural (13)C and (15)N abundance in soil aggregates in central China.

PubMed

Wu, Junjun; Zhang, Qian; Yang, Fan; Lei, Yao; Zhang, Quanfa; Cheng, Xiaoli

2016-10-15

We investigated soil microbial biomass and its natural abundance of δ(13)C and δ(15)N in aggregates (>2000μm, 250-2000μm, 53-250μm and <53μm) of afforested (implementing woodland and shrubland plantations) soils, adjacent croplands and open area (i.e., control) in the Danjiangkou Reservoir area of central China. The afforested soils averaged higher microbial biomass carbon (MBC) and nitrogen (MBN) levels in all aggregates than in open area and cropland, with higher microbial biomass in micro-aggregates (<250μm) than in macro-aggregates (>2000μm). The δ(13)C of soil microbial biomass was more enriched in woodland soils than in other land use types, while δ(15)N of soil microbial biomass was more enriched compared with that of organic soil in all land use types. The δ(13)C and δ(15)N of microbial biomass were positively correlated with the δ(13)C and δ(15)N of organic soil across aggregates and land use types, whereas the (13)C and (15)N enrichment of microbial biomass exhibited linear decreases with the corresponding C:N ratio of organic soil. Our results suggest that shifts in the natural (13)C and (15)N abundance of microbial biomass reflect changes in the stabilization and turnover of soil organic matter (SOM) and thereby imply that afforestation can greatly impact SOM accumulation over the long-term. Copyright © 2016 Elsevier B.V. All rights reserved.

Erosion and physical transport via overland flow of arsenic and lead bound to silt-sized particles

PubMed Central

Cadwalader, G. Owen; Renshaw, Carl E.; Jackson, Brian P.; Magilligan, Francis J.; Landis, Joshua D.; Bostick, Benjamin C.

2011-01-01

Understanding of the transport mechanisms of contaminated soils and sediment is essential for the sustainable management of contaminated lands. In New England and elsewhere, vast areas of agricultural lands are contaminated by the historical application of lead-arsenate pesticides. Left undisturbed the physical and chemical mobility of As and Pb in these soils is limited due to their strong affinity for adsorption onto solid phases. However, soil disturbance promotes erosion and overland flow during intense rainstorms. Here we investigate the event-scale transport of disturbed As and Pb contaminated soils through measurement of concentrations of As and Pb in suspended sediment and changes in Pb isotopic ratios in overland flow. Investigation of several rain events shows that where land disturbance has occurred, physical transport of silt-sized particles and aggregates is the primary transport vector of As and Pb derived from pesticide-contaminated soil. Although both As and Pb are associated with similarly-sized particles, we find that solid-phase As is more effectively mobilized and transported than Pb. Our results demonstrate that anthropogenic land disturbance of historical lands contaminated with lead-arsenate pesticides may redistribute, through physical transport, significant amounts of As, and lesser amounts of Pb, to riparian and stream sediments, where they are potentially more bioavailable. PMID:21552357

Effects of straw and biochar amendments on aggregate stability, soil organic carbon, and enzyme activities in the Loess Plateau, China.

PubMed

Zhang, Man; Cheng, Gong; Feng, Hao; Sun, Benhua; Zhao, Ying; Chen, Haixin; Chen, Jing; Dyck, Miles; Wang, Xudong; Zhang, Jianguo; Zhang, Afeng

2017-04-01

Soil from the Loess Plateau of China is typically low in organic carbon and generally has poor aggregate stability. Application of organic amendments to these soils could help to increase and sustain soil organic matter levels and thus to enhance soil aggregate stability. A field experiment was carried out to evaluate the effect of the application of wheat straw and wheat straw-derived biochar (pyrolyzed at 350-550 °C) amendments on soil aggregate stability, soil organic carbon (SOC), and enzyme activities in a representative Chinese Loess soil during summer maize and winter wheat growing season from 2013 to 2015. Five treatments were set up as follows: no fertilization (CK), application of inorganic fertilizer (N), wheat straw applied at 8 t ha -1 with inorganic fertilizer (S8), and wheat straw-derived biochar applied at 8 t ha -1 (B8) and 16 t ha -1 (B16) with inorganic fertilizer, respectively. Compared to the N treatment, straw and straw-derived biochar amendments significantly increased SOC (by 33.7-79.6%), microbial biomass carbon (by 18.9-46.5%), and microbial biomass nitrogen (by 8.3-38.2%), while total nitrogen (TN) only increased significantly in the B16 plot (by 24.1%). The 8 t ha -1 straw and biochar applications had no significant effects on soil aggregation, but a significant increase in soil macro-aggregates (>2 mm) (by 105.8%) was observed in the B16 treatment. The concentrations of aggregate-associated SOC increased by 40.4-105.8% in macro-aggregates (>2 mm) under straw and biochar amendments relative to the N treatment. No significant differences in invertase and alkaline phosphatase activity were detected among different treatments. However, urease activity was greater in the biochar treatment than the straw treatment, indicating that biochar amendment improved the transformation of nitrogen in the soil. The carbon pool index and carbon management index were increased with straw and biochar amendments, especially in the B16 treatment. In conclusion, application of carbonized crop residue as biochar, especially at a rate of 16 t ha -1 , could be a potential solution to recover the depleted SOC and enhance the formation of macro-aggregates in Loess Plateau soils of China.

Visualizing and Quantifying Bioaccessible Pores in Field-Aged Petroleum Hydrocarbon-Contaminated Clay Soils Using Synchrotron-based X-ray Computed Tomography

NASA Astrophysics Data System (ADS)

Chang, W.; Kim, J.; Zhu, N.; McBeth, J. M.

2015-12-01

Microbial hydrocarbon degradation is environmentally significant and applicable to contaminated site remediation practices only when hydrocarbons (substrates) are physically bioaccessible to bacteria in soil matrices. Powerful X-rays are produced by synchrotron radiation, allowing for bioaccessible pores in soil (larger than 4 microns), where bacteria can be accommodated, colonize and remain active, can be visualized at a much higher resolution. This study visualized and quantified such bioaccessible pores in intact field-aged, oil-contaminated unsaturated soil fractions, and examined the relationship between the abundance of bioaccessible pores and hydrocarbon biodegradation. Using synchrotron-based X-ray Computed Tomography (CT) at the Canadian Light Source, a large dataset of soil particle characteristics, such as pore volumes, surface areas, number of pores and pore size distribution, was generated. Duplicate samples of five different soil fractions with different soil aggregate sizes and water contents (13, 18 and 25%) were examined. The method for calculating the number and distribution of bioaccessible pores using CT images was validated using the known porosity of Ottawa sand. This study indicated that the distribution of bioaccessible pore sizes in soil fractions are very closely related to microbial enhancement. A follow-up aerobic biodegradation experiment for the soils at 17 °C (average site temperature) over 90 days confirmed that a notable decrease in hydrocarbon concentrations occurred in soils fractions with abundant bioaccessible pores and with a larger number of pores between 10 and 100 μm. The hydrocarbon degradation in bioactive soil fractions was extended to relatively high-molecular-weight hydrocarbons (C16-C34). This study provides quantitative information about how internal soil pore characteristics can influence bioremediation performance.

Soil organic matter stabilization in buried paleosols of the Great Plains

NASA Astrophysics Data System (ADS)

Chaopricha, N. T.; Marin-Spiotta, E.; Mason, J. A.; Mueller, C. W.

2010-12-01

Understanding the mechanisms that control soil organic matter (SOM) stabilization is important for understanding how soil carbon is sequestered over millennia, and for predicting how future disturbances may affect soil carbon stocks. We are studying the mechanisms controlling SOM stabilization in the Brady Soil, a buried paleosol in Holocene loess deposits spanning much of the central Great Plains of the United States. The Brady Soil developed 9,000-13,500 years ago during a time of warming and drying that resulted in a shift from C3 to C4 dominated plants. The Brady soil is unusual in that it has very dark coloring, although it contains less than <1 % organic C. Although the Brady Soil has low C concentrations, it contains significant carbon stocks due to its thickness (~1 m) and wide geographic extent. We sampled the modern surface A horizon and multiple buried paleosol horizons from two roadcuts near Wauneta in southwestern Nebraska. We are using isotopic, spectroscopic, and geochemical techniques to examine what plant and microbially-derived compounds are have been preserved in the Brady Soil. We used a combined physical density and particle size fractionation method to separate particulate organic matter associated with minerals from that within and outside of soil aggregates. We found the largest and darkest amounts of organic C in aggregate-protected SOM greater than 20 µm in diameter. Density and textural fractionation revealed that much of the SOM is bound within aggregates, indicating that protection within aggregates is a major contributor to SOM- stabilization in the Brady Soil. We are conducting a long-term lab soil incubation with soils collected from the modern A horizon and the Brady Soil to determine if the buried SOM becomes microbially available when exposed to the modern atmosphere. We are measuring potential rates of respiration and production of CH4 and N2O. Results so far show respiration rates at field moisture for both modern and buried horizons are limited by water, suggesting dry environmental conditions may have helped to preserve SOM in the Brady Soil. We are investigating the potential for chemical stabilization of the dark SOM preserved in the buried paleosol by characterizing C chemistry using solid-state 13C-NMR spectroscopy. Furthermore, we plan to use lipid analyses and pyrolysis GC/MS to determine likely sources for the SOM: microbial vs plant. Combining information on the physical location of SOM in the soil, its chemical composition, decomposability, and radiocarbon based mean residence time estimates will allow us to determine (a) the source of the dark coloration in the Brady soil, (b) the mechanisms that have contributed to its preservation for the last 10,000 years, and (c) the likelihood this large soil C stock will be lost to the atmosphere if exposed during disturbance.

Contribution of raindrop impact to the change of soil physical properties and water erosion under semi-arid rainfalls.

PubMed

Vaezi, Ali Reza; Ahmadi, Morvarid; Cerdà, Artemi

2017-04-01

Soil erosion by water is a three-phase process that consists of detachment of soil particles from the soil mass, transportation of detached particles either by raindrop impact or surface water flow, and sedimentation. Detachment by raindrops is a key component of the soil erosion process. However, little information is available on the role of raindrop impact on soil losses in the semi-arid regions where vegetation cover is often poor and does not protect the soil from rainfall. The objective of this study is to determine the contribution of raindrop impact to changes in soil physical properties and soil losses in a semiarid weakly-aggregated agricultural soil. Soil losses were measured under simulated rainfalls of 10, 20, 30, 40, 50, 60 and 70mmh -1 , and under two conditions: i) with raindrop impact; and, ii) without raindrop impact. Three replications at each rainfall intensity and condition resulted in a total of 42 microplots of 1m×1.4m installed on a 10% slope according to a randomized complete block design. The contribution of raindrop impact to soil loss was computed using the difference between soil loss with raindrop impact and without raindrop impact at each rainfall intensity. Soil physical properties (aggregate size, bulk density and infiltration rate) were strongly damaged by raindrop impact as rainfall intensity increased. Soil loss was significantly affected by rainfall intensity under both soil surface conditions. The contribution of raindrop impact to soil loss decreased steadily with increasing rainfall intensity. At the lower rainfall intensities (20-30mmh -1 ), raindrop impact was the dominant factor controlling soil loss from the plots (68%) while at the higher rainfall intensities (40-70mmh -1 ) soil loss was mostly affected by increasing runoff discharge. At higher rainfall intensities the sheet flow protected the soil from raindrop impact. Copyright © 2017 Elsevier B.V. All rights reserved.

Role of rain intensity and soil colloids in the retention of surfactant-stabilized silver nanoparticles in soil.

PubMed

Makselon, Joanna; Siebers, Nina; Meier, Florian; Vereecken, Harry; Klumpp, Erwin

2018-07-01

Undisturbed outdoor lysimeters containing arable loamy sand soil were used to examine the influence of either heavy rain events (high frequency of high rain intensity), steady rain (continuous rainfall of low rain intensity), and natural rainfall on the transport and retention of surfactant-stabilized silver nanoparticles (AgNP). In addition, the AgNP-soil associations within the A p horizon were analyzed by means of particle-size fractionation, asymmetrical flow field-flow fractionation coupled with UV/Vis-detection and inductively coupled plasma mass spectrometer (AF4-UV/Vis-ICP-MS), and transmission electron microscopy coupled to an energy-dispersive X-ray (TEM-EDX) analyzer. The results showed that AgNP breakthrough for all rain events was less than 0.1% of the total AgNP mass applied, highlighting that nearly all AgNP were retained in the soil. Heavy rain treatment and natural rainfall revealed enhanced AgNP transport within the A p horizon, which was attributed to the high pore water flow velocities and to the mobilization of AgNP-soil colloid associations. Particle-size fractionation of the soil revealed that AgNP were present in each size fraction and therefore indicated strong associations between AgNP and soil. In particular, water-dispersible colloids (WDC) in the size range of 0.45-0.1 μm were found to exhibit high potential for AgNP attachment. The AF4-UV/Vis-ICP-MS and TEM-EDX analyses of the WDC fraction confirmed that AgNP were persistent in soil and associated to soil colloids (mainly composed of Al, Fe, Si, and organic matter). These results confirm the particularly important role of soil colloids in the retention and remobilization of AgNP in soil. Furthermore, AF4-UV/Vis-ICP-MS results indicated the presence of single, homo-aggregated, and small AgNP probably due to dissolution. Copyright © 2018 Elsevier Ltd. All rights reserved.

Enzymatic biofilm digestion in soil aggregates facilitates the release of particulate organic matter by sonication

NASA Astrophysics Data System (ADS)

Büks, Frederick; Kaupenjohann, Martin

2016-10-01

The stability of soil aggregates against shearing and compressive forces as well as water-caused dispersion is an integral marker of soil quality. High stability results in less compaction and erosion and has been linked to enhanced water retention, dynamic water transport and aeration regimes, increased rooting depth, and protection of soil organic matter (SOM) against microbial degradation. In turn, particulate organic matter is supposed to support soil aggregate stabilization. For decades the importance of biofilm extracellular polymeric substances (EPSs) regarding particulate organic matter (POM) occlusion and aggregate stability has been canonical because of its distribution, geometric structure and ability to link primary particles. However, experimental proof is still missing. This lack is mainly due to methodological reasons. Thus, the objective of this work is to develop a method of enzymatic biofilm detachment for studying the effects of EPSs on POM occlusion. The method combines an enzymatic pre-treatment with different activities of α-glucosidase, β-galactosidase, DNAse and lipase with a subsequent sequential ultrasonic treatment for disaggregation and density fractionation of soils. POM releases of treated samples were compared to an enzyme-free control. To test the efficacy of biofilm detachment the ratio of bacterial DNA from suspended cells and the remaining biofilm after enzymatic treatment were measured by quantitative real-time PCR. Although the enzyme treatment was not sufficient for total biofilm removal, our results indicate that EPSs may attach POM within soil aggregates. The tendency to additional POM release with increased application of enzymes was attributed to a slight loss in aggregate stability. This suggests that an effect of agricultural practices on soil microbial populations could influence POM occlusion/aggregate stability and thereby carbon cycle/soil quality.

Feasibility study on the use of soil washing to remediate the As-Hg contamination at an ancient mining and metallurgy area.

PubMed

Sierra, C; Menéndez-Aguado, J M; Afif, E; Carrero, M; Gallego, J R

2011-11-30

Soils in abandoned mining sites generally present high concentrations of trace elements, such as As and Hg. Here we assessed the feasibility of washing procedures to physically separate these toxic elements from soils affected by a considerable amount of mining and metallurgical waste ("La Soterraña", Asturias, NW Spain). After exhaustive soil sampling and subsequent particle-size separation via wet sieving, chemical and mineralogical analysis revealed that the finer fractions held very high concentrations of As (up to 32,500 ppm) and Hg (up to 1600 ppm). These elements were both associated mainly with Fe/Mn oxides and hydroxides. Textural and geochemical data were correlated with the geological substrate by means of a multivariate statistical analysis. In addition, the Hg liberation size (below 200 μm) was determined to be main factor conditioning the selection of suitable soil washing strategies. These studies were finally complemented with a specific-gravity study performed with a C800 Mozley separator together with a grindability test, both novel approaches in soil washing feasibility studies. The results highlighted the difficulties in treating "La Soterraña" soils. These difficulties are attributed to the presence of contaminants embedded in the soil and spoil heap aggregates, caused by the meteorization of gangue and ore minerals. As a result of these two characteristics, high concentrations of the contaminants accumulate in all grain-size fractions. Therefore, the soil washing approach proposed here includes the grinding of particles above 125 μm. Copyright © 2011 Elsevier B.V. All rights reserved.

Soil structural stability assessment with the fluidized bed, aggregate stability, and rainfall simulation on long-term tillage and crop rotation systems

USDA-ARS?s Scientific Manuscript database

The formation of stable soil aggregates is an important indicator of soil susceptibility to erosion and a factor defining soil health. On cropland, tillage practices and crop rotations have shown to control soil biophysical properties with potential consequences on erosion susceptibility. Thus, the ...

Effect of aggregation on SOC transport: linking soil properties to sediment organic matter

NASA Astrophysics Data System (ADS)

Kuhn, Nikolaus J.

2016-04-01

Soils are an interface between the Earth's spheres and shaped by the nature of the interaction between them. The relevance of soil properties for the nature of the interaction between atmosphere, hydrosphere and biosphere is well-studied and accepted, on point- or ecotone-scale. However, this understanding of the largely vertical connections between spheres is not matched by a similar recognition of soil properties affecting processes acting largely in a lateral way across the land surface, such as erosion, transport and deposition of soil and the associated organic matter. Understanding the redistribution of eroded soil organic matter falls into several disciplines, most notably soil science, agronomy, hydrology and geomorphology, and recently into biogeochemistry. Accordingly, the way soil and sediment are described differs: in soil science, aggregation and structure are essential properties, while most process-based soil erosion models treat soil as a mixture of individual mineral grains, based on concepts derived in fluvial geomorphology or civil engineering. The actual behavior of aggregated sediment and the associated organic matter is not reflected by either approach and difficult to capture due to the dynamic nature of aggregation, especially in an environment such as running water. Still, a proxy to assess the uncertainties introduced by aggregation on the behavior of soil/sediment organic while moving in water across landscapes and into the aquatic system would represent a major step forward. To develop such a proxy, a database collating relevant soil, organic matter and sediment properties could serve as an initial step to identify which soil types and erosion scenarios are prone to generate a high uncertainty compared to the use of soil texture in erosion models. Furthermore, it could serve to develop standardized analytical procedures for appropriate description of soil and organic matter as sediment.

Enzymatic activity inside and outside of water-stable aggregates in soils under different land use

NASA Astrophysics Data System (ADS)

Garbuz, S. A.; Yaroslavtseva, N. V.; Kholodov, V. A.

2016-03-01

A method is presented for assessing the distribution of enzymatic activity inside and outside of water-stable aggregates. Two samples of water-stable aggregates >1 mm have been isolated from dry aggregates of 1-2 mm. To determine the enzymatic activity, a substrate has been added to one of the samples without disaggregation; the other sample has been preliminarily disaggregated. Enzymatic activity within waterstable aggregates has been assessed from the difference between the obtained results under the supposition that the penetration of substrate within the water-saturated aggregates is hampered, and enzymatic reactions occur only at the periphery. The levels and distributions of enzymatic (peroxidase, polyphenol oxidase, and catalase) activities in water-stable aggregates of soddy-podzolic soils under forest and plowland and typical chernozems of long-term field experiments have been studied. The peroxidase, polyphenol oxidase, and catalase activities of water-stable aggregates vary from 6 to 23, from 7 to 30, and from 5 to 7 mmol/(g h), respectively. The ratio between the enzymatic activities inside and outside of soil aggregates showed a higher dependence on soil type and land use, as well as on the input of organic matter and the structural state, than the general activity level in water-stable aggregates.

Effect of farmyard manure rate on water erosion of a Mediterranean soil: determination of the critical point of inefficacy

NASA Astrophysics Data System (ADS)

Annabi, Mohamed; Bahri, Haithem; Cheick M'Hamed, Hatem; Hermessi, Taoufik

2016-04-01

Intensive cultivation of soils, using multiple soil tillage, led to the decrease of their organic matter content and structural stability in several cultivated area of the Mediterranean countries. In these degraded soils, the addition of organic products, traditionally the animal manure, should improve soil health among them the resistance of soil to water erosion. The aim of this study was to evaluate after 1 year of the addition to a cambisoil different doses of farmyard manure on soil organic matter content, on microbial activity and on aggregate stability (proxy to soil resistance to water erosion). The statistical process (bilinear model) was used to found a point at which the addition of the organic product no longer influences the soil resistance to erosion. The farmyard manure issued from a cow breeding was composted passively during 4 months and used to amend a small plots of a cultivated cambisol (silty-clay texture, 0.9% TOC) located in the northeast of Tunisia (Morneg region). The manure was intimately incorporate to the soil. The manure organic matter content was 31%, and its isohumic coefficient was 49%. Twelve dose of manure were tested: from 0 to 220 t C.ha-1. The experiment was started on September 2011. In November 2012, soil sampling was done and soil organic carbon content (Walkley-Black method) and soil aggregate stability (wet method of Le Bissonnais) were assessed. A laboratory incubations of soil+manure mixtures, with the same proportions as tested in the field conditions, was carried at 28°C and at 75% of the mixture field capacity water retention. Carbon mineralization was monitored during three months incubation. Results show that the addition of farmyard manure stimulated the microbial activity proportionally to the added dose. This activation is due to the presence of easily biodegradable carbon in the manure, which increases with increasing manure dose. On the other hand, the addition of manure increased the aggregate stability with the manure dose increasing. This aggregate stabilization is due to the stimulation of microbial activity (r= 0.72, n=12) which can improves the aggregate stability by increasing the aggregate cohesion by adhesive substances such as the polysaccharides and by the enmeshment of aggregate by fungal hyphea. The increase of organic matter content due to manure addition contributes also to aggregate stabilization with a high regression slope with the first manure doses (less then 120 t C.ha-1). Using a bi-linear model, reach 2.3% of soil organic carbon seems to be a critical level from which the aggregate stability evolves little.

Sorption of vanadium (V) onto natural soil colloids under various solution pH and ionic strength conditions.

PubMed

Luo, Xiuhua; Yu, Lin; Wang, Changzhao; Yin, Xianqiang; Mosa, Ahmed; Lv, Jialong; Sun, Huimin

2017-02-01

Batch sorption kinetics and isothermal characteristics of V(V) were investigated on three natural soil colloids (manual loessial soil colloid (MSC), aeolian sandy soil colloid (ASC), and cultivated loessial soil colloid (CSC)) under various solution pH and ionic strength (IS) conditions. Colloids were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). AFM micrographs showed CSC with an aggregated shape with larger particle diameter as compared with ASC and MSC. XRD spectra revealed the presence of different minerals in natural soil colloids including biotite, kaolinite, calcite and quartz, which might contribute to sorption process. The sorption ability decreased with increase of colloidal particle size. The sorption was mainly attributed to complexation by active carboxylate and alcohol groups of colloidal components. Sorption kinetics and isotherms of V(V) onto natural soil colloids were best fitted with Pseudo-second-order and Freundlich models. Langmuir model indicated that sorption capacity of MSC and ASC was comparable (285.7 and 238.1 mg g -1 ); however, CSC exhibited the lowest sorption capacity (41.5 mg g -1 ) due to its larger particle diameter and aggregated shape. The maximum V(V) sorption capacity reached plateau values at a solution pH ranged between 5.0 and 9.0 for MSC and ASC, and 6.0-8.0 for CSC. Sorption capacity of V(V) onto natural soil colloids decreased with increasing IS. Based on result of this study we can conclude that sorption of V(V) onto natural soil colloids is pH- and IS-dependent. These findings provide insights on the remediation of vanadium-contaminated soils. Copyright © 2016 Elsevier Ltd. All rights reserved.

Novel Insights in the Fecal Egg Count Reduction Test for Monitoring Drug Efficacy against Soil-Transmitted Helminths in Large-Scale Treatment Programs

PubMed Central

Levecke, Bruno; Speybroeck, Niko; Dobson, Robert J.; Vercruysse, Jozef; Charlier, Johannes

2011-01-01

Background The fecal egg count reduction test (FECRT) is recommended to monitor drug efficacy against soil-transmitted helminths (STHs) in public health. However, the impact of factors inherent to study design (sample size and detection limit of the fecal egg count (FEC) method) and host-parasite interactions (mean baseline FEC and aggregation of FEC across host population) on the reliability of FECRT is poorly understood. Methodology/Principal Findings A simulation study was performed in which FECRT was assessed under varying conditions of the aforementioned factors. Classification trees were built to explore critical values for these factors required to obtain conclusive FECRT results. The outcome of this analysis was subsequently validated on five efficacy trials across Africa, Asia, and Latin America. Unsatisfactory (<85.0%) sensitivity and specificity results to detect reduced efficacy were found if sample sizes were small (<10) or if sample sizes were moderate (10–49) combined with highly aggregated FEC (k<0.25). FECRT remained inconclusive under any evaluated condition for drug efficacies ranging from 87.5% to 92.5% for a reduced-efficacy-threshold of 90% and from 92.5% to 97.5% for a threshold of 95%. The most discriminatory study design required 200 subjects independent of STH status (including subjects who are not excreting eggs). For this sample size, the detection limit of the FEC method and the level of aggregation of the FEC did not affect the interpretation of the FECRT. Only for a threshold of 90%, mean baseline FEC <150 eggs per gram of stool led to a reduced discriminatory power. Conclusions/Significance This study confirms that the interpretation of FECRT is affected by a complex interplay of factors inherent to both study design and host-parasite interactions. The results also highlight that revision of the current World Health Organization guidelines to monitor drug efficacy is indicated. We, therefore, propose novel guidelines to support future monitoring programs. PMID:22180801

Effects of soil aggregates on debris-flow mobilization: Results from ring-shear experiments

USGS Publications Warehouse

Iverson, Neal R.; Mann, Janet E.; Iverson, Richard M.

2010-01-01

Rates and styles of landslide motion are sensitive to pore-water pressure changes caused by changes in soil porosity accompanying shear deformation. Soil may either contract or dilate upon shearing, depending upon whether its initial porosity is greater or less, respectively, than a critical-state porosity attained after sufficiently high strain. We observed complications in this behavior, however, during rate-controlled (0.02 m s−1) ring-shear experiments conducted on naturally aggregated dense loamy sand at low confining stresses (10.6 and 40 kPa). The aggregated soil first dilated and then contracted to porosities less than initial values, whereas the same soil with its aggregates destroyed monotonically dilated. We infer that aggregates persisted initially during shear and caused dilation before their eventual breakdown enabled net contraction. An implication of this contraction, demonstrated in experiments in which initial soil porosity was varied, is that the value of porosity distinguishing initially contractive from dilative behavior can be significantly larger than the critical-state porosity, which develops only after disaggregation ceases at high strains. In addition, post-dilative contraction may produce excess pore pressures, thereby reducing frictional strength and facilitating debris-flow mobilization. We infer that results of triaxial tests, which generally produce strains at least a factor of ∼ 4 smaller than those we observed at the inception of post-dilative contraction, do not allow soil contraction to be ruled out as a mechanism for debris-flow mobilization in dense soils containing aggregates.

Instability improvement of the subgrade soils by lime addition at Borg El-Arab, Alexandria, Egypt

NASA Astrophysics Data System (ADS)

El Shinawi, A.

2017-06-01

Subgrade soils can affect the stability of any construction elsewhere, instability problems were found at Borg El-Arab, Alexandria, Egypt. This paper investigates geoengineering properties of lime treated subgrade soils at Borg El-Arab. Basic laboratory tests, such as water content, wet and dry density, grain size, specific gravity and Atterberg limits, were performed for twenty-five samples. Moisture-density (compaction); California Bearing Ratio (CBR) and Unconfined Compression Strength (UCS) were conducted on treated and natural soils. The measured geotechnical parameters of the treated soil shows that 6% lime is good enough to stabilize the subgrade soils. It was found that by adding lime, samples shifted to coarser side, Atterberg limits values of the treated soil samples decreased and this will improve the soil to be more stable. On the other hand, Subgrade soils improved as a result of the bonding fine particles, cemented together to form larger size and reduce the plastiCity index which increase soils strength. The environmental scanning electron microscope (ESEM) is point to the presence of innovative aggregated cement materials which reduce the porosity and increase the strength as a long-term curing. Consequently, the mixture of soil with the lime has acceptable mechanical characteristics where, it composed of a high strength base or sub-base materials and this mixture considered as subgrade soil for stabilizations and mitigation the instability problems that found at Borg Al-Arab, Egypt.

Relationships between slope erosion processes and aggregate stability of Ultisols from subtropical China during rainstorms

NASA Astrophysics Data System (ADS)

Liu, Gang; Xiao, Hai; Liu, Puling

2017-04-01

Soil aggregates, being a key soil structural unit, influence several soil physical properties such as water infiltration, runoff and erosion. The relationship between soil aggregate stability and interrill and rill erodibility is unclear but critical to process-based erosion prediction models. One obvious reason is that it is hard to distinguish between interrill and rill-eroded sediment during the erosion process. This study was designed to partition interrill and rill erosion rates and relates them to the aggregate stability of Ultisols in subtropical China. Six kinds of rare earth element (REE) were applied as tracers mixed with two cultivated soils derived from the Quaternary red clay soil and the shale soil at six slope positions. Soil aggregate stability was determined by the Le Bissonnais (LB)-method. Simulated rainfall with three intensities (60, 90 and 120 mm/h) were applied to a soil plot (2.25 m long, 0.5 m wide, 0.2 m deep) at three slope gradients (10°, 20° and 30°) with duration of 30 min after runoff initiation. The results indicated that interrill and rill erosion increased with increasing rainfall intensity and slope gradient for both types of soil. Rill and interrill erosion rates of the shale soil were much higher than those of the Quaternary red clay soil. Rill erosion contribution enhanced with increasing rainfall intensity and slope gradient for both soils. Percentage of the downslope area erosion to total erosion was the largest, followed by the mid-slope area and then upslope area. Equations using an aggregate stability index As to replace the erodibility factor of interrill and rill erosion in the Water Erosion Prediction Project (WEPP) model were constructed after analyzing the relationships between estimated and measured rill and interrill erosion data. It was shown that these equations based on the stability index, As, have the potential to improve methods for assessing interrill and rill erosion erodibility synchronously for the subtropical Ultisols by using REE tracing method.

Arbuscular mycorrhizal fungi make a complex contribution to soil aggregation

NASA Astrophysics Data System (ADS)

McGee, Peter; Daynes, Cathal; Damien, Field

2013-04-01

Soil aggregates contain solid and fluid components. Aggregates develop as a consequence of the organic materials, plants and hyphae of arbuscular mycorrhizal (AM) fungi acting on the solid phase. Various correlative studies indicate hyphae of AM fungi enmesh soil particles, but their impact on the pore space is poorly understood. Hyphae may penetrate between particles, remove water from interstitial spaces, and otherwise re-arrange the solid phase. Thus we might predict that AM fungi also change the pore architecture of aggregates. Direct observations of pore architecture of soil, such as by computer-aided tomography (CT), is difficult. The refractive natures of solid and biological material are similar. The plant-available water in various treatments allows us to infer changes in pore architecture. Our experimental studies indicate AM fungi have a complex role in the formation and development of aggregates. Soils formed from compost and coarse subsoil materials were planted with mycorrhizal or non-mycorrhizal seedlings and the resultant soils compared after 6 or 14 months in separate experiments. As well as enmeshing particles, AM fungi were associated with the development of a complex pore space and greater pore volume. Even though AM fungi add organic matter to soil, the modification of pore space is not correlated with organic carbon. In a separate study, we visualised hyphae of AM fungi in a coarse material using CT. In this study, hyphae appeared to grow close to the surfaces of particles with limited ramification across the pore spaces. Hyphae of AM fungi appear to utilise soil moisture for their growth and development of mycelium. The strong correlation between moisture and hyphae has profound implications for soil aggregation, plant utilisation of soil water, and the distribution of water as water availability declines.

Composition and molecular scale structure of nanophases formed by precipitation of biotite weathering products

NASA Astrophysics Data System (ADS)

Tamrat, Wuhib Zewde; Rose, Jérôme; Grauby, Olivier; Doelsch, Emmanuel; Levard, Clément; Chaurand, Perrine; Basile-Doelsch, Isabelle

2018-05-01

Because of their large surface area and reactivity, nanometric-size soil mineral phases have a high potential for soil organic matter stabilization, contaminant sorption or soil aggregation. In the literature, Fe and Al phases have been the main targets of batch-synthesized nanomineral studies while nano-aluminosilicates (Al and Si phases) have been mainly studied in Andic soils. In the present work, we synthesized secondary nanophases of Fe, Al and Si. To simulate a system as close as possible to soil conditions, we conducted laboratory simulations of the processes of (1) biotite alteration in acidic conditions producing a Al Si Fe Mg K leachate solution and (2) the following neoformation of secondary nanophases by titrating the leachate solution to pH 4.2, 5 and 7. The morphology of the nanophases, their size, crystallinity and chemistry were characterized by TEM-EDX on single particles and their local atomic structure by EXAFS (Extended X-ray Absorption Fine Structure) at the Fe absorption K-edge. The main nanophases formed were amorphous particles 10-60 nm in size whose composition (dominated by Fe and Si) was strongly controlled by the pH conditions at the end of the titration. At pH 4.2 and pH 7, the structure of the nanophases was dominated by the polymerization of Fe, which was hindered by Al, Si, Mg and K. Conversely, at pH 5, the polymerization of Fe was counteracted by precipitation of high amounts of Si. The synthetized nanophases were estimated to be rather analogous to nanophases formed in natural biotite-bearing soils. Because of their small size and potential high surface reactivity, the adsorption capacities of these nanophases with respect to the OM should be revisited in the framework of soil C storage.

The physico-chemical properties and structural characteristics of artificial soil for cut slope restoration in Southwestern China

PubMed Central

Chen, Shunan; Ai, Xiaoyan; Dong, Tengyun; Li, Binbin; Luo, Ruihong; Ai, Yingwei; Chen, Zhaoqiong; Li, Chuanren

2016-01-01

Cut slopes are frequently generated by construction work in hilly areas, and artificial soil is often sprayed onto them to promote ecological rehabilitation. The artificial soil properties are very important for effective management of the slopes. This paper uses fractal and moment methods to characterize soil particle size distribution (PSD) and aggregates composition. The fractal dimension (D) showed linear relationships between clay, silt, and sand contents, with coefficients of determination from 0.843 to 0.875, suggesting that using of D to evaluate the PSD of artificial soils is reasonable. The bias (CS) and peak convex (CE) coefficients showed significant correlations with structure failure rate, moisture content, and total porosity, which validated the moment method to quantitatively describe soil structure. Railway slope (RS) soil has lower organic carbon and soil moisture, and higher pH than natural slope soil. Overall, RS exhibited poor soil structure and physicochemical properties, increasing the risk of soil erosion. Hence, more effective management measures should be adopted to promote the restoration of cut slopes. PMID:26883986

Soil Aggregates and Associated Organic Matter under Conventional Tillage, No-Tillage, and Forest Succession after Three Decades

PubMed Central

Devine, Scott; Markewitz, Daniel; Hendrix, Paul; Coleman, David

2014-01-01

Impacts of land use on soil organic C (SOC) are of interest relative to SOC sequestration and soil sustainability. The role of aggregate stability in SOC storage under contrasting land uses has been of particular interest relative to conventional tillage (CT) and no-till (NT) agriculture. This study compares soil structure and SOC fractions at the 30-yr-old Horseshoe Bend Agroecosystem Experiment (HSB). This research is unique in comparing NT and CT with adjacent land concurrently undergoing forest succession (FS) and in sampling to depths (15–28 cm) previously not studied at HSB. A soil moving experiment (SME) was also undertaken to monitor 1-yr changes in SOC and aggregation. After 30 years, enhanced aggregate stability under NT compared to CT was limited to a depth of 5 cm, while enhanced aggregate stability under FS compared to CT occurred to a depth of 28 cm and FS exceeded NT from 5–28 cm. Increases in SOC concentrations generally followed the increases in stability, except that no differences in SOC concentration were observed from 15–28 cm despite greater aggregate stability. Land use differences in SOC were explained equally by differences in particulate organic carbon (POC) and in silt-clay associated fine C. Enhanced structural stability of the SME soil was observed under FS and was linked to an increase of 1 Mg SOC ha−1 in 0–5 cm, of which 90% could be attributed to a POC increase. The crushing of macroaggregates in the SME soil also induced a 10% reduction in SOC over 1 yr that occurred under all three land uses from 5–15 cm. The majority of this loss was in the fine C fraction. NT and FS ecosystems had greater aggregation and carbon storage at the soil surface but only FS increased aggregation below the surface, although in the absence of increased carbon storage. PMID:24465460

Biochar Improves Soil Aggregate Stability and Water Availability in a Mollisol after Three Years of Field Application

PubMed Central

Zhang, Yulan; Yang, Lijie; Yu, Chunxiao; Yin, Guanghua; Doane, Timothy A.; Wu, Zhijie; Zhu, Ping; Ma, Xingzhu

2016-01-01

A field experiment was carried out to evaluate the effect of organic amendments on soil organic carbon, total nitrogen, bulk density, aggregate stability, field capacity and plant available water in a representative Chinese Mollisol. Four treatments were as follows: no fertilization (CK), application of inorganic fertilizer (NPK), combined application of inorganic fertilizer with maize straw (NPK+S) and addition of biochar with inorganic fertilizer (NPK+B). Our results showed that after three consecutive years of application, the values of soil bulk density were significantly lower in both organic amendment-treated plots than in unamended (CK and NPK) plots. Compared with NPK, NPK+B more effectively increased the contents of soil organic carbon, improved the relative proportion of soil macro-aggregates and mean weight diameter, and enhanced field capacity as well as plant available water. Organic amendments had no obvious effect on soil C/N ratio or wilting coefficient. The results of linear regression indicated that the improvement in soil water retention could be attributed to the increases in soil organic carbon and aggregate stability. PMID:27191160

Biochar Improves Soil Aggregate Stability and Water Availability in a Mollisol after Three Years of Field Application.

PubMed

Ma, Ningning; Zhang, Lili; Zhang, Yulan; Yang, Lijie; Yu, Chunxiao; Yin, Guanghua; Doane, Timothy A; Wu, Zhijie; Zhu, Ping; Ma, Xingzhu

2016-01-01

A field experiment was carried out to evaluate the effect of organic amendments on soil organic carbon, total nitrogen, bulk density, aggregate stability, field capacity and plant available water in a representative Chinese Mollisol. Four treatments were as follows: no fertilization (CK), application of inorganic fertilizer (NPK), combined application of inorganic fertilizer with maize straw (NPK+S) and addition of biochar with inorganic fertilizer (NPK+B). Our results showed that after three consecutive years of application, the values of soil bulk density were significantly lower in both organic amendment-treated plots than in unamended (CK and NPK) plots. Compared with NPK, NPK+B more effectively increased the contents of soil organic carbon, improved the relative proportion of soil macro-aggregates and mean weight diameter, and enhanced field capacity as well as plant available water. Organic amendments had no obvious effect on soil C/N ratio or wilting coefficient. The results of linear regression indicated that the improvement in soil water retention could be attributed to the increases in soil organic carbon and aggregate stability.

Fate of small charred particles in soils - importance of aggregation

NASA Astrophysics Data System (ADS)

Mueller, C. W.; Pechenkina, N.; Grünz, G.; Kölbl, A.; Steffens, M.; Heister, K.; Kögel-Knabner, I.

2009-04-01

Historic and recent fires affect a broad range of terrestrial ecosystems and are reflected in the composition of soil organic matter (SOM). Although the assignments of different sources and pools of black carbon (BC) are still under debate, the importance of BC for carbon (C) storage, nutrient supply and contaminant sorption is well recognized. Nevertheless, how processes of encapsulation of BC into aggregates may influence fate and properties of BC still needs further research. We observed small highly aromatic particulate OM (oPOMsmall, <20 µm) exclusively occluded within aggregates in a range of soils. As these particles were absent in the inter-aggregate soil space the question of the importance of soil aggregation for the fate of these particles is raised. In the presented study we analysed intact soil aggregates and the distribution of highly aromatic micro-scale charred particles and mineral bound SOM in Haplic Chernozems from Central Russia. We fractionated the soils by means of density to obtain particulate and mineral bound SOM fractions. The chemical composition of the obtained fractions was studied by solid-state 13C-NMR spectroscopy and energy dispersive X-ray spectroscopy (EDX). For visualization of the particles and aggregates we used scanning electron microscopy (SEM) and nano-scale secondary ion mass spectrometry (NanoSIMS). The importance of oxides for aggregate formation was elucidated by analyses of extractable Fe. Furthermore, we incubated the oPOMsmall fraction at 20°C in batch experiments to study the aggregate formation of charred particles with time. To track the fate of OM on new formed aggregates, we used a labelled amino acid mixture (min. 98 atom% 13C and 15N) as readily bioavailable OM input and isotopic tracer. The matrix of the intact soil aggregates, embedded in epoxy resin, was dominated by densely packed clay particles. At all depths particulate SOM was quantitatively dominated by the aromatic oPOM fractions, inter-aggregate POM was almost absent at higher depths. The oPOMsmall showed mainly amorphous structures and very few plant tissue structures as revealed by SEM. The oPOMsmall fraction showed a drastic increase in the content of aromatic C with depth along with decreasing aliphatic C in the thick A horizons. Almost the entire OM of the oPOMsmall fraction was composed of aromatic C compounds in the AB horizons. The incubation experiment with particles from the oPOMsmall fraction revealed a fast aggregate formation in water within a few days. With the isotopic sensitivity of the NanoSIMS 50, we were able to show spatial heterogeneous enrichments in 13C and 15N on new formed aggregates of aromatic particles.

Aggregate Stability of Tropical Soils Under Long-Term Eucalyptus Cultivation

USDA-ARS?s Scientific Manuscript database

Eucalyptus cultivation has increased in all Brazilian regions. Despite the large amount of cultivated area, little is known about how this kind of management system affects soil properties, mainly the aggregate stability. Aggregate stability analyses have proved to be a sensitive tool to measure soi...

Implications of Using Corn Stalks as a Biofuel Source: A Joint ARS and DOE Project

NASA Astrophysics Data System (ADS)

Wilhelm, W. W.; Cushman, J.

2003-12-01

Corn stover is a readily source of biomass for cellulosic ethanol production, and may provide additional income for growers. Published research shows that residue removal changes the rate of soil physical, chemical, and biological processes, and in turn, crop growth. Building a sustainable cellulosic ethanol industry based on corn residue requires residue management practices that do not reduce long-term productivity. To develop such systems, impacts of stover removal on the soil and subsequent crops must be quantified. The ARS/DOE Biofuel Project is the cooperative endeavor among scientists from six western Corn Belt US Dept. of Agriculture, Agricultural Research Service (ARS) locations and US Dept. of Energy. The objectives of the project are to determine the influence of stover removal on crop productivity, soil aggregation, quality, carbon content, and seasonal energy balance, and carbon sequestration. When residue is removed soil temperatures fluctuate more and soil water evaporation is greater. Residue removal reduces the amount of soil organic carbon (SOC), but the degree of reduction is highly dependent on degree of tillage, quantity of stover removed, and frequency of stover removal. Of the three cultural factors (stover removal, tillage, and N fertilization) tillage had the greatest effect on amount of corn-derived SOC. No tillage tends to increase the fraction of aggregates in the 2.00 to 0.25 mm size range at all removal rates. Stover harvest reduces corn-derived SOC by 35% compared to retaining stover on the soil averaged over all tillage systems. Corn stover yield has not differed across stover removal treatments in these studies. In the irrigated study, grain yield increased with stover removal. In the rain-fed studies, grain yield has not differed among residue management treatments. Incorporating the biomass ethanol fermentation by-product into a soil with low SOC showed a positive relationship between the amount of lignin added and the subsequent humic acid concentration and aggregate stability. These and future outcomes from this effort will provide DOE and the developing biomass ethanol industry knowledge and guidelines on the environmental and crop productivity consequences of large-scale collection of corn stover.

Effects of Agaricus lilaceps fairy rings on soil aggregation and microbial community structure in relation to growth stimulation of western wheatgrass (Pascopyrum smithii) in Eastern Montana rangeland.

PubMed

Caesar-Tonthat, The Can; Espeland, Erin; Caesar, Anthony J; Sainju, Upendra M; Lartey, Robert T; Gaskin, John F

2013-07-01

Stimulation of plant productivity caused by Agaricus fairy rings has been reported, but little is known about the effects of these fungi on soil aggregation and the microbial community structure, particularly the communities that can bind soil particles. We studied three concentric zones of Agaricus lilaceps fairy rings in Eastern Montana that stimulate western wheatgrass (Pascopyrum smithii): outside the ring (OUT), inside the ring (IN), and stimulated zone adjacent to the fungal fruiting bodies (SZ) to determine (1) soil aggregate proportion and stability, (2) the microbial community composition and the N-acetyl-β-D-glucosaminidase activity associated with bulk soil at 0-15 cm depth, (3) the predominant culturable bacterial communities that can bind to soil adhering to wheatgrass roots, and (4) the stimulation of wheatgrass production. In bulk soil, macroaggregates (4.75-2.00 and 2.00-0.25 mm) and aggregate stability increased in SZ compared to IN and OUT. The high ratio of fungal to bacteria (fatty acid methyl ester) and N-acetyl-β-D-glucosaminidase activity in SZ compared to IN and OUT suggest high fungal biomass. A soil sedimentation assay performed on the predominant isolates from root-adhering soil indicated more soil-binding bacteria in SZ than IN and OUT; Pseudomonas fluorescens and Stenotrophomonas maltophilia isolates predominated in SZ, whereas Bacillus spp. isolates predominated in IN and OUT. This study suggests that growth stimulation of wheatgrass in A. lilaceps fairy rings may be attributed to the activity of the fungus by enhancing soil aggregation of bulk soil at 0-15 cm depth and influencing the amount and functionality of specific predominant microbial communities in the wheatgrass root-adhering soil.

Spatial variation in microbial processes controlling carbon mineralization within soils and sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fendorf, Scott; Kleber, Markus; Nico, Peter

Soils have a defining role in global carbon cycling, having one of the largest dynamic stocks of C on earth—3300 Pg of C are stored in soils, which is three-times the amount stored in the atmosphere and more than the terrestrial land plants. An important control on soil organic matter (SOM) quantities is the mineralization rate. It is well recognized that the rate and extent of SOM mineralization is affected by climatic factors and mineral-organic matter associations. What remained elusive is to what extent constraints on microbial metabolism induced by the respiratory pathway, and specifically the electron acceptor in respiration,more » control overall rates of carbon mineralization in soils. Therefore, physical factors limiting oxygen diffusion such as soil texture and aggregate size (soil structure) may therefore be central controls on C mineralization rates. The goal of our research was therefore to determine if variations in microbial metabolic rates induced by anaerobic microsites in soils are a major control on SOM mineralization rates and thus storage. We performed a combination of laboratory experiments and field investigations will be performed to fulfill our research objectives. We used laboratory studies to examine fundamental factors of respiratory constraints (i.e., electron acceptor) on organic matter mineralization rates. We ground our laboratory studies with both manipulation of field samples and in-field measurements. Selection of the field sites is guided by variation in soil texture and structure while having (other environmental/soil factors constant. Our laboratory studies defined redox gradients and variations in microbial metabolism operating at the aggregate-scale (cm-scale) within soils using a novel constructed diffusion reactor. We further examined micro-scale variation in terminal electron accepting processes and resulting C mineralization rates within re-packed soils. A major outcome of our research is the ability to quantitatively place the importance of aggregate-based heterogeneity in microbial redox processes and the resulting lack of oxygen on the rate of carbon mineralization. Collectively, our research shows that anaerobic microsites are prevalent in soils and are important regulators of soil carbon persistence, shifting microbial metabolism to less efficient anaerobic respiration and selectively protecting otherwise bioavailable, reduced organic compounds such as lipids and waxes from decomposition. Further, shifting from anaerobic to aerobic conditions leads to a 10-fold increase in volume-specific mineralization rate, illustrating the sensitivity of anaerobically protected carbon to disturbance. Vulnerability of anaerobically protected carbon to future climate or land use change thus constitutes a yet unrecognized soil carbon-climate feedback that should be incorporated into terrestrial ecosystem models.« less

A new simplified method for measuring the permeability characteristics of highly porous media

NASA Astrophysics Data System (ADS)

Qin, Yinghong; Zhang, Mingyi; Mei, Guoxiong

2018-07-01

Fluid flow through highly porous media is important in a variety of science and technology fields, including hydrology, chemical engineering, convections in porous media, and others. While many methods have been available to measure the permeability of tight solid materials, such as concrete and rock, the technique for measuring the permeability of highly porous media is limited (such as gravel, aggregated soils, and crushed rock). This study proposes a new simplified method for measuring the permeability of highly porous media with a permeability of 10-8-10-4 m2, using a Venturi tube to gauge the gas flowing rate through the sample. Using crushed rocks and glass beads as the test media, we measure the permeability and inertial resistance factor of six types of single-size aggregate columns. We compare the testing results with the published permeability and inertial resistance factor of crushed rock and of glass beads. We found that in a log-log graph, the permeability and inertial resistance factor of a single-size aggregate heap increases linearly with the mean diameter of the aggregate. We speculate that the proposed simplified method is suitable to efficiently test the permeability and inertial resistance factor of a variety of porous media with an intrinsic permeability of 10-8-10-4 m2.

Electrical resisitivity of mechancially stablized earth wall backfill

NASA Astrophysics Data System (ADS)

Snapp, Michael; Tucker-Kulesza, Stacey; Koehn, Weston

2017-06-01

Mechanically stabilized earth (MSE) retaining walls utilized in transportation projects are typically backfilled with coarse aggregate. One of the current testing procedures to select backfill material for construction of MSE walls is the American Association of State Highway and Transportation Officials standard T 288: ;Standard Method of Test for Determining Minimum Laboratory Soil Resistivity.; T 288 is designed to test a soil sample's electrical resistivity which correlates to its corrosive potential. The test is run on soil material passing the No. 10 sieve and believed to be inappropriate for coarse aggregate. Therefore, researchers have proposed new methods to measure the electrical resistivity of coarse aggregate samples in the laboratory. There is a need to verify that the proposed methods yield results representative of the in situ conditions; however, no in situ measurement of the electrical resistivity of MSE wall backfill is established. Electrical resistivity tomography (ERT) provides a two-dimensional (2D) profile of the bulk resistivity of backfill material in situ. The objective of this study was to characterize bulk resistivity of in-place MSE wall backfill aggregate using ERT. Five MSE walls were tested via ERT to determine the bulk resistivity of the backfill. Three of the walls were reinforced with polymeric geogrid, one wall was reinforced with metallic strips, and one wall was a gravity retaining wall with no reinforcement. Variability of the measured resistivity distribution within the backfill may be a result of non-uniform particle sizes, thoroughness of compaction, and the presence of water. A quantitative post processing algorithm was developed to calculate mean bulk resistivity of in-situ backfill. Recommendations of the study were that the ERT data be used to verify proposed testing methods for coarse aggregate that are designed to yield data representative of in situ conditions. A preliminary analysis suggests that ERT may be utilized as construction quality assurance for thoroughness of compaction in MSE construction; however more data are needed at this time.

Developing and using artificial soils to analyze soil microbial processes

NASA Astrophysics Data System (ADS)

Gao, X.; Cheng, H. Y.; Boynton, L.; Masiello, C. A.; Silberg, J. J.

2017-12-01

Microbial diversity and function in soils are governed by soil characteristics such as mineral composition, particles size and aggregations, soil organic matter (SOM), and availability of nutrients and H2O. The spatial and temporal heterogeneity of soils creates a range of niches (hotspots) differing in the availability of O2, H2O, and nutrients, which shapes microbial activities at scales ranging from nanometer to landscape. Synthetic biologists often examine microbial response trigged by their environment conditions in nutrient-rich aqueous media using single strain microbes. While these studies provided useful insight in the role of soil microbes in important soil biogeochemical processes (e.g., C cycling, N cycling, etc.), the results obtained from the over-simplified model systems are often not applicable natural soil systems. On the contrary, soil microbiologists examine microbial processes in natural soils using longer incubation time. However, due to its physical, chemical and biological complexity of natural soils, it is often difficult to examine soil characteristics independently and understand how each characteristic influences soil microbial activities and their corresponding soil functioning. Therefore, it is necessary to bridge the gap and develop a model matrix to exclude unpredictable influences from the environment while still reliably mimicking real environmental conditions. The objective of this study is to design a range of ecologically-relevant artificial soils with varying texture (particle size distribution), structure, mineralogy, SOM content, and nutrient heterogeneity. We thoroughly characterize the artificial soils for pH, active surface area and surface morphology, cation exchange capacity (CEC), and water retention curve. We demonstrate the effectiveness of the artificial soils as useful matrix for microbial processes, such as microbial growth and horizontal gene transfer (HGT), using the gas-reporting biosensors recently developed in our lab.

Aggregate stability in soils cultivated with eucalyptus

USDA-ARS?s Scientific Manuscript database

Eucalyptus cultivation has increased in many Brazilian regions. In order to recommend good management practices, it is necessary to understand changes in soil properties where eucalyptus is planted. Aggregate stability analyses have proved to be a useful tool to measure soil effects caused by change...

Nutrient and dust enrichment in Danish wind erosion sediments for different tillage directions

NASA Astrophysics Data System (ADS)

Mohammadian Behbahani, Ali; Fister, Wolfgang; Heckrath, Goswin; Kuhn, Nikolaus J.

2015-04-01

More than 80% of the soil types in Denmark have a sandy texture. Denmark is also subject to strong offshore and onshore winds, therefore, Danish soils are considered especially vulnerable to wind erosion. Where conventional tillage operations are applied on poorly aggregated soils, tillage ridges are more or less the only roughness element that can be used to protect soils against wind erosion until crop plants are large enough to provide sufficient breaks. Since wind erosion is a selective process, it can be assumed that increasing erosion rates are associated with increasing loss of dust sized particles and nutrients. However, selective erosion is strongly affected by the orientation and respective trapping efficiency of tillage ridges and furrows. The main objective of this study, therefore, was to determine the effect of tillage direction on nutrient mobilization by wind erosion from agricultural land in Denmark. In order to assess the relationship between the enrichment ratio of specific particle sizes and the amount of eroded nutrients, three soils with loamy sand texture, but varying amounts of sand-sized particles, were selected. In addition, a soil with slightly less sand, but much higher organic matter content was chosen. The soils were tested with three different soil surface scenarios (flat surface, parallel tillage, perpendicular tillage) in a wind tunnel simulation. The parallel tillage operation experienced the greatest erosion rates, independent of soil type. Particles with D50 between 100-155 µm showed the greatest risk of erosion. However, due to a greater loss of dust sized particles from perpendicularly tilled surfaces, this wind-surface arrangement showed a significant increase in nutrient enrichment ratio compared to parallel tillage and flat surfaces. The main reason for this phenomenon is most probably the trapping of larger particles in the perpendicular furrows. This indicates that the highest rate of soil protection does not necessarily coincide with lowest soil nutrient losses and dust emissions. For the evaluation of protection measures on these soil types in Denmark it is, therefore, important to differentiate between their effectivity to reduce total soil erosion amount, dust emission, and nutrient loss.

Metal concentrations in aggregate interiors, exteriors, whole aggregates, and bulk of Costa Rican soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilcke, W.; Kretzschmar, S.; Bundt, M.

1999-10-01

In many temperate soils the preferential weathering and leaching of aggregate surfaces and the nonaggregated material between aggregates depletes geogenic metals. It also shifts metals from strongly to more weakly bound metal forms. Deposited metals are sorbed preferentially on aggregate surfaces and between aggregates. The authors examined whether preferential desilication under tropical climate causes an enrichment in the aggregate exteriors in oxidic forms of metals. They also studied where deposited metals are bound in these soils. Aggregates (2--20 mm) were selected manually from the A horizons of eight Oxisols, six Andisols, two Mollisols, and two Inceptisols in Costa Rica. Allmore » samples were fractionated into interior and exterior portions and treated with a seven-step sequence to extract Al, Cd, Cu, Fe, Mn, Pb, and Zn. Total concentrations of all metals except Zn were higher in the aggregate exteriors than in the interiors. The average Cd and Pb concentrations in easily extractable fractions were significantly higher in the aggregate exteriors. There were no significant differences in metal partitioning between interiors and exteriors except for Pb, which had higher proportions in extractable forms with NH{sub 2}OH {center{underscore}dot} HCl {gt} NH{sub 4} - acetate, pH 6.0 {gt} EDTA in the exteriors. There were few significant differences in metal concentrations and partitioning between bulk soil and whole aggregates. The results may be explained by (i) preferential desilication of the aggregate exteriors and (ii) preferential sorption of deposited heavy metals mainly in easily extractable forms.« less

State-Space Estimation of Soil Organic Carbon Stock

NASA Astrophysics Data System (ADS)

Ogunwole, Joshua O.; Timm, Luis C.; Obidike-Ugwu, Evelyn O.; Gabriels, Donald M.

2014-04-01

Understanding soil spatial variability and identifying soil parameters most determinant to soil organic carbon stock is pivotal to precision in ecological modelling, prediction, estimation and management of soil within a landscape. This study investigates and describes field soil variability and its structural pattern for agricultural management decisions. The main aim was to relate variation in soil organic carbon stock to soil properties and to estimate soil organic carbon stock from the soil properties. A transect sampling of 100 points at 3 m intervals was carried out. Soils were sampled and analyzed for soil organic carbon and other selected soil properties along with determination of dry aggregate and water-stable aggregate fractions. Principal component analysis, geostatistics, and state-space analysis were conducted on the analyzed soil properties. The first three principal components explained 53.2% of the total variation; Principal Component 1 was dominated by soil exchange complex and dry sieved macroaggregates clusters. Exponential semivariogram model described the structure of soil organic carbon stock with a strong dependence indicating that soil organic carbon values were correlated up to 10.8m.Neighbouring values of soil organic carbon stock, all waterstable aggregate fractions, and dithionite and pyrophosphate iron gave reliable estimate of soil organic carbon stock by state-space.

Bed bug aggregation on dirty laundry: a mechanism for passive dispersal.

PubMed

Hentley, William T; Webster, Ben; Evison, Sophie E F; Siva-Jothy, Michael T

2017-09-28

Bed bugs have shown a recent and rapid global expansion that has been suggested to be caused by cheap air travel. How a small, flightless and anachoretic insect that hides within its host's sleeping area manages to travel long distances is not yet clear. Bed bugs are attracted to the odour of sleeping humans and we suggest that soiled clothing may present a similarly attractive cue, allowing bed bugs to 'hitch-hike' around the world after aggregating in the laundry bags of travellers. We show that (1) soiled clothing is significantly more attractive than clean clothing to active bed bugs moving within a bedroom sized arena and (2) elevation of CO 2 to a level that simulates human occupancy in the same arena appears to initiate search behaviour rather than direct it. Our results show, for the first time, how leaving worn clothing exposed in sleeping areas when travelling can be exploited by bed bugs to facilitate passive dispersal.

Physical and mechanical properties of carbon fiber reinforced smart porous concrete for planting

NASA Astrophysics Data System (ADS)

Park, Seung-Bum; Kim, Jung-Hwan; Seo, Dae-Seuk

2005-05-01

The reinforcement strength of porous concrete and its applicability as a recycled aggregate was measured. Changes in physical and mechanical properties, subsequent to the mixing of carbon fiber and silica fume, were examined, and the effect of recycled aggregate depending on their mixing rate was evaluated. The applicability of planting to concrete material was also assessed. The results showed that there were not any remarkable change in the porosity and strength characteristics although its proportion of recycled aggregate increased. Also, the mixture of 10% of silica was found to be most effective for strength enforcement. In case of carbon fiber, the highest flexural strength was obtained with its mixing rate being 3%. It was also noticed that PAN-derived carbon fiber was superior to Pitch-derived ones in view of strength. The evaluation of its use for vegetation proved that the growth of plants was directly affected by the existence of covering soil, in case of having the similar size of aggregate and void.

Photothermal Beam Deflection Spectroscopy for the Determination of Thermal Diffusivity of Soils and Soil Aggregates

NASA Astrophysics Data System (ADS)

Proskurnin, M. A.; Korte, D.; Rogova, O. B.; Volkov, D. S.; Franko, M.

2018-07-01

Photothermal beam deflection spectroscopy (BDS) with a red He-Ne laser (632.8 nm, 35 mW) as an excitation beam source and a green He-Ne laser (543.1 nm, 2 mW) as a probe was used for estimating thermal diffusivity of several types of soil samples and individual soil aggregates with small surfaces (2 × 2 mm). It is shown that BDS can be used on demand for studies of changes in properties of soil entities of different hierarchical levels under the action of agrogenesis. It is presented that BDS clearly distinguishes between thermal diffusivities of different soil types: Sod-podzolic [Umbric Albeluvisols, Abruptic], 29 ± 3; Chernozem typical [Voronic Chernozems, Pachic], 9.9 ± 0.9; and Light Chestnut [Haplic Kastanozems, Chromic], 9.7 ± 0.9 cm2·h-1. Aggregates of chernozem soil show a significantly higher thermal diffusivity compared to the bulk soil. Thermal diffusivities of aggregates of Chernozem for virgin and bare fallow samples differ, 53 ± 4 cm2·h-1 and 45 ± 4 cm2·h-1, respectively. Micromonoliths of different Sod-podzolic soil horizons within the same profile (topsoil, depth 10-14 cm, and a parent rock with Fe illuviation, depth 180-185 cm) also show a significant difference, thermal diffusivities are 9.5 ± 0.8 cm2·h-1 and 27 ± 2 cm2·h-1, respectively. For soil micromonoliths, BDS is capable to distinguish the difference in thermal diffusivity resulting from the changes in the structure of aggregates.

Simulation of soil organic carbon in different soil size fractions using 13Carbon measurement data

NASA Astrophysics Data System (ADS)

Gottschalk, P.; Bellarby, J.; Chenu, C.; Foereid, B.; Wattenbach, M.; Zingore, S.; Smith, J.

2009-04-01

We simulate the soil organic carbon (SOC) dynamics at a chronoseqeunce site in France, using the Rothamsted Carbon model. The site exhibits a transition from C3 plants, dominated by pine forest, to a conventional C4 maize rotation. The different 13C signatures of the forest plants and maize are used to distinguish between the woodland derived carbon (C) and the maize derived C. The model is evaluated against total SOC and C derived from forest and maize, respectively. The SOC dynamics of the five SOC pools of the model, decomposable plant material (DPM), resistant plant material (RPM), biomass, humus and inert C, are also compared to the SOC dynamics measured in different soil size fractions. These fractions are > 50 μm (particulate organic matter), 2-50 μm (silt associated SOC) and <2 μm (clay associated SOC). Other authors had shown that the RPM pool of the model corresponds well to SOC measured in the soil size fraction > 50 μm and the sum of the other pools corresponds well to the SOC measured in the soil size fraction < 50 μm. Default model applications show that the model underestimates the fast drop in forest C stocks in the first 20 years after land-use change and overestimates the C accumulation of maize C. Several hypotheses were tested to evaluate the simulations. Input data and internal model parameter uncertainties had minor effects on the simulations results. Accounting for erosion and implementing a simple tillage routine did not improve the simulation fit to the data. We therefore hypothesize that a generic process that is not yet explicitly accounted for in the ROTHC model could explain the loss in soil C after land use change. Such a process could be the loss of the physical protection of soil organic matter as would be observed following cultivation of a previously uncultivated soil. Under native conditions a fraction of organic matter is protected in stable soil aggregates. These aggregates are physically disrupted by continuous and repeated cultivation of the soil. The underestimation of SOC loss by the model can be mainly attributed to the slow turnover of the humus pool. This pool was shown to represent mainly the SOC associated with the silt and clay soil fraction. Here, the clay associated SOC shows as similar turnover time as the humus pool in the model. We split the humus pool into a clay and a silt associated pool. The clay pool now corresponds to the clay associated SOC with the turnover time of the humus pool. The silt pool now corresponds to the silt associated SOC. From the measurements, the latter has a turnover time similar to the turnover time of the particulate organic matter. We therefore use the turnover time of the RPM pool for the silt pool. These modifications improve the simulations of the forest derived C significantly and improve the simulations of the maize derived C. Future work will further evaluate and refine this approach to eventually capture the SOC dynamics associated with physical protection, including the effect of tillage/no-tillage, in a simple approach.

Quantitative analysis of liquid penetration kinetics and slaking of aggregates as related to solid-liquid interfacial properties

NASA Astrophysics Data System (ADS)

Goebel, Marc-O.; Woche, Susanne K.; Bachmann, Jörg

2012-06-01

SummaryAggregate stability is frequently shown to be enhanced by strong soil water repellency, however, there is limited systematic evidence on this effect for moderately (subcritically) water repellent soils. This study aimed to investigate the specific effects of interfacial properties on the liquid penetration kinetics in relation to the stability of subcritically water repellent aggregates (4-6.3 mm) from various arable and forest soils against breakdown by slaking. In contrast to many other studies, where aggregate stability was determined by wet sieving, we here assessed the stability by immersion of air-dry aggregates in water-ethanol solutions with surface tensions ranging from 30 to 70 mN m-1. This approach allowed a highly sensitive discrimination of different stability levels and the determination of breakdown kinetics also for less stable aggregates. Interfacial properties were characterized in terms of contact angle measured on crushed aggregates, θc, and calculated for intact aggregates, θi, based on infiltration measurements with water and ethanol. Aggregate stability turned out to be higher in forest soils compared to arable soils with topsoil aggregates generally found to be more stable than subsoil aggregates. For water repellent aggregates, characterized by contact angles >40° and low water infiltration rates (<0.2 mm3 s-0.5), the fraction of disrupted aggregates after 30 s of immersion was generally below 10%, whereas in case of the more wettable aggregates, characterized by contact angles <10° and higher infiltration rates (>0.25 mm3 s-0.5) more than 80% of the aggregates were disrupted. In accordance, we found a close relationship between aggregate stability and wettability with differences between θc and θi being generally small. In addition, aggregate stability turned out to be related to organic carbon content. However, correlation analysis revealed that both persistence of aggregate stability and kinetics of aggregate breakdown were more strongly affected by the contact angle, θc (r = 0.90 and r = -0.83, respectively) and θi (r = 0.89 and r = -0.76, respectively) than the organic carbon content (r = 0.62 and -0.52, respectively), suggesting that stability was primarily controlled by aggregate interfacial properties. Calculation of liquid penetrativity as a function of surface tension and contact angle clearly demonstrated the importance of both solid and liquid interfacial properties in determining the stability of subcritically water repellent aggregates against slaking.

Stabilization of ancient organic matter in deep buried paleosols

NASA Astrophysics Data System (ADS)

Marin-Spiotta, E.; Chaopricha, N. T.; Mueller, C.; Diefendorf, A. F.; Plante, A. F.; Grandy, S.; Mason, J. A.

2012-12-01

Buried soils representing ancient surface horizons can contain large organic carbon reservoirs that may interact with the atmosphere if exposed by erosion, road construction, or strip mining. Paleosols in long-term depositional sites provide a unique opportunity for studying the importance of different mechanisms on the persistence of organic matter (OM) over millennial time-scales. We report on the chemistry and bioavailability of OM stored in the Brady soil, a deeply buried (7 m) paleosol in loess deposits of southwestern Nebraska, USA. The Brady Soil developed 9,000-13,500 years ago during a time of warming and drying. The Brady soil represents a dark brown horizon enriched in C relative to loess immediately above and below. Spanning much of the central Great Plains, this buried soil contains large C stocks due to the thickness of its A horizon (0.5 to 1 m) and wide geographic extent. Our research provides a unique perspective on long-term OM stabilization in deep soils using multiple analytical approaches. Soils were collected from the Brady soil A horizon (at 7 m depth) and modern surface A horizons (0-15 cm) at two sites for comparison. Soils were separated by density fractionation using 1.85 g ml-1 sodium polytungstate into: free particulate organic matter (fPOM) and aggregate-occluded (oPOM) of two size classes (large: >20 μm, and small: < 20 μm). The remaining dense fraction was separated into sand, silt, and clay size fractions. The distribution and age of C among density and particle-size fractions differed between surface and Brady soils. We isolated the source of the characteristic dark coloring of the Brady soil to the oPOM-small fraction, which also contained 20% of the total organic C pool in the Brady soil. The oPOM-small fraction and the bulk soil in the middle of the Brady A horizon had 14C ages of 10,500-12,400 cal yr BP, within the time that the soil was actively forming at the land surface. Surface soils showed modern ages. Lipid analyses of the Brady soil indicate a predominance of terrestrial vegetation biomarkers. The strong presence of vascular plant-derived terpenoids and long-chain n-alkyl lipids suggest a grassland origin. Respiration rates of the buried soil in a laboratory incubation were negligible compared to modern surface A and B horizons, and responded little to wetting. These results suggest that moisture alone does not limit decomposition in the buried soil, at least over the 120-day incubation. Solid-state 13C-NMR spectroscopy reveals that the Brady soil is enriched in aromatic C, with high contributions of char, especially in the oPOM-small fraction. Thermal analysis showed high thermal stability of oPOM-small and bulk soils in the Brady soil compared to modern surface horizons. Radiocarbon ages and chemical composition of OM isolated from a deep paleosol suggest little modification since burial and may indicate rapid stabilization of plant-derived organic C by burial. The accumulation of char in the aggregate-protected fraction of the Brady soil provides additional evidence for warming and drying conditions during the time of loess deposition at this site. Developing a better understanding of the mechanisms that control long-term SOM stabilization is important for understanding how soil C is sequestered over millennia and for predicting how future disturbances may affect deep soil C.

Soil wet aggregate stability in dryland Pacific Northwest intensified crop rotations

USDA-ARS?s Scientific Manuscript database

Improving soil aggregation in the semiarid inland Pacific Northwest cropping region can reduce the erodibility and improve water infiltration in the silt loam soils. We compared the individual crop phases of six different crop rotations in plots located in 300 mm mean annual precipitation area of t...

Vegetation effects on soil organic matter chemistry of aggregate fractions in a Hawaiian forest

USDA-ARS?s Scientific Manuscript database

We examined chemical changes from live plant tissue to soil organic matter (SOM) to determine the persistence of individual plant compounds into soil aggregate fractions. We characterized the tissue chemistry of a slow- (Dicranopteris linearis) and fast-decomposing species (Cheirodendron trigynum) a...

Does mycorrhizal inoculation improve plant survival, aggregate stability, and fine root development on a coarse-grained soil in an alpine eco-engineering field experiment?

NASA Astrophysics Data System (ADS)

Bast, A.; Wilcke, W.; Graf, F.; Lüscher, P.; Gärtner, H.

2016-08-01

Steep vegetation-free talus slopes in high mountain environments are prone to superficial slope failures and surface erosion. Eco-engineering measures can reduce slope instabilities and thus contribute to risk mitigation. In a field experiment, we established mycorrhizal and nonmycorrhizal research plots and determined their biophysical contribution to small-scale soil fixation. Mycorrhizal inoculation impact on plant survival, aggregate stability, and fine root development was analyzed. Here we present plant survival (ntotal = 1248) and soil core (ntotal = 108) analyses of three consecutive years in the Swiss Alps. Soil cores were assayed for their aggregate stability coefficient (ASC), root length density (RLD), and mean root diameter (MRD). Inoculation improved plant survival significantly, but it delayed aggregate stabilization relative to the noninoculated site. Higher aggregate stability occurred only after three growing seasons. Then also RLD tended to be higher and MRD increased significantly at the mycorrhizal treated site. There was a positive correlation between RLD, ASC, and roots <0.5 mm, which had the strongest impact on soil aggregation. Our results revealed a temporal offset between inoculation effects tested in laboratory and field experiments. Consequently, we recommend to establish an intermediate to long-term field experimental monitoring before transferring laboratory results to the field.

Impact of spatial and temporal aggregation of input parameters on the assessment of irrigation scheme performance

NASA Astrophysics Data System (ADS)

Lorite, I. J.; Mateos, L.; Fereres, E.

2005-01-01

SummaryThe simulations of dynamic, spatially distributed non-linear models are impacted by the degree of spatial and temporal aggregation of their input parameters and variables. This paper deals with the impact of these aggregations on the assessment of irrigation scheme performance by simulating water use and crop yield. The analysis was carried out on a 7000 ha irrigation scheme located in Southern Spain. Four irrigation seasons differing in rainfall patterns were simulated (from 1996/1997 to 1999/2000) with the actual soil parameters and with hypothetical soil parameters representing wider ranges of soil variability. Three spatial aggregation levels were considered: (I) individual parcels (about 800), (II) command areas (83) and (III) the whole irrigation scheme. Equally, five temporal aggregation levels were defined: daily, weekly, monthly, quarterly and annually. The results showed little impact of spatial aggregation in the predictions of irrigation requirements and of crop yield for the scheme. The impact of aggregation was greater in rainy years, for deep-rooted crops (sunflower) and in scenarios with heterogeneous soils. The highest impact on irrigation requirement estimations was in the scenario of most heterogeneous soil and in 1999/2000, a year with frequent rainfall during the irrigation season: difference of 7% between aggregation levels I and III was found. Equally, it was found that temporal aggregation had only significant impact on irrigation requirements predictions for time steps longer than 4 months. In general, simulated annual irrigation requirements decreased as the time step increased. The impact was greater in rainy years (specially with abundant and concentrated rain events) and in crops which cycles coincide in part with the rainy season (garlic, winter cereals and olive). It is concluded that in this case, average, representative values for the main inputs of the model (crop, soil properties and sowing dates) can generate results within 1% of those obtained by providing spatially specific values for about 800 parcels.

Impact of natural organic matter coatings on the microbial reduction of iron oxides

NASA Astrophysics Data System (ADS)

Poggenburg, Christine; Mikutta, Robert; Schippers, Axel; Dohrmann, Reiner; Guggenberger, Georg

2018-03-01

Iron (Fe) oxyhydroxides are important constituents of the soil mineral phase known to stabilize organic matter (OM) under oxic conditions. In an anoxic milieu, however, these Fe-organic associations are exposed to microbial reduction, releasing OM into soil solution. At present, only few studies have addressed the influence of adsorbed natural OM (NOM) on the reductive dissolution of Fe oxyhydroxides. This study therefore examined the impact of both the composition and concentration of adsorbed NOM on microbial Fe reduction with regard to (i) electron shuttling, (ii) complexation of Fe(II,III), (iii) surface site coverage and/or pore blockage, and (iv) aggregation. Adsorption complexes with varying carbon loadings were synthesized using different Fe oxyhydroxides (ferrihydrite, lepidocrocite, goethite, hematite, magnetite) and NOM of different origin (extracellular polymeric substances from Bacillus subtilis, OM extracted from soil Oi and Oa horizons). The adsorption complexes were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), N2 gas adsorption, electrophoretic mobility and particle size measurements, and OM desorption. Incubation experiments under anaerobic conditions were conducted for 16 days comparing two different strains of dissimilatory Fe(III)-reducing bacteria (Shewanella putrefaciens, Geobacter metallireducens). Mineral transformation during reduction was assessed via XRD and FTIR. Microbial reduction of the pure Fe oxyhydroxides was controlled by the specific surface area (SSA) and solubility of the minerals. For Shewanella putrefaciens, the Fe reduction of adsorption complexes strongly correlated with the concentration of potentially usable electron-shuttling molecules for NOM concentrations <2 mg C L-1, whereas for Geobacter metallireducens, Fe reduction depended on the particle size and thus aggregation of the adsorption complexes. These diverging results suggest that the influence of NOM on the stability of Fe-organic associations in soils cannot easily be assessed without considering the composition of the microbial soil community.

Can conservation agriculture reduce the impact of soil erosion in northern Tunisia ?

NASA Astrophysics Data System (ADS)

Bahri, Haithem; Annabi, Mohamed; Chibani, Roukaya; Cheick M'Hamed, Hatem; Hermessi, Taoufik

2016-04-01

Mediterranean countries are prone to soil erosion, therefore Tunisia, with Mediterranean climate, is threatened by water erosion phenomena. In fact, 3 million ha of land is threatened by erosion, and 50% is seriously affected. Soils under conservation agriculture (CA) have high water infiltration capacities reducing significantly surface runoff and thus soil erosion. This improves the quality of surface water, reduces pollution from soil erosion, and enhances groundwater resources. CA is characterized by three interlinked principles, namely continuous minimum mechanical soil disturbance, permanent organic soil cover and diversification of crop species grown in sequence or associations. Soil aggregate stability was used as an indicator of soil susceptibility to water erosion. Since 1999, In Tunisia CA has been introduced in rainfed cereal areas in order to move towards more sustainable agricultural systems. CA areas increased from 52 ha in 1999 to 15000 ha in 2015. The objective of this paper is to study the effect of CA on soil erosion in northern Tunisia. Soil samples were collected at 10 cm of depth from 6 farmers' fields in northern Tunisia. Conventional tillage (CT), CA during less than 5 years (CA<5 years) and CA during more than 5 years (CA>5 years) have been practiced in each farmers field experiment of wheat crop. Soil aggregate stability was evaluated according to the method described by Le Bissonnais (1996), results were expressed as a mean weight diameter (MWD); higher values of MWD indicate higher aggregate stability. Total organic carbon (TOC) was determined using the wet oxidation method of Walkley-Black. A significant increase in SOC content was observed in CA>5years (1.64 %) compared to CT (0.97 %). This result highlights the importance of CA to improve soil fertility. For aggregate stability, a net increase was observed in CA compared to CT. After 5 years of CA the MWD was increased by 16% (MWD=1.8 mm for CT and MWD=2.1 mm for CA<5years). No improvement of aggregate stability level was observed after the 5th year of CA conversion. A positive correlation was observed between aggregate stability and total soil organic carbon (r=0.52, n=18). It is assumed that this correlation could be due to increased microbial activity under CA. A positive and statistically significant relationship was also noted between aggregate stability and the number of years after the no-till conversion (r= 0.46, n=18) for all plots.

Control of Mercury Accumulation And Mobility in a Forest Soil as Indicated by δ13C

NASA Astrophysics Data System (ADS)

Bajracharya, U.; Jackson, B.; Feng, X.

2015-12-01

Mobility and cycling of mercury (Hg) in soils is important. Hg leaching results in its transport to wetlands, where Hg methylates and bioaccumulates through aquatic food webs. It has been shown that Hg cycle in soil is controlled by organic matter (OM) quantity as well as quality. The latter is indicated by increase of Hg/C ratio as C/N decreases by decomposition. Here we investigate the Hg-C relationship in a temperate forest soil in Hanover, NH, with a focus of examining the control of OM quality on soil Hg accumulation and mobility. We use δ13C as an indicator of carbon quality. The soil samples from A, B and C horizons were separated into six particle size fractionations from <25 µm to 1 mm. Both the bulk soil and particle size separates were analyzed for Hg concentrations, carbon content (C%), δ13C, and Hg partition coefficient (Kd =mg gSoil-1/mg Lsolution-1). We found that the bulk Hg concentration decreases significantly with increasing δ13C (R2=0.90, p <0.0001), but Hg/C increases with δ13C (R2=0.59, p =0.009). Both Hg/C and δ13C increase with soil depth, and at a given horizon, they both increase with decreasing particle size. These results indicate that high Hg/C ratios are associated with aged, decomposed, and low quality OM. Mostly likely, this accumulation of Hg in older OM is a result of retention of Hg upon carbon loss during soil respiration. However, the relationship between particle size and Hg/C is significantly different among different horizons; the most prominent relationship occurs at the deepest C horizon. This cross effect of horizon and particle size cannot be explained by normal aging of the OM through decomposition, pointing to mechanisms of changing in Hg bonding characteristics with OM aging or particle aggregation. The measured Kd value decreased with increasing δ13C (R2=0.43, p =0.0031), indicating that Hg associated with older OM is more subject to leaching compared to younger, fresher OM. This association can also be partitioned into effects of of both soil horizon and particle size. This work demonstrates that soil δ13C is a useful tool for studying coupled Hg and C cycles in soils. Linking other methods characterizing bonding characteristics of Hg may bring additional insights to accumulation and mobility of Hg in association with changing chemical and physical properties of OM.

Soil moisture data as a constraint for groundwater recharge estimation

NASA Astrophysics Data System (ADS)

Mathias, Simon A.; Sorensen, James P. R.; Butler, Adrian P.

2017-09-01

Estimating groundwater recharge rates is important for water resource management studies. Modeling approaches to forecast groundwater recharge typically require observed historic data to assist calibration. It is generally not possible to observe groundwater recharge rates directly. Therefore, in the past, much effort has been invested to record soil moisture content (SMC) data, which can be used in a water balance calculation to estimate groundwater recharge. In this context, SMC data is measured at different depths and then typically integrated with respect to depth to obtain a single set of aggregated SMC values, which are used as an estimate of the total water stored within a given soil profile. This article seeks to investigate the value of such aggregated SMC data for conditioning groundwater recharge models in this respect. A simple modeling approach is adopted, which utilizes an emulation of Richards' equation in conjunction with a soil texture pedotransfer function. The only unknown parameters are soil texture. Monte Carlo simulation is performed for four different SMC monitoring sites. The model is used to estimate both aggregated SMC and groundwater recharge. The impact of conditioning the model to the aggregated SMC data is then explored in terms of its ability to reduce the uncertainty associated with recharge estimation. Whilst uncertainty in soil texture can lead to significant uncertainty in groundwater recharge estimation, it is found that aggregated SMC is virtually insensitive to soil texture.

Soils as Sediment database: closing a gap between soil science and geomorphology

NASA Astrophysics Data System (ADS)

Kuhn, Nikolaus J.

2016-04-01

Soils are an interface between the Earth's spheres and shaped by the nature of the interaction between them. The relevance of soil properties for the nature of the interaction between atmosphere, hydrosphere and biosphere is well-studied and accepted, on point- or ecotone-scale. However, this understanding of the largely vertical connections between spheres is not matched by a similar recognition of soil properties affecting processes acting largely in a lateral way across the land surface, such as erosion, transport and deposition of soil. Key areas where such an understanding is essential are all issues related to the lateral movement of soil-bound substances that affect the nature of soils itself, as well as water or vegetation downslope from the source area. The redistribution of eroded soil falls several disciplines, most notably soil science, agronomy, hydrology and geomorphology. Accordingly, the way sediment is described differs: in soil science, aggregation and structure are essential properties, while most process-based soil erosion models treat soil as a mixture of individual mineral grains, based on concepts derived in fluvial geomorphology or civil engineering. The actual behavior of aggregated sediment is not reflected by either approach and difficult to capture due to the dynamic nature of aggregation, especially in an environment such as running water. Still, a proxy to assess the uncertainties introduced by aggregation on the behavior of soil as sediment would represent a step forward. To develop such a proxy, a database collating relevant soil and sediment properties could serve as an initial step to identify which soil types and erosion scenarios are prone to generate a high uncertainty compared to the use of soil texture in erosion models. Furthermore, it could serve to develop standardized analytical procedures for appropriate description of soil as sediment.

Reduced tillage and cover crops as a strategy for mitigating atmospheric CO2 increase through soil organic carbon sequestration in dry Mediterranean agroecosystems.

NASA Astrophysics Data System (ADS)

Almagro, María; Garcia-Franco, Noelia; de Vente, Joris; Boix-Fayos, Carolina; Díaz-Pereira, Elvira; Martínez-Mena, María

2016-04-01

The implementation of sustainable land management (SLM) practices in semiarid Mediterranean agroecosystems can be beneficial to maintain or enhance levels of soil organic carbon and mitigate current atmospheric CO2 increase. In this study, we assess the effects of different tillage treatments (conventional tillage (CT), reduced tillage (RT), reduced tillage combined with green manure (RTG), and no tillage (NT)) on soil CO2 efflux, aggregation and organic carbon stabilization in two semiarid organic rainfed almond (Prunus dulcis Mill., var. Ferragnes) orchards located in SE Spain Soil CO2 efflux, temperature and moisture were measured monthly between May 2012 and December 2014 (site 1), and between February 2013 and December 2014 (site 2). In site 1, soil CO2 efflux rates were also measured immediately following winter and spring tillage operations. Aboveground biomass inputs were estimated at the end of the growing season in each tillage treatment. Soil samples (0-15 cm) were collected in the rows between the trees (n=4) in October 2012. Four aggregate size classes were distinguished by sieving (large and small macroaggregates, free microaggregates, and free silt plus clay fraction), and the microaggregates occluded within macroaggregates (SMm) were isolated. Soil CO2efflux rates in all tillage treatments varied significantly during the year, following changes during the autumn, winter and early spring, or changes in soil moisture during late spring and summer. Repeated measures analyses of variance revealed that there were no significant differences in soil CO2 efflux between tillage treatments throughout the study period at both sites. Average annual values of C lost by soil respiration were slightly but not significantly higher under RT and RTG treatments (492 g C-CO2 m-2 yr-1) than under NT treatment (405 g C-CO2 m-2 yr-1) in site 1, while slightly but not significantly lower values were observed under RT and RTG treatments (468 and 439 g C-CO2 m-2 yr-1, respectively) than under CT treatment (399 g C-CO2 m-2 yr-1) in site 2. Tillage operations had a rapid but short-lived effect on soil CO2 efflux rates, with no significant influence on the annual soil CO2 emissions. The larger amounts of plant biomass incorporated into soil annually in the reduced tillage treatments compared to the conventional tillage treatment promoted soil aggregation and the physico-chemical soil organic carbon stabilization while soil CO2 emissions did not significantly increase. According to our results, reduced-tillage is strongly recommended as a beneficial SLM strategy for mitigating atmospheric CO2 increase through soil carbon sequestration and stabilization in semiarid Mediterranean agroecosystems.

Using fourier-transform mid-infrared spectroscopy to distinguish soil organic matter composition dynamics in aggregate fractions of two agroecosystems

USDA-ARS?s Scientific Manuscript database

The relationship between soil organic carbon (SOC) content and quality of SOC as impacted by land management is not well understood and may influence long-term storage of SOC. To better understand the potential for SOC storage in specific aggregate pools (i.e. physically protected intra-aggregate C)...

Dust and nutrient enrichment by wind erosion from Danish soils in dependence of tillage direction

NASA Astrophysics Data System (ADS)

Mohammadian Behbahani, Ali; Fister, Wolfgang; Heckrath, Goswin; Kuhn, Nikolaus J.

2016-04-01

Wind erosion is a selective process, which promotes erosion of fine particles. Therefore, it can be assumed that increasing erosion rates are generally associated with increasing loss of dust sized particles and nutrients. However, this selective process is strongly affected by the orientation and respective trapping efficiency of tillage ridges and furrows. Since tillage ridges are often the only protection measure available on poorly aggregated soils in absence of a protective vegetation cover, it is very important to know which orientation respective to the dominant wind direction provides best protection. This knowledge could be very helpful for planning erosion protection measures on fields with high wind erosion susceptibility. The main objective of this study, therefore, was to determine the effect of tillage direction on dust and nutrient mobilization by wind, using wind tunnel simulations. In order to assess the relationship between the enrichment ratio of specific particle sizes and the amount of eroded nutrients, three soils with loamy sand texture, but varying amounts of sand-sized particles, were selected. In addition, a soil with slightly less sand, but much higher organic matter content was chosen. The soils were tested with three different soil surface scenarios - flat surface, parallel tillage, perpendicular tillage. The parallel tillage operation experienced the greatest erosion rates, independent of soil type. Particles with D50 between 100-155 μm showed the greatest risk of erosion. However, due to a greater loss of dust sized particles from perpendicularly tilled surfaces, this wind-surface arrangement showed a significant increase in nutrient enrichment ratio compared to parallel tillage and flat surfaces. The main reason for this phenomenon is most probably the trapping of larger particles in the perpendicular furrows. This indicates that the highest rate of soil protection does not necessarily coincide with lowest soil nutrient losses and dust emissions. For the evaluation of protection measures on these soil types in Denmark it is, therefore, important to differentiate between their effectivity to reduce total soil erosion amount, dust emission, and nutrient loss.

Estimating Surface Soil Moisture in Simulated AVIRIS Spectra

NASA Technical Reports Server (NTRS)

Whiting, Michael L.; Li, Lin; Ustin, Susan L.

2004-01-01

Soil albedo is influenced by many physical and chemical constituents, with moisture being the most influential on the spectra general shape and albedo (Stoner and Baumgardner, 1981). Without moisture, the intrinsic or matrix reflectance of dissimilar soils varies widely due to differences in surface roughness, particle and aggregate sizes, mineral types, including salts, and organic matter contents. The influence of moisture on soil reflectance can be isolated by comparing similar soils in a study of the effects that small differences in moisture content have on reflectance. However, without prior knowledge of the soil physical and chemical constituents within every pixel, it is nearly impossible to accurately attribute the reflectance variability in an image to moisture or to differences in the physical and chemical constituents in the soil. The effect of moisture on the spectra must be eliminated to use hyperspectral imagery for determining minerals and organic matter abundances of bare agricultural soils. Accurate soil mineral and organic matter abundance maps from air- and space-borne imagery can improve GIS models for precision farming prescription, and managing irrigation and salinity. Better models of soil moisture and reflectance will also improve the selection of soil endmembers for spectral mixture analysis.

[Distribution of soil organic carbon, total nitrogen, total phosphorus and water stable aggregates of cropland with different soil textures on the Loess Plateau, Northwest China].

PubMed

Ge, Nan Nan; Shi, Yun; Yang, Xian Long; Zhang, Qing Yin; Li, Xue Zhang; Jia, Xiao Xu; Shao, Ming An; Wei, Xiao Rong

2017-05-18

In this study, combined with field investigation and laboratory analyses, we assessed the distribution of soil organic carbon, nitrogen, phosphorous contents and their stoichiometric ratios, and the distribution of soil water stable aggregates along a soil texture gradient in the cropland of the Loess Plateau to understand the effect of soil texture and the regulation of soil aggregates on soil fertility in cropland. The results showed that, with the change from fine soils to coarse soils along the texture gradient (loam clay→ clay loam→ sandy loam), the contents of macroaggregates, organic carbon, nitrogen, phosphorous and their stoichiometric ratios decreased, while pH value and microaggregates content showed an opposite changing pattern. The contents of macroaggregates, organic carbon, nitrogen, phosphorous, and C/P and N/P were significantly increased, but pH value and microaggregates content were significantly decreased with increasing the soil clay content. Furthermore, the contents of organic carbon, nitrogen, phosphorous, and C/P and N/P increased with the increase of macroaggregates content. These results indicated that soil fertility in croplands at a regional scale was mainly determined by soil texture, and was regulated by soil macroaggregates.

Multiscale modelling of dual-porosity porous media; a computational pore-scale study for flow and solute transport

NASA Astrophysics Data System (ADS)

de Vries, Enno T.; Raoof, Amir; van Genuchten, Martinus Th.

2017-07-01

Many environmental and agricultural applications involve the transport of water and dissolved constituents through aggregated soil profiles, or porous media that are structured, fractured or macroporous in other ways. During the past several decades, various process-based macroscopic models have been used to simulate contaminant transport in such media. Many of these models consider advective-dispersive transport through relatively large inter-aggregate pore domains, while exchange with the smaller intra-aggregate pores is assumed to be controlled by diffusion. Exchange of solute between the two domains is often represented using a first-order mass transfer coefficient, which is commonly obtained by fitting to observed data. This study aims to understand and quantify the solute exchange term by applying a dual-porosity pore-scale network model to relatively large domains, and analysing the pore-scale results in terms of the classical dual-porosity (mobile-immobile) transport formulation. We examined the effects of key parameters (notably aggregate porosity and aggregate permeability) on the main dual-porosity model parameters, i.e., the mobile water fraction (ϕm) and the mass transfer coefficient (α). Results were obtained for a wide range of aggregate porosities (between 0.082 and 0.700). The effect of aggregate permeability was explored by varying pore throat sizes within the aggregates. Solute breakthrough curves (BTCs) obtained with the pore-scale network model at several locations along the domain were analysed using analytical solutions of the dual-porosity model to obtain estimates of ϕm and α. An increase in aggregate porosity was found to decrease ϕm and increase α, leading to considerable tailing in the BTCs. Changes in the aggregate pore throat size affected the relative flow velocity between the intra- and inter-aggregate domains. Higher flow velocities within the aggregates caused a change in the transport regime from diffusion dominated to more advection dominated. This change increased the exchange rate of solutes between the mobile and immobile domains, with a related increase in the value of the mass transfer coefficient and less tailing in the BTCs.

Nutrient Characterization of Rainwater, Soil and Groundwater from Two Different Watersheds, Lake Taihu, China

NASA Astrophysics Data System (ADS)

Thaw, M.; Gao, F.; Yu, Z.; Acharya, K.

2012-12-01

Over the past two decades, an increase of nutrients to Lake Taihu, China has resulted in hyper-eutrophication and the production of severe cyanobacterial blooms. While many past studies have focused on how surface water transports nutrients to the lake, this study seeks to characterize the concentration of nutrients in different media, including rainwater, soil and groundwater from two different watersheds. These two watersheds varied in overall land use, and agricultural sites within each watershed varied by crop type and growing method. Samples were collected from the Meilin watershed, a mix of forest and agricultural land and the Zhangjiagang watershed, which consisted of industrial, urban and agricultural lands. Samples included soils, groundwater and rain water. Soils from each site were characterized by aggregate size class and analyzed for total nitrogen and total phosphorus. Rainwater and groundwater samples were analyzed for total nitrogen and total phosphorus.

Nature and origin of the resistant carbonaceous polymorphs involved the fossilization of biogenic soil-aggregates

NASA Astrophysics Data System (ADS)

Courty, M.-A.

2012-04-01

The rare occurrence of organic-rich surface horizons in soil archives is widely accepted to resulting from their rapid degradation. We intend here to further elucidate how pedogenic signatures that initially formed at the soil surface could resist over long timescales to burial processes. We focus on the structural evolution of the biogenic soil aggregates that is controlled by the complex interaction of bioturbation, root colonization, microbial decomposition, chemical weathering and physical processes. The nature and origin of carbonaceous components that could possibly contribute to the long term preservation of biogenic soil-aggregates is particularly examined. The study is based on the comparison of pedogenic aggregated microfacies from present-day situations and the ones encountered in soil archives from contrasting edaphic conditions: Arctic Holocene soils from Spitsbergen, hyper-arid soils from the Moche valley (Peru), Holocene semi-arid Mediterranean soils from Northern Syria, late Pleistocene paleosols from lake Mungo (South Wales Australia) and late Pleistocene paleosols from the Ardeche valley (France). The assemblage and composition of biogenic soil-aggregated horizons has been characterized under the binocular microscope and in thin sections. The basic components have been separated by water sieving. A typology of carbonaceous polymorphs and associated composite materials has been established under the binocular. They have been characterized by SEM-EDS, Raman spectrometry, X-ray diffraction and TEM. The comparative study shows that all the biogenic soil-aggregates from the soil archives contain a high amount of similar exotic components that contrast from the parent materials by their fresh aspect and their hydrophobic properties. This exotic assemblage comprises various types of aliphatic carbonaceous polymorphs (filaments, agglutinates, spherules) and aromatic ones (vitrous char, graphite), carbon cenospheres, fine grained sandstones and rock clasts which are all finely imbricated with phosphides, phosphates, sulphides, sulphates and native metals (Fe-Cr-Ni and Fe-Cr alloys, Ni, Al, Cu, Zn, Pb, As, Sn, Ag, Au, Bi). The 3D observations show that the carbonaceous filaments play a major role in the cohesion of the fine fraction. The carbonaceous components only start to decompose under HF attack and from 400°C heating. They do not display evidence of microbial degradation. The biogenic aggregates with high amount of carbonaceous polymorphs appear to have resisted to cryoturbation and to hard setting under water saturation. Biogenic micro-aggregates from present-day top soils only contain rare exotic components. In contrast to the ones of the soil archives, they display highly variable structural stability depending upon local edaphic conditions. The exotic assemblage of the stable biogenic micro-aggregates from the soil archives is shown to be similar to the range of terrestrial aerosols that are associated to meteor explosion (Courty et al., this volume). This suggests that the fossilized organic-rich surface horizons in soil archives would trace singular situations possibly marked by recurrent meteor explosion with high stratospheric aerosol production. Mechanisms explaining how the dual stratospheric/cosmic processes formed resistant carbon species from fossil combustible precursors yet remain to be investigated. Courty, Benoît and Vaillant (2012). Possible interaction of meteor explosion with stratospheric aerosols on cloud nucleation based on 2011 observations. Geophysical Research Abstracts Vol. 14, EGU2012.

Evaluation of conceptual models of natural organic matter (humus) from a consideration of the chemical and biochemical processes of humification

USGS Publications Warehouse

Wershaw, Robert L.

2004-01-01

Natural organic matter (NOM) has been studied for more than 200 years because of its importance in enhancing soil fertility, soil structure, and water-holding capacity and as a carbon sink in the global carbon cycle. Two different types of models have been proposed for NOM: (1) the humic polymer models and (2) the molecular aggregate models. In the humic polymer models, NOM molecules are depicted as large (humic) polymers that have unique chemical structures that are different from those of the precursor plant degradation products. In the molecular aggregate models, NOM is depicted as being composed of molecular aggregates (supramolecular aggregates) of plant degradation products held together by non-covalent bonds. The preponderance of evidence favors the supramolecular aggregate models. These models were developed by studying the properties of NOM extracted from soils and natural waters, and as such, they provide only a very generalized picture of the structure of NOM aggregates in soils and natural waters prior to extraction. A compartmental model, in which the structure of the NOM in each of the compartments is treated separately, should provide a more accurate representation of NOM in soil and sediment systems. The proposed NOM compartments are: (1) partially degraded plant tissue, (2) biomass from microorganisms, (3) organic coatings on mineral grains, (4) pyrolytic carbon, (5) organic precipitates, and (6) dissolved organic matter (DOM) in interstitial water. Within each of these compartments there are NOM supramolecular aggregates that will be dissolved by the solvent systems that are used by researchers for extraction of NOM from soils and sediments. In natural water systems DOM may be considered as existing in two subcompartments: (1) truly dissolved DOM and (2) colloidal DOM.

[Effects of different cultivation patterns on soil aggregates and organic carbon fractions].

PubMed

Qiu, Xiao-Lei; Zong, Liang-Gang; Liu, Yi-Fan; Du, Xia-Fei; Luo, Min; Wang, Run-Chi

2015-03-01

Combined with the research in an organic farm in the past 10 years, differences of soil aggregates composition, distribution and organic carbon fractions between organic and conventional cultivation were studied by simultaneous sampling analysis. The results showed that the percentages of aggregates (> 1 mm, 1-0.5 mm, 0.5-0.25 mm and < 0.25 mm) in the conventional cultivation were 23.75%, 15.15%, 19.98% and 38.09%, while those in organic cultivation were 9.73%, 18.41%, 24.46% and 43.90%, respectively. The percentage of < 0.25 mm micro-aggregates was significantly higher in organic cultivation than that in conventional cultivation. Organic cultivation increased soil organic carbon (average of 17.95 g x kg(-1)) and total nitrogen contents (average of 1.51 g x kg(-1)). Among the same aggregates in organic cultivation, the average content of heavy organic carbon fraction was significantly higher than that in conventional cultivation. This fraction accumulated in < 0. 25 mm micro-aggregates, which were main storage sites of stable organic carbon. In organic cultivation, the content of labile organic carbon in > 1 mm macro-aggregates was significantly higher than that in conventional cultivation, while no significant difference was found among the other aggregates, indicating that the labile organic carbon was enriched in > 1 mm macro-aggregates. Organic cultivation increased the amounts of organic carbon and its fractions, reduced tillage damage to aggregates, and enhanced the stability of organic carbon. Organic cultivation was therefore beneficial for soil carbon sequestration. The findings of this research may provide theoretical basis for further acceleration of the organic agriculture development.

Hydrological controls on rate of organic matter mineralization in peats

NASA Astrophysics Data System (ADS)

Ghezzehei, Teamrat; Arnold, Chelsea; Asefaw Berhe, Asmeret

2016-04-01

The predominant factor that ties together the formation and persistence of peat soils across regions is their dependence on localized hydrology. Hydrology also plays a dominant role in the relative strength of peatlands as sinks for atmospheric carbon dioxide and sources of methane, and thus on peatland net climate impact. Drying of peat soils by climate change and/or drainage is typically followed by reduction in methane emissions. However, this may easily be offset by the increase in carbon dioxide production. Therefore, mechanistic understanding of peatland hydrology and its association with carbon cycling is a prerequisite for assessing vulnerability of peats to disturbances and for incorporating the associated feedbacks in carbon-climate models. We will present physically based model that ties together the structure of peat soils (mainly pore size distribution and mechanical stability) to rates of aerobic and anaerobic decomposition over a wide range of soil water potentials. Peats consist of hierarchical structure with clear separation of the pores into a population of micropores within clumps of organic matter and/or soil aggregates and a group of macropores between clumps and/or aggregates. This essentially partitions the carbon stock in peat soils in to multiple pools that become mineralizable at disparate water potential ranges. While the carbon in macropores can readily be decomposed by aerobic microorganisms when the soil is only slightly drained, the carbon in fine pores remains largely protected from aerobic microbes until the water potential exceeds a threshold that lets in oxygen. In this presentation we will show the mathematical development of the model and illustrative examples that compare projections with data derived from the literature.

Soil aggregate stratification of nematodes and ammonia oxidizers affects nitrification in an acid soil.

PubMed

Jiang, Yuji; Jin, Chen; Sun, Bo

2014-10-01

Nitrification plays a central role in global nitrogen cycle, which is affected by interaction between soil microfauna and microorganisms. The impact of synchronized changes in nematodes and ammonia oxidizers within aggregate fractions on nitrification was investigated in an acid soil under 10-year manure application. Nematodes, ammonia oxidizers and potential nitrification activity (PNA) were examined in three soil aggregate fractions under four fertilization regimes. Pyrosequencing data revealed that the dominant bacterial amoA operational taxonomic units (OTUs) were related to Nitrosospira species, while archaeal OTUs were affiliated with Nitrososphaera and Nitrosotalea species. PNA was more strongly correlated with ammonia-oxidizing bacteria (AOB) abundance than ammonia-oxidizing archaea (AOA) abundance, although AOA were dominant in the acid soil. Plant parasites had a negative effect on AOB abundance; however, bacterivores stimulated AOB abundance and contributed more to PNA than plant parasites. Aggregate fractions exerted significant impacts on AOA abundance and AOB community composition. Total carbon content strongly affected the abundance and composition of AOA community, while soil pH primarily affected that of AOB community. Soil variables explained 62.7% and 58.1% variations, and nematode variables explained 11.7% and 19.5% variations in the AOA and AOB community composition respectively. © 2013 Society for Applied Microbiology and John Wiley & Sons Ltd.

Dynamics of Soil Organic Carbon and Aggregate Stability with Grazing Exclusion in the Inner Mongolian Grasslands

PubMed Central

Wen, Ding; He, Nianpeng; Zhang, Jinjing

2016-01-01

Grazing exclusion (GE) has been deemed as an important approach to enhance the soil carbon storage of semiarid grasslands in China; however, it remains unclear how different organic carbon (OC) components in soils vary with the duration of GE. Here, we observed the changing trends of different OC components in soils with increased GE duration in five grassland succession series plots, ranging from free grazing to 31-year GE. Specifically, we measured microbial biomass carbon (MBC), easily oxidizable OC (EOC), water-soluble OC (WSOC), and OC in water stable aggregates (macroaggregates [250–2000 μm], microaggregates [53–250 μm], and mineral fraction [< 53 μm]) at 0–20 cm soil depths. The results showed that GE significantly enhanced EOC and WSOC contents in soils, but caused a decline of MBC at the three decade scale. Macroaggregate content (F = 425.8, P < 0.001), OC stored in macroaggregates (F = 84.1, P < 0.001), and the mean weight diameter (MWD) of soil aggregates (F = 371.3, P < 0.001) increased linearly with increasing GE duration. These findings indicate that OC stored in soil increases under three-decade GE with soil organic matter (SOM) stability improving to some extent. Long-term GE practices enhance the formation of soil aggregates through higher SOM input and an exclusion of animal trampling. Therefore, the practice of GE may be further encouraged to realize the soil carbon sequestration potential of semi-arid grasslands, China. PMID:26751370

Dynamics of Soil Organic Carbon and Aggregate Stability with Grazing Exclusion in the Inner Mongolian Grasslands.

PubMed

Wen, Ding; He, Nianpeng; Zhang, Jinjing

2016-01-01

Grazing exclusion (GE) has been deemed as an important approach to enhance the soil carbon storage of semiarid grasslands in China; however, it remains unclear how different organic carbon (OC) components in soils vary with the duration of GE. Here, we observed the changing trends of different OC components in soils with increased GE duration in five grassland succession series plots, ranging from free grazing to 31-year GE. Specifically, we measured microbial biomass carbon (MBC), easily oxidizable OC (EOC), water-soluble OC (WSOC), and OC in water stable aggregates (macroaggregates [250-2000 μm], microaggregates [53-250 μm], and mineral fraction [< 53 μm]) at 0-20 cm soil depths. The results showed that GE significantly enhanced EOC and WSOC contents in soils, but caused a decline of MBC at the three decade scale. Macroaggregate content (F = 425.8, P < 0.001), OC stored in macroaggregates (F = 84.1, P < 0.001), and the mean weight diameter (MWD) of soil aggregates (F = 371.3, P < 0.001) increased linearly with increasing GE duration. These findings indicate that OC stored in soil increases under three-decade GE with soil organic matter (SOM) stability improving to some extent. Long-term GE practices enhance the formation of soil aggregates through higher SOM input and an exclusion of animal trampling. Therefore, the practice of GE may be further encouraged to realize the soil carbon sequestration potential of semi-arid grasslands, China.

Composition and structure of aggregates from compacted soil horizons in the southern steppe zone of European Russia

NASA Astrophysics Data System (ADS)

Sorokin, A. S.; Abrosimov, K. N.; Lebedeva, M. P.; Kust, G. S.

2016-03-01

The composition and structure of aggregates from different agrogenic soils in the southern steppe zone of European Russia have been studied. It is shown that the multi-level study (from the macro- to microlevel) of these horizons makes it possible to identify soil compaction caused by different elementary soil processes: solonetz-forming, vertisol-forming, and mechanical (wheel) compaction in the rainfed and irrigated soils. The understanding of the genesis of the compaction of soil horizons (natural or anthropogenic) is important for the economic evaluation of soil degradation. It should enable us to make more exact predictions of the rates of degradation processes and undertake adequate mitigation measures. The combined tomographic and micromorphological studies of aggregates of 1-2 and 3-5 mm in diameter from compacted horizons of different soils have been performed for the first time. Additional diagnostic features of negative solonetz- forming processes (low open porosity of aggregates seen on tomograms and filling of a considerable part of the intraped pores with mobile substance) and the vertisol-forming processes (large amount of fine intraaggregate pores seen on tomograms and a virtual absence of humus-clay plasma in the intraped zone)—have been identified. It is shown that the combination of microtomographic and micromorphological methods is helpful for studying the pore space of compacted horizons in cultivated soils.

Interaction of Land Management Intensity and Micro-topography Controls on Geochemistry of Raindrop-Liberated/Mobilized Soil Particles

NASA Astrophysics Data System (ADS)

Hou, T.; Filley, T. R.; Berry, T.; Singh, S.; Hughes, M.; Tong, Y.; Papanicolaou, T.; Wacha, K.; Wilson, C. G.; Chaubey, I.

2017-12-01

The dynamics of raindrop-induced breakdown of soil aggregates, a critical factor in the initial process of surface erosion and lateral redistribution of soil, are strongly tied to land use intensity. What is unclear however is the relative control of rain and mechanical disturbance on the development of landscape-level heterogeneity in surface soil geochemistry. We used artificial rainfall simulated experiments including an aggregate stability test and time course rainfall-erosional test to evaluate the role of management intensity and micro-topography on the geochemistry of raindrop-liberated/mobilized particles from landscapes in southeastern Iowa. Comparing restored prairie, conservation tillage, and conventional tillage sites we found, and with a trend toward increasing tillage intensity, a decrease in aggregate stability and raindrop-liberated particles that were lower in organic carbon, nitrogen, and plant-derived biopolymers, while containing higher proportions of microbially-processed nitrogen than the raindrop stable aggregates. Time evolution of the geochemistry (e.g. elemental, stable isotope, and biopolymer composition) of transported soil particles exhibited distinct patterns based upon both position of the hillslope and oriented soil roughness. Additionally, in the restored prairie, raindrop liberated particles had identical geochemical composition to the raindrop stable aggregates. Our results demonstrate that agricultural sites under intensive tillage have not only a greater potential to liberate and mobilize soil particles during storms, but the mobilized particles will have a distinct chemical character based on tillage intensity, hillslope position and oriented roughness thus lead to a greater potential for landscape level heterogeneity in surface and buried soil chemistry upon mobilization and burial.

Geometrical appearance and spatial arrangement of structural blocks of the Malan loess in NW China: implications for the formation of loess columns

NASA Astrophysics Data System (ADS)

Li, Yanrong; Zhang, Tao; Zhang, Yongbo; Xu, Qiang

2018-06-01

Loess, as one of the main Quaternary deposits, covers approximately 6% of the land surface of the Earth. Although loess is loose and fragile, loess columns are popular and they can stand stably for hundreds of years, thereby forming a spectacular landform. The formation of such special column-shaped soil structures is puzzling, and the underlying fundamentals remain unclear. The present study focuses on quantifying and examining the geometrical shape and spatial alignment of structural blocks of the Malan loess at different locations in the Loess Plateau of China. The structural blocks under investigation include clay- and silt-sized particles, aggregates, fragments, lumps, and columns, which vary in size from microns to tens of meters. Regardless of their size, the structural blocks of the Malan loess are found to be similar in shape, i.e., elongated with a length-to-width ratio of approximately 2.6. The aggregates, fragments, lumps, columns, and macropores between aggregates exhibit strong concentration in the vertical or subvertical alignment. These phenomena imply that the Malan loess is anisotropic and it is composed of a combination of vertically aligned strong units and vertically aligned weak segments. Based on this, "vertiloess" structure is proposed to denote this combination. The vertiloess structure prevents horizontal erosion, but favors spalling, peeling, toppling, falling and cracking-sliding of vertical loess pieces, thereby forming loess columns.

Carbon dynamics and aggregation in a Vicia faba crop: influence of management practice and cultivar

NASA Astrophysics Data System (ADS)

Sánchez-Navarro, Virginia; Zornoza, Raúl; Faz, Ángel; Fernández, Juan

2016-04-01

In this study, we assessed the influence of a legume crop (Vicia faba) on the soil properties related to the carbon (C) cycle and soil aggregation, taking into account two cultivars (Muchamiel and Palenca) and two different management practices (conventional and organic). The study was randomly designed in blocks with four replications, in plots of 10 m2. Faba bean crop spanned from 24 November 2014 to 2 March 2015. We took a soil sampling (0-30 cm) from each plot at the end of the cycle to measure soil organic C, recalcitrant C, labile C fractions, microbial biomass C (MBC), aggregate stability and the enzyme activities β-glucosidase, β-glucosaminidase, dehydrogenase, cellulose and arylesterase. Results showed that the cultivar and the management practice had no significant effect on any of the analyzed properties. Significant positive correlations were only observed between soil organic C and arylesterase activity, recalcitrant C and labile C fractions, and recalcitrant C with arylesterase and cellulase activities. So, it seems that the selected cultivars and management practices had similar effects on C dynamics and aggregation. Both management practices maintain the same levels of soil organic C, the different organic C pools, and aggregate stability. In addition, soil microorganisms are responding to the recalcitrant fraction of the organic carbon by release of cellulases and arylesterases. Acknowledgements: This research was financed by the FP7 European Project Eurolegume (FP7-KBBE- 613781).

Slow reaction of soil structure to conservation agriculture practices in Veneto silty soils (North-Easter Italy)

NASA Astrophysics Data System (ADS)

Piccoli, Ilaria; Camarotto, Carlo; Lazzaro, Barbara; Furlan, Lorenzo; Morari, Francesco

2017-04-01

Soil structure plays a pivotal role in soil functioning and can inform of the degradation of the soil ecosystem. Intensive and repeated tillage operations have been known to negatively affect the soil structure characteristics while conservation agriculture (CA) practices were demonstrated to improve soil structure and related ecosystem services. The aim of this study is to evaluate the effect of conservation agriculture practices on total porosity, pore size distribution, pore architecture and morphology on silty soils of Veneto low-lying plain (North-Eastern Italy). Experimental design was established in 2010 on 4 farms in North-Eastern Italy to compare conventional intensive tillage system "IT" versus conservation agriculture "CA" (no-tillage, cover-crop and residue retention). 96 samples were collected in 2015 at four depths down to 50 cm depth, and investigated for porosity from micro to macro by coupling mercury intrusion porosimetry (MIP) (0.0074-100 µm) and x-ray computed microtomography (µCT) (>26 µm). Pore morphology and architecture were studied from 3D images analysis and MIP pore size curve. Ultramicroporosity class (0.1-5 μm) positively responded to CA after 5-yr of practices adoption while no significant effects were observed in the x-ray µCT domain (> 26 µm). Silty soils of Veneto plain showed a slow reaction to conservation agriculture because of the low soil organic carbon content and poor aggregate stability. Nevertheless the positive influence of CA on ultramicroporosity, which is strictly linked to soil organic carbon (SOC) stabilization, indicated that a virtuous cycle was initiated between SOC and porosity, hopefully leading to well-developed macropore systems and, in turn, enhanced soil functions and ecosystem services.

Using semi-variogram analysis for providing spatially distributed information on soil surface condition for land surface modeling

NASA Astrophysics Data System (ADS)

Croft, Holly; Anderson, Karen; Kuhn, Nikolaus J.

2010-05-01

The ability to quantitatively and spatially assess soil surface roughness is important in geomorphology and land degradation studies. Soils can experience rapid structural degradation in response to land cover changes, resulting in increased susceptibility to erosion and a loss of Soil Organic Matter (SOM). Changes in soil surface condition can also alter sediment detachment, transport and deposition processes, infiltration rates and surface runoff characteristics. Deriving spatially distributed quantitative information on soil surface condition for inclusion in hydrological and soil erosion models is therefore paramount. However, due to the time and resources involved in using traditional field sampling techniques, there is a lack of spatially distributed information on soil surface condition. Laser techniques can provide data for a rapid three dimensional representation of the soil surface at a fine spatial resolution. This provides the ability to capture changes at the soil surface associated with aggregate breakdown, flow routing, erosion and sediment re-distribution. Semi-variogram analysis of the laser data can be used to represent spatial dependence within the dataset; providing information about the spatial character of soil surface structure. This experiment details the ability of semi-variogram analysis to spatially describe changes in soil surface condition. Soil for three soil types (silt, silt loam and silty clay) was sieved to produce aggregates between 1 mm and 16 mm in size and placed evenly in sample trays (25 x 20 x 2 cm). Soil samples for each soil type were exposed to five different durations of artificial rainfall, to produce progressively structurally degraded soil states. A calibrated laser profiling instrument was used to measure surface roughness over a central 10 x 10 cm plot of each soil state, at 2 mm sample spacing. The laser data were analysed within a geostatistical framework, where semi-variogram analysis quantitatively represented the change in soil surface structure during crusting. The laser data were also used to create digital surface models (DSM) of the soil states for visual comparison. This research has shown that aggregate breakdown and soil crusting can be shown quantitatively by a decrease in sill variance (silt soil: 11.67 (control) to 1.08 (after 90 mins rainfall)). Features present within semi-variograms were spatially linked to features at the soil surface, such as soil cracks, tillage lines and areas of deposition. Directional semi-variograms were used to provide a spatially orientated component, where the directional sill variance associated with a soil crack was shown to increase from 7.95 to 19.33. Periodicity within semi-variogram was also shown to quantify the spatial scale of soil cracking networks and potentially surface flowpaths; an average distance between soil cracks of 37 mm closely corresponded to the distance of 38 mm shown in the semi-variogram. The results provide a strong basis for the future retrieval of spatio-temporal variations in soil surface condition. Furthermore, the presence of process-based information on hydrological pathways within semi-variograms may work towards an inclusion of geostatisically-derived information in land surface models and the understanding of complex surface processes at different spatial scales.

Emerging Patterns for Engineered Nanomaterials in the Environment: A Review of Fate and Toxicity Studies

NASA Astrophysics Data System (ADS)

Garner, K.; Keller, A. A.

2014-12-01

The technical complexity of measuring ENM fate and transport processes in all environments necessitates identifying trends in these same processes. As part of our research, we collected emerging information on the environmental fate and toxicity of many ENMs and investigated transportation and transformation processes in air, water, and soil. Generally, studies suggest that (i) ENMs will have limited transport in the atmosphere, because they settle rapidly; (ii) ENMs are more stable in freshwater and stormwater than in seawater or groundwater primarily due to variations in ionic strength and the presence of natural organic matter; and (iii) in soil, the fate of ENMs strongly depends on the size of the ENM aggregates and groundwater chemistry, as well as pore and soil particle size. Emerging patterns regarding ENM fate, transport, and exposure combined with emerging information on toxicity indicate the risk is low for most ENMs although current exposure estimates compared with current data on toxicity indicate that at current production and release levels, exposure to Ag, nZVI, and ZnO may cause a toxic response to freshwater and marine species.

Influence of ultrasonic energy on dispersion of aggregates and released amounts of organic matter and polyvalent cations

NASA Astrophysics Data System (ADS)

Kaiser, M.; Kleber, M.; Berhe, A. A.

2010-12-01

Aggregates play important roles in soil carbon storage and stabilization. Identification of scale-dependent mechanisms of soil aggregate formation and stability is necessary to predict and eventually manage the flow of carbon through terrestrial ecosystems. Application of ultrasonic energy is a common tool to disperse soil aggregates. In this study, we used ultra sonic energy (100 to 2000 J cm-3) to determine the amount of polyvalent cations and organic matter involved in aggregation processes in three arable and three forest soils that varied in soil mineral composition. To determine the amount of organic matter and cations released after application of different amount of ultrasonic energy, we removed the coarse fraction (>250 µm). The remaining residue (<250 µm) was mixed with water and ultrasonically dispersed by application of 100, 200, 400, 500, 1000, 1500 and 2000 J cm-3 energy. After centrifugation the supernatant was filtered and the solid residue freeze dried before we analyzed the amounts of water-extracted organic carbon (OC), Fe, Al, Ca, Mn, and Mg in the filtrates. The extracted OM and solid residues were further characterized by Fourier Transformed Infra Red spectroscopy and Scanning Electron Microscopy. Our results show a linear increase in amount of dissolved OC with increasing amounts of ultra sonic energy up to 1500 J cm-3 indicating maximum dispersion of soil aggregates at this energy level independent from soil type or land use. In contrast to Mn, and Mg, the amounts of dissolved Ca, Fe, and Al increase with increasing ultra sonic energy up to 1500 J cm-3. At 1500 J cm-3, the absolute amounts of OC, Ca, Fe, and Al released were specific for each soil type, likely indicating differences in type of OM-mineral interactions involved in micro-scaled aggregation processes. The amounts of dissolved Fe, and Al released after an application of 1500 J cm-3 are not related to oxalate- and dithionite- extractable, or total Al content indicating less disintegration of pedogenic oxides or clay minerals due to high levels of ultrasonic energy.

Distribution and speciation of ambient selenium in contrasted soils, from mineral to organic rich.

PubMed

Tolu, Julie; Thiry, Yves; Bueno, Maïté; Jolivet, Claudy; Potin-Gautier, Martine; Le Hécho, Isabelle

2014-05-01

Selenium adsorption onto oxy-hydroxides mainly controls its mobility in volcanic soils, red earths and soils poor in organic matter (OM) while the influence of OM was emphasized in podzol and peat soils. This work aims at deciphering how those solid phases influence ambient Se mobility and speciation under less contrasted conditions in 26 soils spanning extensive ranges of OM (1-32%), Fe/Al oxy-hydroxides (0.3-6.1%) contents and pH (4.0-8.3). The soil collection included agriculture, meadow and forest soils to assess the influence of OM quality as well. Trace concentrations of six ambient Se species (Se(IV), Se(VI) and 4 organo-Se compounds) were analyzed by HPLC-ICP-MS in three extractants (ultrapure water, phosphate and sodium hydroxide) targeting Se associated to different soil phases. The Kd values determined from ultrapure water extraction were higher than those reported in commonly used short-term experiments after Se-spiking. Correlations of ambient Se content and distribution with soil parameters explained this difference by an involvement of slow processes in Se retention in soils. The 26 Kd values determined here for a wide variety of soils thus represent a relevant database for long-term prediction of Se mobility. For soils containing less than 20% OM, ambient Se solubility is primarily controlled by its adsorption onto crystalline oxy-hydroxides. However, OM plays an important role in Se mobility by forming organo-mineral associations that may protect adsorbed Se from leaching and/or create anoxic zones (aggregates) where Se is immobilized after its reduction. Although for the first time, inorganic Se(IV), Se(VI) and organo-Se compounds were simultaneously investigated in a large soil collection, high Se proportions remain unidentified in each soil extract, most probably due to Se incorporation and/or binding to colloidal-sized OM. Variations of environmental factors regulating the extent of OM-mineral associations/aggregation may thus lead to changes in Se mobility and bio-availability. Copyright © 2014 Elsevier B.V. All rights reserved.

Physical disturbance to ecological niches created by soil structure alters community composition of methanotrophs.

PubMed

Kumaresan, Deepak; Stralis-Pavese, Nancy; Abell, Guy C J; Bodrossy, Levente; Murrell, J Colin

2011-10-01

Aggregates of different sizes and stability in soil create a composite of ecological niches differing in terms of physico-chemical and structural characteristics. The aim of this study was to identify, using DNA-SIP and mRNA-based microarray analysis, whether shifts in activity and community composition of methanotrophs occur when ecological niches created by soil structure are physically perturbed. Landfill cover soil was subject to three treatments termed: 'control' (minimal structural disruption), 'sieved' (sieved soil using 2 mm mesh) and 'ground' (grinding using mortar and pestle). 'Sieved' and 'ground' soil treatments exhibited higher methane oxidation potentials compared with the 'control' soil treatment. Analysis of the active community composition revealed an effect of physical disruption on active methanotrophs. Type I methanotrophs were the most active methanotrophs in 'sieved' and 'ground' soil treatments, whereas both Type I and Type II methanotrophs were active in the 'control' soil treatment. The result emphasize that changes to a particular ecological niche may not result in an immediate change to the active bacterial composition and change in composition will depend on the ability of the bacterial communities to respond to the perturbation. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.

Regulation of aggregate size and pattern by adenosine and caffeine in cellular slime molds

PubMed Central

2012-01-01

Background Multicellularity in cellular slime molds is achieved by aggregation of several hundreds to thousands of cells. In the model slime mold Dictyostelium discoideum, adenosine is known to increase the aggregate size and its antagonist caffeine reduces the aggregate size. However, it is not clear if the actions of adenosine and caffeine are evolutionarily conserved among other slime molds known to use structurally unrelated chemoattractants. We have examined how the known factors affecting aggregate size are modulated by adenosine and caffeine. Result Adenosine and caffeine induced the formation of large and small aggregates respectively, in evolutionarily distinct slime molds known to use diverse chemoattractants for their aggregation. Due to its genetic tractability, we chose D. discoideum to further investigate the factors affecting aggregate size. The changes in aggregate size are caused by the effect of the compounds on several parameters such as cell number and size, cell-cell adhesion, cAMP signal relay and cell counting mechanisms. While some of the effects of these two compounds are opposite to each other, interestingly, both compounds increase the intracellular glucose level and strengthen cell-cell adhesion. These compounds also inhibit the synthesis of cAMP phosphodiesterase (PdsA), weakening the relay of extracellular cAMP signal. Adenosine as well as caffeine rescue mutants impaired in stream formation (pde4- and pdiA-) and colony size (smlA- and ctnA-) and restore their parental aggregate size. Conclusion Adenosine increased the cell division timings thereby making large number of cells available for aggregation and also it marginally increased the cell size contributing to large aggregate size. Reduced cell division rates and decreased cell size in the presence of caffeine makes the aggregates smaller than controls. Both the compounds altered the speed of the chemotactic amoebae causing a variation in aggregate size. Our data strongly suggests that cytosolic glucose and extracellular cAMP levels are the other major determinants regulating aggregate size and pattern. Importantly, the aggregation process is conserved among different lineages of cellular slime molds despite using unrelated signalling molecules for aggregation. PMID:22269093

Regulation of aggregate size and pattern by adenosine and caffeine in cellular slime molds.

PubMed

Jaiswal, Pundrik; Soldati, Thierry; Thewes, Sascha; Baskar, Ramamurthy

2012-01-23

Multicellularity in cellular slime molds is achieved by aggregation of several hundreds to thousands of cells. In the model slime mold Dictyostelium discoideum, adenosine is known to increase the aggregate size and its antagonist caffeine reduces the aggregate size. However, it is not clear if the actions of adenosine and caffeine are evolutionarily conserved among other slime molds known to use structurally unrelated chemoattractants. We have examined how the known factors affecting aggregate size are modulated by adenosine and caffeine. Adenosine and caffeine induced the formation of large and small aggregates respectively, in evolutionarily distinct slime molds known to use diverse chemoattractants for their aggregation. Due to its genetic tractability, we chose D. discoideum to further investigate the factors affecting aggregate size. The changes in aggregate size are caused by the effect of the compounds on several parameters such as cell number and size, cell-cell adhesion, cAMP signal relay and cell counting mechanisms. While some of the effects of these two compounds are opposite to each other, interestingly, both compounds increase the intracellular glucose level and strengthen cell-cell adhesion. These compounds also inhibit the synthesis of cAMP phosphodiesterase (PdsA), weakening the relay of extracellular cAMP signal. Adenosine as well as caffeine rescue mutants impaired in stream formation (pde4- and pdiA-) and colony size (smlA- and ctnA-) and restore their parental aggregate size. Adenosine increased the cell division timings thereby making large number of cells available for aggregation and also it marginally increased the cell size contributing to large aggregate size. Reduced cell division rates and decreased cell size in the presence of caffeine makes the aggregates smaller than controls. Both the compounds altered the speed of the chemotactic amoebae causing a variation in aggregate size. Our data strongly suggests that cytosolic glucose and extracellular cAMP levels are the other major determinants regulating aggregate size and pattern. Importantly, the aggregation process is conserved among different lineages of cellular slime molds despite using unrelated signalling molecules for aggregation.

Factors influencing soil aggregation and particulate organic matter responses to bioenergy crops across a topographic gradient

Treesearch

Todd A. Ontl; Cynthia A. Cambardella; Lisa A. Schulte; Randall K. Kolka

2015-01-01

Bioenergy crops have the potential to enhance soil carbon (C) pools from increased aggregation and the physical protection of organic matter; however, our understanding of the variation in these processes over heterogeneous landscapes is limited. In particular, little is known about the relative importance of soil properties and root characteristics for the physical...

Increases in soil aggregation following phosphorus additions in a tropical premontane forest are not driven by root and arbuscular mycorrhizal fungal abundances

NASA Astrophysics Data System (ADS)

Camenzind, Tessa; Papathanasiou, Helena; Foerster, Antje; Dietrich, Karla; Hertel, Dietrich; Homeier, Juergen; Oelmann, Yvonne; Olsson, Pål Axel; Suárez, Juan; Rillig, Matthias

2015-12-01

Tropical ecosystems have an important role in global change scenarios, in part because they serve as a large terrestrial carbon pool. Carbon protection is mediated by soil aggregation processes, whereby biotic and abiotic factors influence the formation and stability of aggregates. Nutrient additions may affect soil structure indirectly by simultaneous shifts in biotic factors, mainly roots and fungal hyphae, but also via impacts on abiotic soil properties. Here, we tested the hypothesis that soil aggregation will be affected by nutrient additions primarily via changes in arbuscular mycorrhizal fungal (AMF) hyphae and root length in a pristine tropical forest system. Therefore, the percentage of water-stable macroaggregates (> 250µm) (WSA) and the soil mean weight diameter (MWD) was analyzed, as well as nutrient contents, pH, root length and AMF abundance. Phosphorus additions significantly increased the amount of WSA, which was consistent across two different sampling times. Despite a positive effect of phosphorus additions on extraradical AMF biomass, no relationship between WSA and extra-radical AMF nor roots was revealed by regression analyses, contrary to the proposed hypothesis. These findings emphasize the importance of analyzing soil structure in understudied tropical systems, since it might be affected by increasing nutrient deposition expected in the future.

Development of soil quality along a chronosequence under natural succession in the Dragonja catchment, SW Slovenia

NASA Astrophysics Data System (ADS)

van Hall, Rutger; Cammeraat, Erik

2015-04-01

Agricultural fields have been increasingly abandoned in several regions in Southern Europe. In many cases this leads to natural vegetation succession which may have a direct impact on soil quality,biodiversity and hydrological connectivity. This research aims at getting insight on the effects of natural vegetation succession on the development of soil quality in the Sub-Mediterranean Dragonja catchment in SW Slovenia. This site was chosen due to its uniform geology, geomorphology and soil types. Four different stages of vegetation succession (i.e. field, abandoned field, young forest, semi-mature forest) were selected and sampled on both north-, and south-facing slopes, resulting in 8 treatments for which 6 representative sites were sampled. Samples were analysed on OC and TN content, EC, pH, bulk density, aggregate stability and grain size distribution. To get insight on the changes in biodiversity vegetation records were made distinguishing five different plant functional groups (i.e. juveniles, grasses, herbs, shrubs and trees). Age group (i.e. stage of vegetation succession) significantly influenced the OC and TN content, aggregate stability, bulk density and pH. Directly after abandonment, between age group 0 and 1, OC and TN content, aggregate stability and pH increased significantly and bulk density decreased significantly. OC content was most affected by age group and furthermore significantly correlated to TN content, aggregate stability, bulk density and pH. Regarding biodiversity, there was a significant increase in cover by trees between age group 1 and 2 and a significant decrease between age group 2 and 3. Cover by herbs decreased significantly between age group 1 and 2. The number of different trees and shrubs increased significantly between age group 0 and 1, and the number of different juveniles increased significantly between age group 2 and 3. Another factor significantly influencing the soil's quality is aspect. Although not found for each age group south-facing slopes generally had higher OC and TN content, and higher pH than north-facing slopes. On average OC content was 28% higher and TN content 25% higher on south facing slopes. Aspect did not have a significant influence on the biodiversity although on average vegetation cover is slightly (7%) higher and 16% mores species were found on north facing slopes.

The effects of the mineral phase on C stabilization mechanisms and the microbial community along an eroding slope transect

NASA Astrophysics Data System (ADS)

Doetterl, S.; Opfergelt, S.; Cornelis, J.; Boeckx, P. F.; van oost, K.; Six, J.

2013-12-01

An increasing number of studies show the importance of including soil redistribution processes in understanding carbon (C) dynamics in eroding landscapes. The quality and quantity of soil organic carbon in sloping cropland differs with topographic position. These differences are commonly more visible in the subsoil, while the size and composition of topsoil C pools are similar along the hillslope. The type (plant- or microbial-derived) and quality (level of degradation) of C found in a specific soil fraction depends on the interplay between the temporal dynamic of the specific mechanism and it's strength to protect C from decomposition. Here, we present an analysis that aims to clarify the bio/geo-chemical and mineralogical components involved in stabilizing C at various depths and slope positions and how they affect the microbial community and the degradation of C. For this we analyzed soil samples from different soil depths along a slope transect applying (i) a sequential extraction of the reactive soil phase using pyrophosphate, oxalate and dithionite-citrate-bicarbonate, (ii) a semi-quantitative and qualitative analysis of the clay mineralogy, (iii) an analysis of the microbial community using amino sugars and (iv) an analysis of the level of degradation of C in different soil fractions focusing on the soil Lignin signature. The results show that the pattern of minerals and their relative importance in stabilizing C varies greatly along the transect. In the investigated soils, pyrophosphate extractable Manganese, and not Iron or Aluminum as often observed, is strongly correlated to C in the bulk soil and in the non-aggregated silt and clay fractions. This suggests a certain role of Manganese for C stabilization where physical protection is absent. In contrast, pyrophosphate extractable Iron and Aluminum components are largely abundant in water-stable soil aggregates but not correlated to C, suggesting importance of these extracts to stabilize aggregates and, hence, providing physical protection of C. Oxalate extractable amorphous and poorly crystalline minerals are correlated to C, especially for the more recalcitrant C fractions, but only at the depositional site. However, decreasing contents of oxalate extractable elements with depth indicate a temporal limitation of this stabilization mechanism and this is also supported by the results of our lignin extraction. Non-expandable clay minerals experience a relative enrichment at the depositional site while expandable clay minerals experience the same at the eroding site. These changes in clay mineralogy along the slope are partly responsible for the abundance of silt and clay associated C. The changes in soil mineralogy and micro-scale environmental conditions led to an adaptation of the microbial community in comparison to sites not affected by soil redistribution.

Comparison of transport and attachment behaviors of Cryptosporidium parvum oocysts and oocyst-sized microspheres being advected through three minerologically different granular porous media.

PubMed

Mohanram, Arvind; Ray, Chittaranjan; Harvey, Ronald W; Metge, David W; Ryan, Joseph N; Chorover, Jon; Eberl, D D

2010-10-01

In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43-46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22-29% by mass), aluminum (29-45% by mass), and clay-rich (68-76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-μm microspheres, almost all (>99%) predictably would be recovered within ∼4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was observed for the red, metal-oxide rich soil from Oahu. In contrast, colloidal attachment in the organic-rich, volcanic ash soil was relatively insensitive to changes in pH in spite of the high iron content. Given the fundamental differences in transport behavior of oocyst-sized colloids within the two volcanic soils of similar origin, agricultural practices modified to lessen C. parvum contamination of ground or surface water would necessitate taking the individual soil properties into account. Copyright © 2010 Elsevier Ltd. All rights reserved.

Comparison of transport and attachment behaviors of Cryptosporidium parvum oocysts and oocyst-sized microspheres being advected through three minerologically different granular porous media

USGS Publications Warehouse

Mohanram, Arvind; Ray, Chittaranjan; Harvey, Ronald W.; Metge, David W.; Ryan, Joseph N.; Chorover, Jon; Eberl, D.D.

2010-01-01

In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43–46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22–29% by mass), aluminum (29–45% by mass), and clay-rich (68–76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-μm microspheres, almost all (>99%) predictably would be recovered within ∼4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was observed for the red, metal-oxide rich soil from Oahu. In contrast, colloidal attachment in the organic-rich, volcanic ash soil was relatively insensitive to changes in pH in spite of the high iron content. Given the fundamental differences in transport behavior of oocyst-sized colloids within the two volcanic soils of similar origin, agricultural practices modified to lessen C. parvum contamination of ground or surface water would necessitate taking the individual soil properties into account.

Comparison of transport and attachment behaviors of Cryptosporidium parvum oocysts and oocyst-sized microspheres being advected through three minerologically different granular porous media

USGS Publications Warehouse

Mohanram, A.; Ray, C.; Harvey, R.W.; Metge, D.W.; Ryan, J.N.; Chorover, J.; Eberl, D.D.

2010-01-01

In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43-46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22-29% by mass), aluminum (29-45% by mass), and clay-rich (68-76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-??m microspheres, almost all (>99%) predictably would be recovered within ~4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was observed for the red, metal-oxide rich soil from Oahu. In contrast, colloidal attachment in the organic-rich, volcanic ash soil was relatively insensitive to changes in pH in spite of the high iron content. Given the fundamental differences in transport behavior of oocyst-sized colloids within the two volcanic soils of similar origin, agricultural practices modified to lessen C. parvum contamination of ground or surface water would necessitate taking the individual soil properties into account. ?? 2010.

Effect of polyacrylamide on soil physical and hydraulic properties

NASA Astrophysics Data System (ADS)

Albalasmeh, Ammar; Gharaibeh, Mamoun; Hamdan, Enas

2017-04-01

The effect of polyacrylamide (PAM), as a soil conditioner, on selected soil physical and hydraulic properties (infiltration rate (f(t)), hydraulic conductivity (HC), soil moisture content, aggregate stability (AS), and soil aggregation) was studied. Two types of anionic PAM were used: Low molecular weight (LPAM) (1×105 g/mol) with medium charge density (33-43) and high molecular weight (HPAM) (1-6×106 g/mol) with medium charge density (33-43). Sandy loam soil was packed into plastic columns; PAM solutions at different concentrations (100, 250, 500, and 1000 mg L-1) were used every two weeks in four wetting and drying cycles. The highest infiltration rate value was 0.16 mm s-1 at 1000 mg/L low molecular weight PAM while the highest value of infiltration rate in high PAM molecular weight was 0.11 mm s-1 compared to the control (0.01 mm s-1). Soil HC was about 3.00 cm h-1 for LPAM at 1000 mg L-1 PAM, while the highest value for HPAM was about 2 cm h-1 for the same concentration, compared to the control. The amount of water that can be held by soil increased with the addition of PAM compared to the control. Differences in water content were more pronounced in LPAM compared to HPAM. The addition of LPAM increased aggregate stability proportional to PAM concentration. Moreover, 1000 mg L-1 produced the highest aggregate stability (19{%}) compared to HPAM and control (7{%} and 5{%}), respectively. As PAM concentration increased, the geometric mean diameter (GMD) increased for both PAM molecular weights compared to control (0.4 mm). At 1000 mg L-1 the GMD values were 0.88 mm and 0.79 mm for LPAM and HPAM, respectively. The addition of PAM improved soil physical and hydraulic properties, with an advantage to LPAM owing that to its ability to penetrate soil aggregates and therefore stabilizing them.

Effect of sustainable land management practices on soil aggregation and stabilization of organic carbon in semiarid mediterranean ecosystems

NASA Astrophysics Data System (ADS)

Garcia-Franco, Noelia; Albaladejo, Juan; Almagro, María; Wiesmeier, Martin; Martínez-Mena, María

2016-04-01

Arid and semiarid regions represent about 47% of the total land area of the world (UNEP, 1992). At present, there is a priority interest for carbon (C) sequestration in drylands. These areas are considered as very fragile ecosystems with low organic carbon (OC) saturation, and potentially, high capacity for soil OC sequestration. In addition, the restoration of these areas is one of the major challenges for scientists, who will be able to identify and recommended the best land uses and sustainable land management (SLM) practices for soil conservation and mitigation of climate change in these environments. In this regard, in semiarid Mediterranean ecosystems there is an urgent need for the implementation of SLM practices regardless of land-use type (forest, agricultural and shrubland) to maintain acceptable levels of soil organic matter (SOM) and the physico-chemical protection of the OC. Long- and short-term effects of SLM practices on soil aggregation and SOC stabilization were studied in two land uses. The long-term experiment was conducted in a reforestation area with Pinus halepensis Mill., where two afforestation techniques were implemented 20 years ago: a) mechanical terracing with a single application of organic waste of urban soil refuse, and b) mechanical terracing without organic amendment. An adjacent shrubland was considered as the reference plot. The short-term experiment was conducted in a rain-fed almond (Prunus dulcis Mill., var. Ferragnes) orchard where two SLM practices were introduced 4 years ago: a) reduced tillage plus green manure, and b) no tillage. Reduced tillage was considered as the reference plot given that it is the habitual management practice. Four aggregate size classes were differentiated by sieving (large and small macroaggregates, microaggregates, and the silt plus clay fraction), and the microaggregates occluded within small macroaggregates (SMm) were isolated. In addition, different organic C fractions corresponding with active, slow and passive pools were separated using a density fractionation method. Our results showed that the chemical stabilization of OC, was the main mechanisms of C sequestration in the two study sites, which occurred through the formation of complexes with silt and clay particles and its physical protection in microaggregates formed within macroaggregates. In addition, the chemical stabilization was promoted by the mineral composition of the soil matrix. Both studied sites, especially that involving organic soil amendment in the forest system, and the green manure treatment in the agricultural system exhibited an increase in the labile pool of OC in the soil. This increase promoted the formation of macroaggregates, in two ways: 1) directly, by acting as a binding agent between soil particles, and 2) indirectly, by stimulating the microbiological activity, especially that of the fungi - which "package" the particles with their hyphae. The establishment of these new macroaggregates favors the formation of microaggregates. In addition, in the agricultural soils, minimum tillage seems to be necessary, from the point of view of carbon sequestration, since it promotes the incorporation of plant material and the formation of aggregates into deeper layers

Factors Associated with the Performance and Cost-Effectiveness of Using Lymphatic Filariasis Transmission Assessment Surveys for Monitoring Soil-Transmitted Helminths: A Case Study in Kenya

PubMed Central

Smith, Jennifer L.; Sturrock, Hugh J. W.; Assefa, Liya; Nikolay, Birgit; Njenga, Sammy M.; Kihara, Jimmy; Mwandawiro, Charles S.; Brooker, Simon J.

2015-01-01

Transmission assessment surveys (TAS) for lymphatic filariasis have been proposed as a platform to assess the impact of mass drug administration (MDA) on soil-transmitted helminths (STHs). This study used computer simulation and field data from pre- and post-MDA settings across Kenya to evaluate the performance and cost-effectiveness of the TAS design for STH assessment compared with alternative survey designs. Variations in the TAS design and different sample sizes and diagnostic methods were also evaluated. The district-level TAS design correctly classified more districts compared with standard STH designs in pre-MDA settings. Aggregating districts into larger evaluation units in a TAS design decreased performance, whereas age group sampled and sample size had minimal impact. The low diagnostic sensitivity of Kato-Katz and mini-FLOTAC methods was found to increase misclassification. We recommend using a district-level TAS among children 8–10 years of age to assess STH but suggest that key consideration is given to evaluation unit size. PMID:25487730

The Impact of Fire on Mercury Cycling in Watershed Systems

NASA Astrophysics Data System (ADS)

Lopez, S.; Mendez, C.; Hogue, T.; Jay, J.

2006-12-01

Mercury methylation is a process by which the less-toxic inorganic mercury is transformed into methylmercury (MeHg). MeHg is a potent neurotoxin with a strong tendency to biomagnify within the food chain. Limited studies suggest that wildfires change the soil characteristics and contribute to Hg transport and possibly methylation in downstream ecosystems. We propose that post-fire Hg cycling can be related to various soil properties and burn characteristics. In order to better understand the effects of wildfires on Hg cycling, studies were undertaken within a burned watershed and a neighboring unburned site, Malibu Creek and Cold Creek, respectively. Soil sampling of the burned and control (unburned) regions were composed of 25 square foot grids with nine equidistant sampling points. Sediment samples for soil sieve analysis were collected at all grid points to determine the particle size distribution of the fine and coarse grain aggregates. Total Hg sediments were collected from the three middle points of the grid at two soil horizons to provide a vertical profile. Total Hg concentrations of the sediment samples were measured using the Direct Mercury Analyzer (DMA80). Initial analysis of the soil profiles reveals a decrease in Hg concentration at the soil surface (89 percent loss). Preliminary results indicate sites with the lowest concentration of Hg are characterized by a higher percentage of finer grain aggregates. Runoff from the first post-fire storm was extremely turbid and dark gray in color due to high levels of suspended solids (3980 mg/L). Total Hg concentrations in unfiltered and filtered samples (0.2 micron) were 196 and 4.7 ng/L, respectively, compared to the control which had unfiltered and filtered Hg levels of 6.1 and 2.3 ng/L, respectively, and 450 mg/L total suspended solids. The concentration of Hg on the particles was six times higher than the Hg content of suspended particles at the control site. Results also show much stronger partitioning (three-fold higher Kd's) to the solid phase in the fire- impacted site. On-going work includes: 1) analysis of Hg and ancillary geochemical parameters overlying water and porewater from samples collected in the streambed downstream of the fire, 2) analysis of Hg concentrations in various particle size fractions of soil; and 3) preliminary characterization of recovery through analysis of soil properties and Hg levels at the burned and control sites, one-year post-fire.

How rice roots form their surrounding: Distinctive sub-zones of oxides, silicates and organic matter

NASA Astrophysics Data System (ADS)

Koelbl, Angelika; Mueller, Carsten; Hoeschen, Carmen; Lugmeier, Johann; Said-Pullicino, Daniel; Romani, Marco; Koegel-Knabner, Ingrid

2016-04-01

Most of the rice (Oryza sativa) worldwide is grown under flooded conditions in bunded fields (paddies). Inundation during long periods of the year leads to anoxic conditions in the soil. The rice plant is well adapted to these conditions by being able to transport oxygen via aerenchyma from the atmosphere to the roots. This plant mediated O2 transport also influences the adjacent soil. Driven by the O2 leakage into the rhizosphere, reddish ferric oxides and ferric hydroxides precipitate along the root channels. Thus, radial gradients of ferric Fe and with it co-precipitated organic substances form. Detailed investigations of element gradients on a submicron scale within the oxide coatings are still missing. Nano-scale secondary ion mass spectrometry (NanoSIMS) analyses can help to visualize and study the interplay of the various soil components at a submicron scale like, e.g., the attachment of organic material to minerals or the architecture of microstructures. The aim of the present study was to evaluate the composition and size of oxide coatings around rice roots concerning the distribution of organic matter and its spatial relation to oxides and silicates. Samples were taken from the plough pan of a paddy field close to the National Rice Research Centre, Castello d'Agogna (Pavia, Italy). Intact soil aggregates were air-dried, embedded in epoxy resin and then cut and polished in order to obtain a surface with low topography. Reflected-light microscopy was used (mm to μm scale) to visualize the aggregate architecture and to identify root channels in the embedded aggregate. In the next step, scanning electron microscopy (SEM) was applied to obtain images of high resolution and to define distinctive spots for subsequent NanoSIMS analyses. Using the Cameca NanoSIMS 50L at TU München, we simultaneously detected 12C-, 12C14N-, 28Si-, 32S-, 27Al16O- and 56Fe16O- at several areas around root channels in order to distinguish between organic material and different mineral particles (e.g. oxides, clay minerals). Beside single 40 x 40 μm sized spots, mosaics of 20 x 20 μm sized images were combined to investigate the region from the surface of the root channels into the soil matrix. The image data of all detected secondary ions was analysed using line scans and designation of regions of interest (ROI) to evaluate relative occurrences and spatial distributions. The results revealed that the oxic zone around rice roots can be subdivided in distinctive sub-zones. We identified a distinctive zone of approx. 20 μm around the root channels, where exclusively oxide-associated organic matter occurred. This zone can be clearly distinguished from a clay mineral-dominated zone. In addition, oxide-incrusted root cells revealed coexisting regions of Fe (hydr)oxides and Al-organic complexes.

Soils are sensitive reactors - do we need a paradigm change towards a more sustainable soil use?

NASA Astrophysics Data System (ADS)

Horn, Rainer; Holthusen, Dörthe

2015-04-01

The aim of the lecture is to clarify the effect of soil management and the consequences of physical degradation on processes like soil aggregation and changes in the accessibility and functionality of structured soils. If due to soil management strategies the internal soil strength will be exceeded by external stresses applied not only the available pore space is reduced while the solid mass is increased but especially the pore continuity and the accessibility of exchange places for nutrients or heavy metals are altered. In addition, the root distribution in soils becomes not only reduced but also unevenly distributed which again hinders the possibility to evenly uptake plant available water and nutrient out of the pores. The applied stresses also create an anisotropic arrangement of the pores and their functions and also result in a more pronounced lateral mass transport by surface runoff including soil erosion by water and wind. Thus, also the water balance on all scales (from the pedon to the catchment) shows an increased water loss by evaporation and surface water while the groundwater recharge and the transpiration rates are reduced. If we analyze the scale dependency of nutrient adsorption and desorption phenomena it has to be stated, that the accessibility of exchange places within soil aggregates are the better the more structured and the more rigid these aggregates are, while with increasing mechanical stress applied aggregates are deformed and as a consequences they become less porous with a severe differentiation between the outer and the inner part of the aggregate volume. On the bulk soil scale, we can analyze the platy structure as a visible hint for anthropogenic soil degradation which affects amongst others also the ion exchange processes. Furthermore an uneven aeration within such degraded soils results in a very pronounced anoxia on all scales (from the aggregate to the hectare scale) which can be quantified not only by corresponding measurements of the spatial distribution of redox potential values. In recent studies under "normal" wheeling conditions in arable fields and also in harvested forest sites it was proofed that Eh values close to 0 mV or even a methane emission have to be expected (with consequences for the global warming). Finally anoxic conditions also affect the redox induced mobilization of Fe and Mn which even results in a more rapid soil development with consequences also for yield and further soil functions. Consequently a shift to a more sustainable landuse or soil management strategy is urgently requested in order to prevent a further soil degradation. The scenario of peak soil must and can be prevented by a more site specific soil management. In the lecture, these effects will be discussed as well as a soil protection guide line (based on the German soil protection law) will be presented in order to prevent further irreversible soil degradation phenomena. Keywords: mechanical strength, mechanical stress and strain effects soil degradation, pore functions, ad-/desorption processes, redox potential, anoxia;, global change

Recovery of MSWI and soil washing residues as concrete aggregates.

PubMed

Sorlini, Sabrina; Abbà, Alessandro; Collivignarelli, Carlo

2011-02-01

The aim of the present work was to study if municipal solid waste incinerator (MSWI) residues and aggregates derived from contaminated soil washing could be used as alternative aggregates for concrete production. Initially, chemical, physical and geometric characteristics (according to UNI EN 12620) of municipal solid waste incineration bottom ashes and some contaminated soils were evaluated; moreover, the pollutants release was evaluated by means of leaching tests. The results showed that the reuse of pre-treated MSWI bottom ash and washed soil is possible, either from technical or environmental point of view, while it is not possible for the raw wastes. Then, the natural aggregate was partially and totally replaced with these recycled aggregates for the production of concrete mixtures that were characterized by conventional mechanical and leaching tests. Good results were obtained using the same dosage of a high resistance cement (42.5R calcareous Portland cement instead of 32.5R); the concrete mixture containing 400 kg/m(3) of washed bottom ash and high resistance cement was classified as structural concrete (C25/30 class). Regarding the pollutants leaching, all concrete mixtures respected the limit values according to the Italian regulation. Copyright © 2010 Elsevier Ltd. All rights reserved.

Contribution of arbuscular mycorrhizal fungi of sedges to soil aggregation along an altitudinal alpine grassland gradient on the Tibetan Plateau.

PubMed

Li, Xiaoliang; Zhang, Junling; Gai, Jingping; Cai, Xiaobu; Christie, Peter; Li, Xiaolin

2015-08-01

The diversity of arbuscular mycorrhizal fungi (AMF) in sedges on the Tibetan Plateau remains largely unexplored, and their contribution to soil aggregation can be important in understanding the ecological function of AMF in alpine ecosystems. Roots of Kobresia pygmaea C.B. Clarke and Carex pseudofoetida Kük. in alpine Kobresia pastures along an elevational transect (4149-5033 m) on Mount Mila were analysed for AMF diversity. A structural equation model was built to explore the contribution of biotic factors to soil aggregation. Sedges harboured abundant AMF communities covering seven families and some operational taxonomic units are habitat specific. The two plant species hosted similar AMF communities at most altitudes. The relative abundance of the two sedges contributed largely to soil macroaggregates, followed by extraradical mycorrhizal hyphae (EMH) and total glomalin-related soil protein (T-GRSP). The influence of plant richness was mainly due to its indirect influence on T-GRSP and EMH. There was a strong positive correlation between GRSP and soil total carbon and nitrogen. Our results indicate that mycorrhization might not be a major trait leading to niche differentiation of the two co-occurring sedge species. However, AMF contribute to soil aggregation and thus may have the potential to greatly influence C and N cycling in alpine grasslands. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.

Investigations of subsurface flow constructed wetlands and associated geomaterial resources in the Akumal and Reforma regions, Quintana Roo, Mexico

NASA Astrophysics Data System (ADS)

Krekeler, Mark P. S.; Probst, Pete; Samsonov, Misha; Tselepis, Cynthia M.; Bates, William; Kearns, Lance E.; Maynard, J. Barry

2007-12-01

Subsurface flow constructed wetlands in the village of Akumal, Quintana Roo, Mexico were surveyed to determine the general status of the wetland systems and provide baseline information for long term monitoring and further study. Twenty subsurface flow wetlands were surveyed and common problems observed in the systems were overloading, poor plant cover, odor, and no secondary containment. Bulk mineral composition of aggregate from two subsurface flow constructed wetlands was determined to consist solely of calcite using bulk powder X-ray diffraction. Some soil structure is developed in the aggregate and aggregate levels in wetlands drop at an estimated rate between 3 and 10 cm/year for overloaded wetlands owing to dissolution. Mineral composition from fresh aggregate samples commonly is a mixture of calcite and aragonite. Trace amounts of Pb, Zn, Co, and Cr were observed in fresh aggregate. Coefficients of permeability ( k) varied from 0.006 to 0.027 cm/s with an average values being 0.016 cm/s. Grain size analysis of fresh aggregate samples indicates there are unimodal and multimodal size distributions in the samples with modes in the coarse and fine sand being common. Investigations of other geologic media from the Reforma region indicate that a dolomite with minor amounts of Fe-oxide and palygorskite is abundant and may be a better aggregate source that the current materials used. A Ca-montmorillonite bed was identified in the Reforma region as well and this unit is suitable to serve as a clay liner to prevent leaks for new and existing wetland systems. These newly discovered geologic resources should aid in the improvement of subsurface flow constructed wetlands in the region. Although problems do exist in these wetlands with respect to design, these systems represent a successful implementation of constructed wetlands at a community level in developing regions.

Modeling Soil Carbon Dynamics in Northern Forests: Effects of Spatial and Temporal Aggregation of Climatic Input Data.

PubMed

Dalsgaard, Lise; Astrup, Rasmus; Antón-Fernández, Clara; Borgen, Signe Kynding; Breidenbach, Johannes; Lange, Holger; Lehtonen, Aleksi; Liski, Jari

2016-01-01

Boreal forests contain 30% of the global forest carbon with the majority residing in soils. While challenging to quantify, soil carbon changes comprise a significant, and potentially increasing, part of the terrestrial carbon cycle. Thus, their estimation is important when designing forest-based climate change mitigation strategies and soil carbon change estimates are required for the reporting of greenhouse gas emissions. Organic matter decomposition varies with climate in complex nonlinear ways, rendering data aggregation nontrivial. Here, we explored the effects of temporal and spatial aggregation of climatic and litter input data on regional estimates of soil organic carbon stocks and changes for upland forests. We used the soil carbon and decomposition model Yasso07 with input from the Norwegian National Forest Inventory (11275 plots, 1960-2012). Estimates were produced at three spatial and three temporal scales. Results showed that a national level average soil carbon stock estimate varied by 10% depending on the applied spatial and temporal scale of aggregation. Higher stocks were found when applying plot-level input compared to country-level input and when long-term climate was used as compared to annual or 5-year mean values. A national level estimate for soil carbon change was similar across spatial scales, but was considerably (60-70%) lower when applying annual or 5-year mean climate compared to long-term mean climate reflecting the recent climatic changes in Norway. This was particularly evident for the forest-dominated districts in the southeastern and central parts of Norway and in the far north. We concluded that the sensitivity of model estimates to spatial aggregation will depend on the region of interest. Further, that using long-term climate averages during periods with strong climatic trends results in large differences in soil carbon estimates. The largest differences in this study were observed in central and northern regions with strongly increasing temperatures.

Modeling Soil Carbon Dynamics in Northern Forests: Effects of Spatial and Temporal Aggregation of Climatic Input Data

PubMed Central

Dalsgaard, Lise; Astrup, Rasmus; Antón-Fernández, Clara; Borgen, Signe Kynding; Breidenbach, Johannes; Lange, Holger; Lehtonen, Aleksi; Liski, Jari

2016-01-01

Boreal forests contain 30% of the global forest carbon with the majority residing in soils. While challenging to quantify, soil carbon changes comprise a significant, and potentially increasing, part of the terrestrial carbon cycle. Thus, their estimation is important when designing forest-based climate change mitigation strategies and soil carbon change estimates are required for the reporting of greenhouse gas emissions. Organic matter decomposition varies with climate in complex nonlinear ways, rendering data aggregation nontrivial. Here, we explored the effects of temporal and spatial aggregation of climatic and litter input data on regional estimates of soil organic carbon stocks and changes for upland forests. We used the soil carbon and decomposition model Yasso07 with input from the Norwegian National Forest Inventory (11275 plots, 1960–2012). Estimates were produced at three spatial and three temporal scales. Results showed that a national level average soil carbon stock estimate varied by 10% depending on the applied spatial and temporal scale of aggregation. Higher stocks were found when applying plot-level input compared to country-level input and when long-term climate was used as compared to annual or 5-year mean values. A national level estimate for soil carbon change was similar across spatial scales, but was considerably (60–70%) lower when applying annual or 5-year mean climate compared to long-term mean climate reflecting the recent climatic changes in Norway. This was particularly evident for the forest-dominated districts in the southeastern and central parts of Norway and in the far north. We concluded that the sensitivity of model estimates to spatial aggregation will depend on the region of interest. Further, that using long-term climate averages during periods with strong climatic trends results in large differences in soil carbon estimates. The largest differences in this study were observed in central and northern regions with strongly increasing temperatures. PMID:26901763

Analytical Characterisation of Nanoscale Zero-Valent Iron: A ...

EPA Pesticide Factsheets

Zero-valent iron nanoparticles (nZVI) have been widely tested as they are showing significant promise for environmental remediation. However, many recent studies have demonstrated that their mobility and reactivity in subsurface environments are significantly affected by their tendency to aggregate. Both the mobility and reactivity of nZVI mainly depends on properties such as particle size, surface chemistry and bulk composition. In order to ensure efficient remediation, it is crucial to accurately assess and understand the implications of these properties before deploying these materials into contaminated environments. Many analytical techniques are now available to determine these parameters and this paper provides a critical review of their usefulness and limitations for nZVI characterisation. These analytical techniques include microscopy and light scattering techniques for the determination of particle size, size distribution and aggregation state, and X-ray techniques for the characterisation of surface chemistry and bulk composition. Example characterisation data derived from commercial nZVI materials is used to further illustrate method strengths and limitations. Finally, some important challenges with respect to the characterisation of nZVI in groundwater samples are discussed. In recent years, manufactured nanoparticles (MNPs) have attracted increasing interest for their potential applications in the treatment of contaminated soil and water. In compar

Soil Organic Matter Erosion by Interrill Processes from Organically and Conventionally farmed Devon Soil

NASA Astrophysics Data System (ADS)

Armstrong, E.; Ling, A.; Kuhn, N. J.

2012-04-01

Globally, between 0.57 and 1.33 Pg of soil organic carbon (SOC) may be affected by interrill processes. Also, a significant amount of phosphorus (P) is contained in the surface soil layer transformed by raindrop impact, runoff and crust formation. In the EU, the P content of a crusted (2 mm) surface layer corresponds to 4 to 40 kg ha-1 of P on arable land (1.094 mil km2). Therefore, the role of interrill processes for nutrient cycling and the global carbon cycle requires close attention. Interrill erosion is a complex phenomenon involving the detachment, transport and deposition of soil particles by raindrop impacted flow. Resistance to interrill erosion varies between soils depending on their physical, chemical and mineralogical properties. In addition, significant changes in soil resistance to interrill erosion occur during storms as a result of changes in surface roughness, cohesion and particle size. As a consequence, erosion on interrill areas is selective, moving the most easily detached small and/or light soil particles. This leads to the enrichment of clay, phosphorous (P) and carbon (C). Such enrichment in interrill sediment is well documented, however, the role of interrill erosion processes on the enrichment remains unclear. Enrichment of P and C in interrill sediment is attributed to the preferential erosion of the smaller, lighter soil particles. In this study, the P and organic C content of sediment generated from two Devon silts under conventional (CS) and organic (OS) soil management were examined. Artificial rainfall was applied to the soils using two rainfall scenarios of differing intensity and kinetic energy to determine the effects on the P and C enrichment in interrill sediment. Interrill soil erodibility was lower on the OS, irrespective of rainfall intensity. Sediment from both soils showed a significant enrichment in P and C compared to the bulk soil. However, sediment from the OS displayed a much greater degree of P enrichment. This shows that the net P export from organically farmed soils is not reduced by a similar degree than soil erosion compared to conventional soil management. The enrichment of P and C in the interrill sediment was not directly related to SOC, P content of the soil and soil interrill erodibility. A comparison of soil and sediment properties indicates that crusting, P and C content as well as density and size of eroded aggregate fragments control P and C enrichment. Due to complex and dynamic interactions between P, SOC and interrill erosional processes, the nutrient and C status of sediments cannot be predicted based on soil P content, SOC or interrill erodibility alone. Clearly, further research on crust formation and the composition of fragments generated by aggregate breakdown and their transport in raindrop impacted flow under different rainfall conditions is required. Attaining this critical missing knowledge would enable a comprehensive assessment of the benefits of organic farming on nutrient budgets, off-site effects of interrill erosion and its role in the global C cycle.

Whey utilization in furrow irrigation: effects on aggregate stability and erosion.

PubMed

Lehrsch, Gary A; Robbins, Charles W; Brown, Melvin J

2008-11-01

Improving soil structure often reduces furrow erosion and maintains adequate infiltration. Cottage cheese whey, the liquid byproduct from cottage cheese manufacture, was utilized to stabilize soil aggregates and reduce sediment losses from furrow irrigation. We applied either 2.4 or 1.9L of whey per meter of furrow (3.15 or 2.49Lm(-2), respectively) by gravity flow without incorporation to two fields of Portneuf silt loam (Durinodic Xeric Haplocalcid) near Kimberly, ID. Furrows were irrigated with water beginning four days later. We measured sediment losses with furrow flumes during each irrigation and measured aggregate stability by wet sieving about 10 days after the last irrigation. Overall, whey significantly increased aggregate stability 25% at the 0-15mm depth and 14% at 15-30mm, compared to controls. On average, whey reduced sediment losses by 75% from furrows sloped at 2.4%. Whey increased the aggregate stability of structurally degraded calcareous soil in irrigation furrows.

Field soil aggregate stability kit for soil quality and rangeland health evaluations

USGS Publications Warehouse

Herrick, J.E.; Whitford, W.G.; de Soyza, A. G.; Van Zee, J. W.; Havstad, K.M.; Seybold, C.A.; Walton, M.

2001-01-01

Soil aggregate stability is widely recognized as a key indicator of soil quality and rangeland health. However, few standard methods exist for quantifying soil stability in the field. A stability kit is described which can be inexpensively and easily assembled with minimal tools. It permits up to 18 samples to be evaluated in less than 10 min and eliminates the need for transportation, minimizing damage to soil structure. The kit consists of two 21??10.5??3.5 cm plastic boxes divided into eighteen 3.5??3.5 cm sections, eighteen 2.5-cm diameter sieves with 1.5-mm distance openings and a small spatula used for soil sampling. Soil samples are rated on a scale from one to six based on a combination of ocular observations of slaking during the first 5 min following immersion in distilled water, and the percent remaining on a 1.5-mm sieve after five dipping cycles at the end of the 5-min period. A laboratory comparison yielded a correlation between the stability class and percent aggregate stability based on oven dry weight remaining after treatment using a mechanical sieve. We have applied the method in a wide variety of agricultural and natural ecosystems throughout western North America, including northern Mexico, and have found that it is highly sensitive to differences in management and plant community composition. Although the field kit cannot replace the careful laboratory-based measurements of soil aggregate stability, it can clearly provide valuable information when these more intensive procedures are not possible.

[Effects of selective microbial inhibitors on the microbial transformation of phosphorous in aggregates of highly weathered red soil with rice straw amendment].

PubMed

Ding, Long-jun; Xiao, He-ai; Wu, Jin-shui; Ge, Ti-da

2010-07-01

In order to further understand the mechanisms of microbial immobilization of phosphorous (P) in highly weathered red soil with organic amendment, an incubation test was conducted to investigate the roles of microbial functional groups in the transformation of P in 0.2-2 mm soil aggregates. Throughout the 90-day incubation period, amendment with rice straw induced a substantial increase in the amounts of microbial biomass C and P, Olsen-P, and organic P in the aggregates. Comparing with rice straw amendment alone, the amendment with rice straw plus fungal inhibitor actidione decreased the amount of microbial biomass C in the aggregates by 10.5%-31.8% in the first 30 days. Such a decrement was significantly larger than that (6.8%-11.6%) in the treatment amended with rice straw plus bacterial inhibitors tetracycline and streptomycin sulphate (P<0.01). After the first 30 days, the microbial biomass C remained constant. In the first 20 days, the amount of microbial biomass P in the aggregates was 10.0%-28.8% higher in the treatment amended with bacterial inhibitors than in the treatment amended with fungal inhibitor (P<0.01). All the results suggested that that both the fungal and the bacterial groups were involved in the microbial immobilization of P in the soil aggregates, and the fungal group played a relatively larger role.

Nanoparticles with photoinduced precipitation for the extraction of pollutants from water and soil

PubMed Central

Brandl, Ferdinand; Bertrand, Nicolas; Lima, Eliana Martins; Langer, Robert

2015-01-01

Nanotechnology may offer fast and effective solutions for environmental clean-up. Herein, amphiphilic diblock copolymers are used to develop a platform of photosensitive core-shell nanoparticles. Irradiation with ultraviolet light removes the protective layer responsible for colloidal stability; as a result, the nanoparticles are rapidly and irreversibly converted to macroscopic aggregates. The associated phase separation allows measuring the partitioning of small molecules between the aqueous phase and nanoparticles; data suggests that interactions are enhanced by decreasing the particle size. Adsorption onto nanoparticles can be exploited to efficiently remove hydrophobic pollutants from water and contaminated soil. Preliminary in vivo experiments suggest that treatment with photocleavable nanoparticles can significantly reduce the teratogenicity of bisphenol A, triclosan and 17α-ethinyl estradiol without generating obviously toxic byproducts. Small-scale pilot experiments on wastewater, thermal printing paper and contaminated soil demonstrate the applicability of the approach. PMID:26196119

Nanoparticles with photoinduced precipitation for the extraction of pollutants from water and soil

NASA Astrophysics Data System (ADS)

Brandl, Ferdinand; Bertrand, Nicolas; Lima, Eliana Martins; Langer, Robert

2015-07-01

Nanotechnology may offer fast and effective solutions for environmental clean-up. Herein, amphiphilic diblock copolymers are used to develop a platform of photosensitive core-shell nanoparticles. Irradiation with ultraviolet light removes the protective layer responsible for colloidal stability; as a result, the nanoparticles are rapidly and irreversibly converted to macroscopic aggregates. The associated phase separation allows measuring the partitioning of small molecules between the aqueous phase and nanoparticles; data suggests that interactions are enhanced by decreasing the particle size. Adsorption onto nanoparticles can be exploited to efficiently remove hydrophobic pollutants from water and contaminated soil. Preliminary in vivo experiments suggest that treatment with photocleavable nanoparticles can significantly reduce the teratogenicity of bisphenol A, triclosan and 17α-ethinyl estradiol without generating obviously toxic byproducts. Small-scale pilot experiments on wastewater, thermal printing paper and contaminated soil demonstrate the applicability of the approach.

Efficacy of Natural Polymer Derivatives on Soil Physical Properties and Erosion on an Experimental Loess Hillslope.

PubMed

Liu, Jun'e; Wang, Zhanli; Li, Yuanyuan

2017-12-22

Raindrops disperse large soil aggregates into smaller particles, which can clog soil pores, cause soil crusting, reduce rainfall infiltration and increase soil loss. It was found that natural polymer derivatives were effective in improving soil physical properties and decreasing soil erosion on an experimental loess hillslope. This study investigated the effect of new natural polymer derivatives (Jag S and Jag C162) on soil properties, rainfall infiltration and sediment yield at four rates of sprayed polymers (0, 1, 3 and 5 g/m²), three rainfall intensities (1, 1.5 and 2 mm/min) and a slope gradient of 15° with a silt loam soil through simulated rain. The results showed that both Jag S and Jag C162 significantly increased the shear strength and improved the aggregates composition of the soil surface. The water-stable soil aggregates >0.25 mm increased from 9% to 50% with increasing rates of Jag S and Jag C162. Jag S and Jag C162 also effectively increased rainfall infiltration and final infiltration rate, and reduced erosion compared to controls without natural polymer derivatives added. However, higher rates of Jag S produced lower infiltration rates. Although both Jag S and Jag C162 effectively influenced soil physical properties and erosion, the effect of Jag C162 was more significant than that of Jag S.

Efficacy of Natural Polymer Derivatives on Soil Physical Properties and Erosion on an Experimental Loess Hillslope

PubMed Central

Liu, Jun’e; Wang, Zhanli; Li, Yuanyuan

2017-01-01

Raindrops disperse large soil aggregates into smaller particles, which can clog soil pores, cause soil crusting, reduce rainfall infiltration and increase soil loss. It was found that natural polymer derivatives were effective in improving soil physical properties and decreasing soil erosion on an experimental loess hillslope. This study investigated the effect of new natural polymer derivatives (Jag S and Jag C162) on soil properties, rainfall infiltration and sediment yield at four rates of sprayed polymers (0, 1, 3 and 5 g/m2), three rainfall intensities (1, 1.5 and 2 mm/min) and a slope gradient of 15° with a silt loam soil through simulated rain. The results showed that both Jag S and Jag C162 significantly increased the shear strength and improved the aggregates composition of the soil surface. The water-stable soil aggregates >0.25 mm increased from 9% to 50% with increasing rates of Jag S and Jag C162. Jag S and Jag C162 also effectively increased rainfall infiltration and final infiltration rate, and reduced erosion compared to controls without natural polymer derivatives added. However, higher rates of Jag S produced lower infiltration rates. Although both Jag S and Jag C162 effectively influenced soil physical properties and erosion, the effect of Jag C162 was more significant than that of Jag S. PMID:29271899

An online detection system for aggregate sizes and shapes based on digital image processing

NASA Astrophysics Data System (ADS)

Yang, Jianhong; Chen, Sijia

2017-02-01

Traditional aggregate size measuring methods are time-consuming, taxing, and do not deliver online measurements. A new online detection system for determining aggregate size and shape based on a digital camera with a charge-coupled device, and subsequent digital image processing, have been developed to overcome these problems. The system captures images of aggregates while falling and flat lying. Using these data, the particle size and shape distribution can be obtained in real time. Here, we calibrate this method using standard globules. Our experiments show that the maximum particle size distribution error was only 3 wt%, while the maximum particle shape distribution error was only 2 wt% for data derived from falling aggregates, having good dispersion. In contrast, the data for flat-lying aggregates had a maximum particle size distribution error of 12 wt%, and a maximum particle shape distribution error of 10 wt%; their accuracy was clearly lower than for falling aggregates. However, they performed well for single-graded aggregates, and did not require a dispersion device. Our system is low-cost and easy to install. It can successfully achieve online detection of aggregate size and shape with good reliability, and it has great potential for aggregate quality assurance.

Nitrogen-mediated effects of elevated CO2 on intra-aggregate soil pore structure.

PubMed

Caplan, Joshua S; Giménez, Daniel; Subroy, Vandana; Heck, Richard J; Prior, Stephen A; Runion, G Brett; Torbert, H Allen

2017-04-01

Soil pore structure has a strong influence on water retention, and is itself influenced by plant and microbial dynamics such as root proliferation and microbial exudation. Although increased nitrogen (N) availability and elevated atmospheric CO 2 concentrations (eCO 2 ) often have interacting effects on root and microbial dynamics, it is unclear whether these biotic effects can translate into altered soil pore structure and water retention. This study was based on a long-term experiment (7 yr at the time of sampling) in which a C 4 pasture grass (Paspalum notatum) was grown on a sandy loam soil while provided factorial additions of N and CO 2 . Through an analysis of soil aggregate fractal properties supported by 3D microtomographic imagery, we found that N fertilization induced an increase in intra-aggregate porosity and a simultaneous shift toward greater accumulation of pore space in larger aggregates. These effects were enhanced by eCO 2 and yielded an increase in water retention at pressure potentials near the wilting point of plants. However, eCO 2 alone induced changes in the opposite direction, with larger aggregates containing less pore space than under control conditions, and water retention decreasing accordingly. Results on biotic factors further suggested that organic matter gains or losses induced the observed structural changes. Based on our results, we postulate that the pore structure of many mineral soils could undergo N-dependent changes as atmospheric CO 2 concentrations rise, having global-scale implications for water balance, carbon storage, and related rhizosphere functions. © 2016 John Wiley & Sons Ltd.

Synchrotron-based Infrared-microspectroscopy reveals the impact of land management on carbon storage in soil micro-aggregates

NASA Astrophysics Data System (ADS)

Hernandez-Soriano, Maria C.; Dalal, Ram C.; Menzies, Neal W.; Kopittke, Peter M.

2015-04-01

Carbon stabilization in soil microaggregates results from chemical and biological processes that are highly sensitive to changes in land use. Indeed, such processes govern soil capability to store carbon, this being essential for soil health and productivity and to regulate emissions of soil organic carbon (SOC) as CO2. The identification of carbon functionalities using traditional mid-infrared analysis can be linked to carbon metabolism in soil but differences associated to land use are generally limited. The spatial resolution of synchrotron-based Infrared-microspectroscopy allows mapping microaggregate-associated forms of SOC because it has 1000 times higher brightness than a conventional thermal globar source. These maps can contribute to better understand molecular organization of SOC, physical protection in the soil particles and co-localization of carbon sources with microbial processes. Spatially-resolved analyses of carbon distribution in micro-aggregates (<200 μm diameter) have been conducted using FTIR microspectroscopy (Infrared Microspectroscopy beamline, Australian Synchrotron). Two soil types (Ferralsol and Vertisol, World Reference Base 2014) were collected from undisturbed areas and from a location(s) immediately adjacent which has a long history of agricultural use (>20 years). Soils were gently screened (250 μm) to obtain intact microaggregates which were humidified and frozen at -20°C, and sectioned (200 μm thickness) using a diamond knife and a cryo-ultramicrotome. The sections were placed between CaF2 windows and the spectra were acquired in transmission mode. The maps obtained (5 µm step-size over ca. 150 × 150 µm) revealed carbon distribution in microaggregates from soils under contrasting land management, namely undisturbed and cropping land. Accumulation of aromatic and carboxylic functions on specific spots and marginal co-localization with clays was observed, which suggests processes other than organo-mineral associations being responsible for carbon stabilization. A substantial decrease in carboxylic compounds was observed for agricultural soils. Clays were mostly co-localized with alkenes and polysaccharides, particularly in agricultural soils, likely due to enhanced microbial activity in those spots. Results will be linked to currently ongoing analysis of soil enzymes activities and characterization of dissolved organic carbon components. This novel methodological approach combines biological and chemical information on organic carbon dynamics in soil at a molecular level and will constitute a substantial advance towards understanding carbon storage in soil and the long term impact of land management.

Influence of Robinia pseudoacacia short rotation coppice on soil physical properties

NASA Astrophysics Data System (ADS)

Xavier, Morvan; Isabelle, Bertrand; Gwenaelle, Gibaud

2015-04-01

Human activities can lead to the degradation of soil physical properties. For instance, machinery traffic across the land can induce the development of compacted areas at the wheel tracks. It leads to a decrease in porosity which results in a decrease of the hydraulic conductivity, and therefore, prevents water infiltration and promotes surface runoff. Land use, soil management and soil cover also have a significant influence on soil physical properties (Kodesova et al., 2011). In the arable land, surface runoff and soil erosion are enhanced by the absence of soil cover for part of the year and by the decrease of aggregate stability due to a decline of soil organic matter. In that context, few studies focused on the effects of a Robinia pseudoacacia short rotation coppice (SRC) on soil physical properties. Therefore, this study aims to determine the effect of the conversion of a grassland in a SRC on soil physical properties. These properties have also been compared to those of arable land and natural forest. For that, in several plots of the experimental farm of Grignon (30 km west of Paris, France), different measurements were performed: i) soil water retention on a pressure plate apparatus for 7 water potential between 0 and 1500 kPa, ii) bulk density using the method for gravelly and rocky soil recommended by the USDA, iii) aggregate stability using the method described in Le Bissonnais (1996), and iv) soil hydraulic conductivity using a Guelph permeameter. All these measurements were performed on the same soil type and on different land uses: arable land (AL), grassland (GL), natural forest (NF) and short rotation coppice (SRC) of Robinia pseudoacacia planted 5 years ago. Soil water retention measurements are still under progress and will be presented in congress. Bulk density measurements of the AL, GL and SRC are not significantly different. They ranged from 1.32 to 1.42. Only the NF measurements are significantly lower than the other (0.97). Aggregate stability measurements showed that the SRC soil had the most stable aggregates compared to the other land uses. SRC also had the highest infiltration rates (656 mm.h-1) compared to NF (54 mm.h-1), GL (23 mm.h-1) and AL (8 mm.h-1). Analyses and explanation of these results are still under progress and will be presented in congress. Kodesova, R., Jirku, V., Kodes, V., Muhlhanselova, M., Nikodem, A., Žigová, A., 2011. Soil structure and soil hydraulic properties of Haplic Luvisol used as arable land and grassland. Soil and Tillage Research 111 (2), pp. 154-161. Le Bissonnais Y., 1996. Aggregate stability and assessment of soil crustability and erodibility: I theory and methodology. European Journal of Soil Science 47, 425-437.

Interrill sediment enrichment of P and C from organically and conventionally farmed silty loams

NASA Astrophysics Data System (ADS)

Kuhn, N. J.

2012-04-01

Globally, between 0.57 and 1.33 Pg of soil organic carbon (SOC) may be affected by interrill processes. Also, a significant amount of phosphorus (P) is contained in the surface soil layer transformed by raindrop impact, runoff and crust formation. In the EU, the P content of a crusted (2 mm) surface layer corresponds to 4 to 40 kg ha-1 of P on arable land (1.094 mil km2). Therefore, the role of interrill processes for nutrient cycling and the global carbon cycle requires close attention. Interrill erosion is a complex phenomen on involving the detachment, transport and deposition of soil particles by raindrop impacted flow. Resistance to interrill erosion varies between soils depending on their physical, chemical and mineralogical properties. In addition, significant changes in soil resistance to interrill erosion occur during storms as a result of changes in surface roughness, cohesion and particle size. As a consequence, erosion on interrill areas is selective, moving the most easily detached small and/or light soil particles. This leads to the enrichment of clay, phosphorous (P)and carbon (C). Such enrichment in interrill sediment is well documented, however, the role of interrill erosion processes on the enrichment remains unclear. Enrichment of P and C in interrill sediment is attributed to the preferential erosion of the smaller, lighter soil particles. In this study, the P and organic C content of sediment generated from two Devon silts under conventional (CS) and organic (OS) soil management were examined. Artificial rainfall was applied to the soils using two rainfall scenarios of differing intensity and kinetic energy to determine the effects on the P and C enrichment in interrill sediment. Interrill soil erodibility was lower on the OS, irrespective of rainfall intensity. Sediment from both soils showed a significant enrichment in P and C compared to the bulk soil. However, sediment from the OS displayed a much greater degree of P enrichment. This shows that the net P export from organically farmed soils is not reduced by a similar degree than soil erosion compared to conventional soil management. The enrichment of P and C in the interrill sediment was not directly related to SOC, P content of the soil and soil interrill erodibility. A comparison of soil and sediment properties indicates that crusting, P and C content as well as density and size of eroded aggregate fragments control P and C enrichment. Due to complex and dynamic interactions between P, SOC and interrill erosional processes, the nutrient and C status of sediments cannot be predicted based on soil P content, SOC or interrill erodibility alone. Clearly, further research on crust formation and the composition of fragments generated by aggregate breakdown and their transport in raindrop impacted flow under different rainfall conditions is required. Attaining this critical missing knowledge would enable a comprehensive assessment of the benefits of organic farming on nutrient budgets, off-site effects of interrill erosion and its role in the global C cycle.

Directional reflectance factors for monitoring spatial changes in soil surface structure and soil organic matter erosion in agricultural systems

NASA Astrophysics Data System (ADS)

Croft, H.; Anderson, K.

2012-04-01

Soils can experience rapid structural degradation in response to land cover changes, resulting in reduced soil productivity, increased erodibility and a loss of soil organic matter (SOM). The breakdown of soil aggregates through slaking and raindrop impact is linked to organic matter turnover, with subsequently eroded material often displaying proportionally more SOM. A reduction in aggregate stability is reflected in a decline in soil surface roughness (SSR), indicating that a soil structural change can be used to highlight soil vulnerability to SOM loss through mineralisation or erosion. Accurate, spatially-continuous measurements of SSR are therefore needed at a variety of spatial and temporal scales to understand the spatial nature of SOM erosion and deposition. Remotely-sensed data can provide a cost-effective means of monitoring changes in soil surface condition over broad spatial extents. Previous work has demonstrated the ability of directional reflectance factors to monitor soil crusting within a controlled laboratory experiment, due to changes in the levels of self-shadowing effects by soil aggregates. However, further research is needed to test this approach in situ, where other soil variables may affect measured reflectance factors and to investigate the use of directional reflectance factors for monitoring soil erosion processes. This experiment assesses the potential of using directional reflectance factors to monitor changes in SSR, aggregate stability and soil organic carbon (SOC) content for two agricultural conditions. Five soil plots representing tilled and seedbed soils were subjected to different durations of natural rainfall, producing a range of different levels of SSR. Directional reflectance factors were measured concomitantly with sampling for soil structural and biochemical tests at each soil plot. Soil samples were taken to measure aggregate stability (wet sieving), SOC (loss on ignition) and soil moisture (gravimetric method). SSM values varied from 8.70 to 20.05% and SOC from 1.33 to 1.05%, across all soil plots. Each plot was characterised using a close-range laser scanning device with a 2 mm sampling interval. The point laser data were geostatistically analysed to provide a spatially-distributed measure of SSR, giving sill variance values from 3.15 to 22.99. Reflectance factors from the soil states were measured using a ground-based hyperspectral spectroradiometer (400-2500 nm) attached to an A-frame device. This method allowed measurement at a range of viewing zenith angles from extreme forwardscatter (-60°) to extreme backscatter (+60°) at a 10° sampling resolution in the solar principal plane. Reflectance measurements were compared to geostatistically-derived indicators of SSR from the laser profile data. Forward-scattered reflectance factors exhibited a very strong relationship to SSR (R2 = 0.84 at -60°; p< 0.05), demonstrating the operational potential of directional reflectance for providing SSR measurements, despite conflicting variation in SSM. SSM also presented an interesting directional signal (R2 = 0.99 at +20°; p< 0.01). Furthermore, the results showed an important link between SRR decline as measured using directional reflectance, with a decline in aggregate stability and SOC content. These findings provide an empirical and theoretical basis for the future retrieval of spatially-continuous assessments of soil surface structure and carbon turnover within a landscape context.

Influence of soil properties on the toxicity of TiO₂ nanoparticles on carbon mineralization and bacterial abundance.

PubMed

Simonin, Marie; Guyonnet, Julien P; Martins, Jean M F; Ginot, Morgane; Richaume, Agnès

2015-01-01

Information regarding the impact of low concentration of engineered nanoparticles on soil microbial communities is currently limited and the importance of soil characteristics is often neglected in ecological risk assessment. To evaluate the impact of TiO2 nanoparticles (NPs) on soil microbial communities (measured on bacterial abundance and carbon mineralization activity), 6 agricultural soils exhibiting contrasted textures and organic matter contents were exposed for 90 days to a low environmentally relevant concentration or to an accidental spiking of TiO2-NPs (1 and 500mgkg(-1) dry soil, respectively) in microcosms. In most soils, TiO2-NPs did not impact the activity and abundance of microbial communities, except in the silty-clay soil (high OM) where C-mineralization was significantly lowered, even with the low NPs concentration. Our results suggest that TiO2-NPs toxicity does not depend on soil texture but likely on pH and OM content. We characterized TiO2-NPs aggregation and zeta potential in soil solutions, in order to explain the difference of TiO2-NPs effects on soil C-mineralization. Zeta potential and aggregation of TiO2-NPs in the silty-clay (high OM) soil solution lead to a lower stability of TiO2-NP-aggregates than in the other soils. Further experiments would be necessary to evaluate the relationship between TiO2-NPs stability and toxicity in the soil. Copyright © 2014 Elsevier B.V. All rights reserved.

Optimizing Mississippi aggregates for concrete bridge decks.

DOT National Transportation Integrated Search

2012-12-01

AASHTO M 43 Standard Specification for Sizes of Aggregate for Road and Bridge Construction : addresses particle size distribution of material included in various maximum nominal size aggregates. This : particle size distribution requires additi...

The influence of organic amendments on soil aggregate stability from semiarid sites

NASA Astrophysics Data System (ADS)

Hueso Gonzalez, Paloma; Francisco Martinez Murillo, Juan; Damian Ruiz Sinoga, Jose

2016-04-01

Restoring the native vegetation is the most effective way to regenerate soil health. Under these conditions, vegetation cover in areas having degraded soils may be better sustained if the soil is amended with an external source of organic matter. The addition of organic materials to soils also increases infiltration rates and reduces erosion rates; these factors contribute to an available water increment and a successful and sustainable land management. The goal of this study was to analyze the effect of various organic amendments on the aggregate stability of soils in afforested plots. An experimental paired-plot layout was established in southern of Spain (homogeneous slope gradient: 7.5%; aspect: N170). Five amendments were applied in an experimental set of plots: straw mulching; mulch with chipped branches of Aleppo Pine (Pinus halepensis L.); TerraCotten hydroabsobent polymers; sewage sludge; sheep manure and control. Plots were afforested following the same spatial pattern, and amendments were mixed with the soil at the rate 10 Mg ha-1. The vegetation was planted in a grid pattern with 0.5 m between plants in each plot. During the afforestation process the soil was tilled to 25 cm depth from the surface. Soil from the afforested plots was sampled in: i) 6 months post-afforestation; ii) 12 months post-afforestation; iii) 18 months post-afforestation; and iv) 24 months post-afforestation. The sampling strategy for each plot involved collection of 4 disturbed soil samples taken from the surface (0-10 cm depth). The stability of aggregates was measured by wet-sieving. Regarding to soil aggregate stability, the percentage of stable aggregates has increased slightly in all the treatments in relation to control. Specifically, the differences were recorded in the fraction of macroaggregates (≥ 0.250 mm). The largest increases have been associated with straw mulch, pinus mulch and sludge. Similar results have been registered for the soil organic carbon content. Independent of the soil management, after six months, no significant differences in microaggregates were found regarding to the control plots. These results showed an increase in the stability of the macroaggregates when soil is amended with sludge, pinus mulch and straw much. This fact has been due to an increase in the number cementing agents due to: (i) the application of pinus, straw and sludge had resulted in the release of carbohydrates to the soil; and thus (ii) it has favored the development of a protective vegetation cover, which has increased the number of roots in the soil and the organic contribution to it.

Micro-structure and Swelling Behaviour of Compacted Clayey Soils: A Quantitative Approach

NASA Astrophysics Data System (ADS)

Ferber, Valéry; Auriol, Jean-Claude; David, Jean-Pierre

In this paper, the clay aggregate volume and inter-aggregate volume in compacted clayey soils are quantified, on the basis of simple hypothesis, using only their water content and dry density. Swelling tests on a highly plastic clay are then interpreted by describing the influence of the inter-aggregate volume before swelling on the total volume of samples after swelling. This approach leads to a linear relation between these latter parameters. Based on these results, a description of the evolution of the microstructure due to imbibition can be proposed. Moreover, this approach enables a general quantification of the influence of initial water content and dry density on the swelling behaviour of compacted clayey soils.

Positive evolution features in soil restoration assessed by means of glomalin and its relationship to aggregate stability

NASA Astrophysics Data System (ADS)

Luna Ramos, Lourdes; Miralles Mellado, Isabel; Gispert Negrell, María; Pardini, Giovanni; Solé Benet, Albert

2014-05-01

Restoration of limestone quarries in arid environments mainly consists of regenerating a highly degraded soil and/or creating a soil-like substrate with minimal physico-chemical and biological properties. In an experimental soil restoration in limestone quarries from Sierra de Gádor (Almería), SE Spain, with the aim to improve soil/substrate properties and to reduce evaporation and erosion, 18 plots 15 x 5 m were prepared to test organic amendments (sludge, compost, control) and different mulches (gravel, chopped forest residue, control). In order to evaluate the soil quality of the different treatments, their chemical, physical and biological properties were analyzed. Among the most efficient biological indicators are arbuscular mycorrhizal fungi (AMF). AMF play an important role in aggregate stability due to the production of a glycoprotein called glomalin. Therefore, the aim of this study was to quantify, 5 years after the start the experiment, the content of total glomalin (TG) and to analyze its relationship with other soil parameters such as organic matter (OM) and aggregate stability soil (AE). Results indicated a remarkable effect of organic amendments on glomalin content, which was higher in the treatments with compost (6.96 mg g -1) than in sludge and control (0.54 and 0.40 mg g-1, respectively). Amendments also significantly influenced aggregate stability: the highest values were recorded in treatments with sludge and compost (23.14 and 25.09%, respectively) compared to control (13.37%). The gravel mulch had a negative influenced on AE: an average of 16% compared to 23.4% for chopped forest residues and 23.1% of control. Data showed a positive and significant correlation between values of TG and OM content (r = 0.95). We also found a positive and significant correlation between abundance of TG and AE when OM contents were lower than 4% (r = 0.93), however, there was no significant correlation to higher OM when it was higher than 4% (r = 0.34). This suggests that all protein sources which are different to glomalin have not been removed by the extraction process with sodium citrate. Other studies have shown that the ratio between proteins associated to glomalin and AE is curvilinear, meaning that increases in aggregate stability are not detected if the amount of these proteins is very high. In soil restoration, glomalin is an adequate indicator of soil/substrate evolution when organic amendments deliver low to medium OM contents. Nevertheless, further studies are necessary to improve the knowledge about AMF activity on soil aggregate formation and stability.

Multi-process herbicide transport in structured soil columns: Experiments and model analysis

NASA Astrophysics Data System (ADS)

Köhne, J. Maximilian; Köhne, Sigrid; Šimůnek, Jirka

2006-05-01

Model predictions of pesticide transport in structured soils are complicated by multiple processes acting concurrently. In this study, the hydraulic, physical, and chemical nonequilibrium (HNE, PNE, and CNE, respectively) processes governing herbicide transport under variably saturated flow conditions were studied. Bromide (Br -), isoproturon (IPU, 3-(4-isoprpylphenyl)-1,1-dimethylurea) and terbuthylazine (TER, N2-tert-butyl-6-chloro- N4-ethyl-1,3,5-triazine-2,4-diamine) were applied to two soil columns. An aggregated Ap soil column and a macroporous, aggregated Ah soil column were irrigated at a rate of 1 cm h - 1 for 3 h. Two more irrigations at the same rate and duration followed in weekly intervals. Nonlinear (Freundlich) equilibrium and two-site kinetic sorption parameters were determined for IPU and TER using batch experiments. The observed water flow and Br - transport were inversely simulated using mobile-immobile (MIM), dual-permeability (DPM), and combined triple-porosity (DP-MIM) numerical models implemented in HYDRUS-1D, with improving correspondence between empirical data and model results. Using the estimated HNE and PNE parameters together with batch-test derived equilibrium sorption parameters, the preferential breakthrough of the weakly adsorbed IPU in the Ah soil could be reasonably well predicted with the DPM approach, whereas leaching of the strongly adsorbed TER was predicted less well. The transport of IPU and TER through the aggregated Ap soil could be described consistently only when HNE, PNE, and CNE were simultaneously accounted for using the DPM. Inverse parameter estimation suggested that two-site kinetic sorption in inter-aggregate flow paths was reduced as compared to within aggregates, and that large values for the first-order degradation rate were an artifact caused by irreversible sorption. Overall, our results should be helpful to enhance the understanding and modeling of multi-process pesticide transport through structured soils during variably saturated water flow.

Potential of scrap tire rubber as lightweight aggregate in flowable fill.

PubMed

Pierce, C E; Blackwell, M C

2003-01-01

Flowable fill is a self-leveling and self-compacting material that is rapidly gaining acceptance and application in construction, particularly in transportation and utility earthworks. When mixed with concrete sand, standard flowable fill produces a mass density ranging from 1.8 to 2.3 g/cm(3) (115-145 pcf). Scrap tires can be granulated to produce crumb rubber, which has a granular texture and ranges in size from very fine powder to coarse sand-sized particles. Due to its low specific gravity, crumb rubber can be considered a lightweight aggregate. This paper describes an experimental study on replacing sand with crumb rubber in flowable fill to produce a lightweight material. To assess the technical feasibility of using crumb rubber, the fluid- and hardened-state properties of nine flowable fill mixtures were measured. Mixture proportions were varied to investigate the effects of water-to-cement ratio and crumb rubber content on fill properties. Experimental results indicate that crumb rubber can be successfully used to produce a lightweight flowable fill (1.2-1.6 g/cm(3) [73-98 pcf]) with excavatable 28-day compressive strengths ranging from 269 to 1194 kPa (39-173 psi). Using a lightweight fill reduces the applied stress on underlying soils, thereby reducing the potential for bearing capacity failure and minimizing soil settlement. Based on these results, a crumb rubber-based flowable fill can be used in a substantial number of construction applications, such as bridge abutment fills, trench fills, and foundation support fills.

Novel predictors of soil genesis following natural weathering processes of bauxite residues.

PubMed

Zhu, Feng; Xue, Shengguo; Hartley, William; Huang, Ling; Wu, Chuan; Li, Xiaofei

2016-02-01

Bauxite residue often has chemical and physical limitations to support plant growth, and improving its matrix properties is crucial to support sustainable vegetation in the long term. Spontaneous vegetation colonization on deposits in Central China, over a period of 20 years, has revealed that natural weathering processes may convert bauxite residue to a soil-like medium. Residue samples from different stacking ages were collected to determine the effect of natural processes on matrix properties over time. It was demonstrated that natural processes decreased pH (10.98 to 9.45), electrical conductivity (EC) (3.73 to 0.36 mS/cm), and exchangeable sodium percentage (ESP) (72.51 to 28.99 %), while increasing bulk density (1.91 to 1.39 g/cm(3)), improving the mean weight diameter (MWD) of water-stable aggregates (0.24 to 0.52 mm), and the proportion of >0.25-mm water-stable aggregates (19.91 to 50.73 %). The accumulation of organic carbon and the reduction of ESP and exchangeable Na had positive effects on soil aggregate formation, while exchangeable Ca and Mg were significantly beneficial to aggregation of water-stable aggregates. Climate, stacking time, and biological factors appear to improve the structure of bauxite residue. Our findings demonstrate soil genesis occurring following natural weathering processes of bauxite residues over time.

Impacts of Biochar on Physical Properties and Erosion Potential of a Mudstone Slopeland Soil

PubMed Central

Chien, Wei-Hsin; Liou, Ruei-Cheng

2014-01-01

Food demand and soil sustainability have become urgent issues recently because of the global climate changes. This study aims to evaluate the application of a biochar produced by rice hull, on changes of physiochemical characteristics and erosion potential of a degraded slopeland soil. Rice hull biochar pyrolized at 400°C was incorporated into the soil at rates of 2.5%, 5%, and 10% (w/w) and was incubated for 168 d in this study. The results indicated that biochar application reduced the Bd by 12% to 25% and the PR by 57% to 92% after incubation, compared with the control. Besides, porosity and aggregate size increased by 16% to 22% and by 0.59 to 0.94 mm, respectively. The results presented that available water contents significantly increased in the amended soils by 18% to 89% because of the obvious increase of micropores. The water conductivity of the biochar-amended soils was only found in 10% biochar treatment, which might result from significant increase of macropores and reduction of soil strength (Bd and PR). During a simulated rainfall event, soil loss contents significantly decreased by 35% to 90% in the biochar-amended soils. In conclusion, biochar application could availably raise soil quality and physical properties for tilth increasing in the degraded mudstone soil. PMID:25548787

Sustainable materials used as stone column filler: A short review

NASA Astrophysics Data System (ADS)

Zukri, Azhani; Nazir, Ramli

2018-04-01

Stone columns (also known as granular piles) are one of the methods for soft soil stabilization and typically used to increase bearing capacity and stability of slope.; Apart from decreasing the compressibility of loose and fine graded soils, it also accelerates the consolidation effect by improving the drainage path for pore water pressure dissipation and reduces the liquefaction potential of soils during earthquake event. Stone columns are probably the most “natural” ground treatment method or foundation system in existence to date. The benefit of stone columns is owing to the partial replacement of compressible soil by more competent materials such as stone aggregate, sand and other granular materials. These substitutes also act as reinforcement material, hence increasing overall strength and stiffness of the soft soil. Nowadays, a number of research has been conducted on the behaviour and performance of stone columns with various materials utilized as column filler replacing the normal aggregate. This paper will review extensively on previously conducted research on some of the materials used as stone column backfill materials, its suitability and the effectiveness as a substitute for regular aggregates in soft soil improvement works.

Adsorption, Aggregation, and Deposition Behaviors of Carbon Dots on Minerals.

PubMed

Liu, Xia; Li, Jiaxing; Huang, Yongshun; Wang, Xiangxue; Zhang, Xiaodong; Wang, Xiangke

2017-06-06

The increased production of carbon dots (CDs) and the release and accumulation of CDs in both surface and groundwater has resulted in the increasing interest in their research. To assess the environmental behavior of CDs, the interaction between CDs and goethite was studied under different environmental conditions. Electrokinetic characterization of CDs suggested that the ζ-potential and size distribution of CDs were affected by pH and electrolyte species, indicating that these factors influenced the stability of CDs in aqueous solutions. Traditional Derjaguin-Landau-Verwey-Overbeek theory did not fit well the aggregation process of CDs. Results of the effects of pH and ionic strength suggested that electronic attraction dominated the aggregation of CDs. Compared with other minerals, hydrogen-bonding interactions and Lewis acid-base interactions contributed to the aggregation of CDs, in addition to van der Waals and electrical double-layer forces. Adsorption isotherms and microscopic Fourier transformed infrared spectroscopy indicated that chemical bonds were formed between CDs and goethite. These findings are useful to understand the interaction of CDs with minerals, as well as the potential fate and toxicity of CDs in the natural environment, especially in soils and sediments.

Non-invasive localization of organic matter in soil aggregates using SR-μCT

NASA Astrophysics Data System (ADS)

Peth, Stephan; Mordhorst, Anneka; Chenu, Claire; Uteau Puschmann, Daniel; Garnier, Patricia; Nunan, Naoise; Pot, Valerie; Beckmann, Felix; Ogurreck, Malte

2014-05-01

Knowledge of the location of soil organic matter (SOM) and its spatial association to soil structure is an important step in improving modeling approaches for simulating organic matter turnover processes. Advanced models for carbon mineralization are able to account for the 3D distribution of SOM which is assumed to influence mineralisation. However, their application is still limited by the fact that no method exists to non-invasively determine the 3D spatial distribution of SOM in structured soils. SR-based X-ray microtomography (SR-µCT) is an advanced and promising tool in gaining knowledge on the 3-dimensional organization of soil phases (minerals, organic matter, water, air) which on a voxel level could be implemented into spatially explicit models. However, since the contrast of linear attenuation coefficients of soil organic matter on the one hand and mineral components and water on the other hand are relatively low, especially when materials are finely dispersed, organic matter within the soil pore space is often not resolved in ordinary X-ray absorption contrast imaging. To circumvent this problem we have developed a staining procedure for organic matter using Osmium-tetroxide since Osmium is an element with an absorption edge at a higher X-ray energy level. Osmium is known from transmission electron microscopy analysis (TEM) to stain organic matter specifically and irreversibly while having an absorption edge at approximately 74 keV. We report on the application of a novel Osmium vapor staining method to analyze differences in organic matter content and identify small scale spatial distribution of SOM in soil aggregates. To achieve this we have taken soil aggregate samples (6-8 mm across) obtained from arable soils differing in soil management. Aggregate samples were investigated by synchrotron-based X-ray microtomography (SR-µCT) after staining the sample with Osmium-tetroxide (OsO4) vapor. We utilized the monochromatic X-ray beam to locate osmium bound to SOM in the stained soil aggregate samples by scanning the aggregates at different photon energies: 30 keV at which the attenuation contrast is optimal for distinguishing other soil constituents, 70 keV (below the absorption of osmium) and 78 keV (above the absorption edge of osmium). The results suggest that particulate organic matter, which was not visibly by scanning samples at energy levels optimal for resolving soil structure (30 keV), was identified after osmium staining and scanning the samples at energy levels just below (70 keV) and above (78 keV) the absorption edge of Osmium. Subtracting the images below from the images above the osmium edged we were able to isolate stained particulate organic matter which otherwise would have been wrongly interpreted as pore space without staining. Combining both pore space and organic matter distribution we are able to investigate the association of SOM with soil structure.

Size and shape of soil humic acids estimated by viscosity and molecular weight.

PubMed

Kawahigashi, Masayuki; Sumida, Hiroaki; Yamamoto, Kazuhiko

2005-04-15

Ultrafiltration fractions of three soil humic acids were characterized by viscometry and high performance size-exclusion chromatography (HPSEC) in order to estimate shapes and hydrodynamic sizes. Intrinsic viscosities under given solute/solvent/temperature conditions were obtained by extrapolating the concentration dependence of reduced viscosities to zero concentration. Molecular mass (weight average molecular weight (M (w)) and number average molecular weight (M (n))) and hydrodynamic radius (R(H)) were determined by HPSEC using pullulan as calibrant. Values of M (w) and M (n) ranged from 15 to 118 x 10(3) and from 9 to 50 x 10(3) (g mol(-1)), respectively. Polydispersity, as indicated by M (w)/M (n), increased with increasing filter size from 1.5 to 2.4. The hydrodynamic radii (R(H)) ranged between 2.2 and 6.4 nm. For each humic acid, M (w) and [eta] were related. Mark-Houwink coefficients calculated on the basis of the M (w)-[eta] relationships suggested restricted flexible chains for two of the humic acids and a branched structure for the third humic acid. Those structures probably behave as hydrated sphere colloids in a good solvent. Hydrodynamic radii of fractions calculated from [eta] using Einstein's equation, which is applicable to hydrated sphere colloids, ranged from 2.2 to 7.1 nm. These dimensions are fit to the size of nanospaces on and between clay minerals and micropores in soil particle aggregates. On the other hand, the good agreement of R(H) values obtained by applying Einstein's equation with those directly determined by HPSEC suggests that pullulan is a suitable calibrant for estimation of molecular mass and size of humic acids by HPSEC.

Influences of thermal decontamination on mercury removal, soil properties, and repartitioning of coexisting heavy metals.

PubMed

Huang, Yu-Tuan; Hseu, Zeng-Yei; Hsi, Hsing-Cheng

2011-08-01

Thermal treatment is a useful tool to remove Hg from contaminated soils. However, thermal treatment may greatly alter the soil properties and cause the coexisting contaminants, especially trace metals, to transform and repartition. The metal repartitioning may increase the difficulty in the subsequent process of a treatment train approach. In this study, three Hg-contaminated soils were thermally treated to evaluate the effects of treating temperature and duration on Hg removal. Thermogravimetric analysis was performed to project the suitable heating parameters for subsequent bench-scale fixed-bed operation. Results showed that thermal decontamination at temperature>400°C successfully lowered the Hg content to<20 mg kg(-1). The organic carbon content decreased by 0.06-0.11% and the change in soil particle size was less significant, even when the soils were thermally treated to 550°C. Soil clay minerals such as kaolinite were shown to be decomposed. Aggregates were observed on the surface of soil particles after the treatment. The heavy metals tended to transform into acid-extractable, organic-matter bound, and residual forms from the Fe/Mn oxide bound form. These results suggest that thermal treatment may markedly influence the effectiveness of subsequent decontamination methods, such as acid washing or solvent extraction. Copyright © 2011 Elsevier Ltd. All rights reserved.

A new mass mortality of juvenile Protoceratops and size-segregated aggregation behaviour in juvenile non-avian dinosaurs.

PubMed

Hone, David W E; Farke, Andrew A; Watabe, Mahito; Shigeru, Suzuki; Tsogtbaatar, Khishigjav

2014-01-01

Monodominant bonebeds are a relatively common occurrence for non-avian dinosaurs, and have been used to infer associative, and potentially genuinely social, behavior. Previously known assemblages are characterized as either mixed size-classes (juvenile and adult-sized specimens together) or single size-classes of individuals (only juveniles or only adult-sized individuals within the assemblage). In the latter case, it is generally unknown if these kinds of size-segregated aggregations characterize only a particular size stage or represent aggregations that happened at all size stages. Ceratopsians ("horned dinosaurs") are known from both types of assemblages. Here we describe a new specimen of the ceratopsian dinosaur Protoceratops andrewsi, Granger and Gregory 1923 from Mongolia representing an aggregation of four mid-sized juvenile animals. In conjunction with existing specimens of groups of P. andrewsi that includes size-clustered aggregations of young juveniles and adult-sized specimens, this new material provides evidence for some degree of size-clustered aggregation behaviour in Protoceratops throughout ontogeny. This continuity of size-segregated (and presumably age-clustered) aggregation is previously undocumented in non-avian dinosaurs. The juvenile group fills a key gap in the available information on aggregations in younger ceratopsians. Although we support the general hypothesis that many non-avian dinosaurs were gregarious and even social animals, we caution that evidence for sociality has been overstated and advocate a more conservative interpretation of some data of 'sociality' in dinosaurs.

A New Mass Mortality of Juvenile Protoceratops and Size-Segregated Aggregation Behaviour in Juvenile Non-Avian Dinosaurs

PubMed Central

Hone, David W. E.; Farke, Andrew A.; Watabe, Mahito; Shigeru, Suzuki; Tsogtbaatar, Khishigjav

2014-01-01

Background Monodominant bonebeds are a relatively common occurrence for non-avian dinosaurs, and have been used to infer associative, and potentially genuinely social, behavior. Previously known assemblages are characterized as either mixed size-classes (juvenile and adult-sized specimens together) or single size-classes of individuals (only juveniles or only adult-sized individuals within the assemblage). In the latter case, it is generally unknown if these kinds of size-segregated aggregations characterize only a particular size stage or represent aggregations that happened at all size stages. Ceratopsians (“horned dinosaurs”) are known from both types of assemblages. Methods/Principal Findings Here we describe a new specimen of the ceratopsian dinosaur Protoceratops andrewsi, Granger and Gregory 1923 from Mongolia representing an aggregation of four mid-sized juvenile animals. In conjunction with existing specimens of groups of P. andrewsi that includes size-clustered aggregations of young juveniles and adult-sized specimens, this new material provides evidence for some degree of size-clustered aggregation behaviour in Protoceratops throughout ontogeny. This continuity of size-segregated (and presumably age-clustered) aggregation is previously undocumented in non-avian dinosaurs. Conclusions The juvenile group fills a key gap in the available information on aggregations in younger ceratopsians. Although we support the general hypothesis that many non-avian dinosaurs were gregarious and even social animals, we caution that evidence for sociality has been overstated and advocate a more conservative interpretation of some data of ‘sociality’ in dinosaurs. PMID:25426957

Physicochemical Characterization of Potential Mobile Organic Matter In Five Typical German Agricultural Soils

NASA Astrophysics Data System (ADS)

Séquaris, J.-M.; Lewandowski, H.; Vereecken, H.

Organic matter (OM) in soils plays an important role, i.e., in maintaining soil structure or as source of nutrients. OM is mainly adsorbed at the surface of clay minerals and oxides and remains mostly immobile. However, mobile OM in dissolved form (DOM) or associated with water dispersible colloids (WDC) in soil water may influence trans- port of pollutants. The goal of this study is to compare 5 typical German agricultural soils in terms of distribution and quality of OM in the top soil (0-15 cm). The present report focuses on the physicochemical characterization of potential mobile OM so- lutions obtained after physical fractionation of soil materials based on sedimentation after a prolonged shaking in water or electrolyte solutions. Three soil fractions dif- fering in particle size were separated in function of sedimentation time: a colloidal fraction: < 2 ţm; a microaggregate fraction: 2-20 ţm and a sediment fraction: > 20 ţm. The soil electrolyte phase containing the DOM fraction was obtained by a high-speed centrifugation of the colloidal phase. After a water or low electrolyte concentration (« 1 mM Ca2+) extraction, it can be shown that the mobile fraction of OM or OC (organic carbon) is distributed between the colloidal and the electrolyte phases in a concentration ratio range of 10-40 to 1. A less mobile OC fraction is associated with the microaggregate fraction while immobile OC remains adsorbed in the sediment fraction. An increasing OC and total-N content with diminishing particle-size of soil (colloidal and microaggregate fractions) has been confirmed. A higher OC input due to special soil management is sensitively detected in fractions with a greater particle size (sediment fraction). Increasing the Ca2+ concentration up to 10 mM during the water extraction diminishes the DOC concentration by an average factor of 3 while the OC associated with the dispersed colloids (OCWDC) vanished almost completely. Thus, a critical coagulation concentration of about 1-2 mM Ca2+ can be estimated which increases the stability of soil aggregates in water. Different titration, electrokinetic and spectroscopic methods were applied to characterize the colloidal and electrolyte phases. These techniques provide information on the physicochemical heterogeneity of mobile OM from various agricultural soils.

Size- and time-dependent growth properties of human induced pluripotent stem cells in the culture of single aggregate.

PubMed

Nath, Suman C; Horie, Masanobu; Nagamori, Eiji; Kino-Oka, Masahiro

2017-10-01

Aggregate culture of human induced pluripotent stem cells (hiPSCs) is a promising method to obtain high number of cells for cell therapy applications. This study quantitatively evaluated the effects of initial cell number and culture time on the growth of hiPSCs in the culture of single aggregate. Small size aggregates ((1.1 ± 0.4) × 10 1 -(2.8 ± 0.5) × 10 1 cells/aggregate) showed a lower growth rate in comparison to medium size aggregates ((8.8 ± 0.8) × 10 1 -(6.8 ± 1.1) × 10 2 cells/aggregate) during early-stage of culture (24-72 h). However, when small size aggregates were cultured in conditioned medium, their growth rate increased significantly. On the other hand, large size aggregates ((1.1 ± 0.2) × 10 3 -(3.5 ± 1.1) × 10 3 cells/aggregate) showed a lower growth rate and lower expression level of proliferation marker (ki-67) in the center region of aggregate in comparison to medium size aggregate during early-stage of culture. Medium size aggregates showed the highest growth rate during early-stage of culture. Furthermore, hiPSCs proliferation was dependent on culture time because the growth rate decreased significantly during late-stage of culture (72-120 h) at which point collagen type I accumulated on the periphery of aggregate, suggesting blockage of diffusive transport of nutrients, oxygen and metabolites into and out of the aggregates. Consideration of initial cell number and culture time are important to maintain balance between autocrine factors secretion and extracellular matrix accumulation on the aggregate periphery to achieve optimal growth of hiPSCs in the culture of single aggregate. Copyright © 2017 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Population Structure of Manganese-Oxidizing Bacteria in Stratified Soils and Properties of Manganese Oxide Aggregates under Manganese–Complex Medium Enrichment

PubMed Central

Zhang, Zhongming; Chen, Hong; Liu, Jin; Ali, Muhammad; Liu, Fan; Li, Lin

2013-01-01

Manganese-oxidizing bacteria in the aquatic environment have been comprehensively investigated. However, little information is available about the distribution and biogeochemical significance of these bacteria in terrestrial soil environments. In this study, stratified soils were initially examined to investigate the community structure and diversity of manganese-oxidizing bacteria. Total 344 culturable bacterial isolates from all substrata exhibited Mn(II)-oxidizing activities at the range of 1 µM to 240 µM of the equivalent MnO2. The high Mn(II)-oxidizing isolates (>50 mM MnO2) were identified as the species of phyla Actinobacteria, Firmicutes and Proteobacteria. Seven novel Mn(II)-oxidizing bacterial genera (species), namely, Escherichia, Agromyces, Cellulomonas, Cupriavidus, Microbacterium, Ralstonia, and Variovorax, were revealed via comparative phylogenetic analysis. Moreover, an increase in the diversity of soil bacterial community was observed after the combined enrichment of Mn(II) and carbon-rich complex. The phylogenetic classification of the enriched bacteria represented by predominant denaturing gradient gel electrophoresis bands, was apparently similar to culturable Mn(II)-oxidizing bacteria. The experiments were further undertaken to investigate the properties of the Mn oxide aggregates formed by the bacterial isolates with high Mn(II)-oxidizing activity. Results showed that these bacteria were closely encrusted with their Mn oxides and formed regular microspherical aggregates under prolonged Mn(II) and carbon-rich medium enrichment for three weeks. The biotic oxidation of Mn(II) to Mn(III/IV) by these isolates was confirmed by kinetic examinations. X-ray diffraction assays showed the characteristic peaks of several Mn oxides and rhodochrosite from these aggregates. Leucoberbelin blue tests also verified the Mn(II)-oxidizing activity of these aggregates. These results demonstrated that Mn oxides were formed at certain amounts under the enrichment conditions, along with the formation of rhodochrosite in such aggregates. Therefore, this study provides insights into the structure and diversity of soil-borne bacterial communities in Mn(II)-oxidizing habitats and supports the contribution of soil-borne Mn(II)-oxidizing bacteria to Mn oxide mineralization in soils. PMID:24069232

Contact angles of wetting and water stability of soil structure

NASA Astrophysics Data System (ADS)

Kholodov, V. A.; Yaroslavtseva, N. V.; Yashin, M. A.; Frid, A. S.; Lazarev, V. I.; Tyugai, Z. N.; Milanovskiy, E. Yu.

2015-06-01

From the soddy-podzolic soils and typical chernozems of different texture and land use, dry 3-1 mm aggregates were isolated and sieved in water. As a result, water-stable aggregates and water-unstable particles composing dry 3-1 mm aggregates were obtained. These preparations were ground, and contact angles of wetting were determined by the static sessile drop method. The angles varied from 11° to 85°. In most cases, the values of the angles for the water-stable aggregates significantly exceeded those for the water-unstable components. In terms of carbon content in structural units, there was no correlation between these parameters. When analyzing the soil varieties separately, the significant positive correlation between the carbon content and contact angle of aggregates was revealed only for the loamy-clayey typical chernozem. Based on the multivariate analysis of variance, the value of contact wetting angle was shown to be determined by the structural units belonging to water-stable or water-unstable components of macroaggregates and by the land use type. In addition, along with these parameters, the texture has an indirect effect.

Soil and Water: Some Teaching Suggestions.

ERIC Educational Resources Information Center

Fischer, Richard B.

1987-01-01

Outlines six soil and water investigations that students can pursue outdoors, in nature centers, or in classrooms: soil characteristics; relationship between soil ph and plant life; what aggregates tell us; differences in soil structure; differences in rate of water absorption by soil; and soil exploration with a Berlesi funnel. (NEC)

Particles size distribution in diluted magnetic fluids

NASA Astrophysics Data System (ADS)

Yerin, Constantine V.

2017-06-01

Changes in particles and aggregates size distribution in diluted kerosene based magnetic fluids is studied by dynamic light scattering method. It has been found that immediately after dilution in magnetic fluids the system of aggregates with sizes ranging from 100 to 250-1000 nm is formed. In 50-100 h after dilution large aggregates are peptized and in the sample stationary particles and aggregates size distribution is fixed.

What is the role played by organic matter fractions from different sieve-size particles in the development of soil water repellency? A case study using analytical pyrolysis.

NASA Astrophysics Data System (ADS)

Jiménez-Morillo, Nicasio T.; González-Pérez, José A.; González-Vila, Francisco J.; Zavala, Lorena M.; Jordán, Antonio; Jiménez-González, Marco A.

2014-05-01

1. INTRODUCTION It is known that soil water repellency (WR) is induced by organic substances covering the surface of minerals particles and aggregates or present as interstitial substances in the soil matrix. It has also been suggested that the persistence of WR is largely conditioned by specific chemical characteristics of soil organic matter (SOM). Most of these substances are abundant in ecosystems and are released into soils as exudates of roots, organic residues in decomposition, or secretions by fungi and other microorganisms. Soil free lipids correspond to a diverse collection of hydrophobic substances including complex substances as sterols, terpenes, polynuclear hydrocarbons, chlorophylls, fatty acids, waxes, and resins. Some of these organic substances, responsible of soil water repellency may be studied using analytical pyrolisis (de la Rosa et al., 2011; González-Pérez et al., 2011). This research aims to study the relation between soil WR and SOM quantity and quality, assessing the impact of organic fractions and its distribution in soil particles of different size on soil WR from sandy soils. 2. METHODS Soil samples were collected under selected species growing in sandy soils from the Doñana National Park (SW Spain), cork oak (Quercus suber, QS), eagle fern (Pteridium aquilinum, PA), pine (Pinus pinea, PP) and rockrose (Halimium halimifolium, HH). Soil WR and physical chemical characteristics including SOM content were assessed in fine earth soil samples (< 2mm) and in soil sieve fractions (1-2, 0.25-1, 0.05-0.25 and <0.05 mm). The composition of common hydrophobic substances present in SOM (n-alkane/alkene pairs and n-alkanoic acids) was assessed by analytical pyrolysis. Analytical pyrolysis techniques do not need a pre-treatment, is fast and easily reproducible 3. RESULTS The severity of soil WR (determined using the WDPT test) may be ordered according to the sequence QS>PA>PP>HH. A positive correlation was observed between WR from each sieve size fraction and SOM content. The most severe WR was detected in QS for all sieve size fractions, followed by the finer fractions form PA, PP and HH samples, which that also shows the highest SOM content, ranging between 20.9% (PP) and 46.9% (QS). Coarser soil fractions (1-2 mm) under PA, PP and HH showed the highest long-chain-even C numbered fatty acids (LCE-FA) in the order PP>PA>HH. No fatty acids were detected neither in sieve fractions 0.25-1, 0.05-0.25 and <0.05 mm from HH samples nor in PA and PP (0.25-1 mm samples). A significant relation was observed between SOM content and severity of soil WR in QS samples and finer fractions of other samples, which is in agreement with previous findings (GOrdillo-Rivero et al., 2013; Jordán et al., 2011). In contrast, 1-2 mm sieve fractions from PP, PA and HH soils showed high severity of soil WR and relatively low SOM contents. This could be explained by a low degree of evolution of organic residues with higher alkane/alkene CPI values and to the presence of a higher diversity of fatty acid structures. These results suggest that soil WR appears as a consequence of lipid compounds in soil. Some similarities were found in the organic molecular assemblages in PA and PP samples, suggesting a fingerprint of pine residues in PA samples, resulting from ancient pine forests. This finding may be also explained by the existence of exogenous organic inputs associated to fine soil particles from border areas of pine forests. REFERENCES de la Rosa, J.M., González-Pérez, J.A., González-Vila, F.J., Knicker, H., Araújo, M.F. 2011. Characterization of wildfire effects on soil organic matter using analytical pyrolysis. Geoderma 191, 24-30. González-Pérez, J.A., González-Vila, F.J., Arias, M.E., Rodríguez, J., de la Rosa, J.M., Marañón, T., Clemente, L. 2011. Geochemical and ecological significance of soil lipids under Rhododendron ponticum stands. Environmental Chemistry Letters 9, 453-464. Gordillo-Rivero, A.J., García-Moreno, J., Jordán, A., Zavala, L.M. 2013. Monitoring fire impacts in soil water repellency and structure stability during 6 years. Flamma 4, 71-75. Jordán, A., Zavala, L.M., Mataix-Solera, J., Nava, A.L., Alanís, N. 2011. Effect of fire severity on water repellency and aggregate stability on Mexican volcanic soils. Catena 84, 136-147.

Impact of roots, mycorrhizas and earthworms on soil physical properties as assessed by shrinkage analysis

NASA Astrophysics Data System (ADS)

Milleret, R.; Le Bayon, R.-C.; Lamy, F.; Gobat, J.-M.; Boivin, P.

2009-07-01

SummarySoil biota such as earthworms, arbuscular mycorrhizal fungi (AMF) and plant roots are known to play a major role in engineering the belowground part of the terrestrial ecosystems, thus strongly influencing the water budget and quality on earth. However, the effect of soil organisms and their interactions on the numerous soil physical properties to be considered are still poorly understood. Shrinkage analysis allows quantifying a large spectrum of soil properties in a single experiment, with small standard errors. The objectives of the present study were, therefore, to assess the ability of the method to quantify changes in soil properties as induced by single or combined effects of leek roots ( Allium porrum), AMF ( Glomus intraradices) and earthworms ( Allolobophora chlorotica). The study was performed on homogenised soil microcosms and the experiments lasted 35 weeks. The volume of the root network and the external fungal hyphae was measured at the end, and undisturbed soil cores were collected. Shrinkage analysis allowed calculating the changes in soil hydro-structural stability, soil plasma and structural pore volumes, soil bulk density and plant available water, and structural pore size distributions. Data analysis revealed different impacts of the experimented soil biota on the soil physical properties. At any water content, the presence of A. chlorotica resulted in a decrease of the specific bulk volume and the hydro-structural stability around 25%, and in a significant increase in the bulk soil density. These changes went with a decrease of the structural pore volumes at any pore size, a disappearing of the thinnest structural pores, a decrease in plant available water, and a hardening of the plasma. On the contrary, leek roots decreased the bulk soil density up to 1.23 g cm -3 despite an initial bulk density of 1.15 g cm -3. This increase in volume was accompanied with a enhanced hydro-structural stability, a larger structural pore volume at any pore size, smaller structural pore radii and an increase in plant available water. Interestingly, a synergistic effect of leek roots and AMF in the absence of the earthworms was highlighted, and this synergistic effect was not observed in presence of earthworms. The structural pore volume generated by root and AMF growth was several orders of magnitude larger than the volume of the organisms. Root exudates as well as other AMF secretion have served as carbon source for bacteria that in turn would enhance soil aggregation and porosity, thus supporting the idea of a self-organization of the soil-plant-microbe complex previously described.

The Impact of Multiple Freeze-Thaw Cycles on the Microstructure of Aggregates from a Soddy-Podzolic Soil: A Microtomographic Analysis

NASA Astrophysics Data System (ADS)

Skvortsova, E. B.; Shein, E. V.; Abrosimov, K. N.; Romanenko, K. A.; Yudina, A. V.; Klyueva, V. V.; Khaidapova, D. D.; Rogov, V. V.

2018-02-01

With the help of computed X-ray microtomography with a resolution of 2.75 μm, changes in the microstructure and pore space of aggregates of 3 mm in diameter from the virgin soddy-podzolic soil (Glossic Retisol (Loamic)) in the air-dry, capillary-moistened, and frozen states after five freeze-thaw cycles were studied in a laboratory experiment. The freezing of the samples was performed at their capillary moistening. It was shown that capillary moistening of initially air-dry samples from the humus (AY), eluvial (EL), and illuvial (BT1) horizons at room temperature resulted in the development of the platy, fine vesicular, and angular blocky microstructure, respectively. The total volume of tomographically visible pores >10 μm increased by 1.3, 2.2, and 3.4 times, respectively. After freeze-thaw cycles, frozen aggregates partly preserved the structural arrangement formed during the capillary moistening. At the same time, in the frozen aggregate from the AY horizon, the total tomographic porosity decreased to the initial level of the air-dry soil. In the frozen aggregate from the EL horizon, large vesicular pores were formed, owing to which the total pore volume retained its increased values. The resistance of aggregate shape to the action of freeze-thaw cycles differed. The aggregate from the EL horizon completely lost its original configuration by the end of the experiment. The aggregate from the AY horizon displayed definite features of sagging after five freeze-thaw cycles, whereas the aggregate from the BT1 horizon preserved its original configuration.

Carbon Limitation Induces ςS-Dependent Gene Expression in Pseudomonas fluorescens in Soil

PubMed Central

Koch, Birgit; Worm, Jakob; Jensen, Linda E.; Højberg, Ole; Nybroe, Ole

2001-01-01

Recent studies employing reporter gene technology indicate that the availabilities of the major nutrients nitrogen, phosphate, and iron to Pseudomonas are not severely limited in bulk soil. Indirect evidence has pointed to carbon limitation as a severe nutritional stress in this environment. We show that a plasmid (pGM115)-borne transcriptional fusion between the ςS-dependent Escherichia coli promoter Pfic and lacZ functions as a reliable reporter for carbon availability in Pseudomonas fluorescens. When P. fluorescens strain DF57(pGM115) was introduced into bulk soil, carbon-limiting conditions were indicated by citrate-repressible induction of β-galactosidase activity. To address carbon availability at the single-cell level, we developed an immunofluorescence double-staining procedure for individual DF57 cells expressing β-galactosidase from Pfic. Changes in cell size and expression of β-galactosidase were analyzed by flow cytometry. Cells extracted from soil microcosms reduced their size less than carbon-starved cells in pure culture and showed an increased tendency to aggregate. The single-cell analysis revealed that for cells residing in soil, the expression of β-galactosidase became heterogeneous and only a DF57 subpopulation appeared to be carbon limited. In soil amended with barley straw, limited nitrogen availability has been determined by use of the bioluminescent reporter strain P. fluorescens DF57-N3. We used strain DF57-N3(pGM115) as a double reporter for carbon and nitrogen limitation that allowed us to study the dynamics of carbon and nitrogen availabilities in more detail. In straw-amended soil β-galactosidase activity remained low, while nitrogen limitation-dependent bioluminescence appeared after a few days. Hence, nitrogen became limited under conditions where carbon resources were not completely exhausted. PMID:11472905

Predicting the mineral composition of dust aerosols - Part 1: Representing key processes

NASA Astrophysics Data System (ADS)

Perlwitz, J. P.; Pérez García-Pando, C.; Miller, R. L.

2015-02-01

Soil dust aerosols created by wind erosion are typically assigned globally uniform physical and chemical properties within Earth system models, despite known regional variations in the mineral content of the parent soil. Mineral composition of the aerosol particles is important to their interaction with climate, including shortwave absorption and radiative forcing, nucleation of cloud droplets and ice crystals, coating by heterogeneous uptake of sulfates and nitrates, and atmospheric processing of iron into bioavailable forms that increase the productivity of marine phytoplankton. Here, aerosol mineral composition is derived by extending a method that provides the composition of a wet-sieved soil. The extension accounts for measurements showing significant differences between the mineral fractions of the wet-sieved soil and the resulting aerosol concentration. For example, some phyllosilicate aerosols are more prevalent at silt sizes, even though they are nearly absent in a soil whose aggregates are dispersed by wet sieving during analysis. We reconstruct the undispersed size distribution of the original soil that is subject to wind erosion. An empirical constraint upon the relative emission of clay and silt is applied that further differentiates the soil and aerosol mineral composition. In addition, a method is proposed for mixing minerals with small impurities composed of iron oxides. These mixtures are important for transporting iron far from the dust source, because pure iron oxides are more dense and vulnerable to gravitational removal than most minerals comprising dust aerosols. A limited comparison to measurements from North Africa shows that the extension brings the model into better agreement, consistent with a more extensive comparison to global observations as well as measurements of elemental composition downwind of the Sahara, as described in companion articles.

Atomic force microscopy measurements of bacterial adhesion and biofilm formation onto clay-sized particles

PubMed Central

Huang, Qiaoyun; Wu, Huayong; Cai, Peng; Fein, Jeremy B.; Chen, Wenli

2015-01-01

Bacterial adhesion onto mineral surfaces and subsequent biofilm formation play key roles in aggregate stability, mineral weathering, and the fate of contaminants in soils. However, the mechanisms of bacteria-mineral interactions are not fully understood. Atomic force microscopy (AFM) was used to determine the adhesion forces between bacteria and goethite in water and to gain insight into the nanoscale surface morphology of the bacteria-mineral aggregates and biofilms formed on clay-sized minerals. This study yields direct evidence of a range of different association mechanisms between bacteria and minerals. All strains studied adhered predominantly to the edge surfaces of kaolinite rather than to the basal surfaces. Bacteria rarely formed aggregates with montmorillonite, but were more tightly adsorbed onto goethite surfaces. This study reports the first measured interaction force between bacteria and a clay surface, and the approach curves exhibited jump-in events with attractive forces of 97 ± 34 pN between E. coli and goethite. Bond strengthening between them occurred within 4 s to the maximum adhesion forces and energies of −3.0 ± 0.4 nN and −330 ± 43 aJ (10−18 J), respectively. Under the conditions studied, bacteria tended to form more extensive biofilms on minerals under low rather than high nutrient conditions. PMID:26585552

Role of organic matter on aggregate stability and related mechanisms through organic amendments

NASA Astrophysics Data System (ADS)

Zaher, Hafida

2010-05-01

To date, only a few studies have tried to simultaneously compare the role of neutral and uronic sugars and lipids on soil structural stability. Moreover, evidence for the mechanisms involved has often been established following wetting of moist aggregates after various pre-treatments thus altering aggregate structure and resulting in manipulations on altered aggregates on which the rapid wetting process may not be involved anymore. To the best of our knowledge, the objective of this work was to study the role of neutral and uronic sugars and lipids in affecting key mechanisms (swelling rate, pressure evolution) involved in the stabilization of soil structure. A long-term incubation study (48-wk) was performed on a clay loam and a silty-clay loam amended with de-inking-secondary sludge mix at three rates (8, 16 and 24 Mg dry matter ha-1), primary-secondary sludge mix at one rate (18 Mg oven-dry ha-1) and composted de-inking sludge at one rate (24 Mg ha-1). Different structural stability indices (stability of moist and dry aggregates, the amount of dispersible clay and loss of soil material following sudden wetting) were measured on a regular basis during the incubation, along with CO2 evolved, neutral and uronic sugar, and lipid contents. During the course of the incubations, significant increases in all stability indices were measured for both soil types. In general, the improvements in stability were proportional to the amount of C added as organic amendments. These improvements were linked to a very intense phase of C mineralization and associated with increases in neutral and uronic sugars as well as lipid contents. The statistical relationships found between the different carbonaceous fractions and stability indices were all highly significant and indicated no clear superiority of one fraction over another. Paper sludge amendments also resulted in significant decreases in maximum internal pressure of aggregate and aggregate swelling following immersion in water, two mechanisms affecting structural stability. Overall, the results suggest that reduction in maximum internal pressure induced by organic amendments most likely resulted from increases in pore surface roughness and pore occlusion rather than by increase in surface wetting angles. This study also supports the view of a non specific action of the lipids, neutral and uronic sugars on aggregate stability to rapid wetting. Key words: soil aggregate stability, polysaccharides, lipids, mechanisms, organic matter

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Kinetics of catalytically activated duplication in aggregation growth

NASA Astrophysics Data System (ADS)

Wang, Hai-Feng; Lin, Zhen-Quan; Gao, Yan; Xu, Chao

2009-08-01

We propose a catalytically activated duplication model to mimic the coagulation and duplication of the DNA polymer system under the catalysis of the primer RNA. In the model, two aggregates of the same species can coagulate themselves and a DNA aggregate of any size can yield a new monomer or double itself with the help of RNA aggregates. By employing the mean-field rate equation approach we analytically investigate the evolution behaviour of the system. For the system with catalysis-driven monomer duplications, the aggregate size distribution of DNA polymers ak(t) always follows a power law in size in the long-time limit, and it decreases with time or approaches a time-independent steady-state form in the case of the duplication rate independent of the size of the mother aggregates, while it increases with time increasing in the case of the duplication rate proportional to the size of the mother aggregates. For the system with complete catalysis-driven duplications, the aggregate size distribution ak(t) approaches a generalized or modified scaling form.

Relating soil biochemistry to sustainable crop production

USDA-ARS?s Scientific Manuscript database

Amino acids, amino sugars, carbohydrates, phenols, and fatty acids together comprise appreciable proportions of soil organic matter (SOM). Their cycling contribute to soil processes, including nitrogen availability, carbon sequestration and aggregation. For example, soil accumulation of phenols has ...

Experimental Investigations in Nonlinear Viscous Behavior of Subgrade Soils Under Traffic-Induced Loading

DOT National Transportation Integrated Search

1999-08-01

This paper concerns experimental investigations of nonlinear viscosity of : subgrade soils under vehicle-induced loading. Subgrade soil samples--collected : from the Soil/Aggregate Laboratory at the Geotechnical Exploration Division at : the Maryland...

Effect of compost supplies on soil bulk density and aggregate stability. Results from a six years trial in two experimental fields in Northern Italy

NASA Astrophysics Data System (ADS)

Calzolari, C.; Ungaro, F.; Salvador, P.; Torri, D.

2009-04-01

Results of a long term trial (2002-2007) on the effect of different organic amendments on topsoil structural properties at the end of the 6th year are presented. Two soils located in two experimental farms of the Emilia-Romagna region (Northern Italy), namely a silty clay loam Haplic Calcisol under sorghum (Sorghum bicolor, L.) continuous cropping, and a silty Calcaric Cambisols under peach (Persica vulgaris, Mill.), have been treated with a different amount of organic amendments. Four different treatments were tested plus control: manure (10 Mg ha-1 y-1), low input compost (5 and 10 Mg ha-1 y-1), high input compost (10 and 40 Mg ha-1 y-1), and no-tillage. In all the plots soil samples were collected three times every year: at the beginning of the growing season, at full crop coverage and after harvest. At each time, samples were collected in three replicates and soil bulk density and aggregate stability were measured. At the end of the 6 years trial 930 bulk density and 405 aggregate stability measurements were made available. The influence of organic amendments on soil physical properties is different according to the considered soil property and to the different soils. Soil bulk density (BD) shows clear and statistically significant differences among the tested theses, all with a marked seasonality and distinct temporal trends. The overall trends observed in the two soils are coherent with the amount of organic matter distributed in the different theses and with the field operations (tillage mainly), but with a short term effect. More important, over the period of observation and within each year, the treatments exhibit cyclical variations due to climate seasonality. Among the treatments, that with distribution of manure exhibits the weakest seasonal variations and a substantially stable general trend, with BD values slightly lower than those observed for the control. Different effects are also observed on soil aggregates stability, but also in this case a temporal trend is not clearly detectable, suggesting that the amendments have no cumulative effect at least during the 6 years of observations, and the responses are different in the two trials: slightly positive for the low compost supply in the silty clay loam Haplic Calcisol and negative for both low and high compost supply in the silty Calcaric Cambisols. The dominant issue is the seasonal variability of aggregate resistance which is well shown at the site where more data are available. Data also hints an ambiguous behavior of the compost: increasing the amount of applied compost leads to a slight increase in aggregate stability which is then followed by a decrease, as if the aggregation capability of the compost is counteracted by a dispersion effect.

Robustness of the Process of Nucleoid Exclusion of Protein Aggregates in Escherichia coli

PubMed Central

Neeli-Venkata, Ramakanth; Martikainen, Antti; Gupta, Abhishekh; Gonçalves, Nadia; Fonseca, Jose

2016-01-01

ABSTRACT Escherichia coli segregates protein aggregates to the poles by nucleoid exclusion. Combined with cell divisions, this generates heterogeneous aggregate distributions in subsequent cell generations. We studied the robustness of this process with differing medium richness and antibiotics stress, which affect nucleoid size, using multimodal, time-lapse microscopy of live cells expressing both a fluorescently tagged chaperone (IbpA), which identifies in vivo the location of aggregates, and HupA-mCherry, a fluorescent variant of a nucleoid-associated protein. We find that the relative sizes of the nucleoid's major and minor axes change widely, in a positively correlated fashion, with medium richness and antibiotic stress. The aggregate's distribution along the major cell axis also changes between conditions and in agreement with the nucleoid exclusion phenomenon. Consequently, the fraction of aggregates at the midcell region prior to cell division differs between conditions, which will affect the degree of asymmetries in the partitioning of aggregates between cells of future generations. Finally, from the location of the peak of anisotropy in the aggregate displacement distribution, the nucleoid relative size, and the spatiotemporal aggregate distribution, we find that the exclusion of detectable aggregates from midcell is most pronounced in cells with mid-sized nucleoids, which are most common under optimal conditions. We conclude that the aggregate management mechanisms of E. coli are significantly robust but are not immune to stresses due to the tangible effect that these have on nucleoid size. IMPORTANCE Escherichia coli segregates protein aggregates to the poles by nucleoid exclusion. From live single-cell microscopy studies of the robustness of this process to various stresses known to affect nucleoid size, we find that nucleoid size and aggregate preferential locations change concordantly between conditions. Also, the degree of influence of the nucleoid on aggregate positioning differs between conditions, causing aggregate numbers at midcell to differ in cell division events, which will affect the degree of asymmetries in the partitioning of aggregates between cells of future generations. Finally, we find that aggregate segregation to the cell poles is most pronounced in cells with mid-sized nucleoids. We conclude that the energy-free process of the midcell exclusion of aggregates partially loses effectiveness under stressful conditions. PMID:26728194

Chemically mediated group formation in soil-dwelling larvae and pupae of the beetle Trypoxylus dichotomus

NASA Astrophysics Data System (ADS)

Kojima, Wataru; Ishikawa, Yukio; Takanashi, Takuma

2014-09-01

Many insects form groups through interactions among individuals, and these are often mediated by chemical, acoustic, or visual cues and signals. In spite of the diversity of soil-dwelling insects, their aggregation behaviour has not been examined as extensively as that of aboveground species. We investigated the aggregation mechanisms of larvae of the Japanese rhinoceros beetle Trypoxylus dichotomus, which live in groups in humus soil. In two-choice laboratory tests, 2nd- and 3rd-instar larvae gathered at conspecific larvae irrespective of the kinship. The ablation of maxillae, which bear chemosensilla, abolished aggregation behaviour. Intact larvae also exhibited aggregation behaviour towards a larval homogenate. These results suggest that larval aggregation is mediated by chemical cues. We also demonstrated that the mature larvae of T. dichotomus built their pupal cells close to a mesh bag containing a conspecific pupal cell, which indicated that larvae utilize chemical cues emanating from these cells to select the pupation site. Thus, the larvae of T. dichotomus may use chemical cues from the conspecifics in two different contexts, i.e. larval aggregation and pupation site selection. Using conspecific cues, larvae may be able to choose suitable locations for foraging or building pupal cells. The results of the present study highlight the importance of chemical information in belowground ecology.

Chemically mediated group formation in soil-dwelling larvae and pupae of the beetle Trypoxylus dichotomus.

PubMed

Kojima, Wataru; Ishikawa, Yukio; Takanashi, Takuma

2014-09-01

Many insects form groups through interactions among individuals, and these are often mediated by chemical, acoustic, or visual cues and signals. In spite of the diversity of soil-dwelling insects, their aggregation behaviour has not been examined as extensively as that of aboveground species. We investigated the aggregation mechanisms of larvae of the Japanese rhinoceros beetle Trypoxylus dichotomus, which live in groups in humus soil. In two-choice laboratory tests, 2nd- and 3rd-instar larvae gathered at conspecific larvae irrespective of the kinship. The ablation of maxillae, which bear chemosensilla, abolished aggregation behaviour. Intact larvae also exhibited aggregation behaviour towards a larval homogenate. These results suggest that larval aggregation is mediated by chemical cues. We also demonstrated that the mature larvae of T. dichotomus built their pupal cells close to a mesh bag containing a conspecific pupal cell, which indicated that larvae utilize chemical cues emanating from these cells to select the pupation site. Thus, the larvae of T. dichotomus may use chemical cues from the conspecifics in two different contexts, i.e. larval aggregation and pupation site selection. Using conspecific cues, larvae may be able to choose suitable locations for foraging or building pupal cells. The results of the present study highlight the importance of chemical information in belowground ecology.

Soil carbon stabilization and turnover at alley-cropping systems, Eastern Germany

NASA Astrophysics Data System (ADS)

Medinski, T.; Freese, D.

2012-04-01

Alley-cropping system is seen as a viable land-use practice for mitigation of greenhouse gas CO2, energy-wood production and soil carbon sequestration. The extent to which carbon is stored in soil varies between ecosystems, and depends on tree species, soil types and on the extent of physical protection of carbon within soil aggregates. This study investigates soil carbon sequestration at alley-cropping systems presented by alleys of fast growing tree species (black locust and poplar) and maize, in Brandenburg, Eastern Germany. Carbon accumulation and turnover are assessed by measuring carbon fractions differing in decomposition rates. For this purpose soil samples were fractionated into labile and recalcitrant soil-size fractions by wet-sieving: macro (>250 µm), micro (53-250 µm) and clay + silt (<53 µm), followed by determination of organic carbon and nitrogen by gas-chromatography. Soil samples were also analysed for the total C&N content, cold-water extractable OC, and microbial C. Litter decomposition was evaluated by litter bags experiment. Soil CO2 flux was measured by LiCor automated device LI-8100A. No differences for the total and stable (clay+silt, <53 µm) carbon fraction were observed between treatment. While cold water-extractable carbon was significantly higher at maize alley compared to black locust alley. This may indicate faster turnover of organic matter at maize alley due to tillage, which influenced greater incorporation of plant residues into the soil, greater soil respiration and microbial activity.

Soil total carbon content, aggregation, bulk density, and penetration resistance of croplands and nearby grasslands

USDA-ARS?s Scientific Manuscript database

Converting native grassland (NGL) to cropland (CL) decreases soil organic matter contents (components of soil total carbon contents, STCCs), which often leads to soil degradation. Reestablishing grass on CL generally increases soil organic matter, which improves soil conditions. This study was condu...

Applicability of five models to simulate water infiltration into soil with added biochar

USDA-ARS?s Scientific Manuscript database

As a soil amendment, biochar can reduce soil bulk density, increase soil porosity, and alter soil aggregates and thus affect the infiltration. Researchers have proposed and revised several theoretical models to describe the process of soil infiltration. Although these models have been successfully u...

Linking soil permeability and soil aggregate stability with root development: a pots experiment (preliminary results)

NASA Astrophysics Data System (ADS)

Vergani, Chiara; Graf, Frank; Gerber, Werner

2015-04-01

Quantifying and monitoring the contribution of vegetation to the stability of the slopes is a key issue for implementing effective soil bioengineering measures. This topic is being widely investigated both from the hydrological and mechanical point of view. Nevertheless, due to the high variability of the biological components, we are still far from a comprehensive understanding of the role of plants in slope stabilization, especially if the different succession phases and the temporal development of vegetation is considered. Graf et al., 2014, found within the scope of aggregate stability investigations that the root length per soil volume of alder specimen grown for 20 weeks under laboratory conditions is comparable to the one of 20 years old vegetation in the field. This means that already relatively short time scales can provide meaningful information at least for the first stage of colonization of soil bioengineering measures, which is also the most critical. In the present study we analyzed the effect of root growth on two soil properties critical to evaluate the performance of vegetation in restoring and re-stabilizing slopes: permeability and soil aggregate stability. We set up a laboratory experiment in order to work under controlled conditions and limit as much as possible the natural variability. Alnus incana was selected as the study species as it is widely used in restoration projects in the Alps, also because of its capacity to fix nitrogen and its symbiosis with both ecto and arbuscular mycorrhizal fungi. After the first month of growth in germination pots, we planted one specimen each in big quasi cylindrical pots of 34 cm diameter and 35 cm height. The pots were filled with the soil fraction smaller than 10 mm coming from an oven dried moraine collected in a subalpine landslide area (Hexenrübi catchment, central Switzerland). The targeted dry unit weight was 16 kN/m3. The plants have been maintained at a daily temperature of 25°C and relative humidity of 75%, and at a night temperature of 17°C and relative humidity of 55% , with 15 hours of light per day. Four different growing periods have been distinguished (1, 2, 4 and 8 months). For each growing period 7 planted replicates have been set up, as well as 3 control pots with only bare soil treated the same way as the planted pots. After each growing period, the soil permeability was measured by means of a falling head procedure (Bagarello and Iovino, 2010) directly in the pots. Furthermore, soil aggregate stability was determined on soil samples applying a wet sieving method (Graf and Frei, 2013). Subsequently, root systems were collected and analyzed using different image software (Smartroot and Winrhizo). The permeability and soil aggregate stability values were finally linked with the root development stage and compared with field data coming from long-term stabilized slopes. Preliminary analysis reveals no significant influence of alder roots on both soil aggregate stability and hydraulic conductivity of soil after the one month growing period compared to the control. However, after two months we observed a decrease in the hydraulic conductivity values.

Spatial Modeling of Iron Transformations Within Artificial Soil Aggregates

NASA Astrophysics Data System (ADS)

Kausch, M.; Meile, C.; Pallud, C.

2008-12-01

Structured soils exhibit significant variations in transport characteristics at the aggregate scale. Preferential flow occurs through macropores while predominantly diffusive exchange takes place in intra-aggregate micropores. Such environments characterized by mass transfer limitations are conducive to the formation of small-scale chemical gradients and promote strong spatial variation in processes controlling the fate of redox-sensitive elements such as Fe. In this study, we present a reactive transport model used to spatially resolve iron bioreductive processes occurring within a spherical aggregate at the interface between advective and diffusive domains. The model is derived from current conceptual models of iron(hydr)oxide (HFO) transformations and constrained by literature and experimental data. Data were obtained from flow-through experiments on artificial soil aggregates inoculated with Shewanella putrefaciens strain CN32, and include the temporal evolution of the bulk solution composition, as well as spatial information on the final solid phase distribution within aggregates. With all iron initially in the form of ferrihydrite, spatially heterogeneous formation of goethite/lepidocrocite, magnetite and siderite was observed during the course of the experiments. These transformations were reproduced by the model, which ascribes a central role to divalent iron as a driver of HFO transformations and master variable in the rate laws of the considered reaction network. The predicted dissolved iron breakthrough curves also match the experimental ones closely. Thus, the computed chemical concentration fields help identify factors governing the observed trends in the solid phase distribution patterns inside the aggregate. Building on a mechanistic description of transformation reactions, fluid flow and solute transport, the model was able to describe the observations and hence illustrates the importance of small-scale gradients and dynamics of bioreductive processes for assessing bulk iron cycling. As HFOs are ubiquitous in soils, such process-level understanding of aggregate-scale iron dynamics has broad implications for the prediction of the subsurface fate of nutrients and contaminants that interact strongly with HFO surfaces.

Long-term effect of land use change on soil quality: Afforestation and land abandonment in semi-arid Spain

NASA Astrophysics Data System (ADS)

Zethof, Jeroen; Cammeraat, Erik; Nadal-Romero, Estela

2016-04-01

Soils under the Mediterranean climate are vulnerable for degradation, especially after land abandonment. Abandonment is an important factor in the Mediterranean landscape as vegetation regeneration is hampered due to the characteristic semi-arid and sub-humid Mediterranean climate regime. During the past 70 year extensive afforestation projects have been conducted with the aim to protect landscapes and soils against degradation. While large investments are still being made, little is known about the impact of afforestation on soil quality on a longer time scale. During the past decade, there is a growing interest in qualifying and quantifying the carbon storage in soils by such afforestation projects, to get a better understanding of the carbon cycle and look for possibilities to fixate atmospheric CO2 in the soil. It is generally accepted that afforestation projects will increase the soil carbon pool, but data on this process is scarce. Therefore an intensive fieldwork has been carried out in Murcia, southeastern Spain to study the effects of land abandonment and afforestation on soil quality along a chronosequence and included two afforested areas (from the early '70s and 1993). The Pinus halepensis trees were planted in rows, for which the underlying calcrete was broken. Samples were taken to study changes in soil quality (Aggregate stability, Corg, N, P, K, Na), Soil Organic Carbon (SOC) stocks and soil hydraulic properties, such as infiltration and water retention, between the afforestation projects, abandoned agricultural plots of similar age, semi-natural vegetation, cereal crop fields and almond orchards. As the natural vegetation is characterized by a spotted pattern of bare areas and trees, forming so-called "islands of fertility", both bare and vegetation covered sub-sites were sampled. First results showed a positive effect of both land abandonment and afforestation on the soil aggregation. Especially the 40-year-old plots showed underneath trees similar values as the semi-natural sites, while the open areas in the afforested sites lag behind. Especially the soil at a depth of 10-20 cm showed a clear decrease in aggregate stability, while the surface layer showed a clear increase in aggregate stability. Abandonment sites showed a non-linear increase in soil quality, which means that aggregate stability slightly declines after 20 year of abandonment, but the positive change was less than on the afforested sites. Changes in vegetation along the chronosequence studied, could be expected to have an impact on organic matter input quality and quantity. Such changes in vegetation cover, structure and composition were not observed for the afforested sites in the field, but preliminary results suggest that the 40-year-old afforested sites could have a higher soil quality than the semi-natural sites.

Structure and composition of Fe-OM co-precipitates that form in soil-derived solutions

NASA Astrophysics Data System (ADS)

Fritzsche, Andreas; Schröder, Christian; Wieczorek, Arkadiusz K.; Händel, Matthias; Ritschel, Thomas; Totsche, Kai U.

2015-11-01

Iron oxides represent a substantial fraction of secondary minerals and particularly affect the reactive properties of natural systems in which they formed, e.g. in soils and sediments. Yet, it is still obscure how transient conditions in the solution will affect the properties of in situ precipitated Fe oxides. Transient compositions, i.e. compositions that change with time, arise due to predominant non-equilibrium states in natural systems, e.g. between liquid and solid phases in soils. In this study, we characterize Fe-OM co-precipitates that formed in pH-neutral exfiltrates from anoxic topsoils under transient conditions. We applied soil column outflow experiments, in which Fe2+ was discharged with the effluent from anoxic soil and subsequently oxidized in the effluent due to contact with air. Our study features three novel aspects being unconsidered so far: (i) the transient composition of soil-derived solutions, (ii) that pedogenic Fe oxides instead of Fe salts serve as major source for Fe2+ in soil solution and (iii) the presence of exclusively soil-derived organic and inorganic compounds during precipitation. The experiments were carried out with two topsoil materials that differed in composition, texture and land use. Derived from Mössbauer spectroscopy, broad distributions in quadrupole splittings (0-2 mm s-1) and magnetic hyperfine fields (35-53 T) indicated the presence of low-crystalline ferrihydrite and even lower crystalline Fe phases in all Fe-OM co-precipitates. There was no unequivocal evidence for other Fe oxides, i.e. lepidocrocite and (nano)goethite. The Fe-OM co-precipitates contained inorganic (P, sulfate, silicate, Al, As) and organic compounds (proteins, polysaccharides), which were concurrently discharged from the soils. Their content in the Fe-OM co-precipitates was controlled by their respective concentration in the soil-derived solution. On a molar basis, OC and Fe were the main components in the Fe-OM co-precipitates (OC/Fe ratio = 0.5-2). The elemental composition of the Fe-OM co-precipitates was in accordance with the sequential precipitation of Fe(III)phosphates/arsenates prior to the formation of ferrihydrite. This explains decreasing Si contents in the Fe-OM co-precipitates with increasing availability of P. With respect to constant mean quadrupole splittings and slightly decreasing mean magnetic hyperfine fields, increasing contents of OC, P and Al in the Fe-OM co-precipitates did not further increase the structural disorder of the Fe polyhedra, while the crystallite interactions slightly decreased. Scanning electron microscopy and dynamic light scattering revealed the coincidental presence of variably sized aggregates and a considerable amount of Fe-OM co-precipitates, which remained dispersed in solution for months. Thus, variably composed Fe-OM co-precipitates with highly diverse aggregate sizes and comparably constant poor crystallinity can be expected after the oxidation of Fe2+ in transient, soil-derived solutions.

The material from Lampung as coarse aggregate to substitute andesite for concrete-making

NASA Astrophysics Data System (ADS)

Amin, M.; Supriyatna, Y. I.; Sumardi, S.

2018-01-01

Andesite stone is usually used for split stone material in the concrete making. However, its availability is decreasing. Lampung province has natural resources that can be used for coarse aggregate materials to substitute andesite stone. These natural materials include limestone, feldspar stone, basalt, granite, and slags from iron processing waste. Therefore, a research on optimizing natural materials in Lampung to substitute andesite stone for concrete making is required. This research used laboratory experiment method. The research activities included making cubical object samples of 150 x 150 x 150 mm with material composition referring to a standard of K.200 and w/c 0.61. Concrete making by using varying types of aggregates (basalt, limestone, slag) and aggregate sizes (A = 5-15 mm, B = 15-25 mm, and 25-50 mm) was followed by compressive strength test. The results showed that the obtained optimal compressive strengths for basalt were 24.47 MPa for 50-150 mm aggregate sizes, 21.2 MPa for 15-25 mm aggregate sizes, and 20.7 MPa for 25-50 mm aggregate sizes. These results of basalt compressive strength values were higher than the same result for andesite (19.69 MPa for 50-150 mm aggregate sizes), slag (22.72 MPa for 50-150 mm aggregate sizes), and limestone (19.69 Mpa for 50-150 mm aggregate sizes). These results indicated that basalt, limestone, and slag aggregates were good enough to substitute andesite as materials for concrete making. Therefore, natural resources in Lampung can be optimized as construction materials in concrete making.

Use of soil stabilizers on highway shoulders.

DOT National Transportation Integrated Search

2005-01-01

This study evaluated soil additives as stabilizers for aggregate and topsoil shoulders. Its purpose was to determine (1) the effect soil stabilizers have on the strength and stability of soil shoulders, and (2) the costs and benefits of using stabili...

Surface properties of heat-induced soluble soy protein aggregates of different molecular masses.

PubMed

Guo, Fengxian; Xiong, Youling L; Qin, Fang; Jian, Huajun; Huang, Xiaolin; Chen, Jie

2015-02-01

Suspensions (2% and 5%, w/v) of soy protein isolate (SPI) were heated at 80, 90, or 100 °C for different time periods to produce soluble aggregates of different molecular sizes to investigate the relationship between particle size and surface properties (emulsions and foams). Soluble aggregates generated in these model systems were characterized by gel permeation chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Heat treatment increased surface hydrophobicity, induced SPI aggregation via hydrophobic interaction and disulfide bonds, and formed soluble aggregates of different sizes. Heating of 5% SPI always promoted large-size aggregate (LA; >1000 kDa) formation irrespective of temperature, whereas the aggregate size distribution in 2% SPI was temperature dependent: the LA fraction progressively rose with temperature (80→90→100 °C), corresponding to the attenuation of medium-size aggregates (MA; 670 to 1000 kDa) initially abundant at 80 °C. Heated SPI with abundant LA (>50%) promoted foam stability. LA also exhibited excellent emulsifying activity and stabilized emulsions by promoting the formation of small oil droplets covered with a thick interfacial protein layer. However, despite a similar influence on emulsion stability, MA enhanced foaming capacity but were less capable of stabilizing emulsions than LA. The functionality variation between heated SPI samples is clearly related to the distribution of aggregates that differ in molecular size and surface activity. The findings may encourage further research to develop functional SPI aggregates for various commercial applications. © 2015 Institute of Food Technologists®

Using 13C labeled glucose to determine soil microbial and physical controls of new C incorporation under drying-rewetting cycles and conservation agricultural management

NASA Astrophysics Data System (ADS)

Li, L.; Schaeffer, S. M.

2017-12-01

Drying-rewetting cycles can induce carbon (C) depletion in soil, while conservation agricultural management aims at soil C sequestration. Understanding the combined effect of drying-rewetting cycles and conservation management is critical for sustaining agricultural soil under climate change. Soil organic C can be stored in a relatively rapidly cycling active pool, or a more slowly cycling passive pool. We conducted a 24-days mesocosm incubation using an agricultural soil from western Tennessee under 35-years of conservation management. Different lengths of drought period before rewetting of 0, 3, 6, and 24 days were applied on the mesocosms. To trace the fate of newly added C, 13C labeled glucose was added to the mesocosms at the beginning of the incubation. After 24 days, dissolvable organic C, microbial biomass C, accumulative microbial respiration, and extracellular enzyme activity were analyzed to evaluate the active C pool; hydrogen peroxide oxidation and aggregate size fractionation were used to examine the passive C pool. The highest cumulative microbial respiration was found in the 6-days treatment combining a N-fixing cover crop with no-tillage, and the lowest in the 24-day treatment with a wheat cover crop combined with conventional-tillage (1000.0±20.5 and 106.8±17.5 µg C-CO2 g-1 dry soil, respectively). The 6-days treatment induced 0.5-4.3 times higher cumulative C-CO2 emission than the 3-days treatment. The proportion of macroaggregates in bulk soil varied between 97.2% and 76.7%, and it was negatively correlated with drying-rewetting frequency. The proportion of microaggregates in bulk soil varied between 21.9% and 2.1%, and it was positively correlated with drying-rewetting frequency. 13C recovery rate in bulk soil varied between 11-53%. The vetch-cover-crop-with-no-tillage treatment facilitated 13C accumulation the most. Our results show that the N fixing cover crops combined with no-tillage treatment induced the highest C accumulation in bulk soil, while the no cover crop combined with conventional tillage induced the lowest C concentration. Our results show that frequent drying-rewetting cycles disrupt macroaggregates and release the microaggregates within macroaggregates, and favor greater C loss combined with greater C storage in less stable aggregate fractions.

A study of the aggregation of cyclodextrins: Determination of the critical aggregation concentration, size of aggregates and thermodynamics using isodesmic and K2-K models.

PubMed

Do, Thao Thi; Van Hooghten, Rob; Van den Mooter, Guy

2017-04-15

The aggregation of three different cyclodextrins (CDs): 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), 2-hydroxypropyl-γ-cyclodextrin (HP-γ-CD) and sulfobutylether-β-cyclodextrin (SBE-β-CD) was studied. The critical aggregation concentration (cac) of these three CDs is quite similar and is situated at ca. 2% (m/v). There was only a small difference in the cac values determined by DLS and 1 H NMR. DLS measurements revealed that CDs in solution have three size populations wherein one of them is that of a single CD molecule. The size of aggregates determined by TEM appears to be similar to the size of the aggregates in the second size distribution determined by DLS. Isodesmic and K 2 -K self-assembly models were used for studying the aggregation process of HP-β-CD, HP-γ-CD and SBE-β-CD. The results showed that the aggregation process of these CDs is a cooperative one, where the first step of aggregation is less favorable than the next steps. The determined thermodynamic parameters showed that the aggregation process of all three CDs is spontaneous and exothermic and it is driven by an increase of the entropy of the environment. Copyright © 2017 Elsevier B.V. All rights reserved.

Non-microbial methane emissions from soils

NASA Astrophysics Data System (ADS)

Wang, Bin; Hou, Longyu; Liu, Wei; Wang, Zhiping

2013-12-01

Traditionally, methane (CH4) is anaerobically formed by methanogenic archaea. However, non-microbial CH4 can also be produced from geologic processes, biomass burning, animals, plants, and recently identified soils. Recognition of non-microbial CH4 emissions from soils remains inadequate. To better understand this phenomenon, a series of laboratory incubations were conducted to examine effects of temperature, water, and hydrogen peroxide (H2O2) on CH4 emissions under both aerobic and anaerobic conditions using autoclaved (30 min, 121 °C) soils and aggregates (>2000 μm, A1; 2000-250 μm, A2; 250-53 μm, M1; and <53 μm, M2). Results show that applying autoclaving to pre-treat soils is effective to inhibit methanogenic activity, ensuring the CH4 emitted being non-microbial. Responses of non-microbial CH4 emissions to temperature, water, and H2O2 were almost identical between aerobic and anaerobic conditions. Increasing temperature, water of proper amount, and H2O2 could significantly enhance CH4 emissions. However, the emission rates were inhibited and enhanced by anaerobic conditions without and with the existence of H2O2, respectively. As regards the aggregates, aggregate-based emission presented an order of M1 > A2 > A1 > M2 and C-based emission an order of M2 > M1 > A1 > A2, demonstrating that both organic carbon quantity and property are responsible for CH4 emissions from soils at the scale of aggregate. Whole soil-based order of A2 > A1 > M1 > M2 suggests that non-microbial CH4 release from forest soils is majorly contributed by macro-aggregates (i.e., >250 μm). The underlying mechanism is that organic matter through thermal treatment, photolysis, or reactions with free radicals produce CH4, which, in essence, is identical with mechanisms of other non-microbial sources, indicating that non-microbial CH4 production may be a widespread phenomenon in nature. This work further elucidates the importance of non-microbial CH4 formation which should be distinguished from the well-known microbial CH4 formation in order to define both roles in the atmospheric CH4 global budget.

MODELING POROUS DUST GRAINS WITH BALLISTIC AGGREGATES. II. LIGHT SCATTERING PROPERTIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen Yue; Draine, B. T.; Johnson, Eric T.

2009-05-10

We study the light scattering properties of random ballistic aggregates constructed in Shen et al. Using the discrete-dipole approximation, we compute the scattering phase function and linear polarization for random aggregates with various sizes and porosities, and with two different compositions: 100% silicate and 50% silicate +50% graphite. We investigate the dependence of light scattering properties on wavelength, cluster size, and porosity using these aggregate models. We find that while the shape of the phase function depends mainly on the size parameter of the aggregates, the linear polarization depends on both the size parameter and the porosity of the aggregates,more » with increasing degree of polarization as the porosity increases. Contrary to previous studies, we argue that the monomer size has negligible effects on the light scattering properties of ballistic aggregates, as long as the constituent monomer is smaller than the incident wavelength up to 2{pi}a {sub 0}/{lambda} {approx} 1.6 where a {sub 0} is the monomer radius. Previous claims for such monomer size effects are in fact the combined effects of size parameter and porosity. Finally, we present aggregate models that can reproduce the phase function and polarization of scattered light from the AU Mic debris disk and from cometary dust, including the negative polarization observed for comets at scattering angles 160 deg. {approx}< {theta} < 180 deg. These aggregates have moderate porosities, P{approx}0.6, and are of sub-{mu}m size for the debris disk case, or {mu}m size for the comet case.« less

Effect of soil structure on the growth of bacteria in soil quantified using CARD-FISH

NASA Astrophysics Data System (ADS)

Juyal, Archana; Eickhorst, Thilo; Falconer, Ruth; Otten, Wilfred

2014-05-01

It has been reported that compaction of soil due to use of heavy machinery has resulted in the reduction of crop yield. Compaction affects the physical properties of soil such as bulk density, soil strength and porosity. This causes an alteration in the soil structure which limits the mobility of nutrients, water and air infiltration and root penetration in soil. Several studies have been conducted to explore the effect of soil compaction on plant growth and development. However, there is scant information on the effect of soil compaction on the microbial community and its activities in soil. Understanding the effect of soil compaction on microbial community is essential as microbial activities are very sensitive to abrupt environmental changes in soil. Therefore, the aim of this work was to investigate the effect of soil structure on growth of bacteria in soil. The bulk density of soil was used as a soil physical parameter to quantify the effect of soil compaction. To detect and quantify bacteria in soil the method of catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) was used. This technique results in high intensity fluorescent signals which make it easy to quantify bacteria against high levels of autofluorescence emitted by soil particles and organic matter. In this study, bacterial strains Pseudomonas fluorescens SBW25 and Bacillus subtilis DSM10 were used. Soils of aggregate size 2-1mm were packed at five different bulk densities in polyethylene rings (4.25 cm3).The soil rings were sampled at four different days. Results showed that the total number of bacteria counts was reduced significantly (P

Soil quality indicator responses to row crop, grazed pasture, and agroforestry buffer management

USDA-ARS?s Scientific Manuscript database

Incorporation of trees and establishment of grass buffers within agroecosystems are management practices shown to enhance soil quality. Soil enzyme activities and water stable aggregates (WSA) have been identified as sensitive soil quality indicators to evaluate early responses to soil management. ...

The Influence of Biochar on Soil Processes

USDA-ARS?s Scientific Manuscript database

Biochar may be a good soil amendment with the potential to sequester Carbon (C) for long periods of time. In addition, biochar added to soils could increase water infiltration and retention, increase cation exchange capacity and perhaps soil aggregation. However the effects of biochar on soil biol...

Quantification of the proliferation of arbuscular mycorrhizal fungi in soil

NASA Astrophysics Data System (ADS)

Zhang, Ning; Lilje, Osu; McGee, Peter

2013-04-01

Good soil structure is important for sustaining agricultural production and preserving functions of the soil ecosystem. Soil aggregation is a critically important component of soil structure. Stable aggregates enable water infiltration, gas exchange for biological activities of plant roots and microorganisms, living space and surfaces for soil microbes, and contribute to stabilization of organic matter and storage of organic carbon (OC) in soil. Soil aggregation involves fine roots, organic matter and hyphae of arbuscular mycorrhizal (AM) fungi. Hyphal proliferation is essential for soil aggregation and sequestration of OC in soil. We do not yet have a mechanism to directly quantify the density of hyphae in soil. Organic materials and available phosphorus are two of the major factors that influence fungi in soil. Organic materials are a source of energy for saprotrophic microbes. Fungal hyphae increase in the presence of organic matter. Phosphorus is an important element usually found in ecosystems. The low availability of phosphorus limits the biological activity of microbes. AM fungi benefit plants by delivering phosphorus to the root system. However, the density and the length of hyphae of AM fungi do not appear to be influenced by available phosphorus. A number of indirect methods have been used to visualize distribution of fungi in soil. Reliable analyses of soil are limited because of soil characteristics. Soils are fragile, and fragility limits opportunity for non-destructive analysis. The soil ecosystem is complex. Soil particles are dense and the density obscures the visualization of fungal hyphae. Fungal hyphae are relatively fine and information at the small scale (<250µm) is key to understanding how fungi respond to environmental stimuli. This experiment tested whether organic carbon (starch), phosphorus (K2HPO4) and their mixture influences proliferation of hyphae of AM fungi. Hyphae were quantified in an artificial soil matrix using micro-computer aided tomography. Micro-computer aided tomography provides three dimensional images of hyphal ramification through electron lucent materials and enables the visualization and quantification of hyphae. Starch and the mixture of starch plus K2HPO4, stimulated hyphal proliferation, while K2HPO4 alone did not change the density of hyphae. The images also indicate that fungal hyphae attached to the surfaces of the particles rather than grow through the spaces between them. The capacity to quantify hyphae in three-dimensional space allows a wide range of questions to now be addressed. Apart from studying mechanisms of carbon turnover, more complex processes may now be considered. Soil is commonly thought of as a black box. That black box is now a shade of grey.

Role of macropore flow in the transport of Escherichia coli cells in undisturbed cores of a brown leached soil.

PubMed

Martins, Jean M F; Majdalani, Samer; Vitorge, Elsa; Desaunay, Aurélien; Navel, Aline; Guiné, Véronique; Daïan, Jean François; Vince, Erwann; Denis, Hervé; Gaudet, Jean Paul

2013-02-01

The objective of this work was to evaluate the transport of Escherichia coli cells in undisturbed cores of a brown leached soil collected at La Côte St André (France). Two undisturbed soil cores subjected to repeated injections of bacterial cells and/or bromide tracer were used to investigate the effect of soil hydrodynamics and ionic strength on cell mobility. Under the tested experimental conditions, E. coli cells were shown to be transported at the water velocity (retardation factor close to 1) and their retention appeared almost insensitive to water flow and ionic strength variations, both factors being known to control bacterial transport in model saturated porous media. In contrast, E. coli breakthrough curves evolved significantly along with the repetition of the cell injections in each soil core, with a progressive acceleration of their transport. The evolution of E. coli cells BTCs was shown to be due to the evolution of the structure of soil hydraulic pathways caused by the repeated water infiltrations and drainage as may occur in the field. This evolution was demonstrated through mercury intrusion porosimetry (MIP) performed on soil aggregates before and after the repeated infiltrations of bacteria. MIP revealed a progressive and important reduction of the soil aggregate porosity, n, that decreased from approximately 0.5 to 0.3, along with a decrease of the soil percolating step from 27 to 2 μm. From this result a clear compaction of soil aggregates was evidenced that concerned preferentially the pores larger than 2 μm equivalent diameter, i.e. those allowing bacterial cell passage. Since no significant reduction of the global soil volume was observed at the core scale, this aggregate compaction was accompanied by macropore formation that became progressively the preferential hydraulic pathway in the soil cores, leading to transiently bi-modal bacterial BTCs. The evolution of the soil pore structure induced a modification of the main hydrodynamic processes, evolving from a matrix-dominant transfer of water and bacteria to a macropore-dominant transfer. This work points out the importance of using undisturbed natural soils to evaluate the mobility of bacteria in the field, since the evolving hydrodynamic properties of soils appeared to dominate most physicochemical factors.

Mechanistic modeling of microbial interactions at pore to profile scale resolve methane emission dynamics from permafrost soil

NASA Astrophysics Data System (ADS)

Ebrahimi, Ali; Or, Dani

2017-05-01

The sensitivity of polar regions to raising global temperatures is reflected in rapidly changing hydrological processes associated with pronounced seasonal thawing of permafrost soil and increased biological activity. Of particular concern is the potential release of large amounts of soil carbon and stimulation of other soil-borne greenhouse gas emissions such as methane. Soil methanotrophic and methanogenic microbial communities rapidly adjust their activity and spatial organization in response to permafrost thawing and other environmental factors. Soil structural elements such as aggregates and layering affect oxygen and nutrient diffusion processes thereby contributing to methanogenic activity within temporal anoxic niches (hot spots). We developed a mechanistic individual-based model to quantify microbial activity dynamics in soil pore networks considering transport processes and enzymatic activity associated with methane production in soil. The model was upscaled from single aggregates to the soil profile where freezing/thawing provides macroscopic boundary conditions for microbial activity at different soil depths. The model distinguishes microbial activity in aerate bulk soil from aggregates (or submerged profile) for resolving methane production and oxidation rates. Methane transport pathways by diffusion and ebullition of bubbles vary with hydration dynamics. The model links seasonal thermal and hydrologic dynamics with evolution of microbial community composition and function affecting net methane emissions in good agreement with experimental data. The mechanistic model enables systematic evaluation of key controlling factors in thawing permafrost and microbial response (e.g., nutrient availability and enzyme activity) on long-term methane emissions and carbon decomposition rates in the rapidly changing polar regions.

Properties of concrete blocks prepared with low grade recycled aggregates.

PubMed

Poon, Chi-Sun; Kou, Shi-cong; Wan, Hui-wen; Etxeberria, Miren

2009-08-01

Low grade recycled aggregates obtained from a construction waste sorting facility were tested to assess the feasibility of using these in the production of concrete blocks. The characteristics of the sorted construction waste are significantly different from that of crushed concrete rubbles that are mostly derived from demolition waste streams. This is due to the presence of higher percentages of non-concrete components (e.g. >10% soil, brick, tiles etc.) in the sorted construction waste. In the study reported in this paper, three series of concrete block mixtures were prepared by using the low grade recycled aggregates to replace (i) natural coarse granite (10mm), and (ii) 0, 25, 50, 75 and 100% replacement levels of crushed stone fine (crushed natural granite <5mm) in the concrete blocks. Test results on properties such as density, compressive strength, transverse strength and drying shrinkage as well as strength reduction after exposure to 800 degrees C are presented below. The results show that the soil content in the recycled fine aggregate was an important factor in affecting the properties of the blocks produced and the mechanical strength deceased with increasing low grade recycled fine aggregate content. But the higher soil content in the recycled aggregates reduced the reduction of compressive strength of the blocks after exposure to high temperature due probably to the formation of a new crystalline phase. The results show that the low grade recycled aggregates obtained from the construction waste sorting facility has potential to be used as aggregates for making non-structural pre-cast concrete blocks.

Impact of an intense rainfall event on soil properties following a wildfire in a Mediterranean environment (North-East Spain).

PubMed

Francos, Marcos; Pereira, Paulo; Alcañiz, Meritxell; Mataix-Solera, Jorge; Úbeda, Xavier

2016-12-01

Intense rainfall events after severe wildfires can have an impact on soil properties, above all in the Mediterranean environment. This study seeks to examine the immediate impact and the effect after a year of an intense rainfall event on a Mediterranean forest affected by a high severity wildfire. The work analyses the following soil properties: soil aggregate stability, total nitrogen, total carbon, organic and inorganic carbon, the C/N ratio, carbonates, pH, electrical conductivity, extractable calcium, magnesium, sodium, potassium, available phosphorous and the sodium and potassium adsorption ratio (SPAR). We sampled soils in the burned area before, immediately after and one year after the rainfall event. The results showed that the intense rainfall event did not have an immediate impact on soil aggregate stability, but a significant difference was recorded one year after. The intense precipitation did not result in any significant changes in soil total nitrogen, total carbon, inorganic carbon, the C/N ratio and carbonates during the study period. Differences were only registered in soil organic carbon. The soil organic carbon content was significantly higher after the rainfall than in the other sampling dates. The rainfall event did increase soil pH, electrical conductivity, major cations, available phosphorous and the SPAR. One year after the fire, a significant decrease in soil aggregate stability was observed that can be attributed to high SPAR levels and human intervention, while the reduction in extractable elements can be attributed to soil leaching and vegetation consumption. Overall, the intense rainfall event, other post-fire rainfall events and human intervention did not have a detrimental impact on soil properties in all probability owing to the flat plot topography. Copyright © 2016 Elsevier B.V. All rights reserved.

Linking crop structure, throughfall, soil surface conditions, runoff and soil detachment: 10 land uses analyzed in Northern Laos.

PubMed

Lacombe, Guillaume; Valentin, Christian; Sounyafong, Phabvilay; de Rouw, Anneke; Soulileuth, Bounsamai; Silvera, Norbert; Pierret, Alain; Sengtaheuanghoung, Oloth; Ribolzi, Olivier

2018-03-01

In Montane Southeast Asia, deforestation and unsuitable combinations of crops and agricultural practices degrade soils at an unprecedented rate. Typically, smallholder farmers gain income from "available" land by replacing fallow or secondary forest by perennial crops. We aimed to understand how these practices increase or reduce soil erosion. Ten land uses were monitored in Northern Laos during the 2015 monsoon, using local farmers' fields. Experiments included plots of the conventional system (food crops and fallow), and land uses corresponding to new market opportunities (e.g. commercial tree plantations). Land uses were characterized by measuring plant cover and plant mean height per vegetation layer. Recorded meteorological variables included rainfall intensity, throughfall amount, throughfall kinetic energy (TKE), and raindrop size. Runoff coefficient, soil loss, and the percentage areas of soil surface types (free aggregates and gravel; crusts; macro-faunal, vegetal and pedestal features; plant litter) were derived from observations and measurements in 1-m 2 micro-plots. Relationships between these variables were explored with multiple regression analyses. Our results indicate that TKE induces soil crusting and soil loss. By reducing rainfall infiltration, crusted area enhances runoff, which removes and transports soil particles detached by splash over non-crusted areas. TKE is lower under land uses reducing the velocity of raindrops and/or preventing an increase in their size. Optimal vegetation structures combine minimum height of the lowest layer (to reduce drop velocity at ground level) and maximum coverage (to intercept the largest amount of rainfall), as exemplified by broom grass (Thysanolaena latifolia). In contrast, high canopies with large leaves will increase TKE by enlarging raindrops, as exemplified by teak trees (Tectona grandis), unless a protective understorey exists under the trees. Policies that ban the burning of multi-layered vegetation structure under tree plantations should be enforced. Shade-tolerant shrubs and grasses with potential economic return could be promoted as understorey. Copyright © 2017 Elsevier B.V. All rights reserved.

Can organic matter hide from decomposers in the labyrinth of soil aggregates? Micro-engineered Soil Chips challenging foraging fungi

NASA Astrophysics Data System (ADS)

Hammer, Edith C.; Aleklett, Kristin; Arellano Caicedo, Carlos G.; Bengtsson, Martin; Micaela Mafla Endara, Paola; Ohlsson, Pelle

2017-04-01

From the point of view of microorganisms, the soil environment is an enormously complex labyrinth with paths and dead-end streets, where resources and shelters are unevenly distributed. We study foraging strategies of soil organisms, especially fungi, and the possibility of physio-spatial stabilization of organic matter by "hiding" in occluded soil spaces. We manipulate growth habitat microstructure with lab-on-a-chip techniques, where we designed complex environments with channels and obstacle at dimensions of the size of hyphae, and construct them in the transparent, gas-permeable polymer PDMS. We fill those with different nutrient solutions or combine with mineral nutrient gradients, and inoculate them with soil organisms. We analyze organisms and substrates with microscopy, fluorescence microscopy and analytical chemistry. We compared different soil litter decomposers and an arbuscular mycorrhizal fungus for their ability to forage through complex air-gap structures and attempt to classify them into functional traits concerning their mycelium directionality, space-exploring approach and ability to grow through acute angles and narrow constrictions. We identified structures which are very difficult to penetrate for most species, and compounds located behind such features may thus be spatially unavailable for decomposers. We discuss our approach in comparison to soil pore space tomographic analyses and findings we made in the pore space of colonized wood biochar.

Effects of soil structure destruction on methane production and carbon partitioning between methanogenic pathways in tropical rain forest soils

NASA Astrophysics Data System (ADS)

Teh, Yit Arn; Silver, Whendee L.

2006-03-01

Controls on methanogenesis are often determined from laboratory incubations of soils converted to slurries. Destruction of soil structure during slurry conversion may disrupt syntrophic associations, kill methanogens, and/or alter the microsite distribution of methanogenic activity, suppressing CH4 production. The effects of slurry conversion on methanogenesis were investigated to determine if disruption of aggregate structure impacted methanogenesis, substrate utilization, and C partitioning between methanogenic pathways. Soils were collected from the tropical rain forest life zone of the Luquillo Experimental Forest, Puerto Rico, and exposed to different physical disturbances, including flooding and physical homogenization. Slurry conversion negatively impacted methanogenesis. Rates of CH4 production declined by a factor of 17 after well-aggregated soils were converted to slurries. Significantly more 13C-acetate was recovered in CO2 compared to CH4 after slurry conversion, suggesting that methanogens consumed less acetate after slurry conversion and may have competed less effectively with other anaerobes for acetate. Isotopic data indicate that the relative partitioning of C between aceticlastic and hydrogenotrophic pathways was unchanged after slurry conversion. These data suggest that experiments which destroy soil structure may significantly underestimate methanogenesis and overestimate the potential for other microorganisms to compete with methanogens for organic substrates. Current knowledge of the factors that regulate methanogenesis in soil may be biased by the findings of slurry-based experiments, that do not accurately represent the complex, spatially heterogeneous conditions found in well-aggregated soils.

Selective nature and inherent variability of interrill erosion across prolonged rainfall simulation

NASA Astrophysics Data System (ADS)

Hu, Y.; Kuhn, N. J.; Fister, W.

2012-04-01

Sediment of interrill erosion has been generally recognized to be selectively enriched with soil organic carbon (SOC) and fine fractions (clay/silt-sized particles or aggregates) in comparison to source area soil. Limited kinetic energy and lack of concentrated runoff are the dominant factors causing selective detachment and transportation. Although enrichment ratios of SOC (ERsoc) in eroded sediment were generally reported > 1, the values varied widely. Causal factors to variation, such as initial soil properties, rainfall properties and experimental conditions, have been extensively discussed. But less attention was directed to the potential influence of prolonged rainfall time onto the temporal pattern of ERsoc. Conservation of mass dictates that ERsoc must be balanced by a decline in the source material which should also lead to a reduced or even negative ERsoc in sediment over time. Besides, the stabilizing effects of structural crust on reducing erosional variation, and the unavoidable variations of erosional response induced by the inherent complexity of interrill erosion, have scarcely been integrated. Moreover, during a prolonged rainfall event surface roughness evolves and affects the movement of eroded aggregates and mineral particles. In this study, two silt loams from Möhlin, Switzerland, organically (OS) and conventionally farmed (CS), were exposed to simulated rainfall of 30 mm h-1 for up to 6 hours. Round donut-flumes with a confined eroding area (1845 cm2) and limited transporting distance (20 cm) were used. Sediments, runoff and subsurface flow were collected in intervals of 30 min. Loose aggregates left on the eroded soil surface, crusts and the soil underneath the crusts were collected after the experiment. All the samples were analyzed for total organic carbon (TOC) content, and texture. Laser scanning of soil surface was applied before and after the rainfall event. The whole experiment was repeated for 10 times. Results from this study showed that: 1) ERsoc in eroded sediment increased at first, then reached steady state and declined afterwards, corresponding well with the formation and completion of structural crust and conservation of mass; 2) the effect of structural crust on stabilizing the surface condition and reducing variation of erosional response was more apparent once steady state discharge was achieved ; and 3) both texture and TOC content in crusts and soil underneath the crusts were comparable to parent soil, explaining the decline in ERsoc. In conclusion, the experiment showed that crusting and conservation of mass lead to a decline and even negative enrichment of organic matter in interrill sediment over time. Enrichment of organic matter should therefore be reported only in conjunction with information about the stage of crust development observed during an erosion event.

Effects of slaking and mechanical breakdown on disaggregation and splash erosion

USDA-ARS?s Scientific Manuscript database

The contributions of different aggregate breakdown mechanisms to splash erosion are still obscure. This study was designed to investigate the effects of different soil disaggregation mechanisms on splash erosion. Loam clay soil, clay loam soil, and sandy loam soil were used in this study. Soil aggre...

Soil quality parameters for row-crop and grazed pasture systems with agroforestry buffers

USDA-ARS?s Scientific Manuscript database

Incorporation of trees and establishment of buffers are practices that can improve soil quality. Soil enzyme activities and water stable aggregates are sensitive indices for assessing soil quality by detecting early changes in soil management. However, studies comparing grazed pasture and row crop...

Evaluation of the strength of cement-treated aggregate for pavement bases.

DOT National Transportation Integrated Search

2006-01-01

Cement-treated aggregate (CTA) is commonly used to provide a stable base for pavements that are placed over weak soil subgrades. Because CTA reduces the thickness of the aggregate required to provide a durable base by approximately one-half, using it...

Microplastics and Nanoplastics in Aquatic Environments: Aggregation, Deposition, and Enhanced Contaminant Transport.

PubMed

Alimi, Olubukola S; Farner Budarz, Jeffrey; Hernandez, Laura M; Tufenkji, Nathalie

2018-02-20

Plastic litter is widely acknowledged as a global environmental threat, and poor management and disposal lead to increasing levels in the environment. Of recent concern is the degradation of plastics from macro- to micro- and even to nanosized particles smaller than 100 nm in size. At the nanoscale, plastics are difficult to detect and can be transported in air, soil, and water compartments. While the impact of plastic debris on marine and fresh waters and organisms has been studied, the loads, transformations, transport, and fate of plastics in terrestrial and subsurface environments are largely overlooked. In this Critical Review, we first present estimated loads of plastics in different environmental compartments. We also provide a critical review of the current knowledge vis-à-vis nanoplastic (NP) and microplastic (MP) aggregation, deposition, and contaminant cotransport in the environment. Important factors that affect aggregation and deposition in natural subsurface environments are identified and critically analyzed. Factors affecting contaminant sorption onto plastic debris are discussed, and we show how polyethylene generally exhibits a greater sorption capacity than other plastic types. Finally, we highlight key knowledge gaps that need to be addressed to improve our ability to predict the risks associated with these ubiquitous contaminants in the environment by understanding their mobility, aggregation behavior and their potential to enhance the transport of other pollutants.

Experimental investigations on mechanical behavior of unsaturated subgrade soil with lime stabilization and fiber reinforcement : final report.

DOT National Transportation Integrated Search

2003-11-01

In the present report, experimental investigations on mechanical behavior of unsaturated subgrade soil : with fiber reinforcement and lime stabilization were conducted. : The soil samples were collected from the soil/aggregate laboratory at the Maryl...

Impact of disturbance on soil microbial activity in the Northern Chihuahuan Desert

USDA-ARS?s Scientific Manuscript database

Cryptobiotic soil crusts in arid regions contribute to ecosystem stability through increased water infiltration, soil aggregate stability, and nutrient cycling between the soil community and vascular plants. These crusts are particularly sensitive to compaction/fracturing disturbances such as livest...

Thermal shock and splash effects on burned gypseous soils from the Ebro Basin (NE Spain)

NASA Astrophysics Data System (ADS)

León, J.; Seeger, M.; Badía, D.; Peters, P.; Echeverría, M. T.

2014-03-01

Fire is a natural factor of landscape evolution in Mediterranean ecosystems. The middle Ebro Valley has extreme aridity, which results in a low plant cover and high soil erodibility, especially on gypseous substrates. The aim of this research is to analyze the effects of moderate heating on physical and chemical soil properties, mineralogical composition and susceptibility to splash erosion. Topsoil samples (15 cm depth) were taken in the Remolinos mountain slopes (Ebro Valley, NE Spain) from two soil types: Leptic Gypsisol (LP) in a convex slope and Haplic Gypsisol (GY) in a concave slope. To assess the heating effects on the mineralogy we burned the soils at 105 and 205 °C in an oven and to assess the splash effects we used a rainfall simulator under laboratory conditions using undisturbed topsoil subsamples (0-5 cm depth of Ah horizon). LP soil has lower soil organic matter (SOM) and soil aggregate stability (SAS) and higher gypsum content than GY soil. Gypsum and dolomite are the main minerals (>80%) in the LP soil, while gypsum, dolomite, calcite and quartz have similar proportions in GY soil. Clay minerals (kaolinite and illite) are scarce in both soils. Heating at 105 °C has no effect on soil mineralogy. However, heating to 205 °C transforms gypsum to bassanite, increases significantly the soil salinity (EC) in both soil units (LP and GY) and decreases pH only in GY soil. Despite differences in the content of organic matter and structural stability, both soils show no significant differences (P < 0.01) in the splash erosion rates. The size of pores is reduced by heating, as derived from variations in soil water retention capacity.

Mechanistic modeling of thermo-hydrological processes and microbial interactions at pore to profile scales resolve methane emission dynamics from permafrost soil

NASA Astrophysics Data System (ADS)

Ebrahimi, Ali; Or, Dani

2017-04-01

The sensitivity of the Earth's polar regions to raising global temperatures is reflected in rapidly changing hydrological processes with pronounced seasonal thawing of permafrost soil and increased biological activity. Of particular concern is the potential release of large amounts of soil carbon and the stimulation of other soil-borne GHG emissions such as methane. Soil methanotrophic and methanogenic microbial communities rapidly adjust their activity and spatial organization in response to permafrost thawing and a host of other environmental factors. Soil structural elements such as aggregates and layering and hydration status affect oxygen and nutrient diffusion processes thereby contributing to methanogenic activity within temporal anoxic niches (hotspots or hot-layers). We developed a mechanistic individual based model to quantify microbial activity dynamics within soil pore networks considering, hydration, temperature, transport processes and enzymatic activity associated with methane production in soil. The model was the upscaled from single aggregates (or hotspots) to quantifying emissions from soil profiles in which freezing/thawing processes provide macroscopic boundary conditions for microbial activity at different soil depths. The model distinguishes microbial activity in aerate bulk soil from aggregates (or submerged parts of the profile) for resolving methane production and oxidation rates. Methane transport pathways through soil by diffusion and ebullition of bubbles vary with hydration dynamics and affect emission patterns. The model links seasonal thermal and hydrologic dynamics with evolution of microbial community composition and function affecting net methane emissions in good agreement with experimental data. The mechanistic model enables systematic evaluation of key controlling factors in thawing permafrost and microbial response (e.g., nutrient availability, enzyme activity, PH) on long term methane emissions and carbon decomposition rates in the rapidly changing polar regions.

Quantification of spatial distribution and spread of bacteria in soil at microscale

NASA Astrophysics Data System (ADS)

Juyal, Archana; Eickhorst, Thilo; Falconer, Ruth; Baveye, Philippe; Otten, Wilfred

2015-04-01

Soil bacteria play an essential role in functioning of ecosystems and maintaining of biogeochemical cycles. Soil is a complex heterogeneous environment comprising of highly variable and dynamic micro-habitats that have significant impacts on the growth and activity of resident microbiota including bacteria and fungi. Bacteria occupy a very small portion of available pore space in soil which demonstrates that their spatial arrangement in soil has a huge impact on the contact to their target and on the way they interact to carry out their functions. Due to limitation of techniques, there is scant information on spatial distribution of indigenous or introduced bacteria at microhabitat scale. There is a need to understand the interaction between soil structure and microorganisms including fungi for ecosystem-level processes such as carbon sequestration and improving the predictive models for soil management. In this work, a combination of techniques was used including X-ray CT to characterize the soil structure and in-situ detection via fluorescence microscopy to visualize and quantify bacteria in soil thin sections. Pseudomonas fluorescens bacteria were introduced in sterilized soil of aggregate size 1-2 mm and packed at bulk-densities 1.3 g cm-3 and 1.5 g cm-3. A subset of samples was fixed with paraformaldehyde and subsequently impregnated with resin. DAPI and fluorescence in situ hybridization (FISH) were used to visualize bacteria in thin sections of soil cores by epifluorescence microscopy to enumerate spatial distribution of bacteria in soil. The pore geometry of soil was quantified after X-ray microtomography scanning. The distribution of bacteria introduced locally reduced significantly (P

Growing into and out of the bouncing barrier in planetesimal formation

NASA Astrophysics Data System (ADS)

Kruss, Maximilian; Teiser, Jens; Wurm, Gerhard

2017-04-01

In recent laboratory studies the robustness of a bouncing barrier in planetesimal formation was studied with an ensemble of pre-formed compact mm-sized aggregates. Here we show that a bouncing barrier indeed evolves self-consistently by hit-and-stick from an ensemble of smaller dust aggregates. In addition, we feed small aggregates to an ensemble of larger bouncing aggregates. The stickiness temporarily increases, but the final number of aggregates still bouncing remains the same. However, feeding on the small particle supply, the size of the bouncing aggregates increases. This suggests that in the presence of a dust reservoir aggregates grow into but also out of a bouncing barrier at larger size.

Local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula

NASA Astrophysics Data System (ADS)

Lorek, S.; Lacerda, P.; Blum, J.

2018-03-01

Context. Comet formation by gravitational instability requires aggregates that trigger the streaming instability and cluster in pebble-clouds. These aggregates form as mixtures of dust and ice from (sub-)micrometre-sized dust and ice grains via coagulation in the solar nebula. Aim. We investigate the growth of aggregates from (sub-)micrometre-sized dust and ice monomer grains. We are interested in the properties of these aggregates: whether they might trigger the streaming instability, how they compare to pebbles found on comets, and what the implications are for comet formation in collapsing pebble-clouds. Methods: We used Monte Carlo simulations to study the growth of aggregates through coagulation locally in the comet-forming region at 30 au. We used a collision model that can accommodate sticking, bouncing, fragmentation, and porosity of dust- and ice-mixed aggregates. We compared our results to measurements of pebbles on comet 67P/Churyumov-Gerasimenko. Results: We find that aggregate growth becomes limited by radial drift towards the Sun for 1 μm sized monomers and by bouncing collisions for 0.1 μm sized monomers before the aggregates reach a Stokes number that would trigger the streaming instability (Stmin). We argue that in a bouncing-dominated system, aggregates can reach Stmin through compression in bouncing collisions if compression is faster than radial drift. In the comet-forming region ( 30 au), aggregates with Stmin have volume-filling factors of 10-2 and radii of a few millimetres. These sizes are comparable to the sizes of pebbles found on comet 67P/Churyumov-Gerasimenko. The porosity of the aggregates formed in the solar nebula would imply that comets formed in pebble-clouds with masses equivalent to planetesimals of the order of 100 km in diameter.

Incorporation of digestate selectively affects physical, chemical and biochemical properties along with CO2 emissions in two contrasting agricultural soils in the Mediterranean area.

NASA Astrophysics Data System (ADS)

Badagliacca, Giuseppe; Petrovičová, Beatrix; Zumbo, Antonino; Romeo, Maurizio; Gullì, Tommaso; Martire, Luigi; Monti, Michele; Gelsomino, Antonio

2017-04-01

Soil incorporation of digestate represents a common practice to dispose the solid residues from biogas producing plants. Although the digestate constitutes a residual biomass rich in partially decomposed organic matter and nutrients, whose content is often highly variable and unbalanced, its potential fertilizer value can vary considerably depending on the recipient soil properties. The aim of the work was to assess short-term changes in the fertility status of two contrasting agricultural soils in Southern Italy (Calabria), olive grove on a clay acid soil (Typic Hapludalfs) and citrus grove on a sandy loam slightly calcareous soil (Typic Xerofluvents), respectively located along the Tyrrhenian or the Ionian coast. An amount of 30 t ha-1 digestate was incorporated into the soil by ploughing. Unamended tilled soil was used as control. The following soil physical, chemical and biochemical variables were monitored during the experimental period: aggregate stability, pH, electrical conductivity, organic C, total N, Olsen-P, N-NH4+, N-NO3-, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and the mineralization quotient (qM). Moreover, in the olive grove soil CO2 emissions have been continuously measured at field scale for 5 months after digestate incorporation. Digestate application in both site exerted a significant positive effect on soil aggregate stability with a greater increase in clay than in sandy loam soil. Over the experimental period, digestate considerably affected the nutrient availability, namely Olsen-P, N-NH4+, N-NO3-, along with the electrical conductivity. The soil type increased significantly the soil N-NH4+ content, which was always higher in the olive than in citrus grove soil. N-NO3- content was markedly increased soon after the organic amendment, followed by a seasonal decline more evident in the sandy loam soil. Moreover, soil properties as CaCO3 content and the pH selectively affected the Olsen-P dynamics. No appreciable variation was recorded in total C and N pools. Interestingly, amendment with digestate altered the soil microbial community size in both soils as MBC and MBN were increased, although the response was more evident in the clay soil (olive) than in the sandy loam (citrus) one. The considerably higher qM observed in the clay soil suggests that the C mineralization was selectively stimulated in this soil. This finding was confirmed by the increase of CO2 emissions. As a whole our results show that digestate application selectively stimulated soil C dynamics and determined an unbalanced nutrient release, strongly depending on the soil physical-chemical properties. The use of digestate can therefore represent an interesting strategy for managing the soil fertility in Mediterranean agroecosystem soils, provided that digestate and recipient soil properties are carefully taken into account.

From the study of fire effects on individual soil properties to the development of soil quality indices. 1. The pioneer research

NASA Astrophysics Data System (ADS)

Mataix-Solera, Jorge; Zornoza, Raúl

2013-04-01

Although forest fires must be considered as a natural factor in Mediterranean ecosystems, the modification of its natural regime during last five decades has thansformed them in an environmental problem. In the Valencia region (E Spain) 1994 was the worst year in the history affecting more than 120,000 hectares. I started my Ph.D that year by studying the effects of fires in soil properties. The availability to be able to analyse a great set of different types of soil properties in the laboratories of University of Alicante allowed me to explore how fires could affect physical, chemical and micobiological soil properties. After years studying different soil properties, finding that several factors are involved, including: fire intensity and severity, vegetation, soil type, climate conditions, etc. (Mataix-Solera and Doerr, 2004; Mataix-Solera et al., 2008, 2011) my research as Ph-D supervisor has been focussed to investigate more in depth some selected properties, such as aggregate stability and water repellency (Arcenegui et al., 2007, 2008). But one of the main problems in the studies conducted with samples affected by wildfires is that for the evaluation of the fire impact in the soil it is necessary to have control (unburned) soil samples from a similar non-affected near area. The existing spatial variability under field conditions does not allow having comparable samples in some acses to develop a correct assessment. With this idea in mind one of my Ph.D researcher (R. Zornoza) dedicated his thesis to develope soil quality indices capable to assess the impact of soil perturbations without comparing groups of samples, but evaluating the equilibrium among different soil properties within each soil sample (Zornoza et al., 2007, 2008). Key words: wildfire, Mediterranean soils, soil degradation, wàter repellency, aggregate stability References: Arcenegui, V., Mataix-Solera, J., Guerrero, C., Zornoza, R., Mayoral, A.M., Morales, J., 2007. Factors controlling the water repellency induced by fire in calcareous Mediterranean forest soils. Eur. J. Soil Sci. 58, 1254-1259. Arcenegui, V., Mataix-Solera, J., Guerrero, C., Zornoza, R., Mataix-Beneyto, J., García-Orenes, F., 2008. Immediate effects of wildfires on water repellency and aggregate stability in Mediterranean calcareous soils. Catena 74, 219-226. Mataix-Solera, J., Doerr, S.H., 2004. Hydrophobicity and aggregate stability in calcareous topsoil from fire affected pine forests in southeastern Spain. Geoderma 118, 77-88. Mataix-Solera, J., Arcenegui, V., Guerrero, C., Jordán, M., Dlapa, P., Tessler, N., Wittenberg, L. 2008. Can terra rossa become water repellent by burning? A laboratory approach. Geoderma, 147, 178-184. Mataix-Solera, J., Cerdà, A., Arcenegui, V., Jordán, A., Zavala, L.M., 2011. Fire effects on soil aggregation: a review. Earth-Science Reviews 109, 44-60 Zornoza, R., Mataix-Solera, J., Guerrero, C., Arcenegui, V., Mayoral, A.M., Morales, J. Mataix-Beneyto, J., 2007b. Soil properties under natural forest in the Alicante Province of Spain. Geoderma. 142, 334-341. Zornoza, R., Mataix-Solera, J., Guerrero, C., Arcenegui, V., Mataix-Beneyto, J., Gómez, I., 2008. Validating the effectiveness and sensitivity of two soil quality indices based on natural forest soils under Mediterranean conditions. Soil Biology & Biochemistry. 40, 2079-2087.

Formation of Nanophase Iron in Lunar Soil Simulant for Use in ISRU Studies

NASA Technical Reports Server (NTRS)

Liu, Yang; Taylor, Lawrence A.; Hill, Eddy; Day, James D. M.

2005-01-01

For the prospective return of humans to the Moon and the extensive amount of premonitory studies necessary, large quantities of lunar soil simulants are required, for a myriad of purposes from construction/engineering purposes all the way to medical testing of its effects from ingestion by humans. And there is only a limited and precious quantity of lunar soil available on Earth (i.e., Apollo soils) - therefore, the immediate need for lunar soil simulants. Since the Apollo era, there have been several simulants; of these JSC-1 (Johnson Space Center) and MLS-1 (Minnesota Lunar Simulant) have been the most widely used. JSC-1 was produced from glassy volcanic tuff in order to approximate lunar soil geotechnical properties; whereas, MLS-1 approximates the chemistry of Apollo 11 high-Ti soil, 10084. Stocks of both simulants are depleted, but JSC-1 has recently gone back into production. The lunar soil simulant workshop, held at Marshall Space Flight Center in January 2005, identified the need to make new simulants for the special properties of lunar soil, such as nanophase iron (np-Fe(sup 0). Hill et al. (2005, this volume) showed the important role of microscale Fe(sup 0) in microwave processing of the lunar soil simulants JSC-1 and MLS-1. Lunar soil is formed by space weathering of lunar rocks (e.g., micrometeorite impact, cosmic particle bombardment). Glass generated during micrometeorite impact cements rock and mineral fragments together to form aggregates called agglutinates, and also produces vapor that is deposited and coats soil grains. Taylor et al. (2001) showed that the relative amount of impact glass in lunar soil increases with decreasing grain size and is the most abundant component in lunar dust (less than 20 micrometer fraction). Notably, the magnetic susceptibility of lunar soil also increases with the decreasing grain size, as a function of the amount of nanophase-sized Fe(sup 0) in impact-melt generated glass. Keller et al. (1997, 1999) also discovered the presence of abundant np-Fe(sup 0) particles in the glass patinas coating most soil particles. Therefore, the correlation of glass content and magnetic susceptibility can be explained by the presence of the np-Feo particles in glass: small particles contain relatively more np-Fe(sup 0) as glass coatings because the surface area versus mass ratio of the grain size is so increased. The magnetic properties of lunar soil are important in dust mitigation on the Moon (Taylor et al. 2005). Thus material simulating this property is important for testing mitigation methods using electromagnetic field. This np- Fe(sup 0) also produces a unique energy coupling to normal microwaves, such as present in kitchen microwave ovens. Effectively, a portion of lunar soil placed in a normal 2.45 GHz oven will melt at greater than 1200 C before your tea will boil at 100 C, a startling and new discovery reported by Taylor and Meek (2004, 2005). Several methods have been investigated in attempts to make nanophase-sized Feo dispersed within silicate glass; like in the lunar glass. We have been successful in synthesizing such a product and continue to improve on our recipe. We have performed extensive experimentation on this subject to date. Ultimately it will probably be necessary to add this np-Fe(sup 0) bearing silicate glass to lunar soil stimulant, like JSC-1, to actually produce the desired magnetic and microwave coupling properties for use in appropriate ISRU experimentation.

Torsional Shear Device for Testing the Dynamic Properties of Recycled Material

NASA Astrophysics Data System (ADS)

Gabryś, Katarzyna; Sas, Wojciech; Soból, Emil; Głuchowski, Andrzej

2016-12-01

From the viewpoint of environmental preservation and effective utilization of resources, it is beneficial and necessary to reuse wastes, for example, concrete, as the recycled aggregates for new materials. In this work, the dynamic behavior of such aggregates under low frequency torsional loading is studied. Results show that the properties of such artificial soils match with those reported in the literature for specific natural soils.

Can biosolids reduce wind erosion of agricultural soils?

USDA-ARS?s Scientific Manuscript database

The application of biosolids to agricultural land has the potential to improve soil health and crop production. In addition, organic material contained in biosolids may enhance biological activity, retention of soil water, and soil aggregation. Thus, there is a likelihood that biosolids applied to s...

Reconciling opposing soil processes in row-crop agroecosystems via soil functional zone management

USDA-ARS?s Scientific Manuscript database

Sustaining soil productivity in agroecosystems presents a fundamental ecological challenge: nutrient provisioning depends upon aggregate turnover and microbial decomposition of organic matter (SOM); yet to prevent soil depletion these processes must be balanced by those that restore nutrients and SO...

Mixed region reactors for in situ treatment of DNAPL contaminated low permeability media

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, O.R.; Siegrist, R.L.

1996-08-01

Fine-textured soils and sediments contaminated by dense non-aqueous phase liquids (DNAPLs) present a significant environmental restoration challenge. An emerging approach to rapid in situ treatment within low permeability media involves the use of soil mixing to create mixed region reactors wherein biological or physical/chemical treatment processes can be employed. In cohesive soils, mixing breaks up the original soil structure and produces soil aggregates or clods separated by interaggregate void spaces. These void spaces create preferential flow paths for more efficient extraction of contaminants from the soil matrix or more rapid diffusion of treatment agents into the soil aggregates. This enhancementmore » technology has been most successfully used with vapor stripping. However, other technologies can also be coupled with soil mixing including chemical degradation, biodegradation and solidification. The application of this technology to DNAPL-contaminated low permeability media appears promising but requires further experiments and models that can simulate the movement of DNAPLs in mixed regions. 11 refs., 6 figs.« less

Can ectomycorrhizal symbiosis and belowground plant traits be used as ecological tools to mitigate erosion on degraded slopes in the ultramafic soils of New Caledonia?

NASA Astrophysics Data System (ADS)

Demenois, Julien; Carriconde, Fabian; Rey, Freddy; Stokes, Alexia

2015-04-01

New Caledonia is an archipelago in the South West Pacific located just above the Tropic of Capricorn. The main island is bisected by a continuous mountain chain whose highest peaks reach more than 1 600 m. With mean annual rainfall above 2 000 mm in the South of the main island, frequent downpours and steep slopes, its soils are prone to water erosion. Deforestation, fires and mining activity are the main drivers of water erosion. Stakes are high to mitigate the phenomenon: extraction of nickel from ultramafic substrates (one third of the whole territory) is the main economic activity; New Caledonia is considered as a biodiversity hotspot. Restoration ecology is seen as a key approach for tackling such environmental challenges. Soil microorganisms could play significant roles in biological processes such as plant nutrition and plant resistance to abiotic and biotic stresses. Microorganisms could increase soil aggregate stability and thus mitigate soil erodibility. Plant roots increase soil cohesion through exudation and decomposition processes. To date, few studies have collected data on the soil aggregate stability of steep slopes affected by erosion and, to our knowledge, interactions between ectomycorrhizas (ECM), roots and erodibility of ultramafic soils have never been considered. The objective of our study is to assess the influence of ECM symbiosis and plant root traits on the erodibility of ultramafic soils of New Caledonia and answer the following questions: 1/ What is the influence of plant root traits of vegetal communities and ECM fungal diversity on soil erodibility? 2/ What are the belowground plant traits of some mycorrhized endemic species used in ecological restoration? 3/ What is the influence of plant root traits and ECM fungal inoculation on soil erodibility? At the scale of plant communities, five types of vegetation have been chosen in the South of the main island: degraded ligno-herbaceous shrubland, ligno-herbaceous shrubland, degraded humid forest with dominance of Arillastrum gummiferum, dense humid forest with dominance of Nothofagus aequilateralis, and finally mixed dense humid forest. These types of vegetation are widely represented on ultramafic soils of New Caledonia and are likely to correspond to different successional phases. At the scale of species, dominant species in the above-mentioned types of vegetation are considered for herbaceous, shrubs and trees strata. Root traits of Costularia nervosa, Tristaniopsis glauca, Nothofagus aequilateralis and Arillastrum gummiferum are then characterized in situ. These species are of particular interest for post-mining ecological restoration in New Caledonia as they are light-tolerant, endemic, associated with ECM (except for Costularia nervosa) and of particular interest or already used by mining operators for post-mining ecological restoration. For both scales (community and species), soil characteristics will be collected. Very fine and fine roots, mean root diameter, root diameter diversity, root mass density, root length density, and specific root length will be considered. Degree of ectomycorrhization and fungal biomass through qPCR will be determined. Soil aggregate stability will be measured according to the standardized method NF X 31-515. Besides, greenhouse trials with Costularia nervosa, Tristaniopsis glauca and Arillastrum gummiferum are carried out to assess the influence of plant root traits, fungal inoculation and soil aggregate stability. Controlled plant inoculations are performed using available pure fungal strains isolated from New Caledonian ultramafic soils. Plants have been bred on sterilized soil samples from the field sites. Through this study, we target to identify associations between ECM fungi and plant species that could mitigate the erodibility of degraded ultramafic soils and then water erosion. A better knowledge of interactions between soil aggregate stability, ECM fungi and plant root traits is then expected to answer the following question: can soil aggregate stability be used as a bio-indicator of ecosystem functioning and services?