Native soil organic matter conditions the response of microbial communities to organic inputs with different stability

NASA Astrophysics Data System (ADS)

Yanardaǧ, Ibrahim H.; Zornoza, Raúl; Bastida, Felipe; Büyükkiliç-Yanardaǧ, Asuman; Acosta, Jose A.; García, Carlos; Faz, Ángel; Mermut, Ahmet R.

2017-04-01

The response of soil microbial communities from soils with different soil organic matter (SOM) content to organic inputs with different stability is still poorly understood. Thus, an incubation experiment was designed to study how the addition of pig slurry (PS), its manure (M) and its biochar (BC) affect soil microbial community and activity in three soils differing in SOM content (Regosol, Luvisol and Kastanozem). The evolution of different C and N fractions, microbial biomass C and N, enzyme activities and microbial community structure by the use of phospholipid fatty acid (PLFA) analysis was assessed for 60 days. Results showed that the different amendments had different effect on microbial properties depending on the soil type. The addition of M caused the highest increase in all microbial properties in the three soils, followed by PS. These changes were more intense in the soil with the lowest SOM (Regosol). The addition of M and PS caused changes in the microbial community structure in all soils, which were more related to the presence of available sources of N than to the labile fractions of C. The addition of BC was followed by increases in the proportions of fungi and Gram positive bacteria in the Regosol, while enhanced the proportion of actinobacteria in all soil types, related to increments in pH and soil C recalcitrance. Thus, native SOM determined the response of microbial communities to external inputs with different stability, soils with low SOM being more prone to increase microbial biomass and activity and change microbial community structure.

Strength Analysis of Coconut Fiber Stabilized Earth for Farm Structures

NASA Astrophysics Data System (ADS)

Enokela, O. S.; P. O, Alada

2012-07-01

Investigation of the strength characteristic of soil from alluvial deposit of River Benue in makurdi stabilized with coconut fiber as a stabilizer was carried as local building material for farm structure. Processed coconut fibers were mixed with the soil at four different mix ratios of 1% fiber, 2% fiber, 3% fiber and 4% fiber by percentage weight with 0% fiber as control. Compaction test and compressive strength were carried out on the various stabilizing ratio. From the compaction test, the correlation between the maximum dry density and optimum moisture content is a second order polynomial with a coefficient of 63% obtained at1.91kg/m3and 20.0% respectively while the compressive strength test shows an optimum failure load of 8.62N/mm2 at 2%fibre:100% soil mix ratio at 2.16 maximum dry density.

Enhancing soil begins with soil biology and a stable soil microclimate

USDA-ARS?s Scientific Manuscript database

Protection of the soil resource from erosion requires reducing the surface impact from raindrop energy and maintaining soil structure and stability to allow more efficient infiltration of water into the soil column. These two processes are linked with practices associated with enhancing and maintain...

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.

Prototype reinforced soil embankment for reconstruction of US route 62 slope failure in Chickasha, OK.

DOT National Transportation Integrated Search

2015-01-01

One of the main concerns in internal stability of reinforced soil structures constructed with fine-grained or : marginal quality soils is the change in shear strength of the soil-reinforcement interface when the soil gravimetric water : content (GWC)...

Prototype reinforced soil embankment for reconstruction of US 62 slope failure in Chickasha, OK.

DOT National Transportation Integrated Search

2013-05-01

One of the main concerns in internal stability of reinforced soil structures constructed with fine-grained or marginal quality soils is the change in shear strength of the soil-reinforcement interface when the soil gravimetric water content (GWC) inc...

Soil physical conditions as livestock treading effect in tropical Agroecosystem of dryland and strategies to mitigate desertification risk

NASA Astrophysics Data System (ADS)

Florentino, A.; Torres, D.; Ospina, A.; Contreras, J.; Palma, Z.; Silvera, J.

2012-04-01

Soil degradation in natural ecosystem of arid and semi-arid zones of Venezuela due to livestock treading (goats) it is an important problem that affect their environment functions; increase soil erodibility, bulk density, water losses and reduce porosity, water infiltration rate and soil structural stability. The presence of biological crust (BSC) in this type of soil it is very common. The objective of this study was to evaluate the soil surface physical quality through the use of selected indicators, mainly some of that related to structural stability, infiltrability and the prediction of soil erosion risk in two zones of Lara state: 1) Quíbor (QUI) and 2) Humocaro Bajo (HB). The study was conducted on two selected plots (30 m x 20 m) in each zone, with natural vegetation and BSC cover, with areas affected by different degree of compaction due to treading in the paths where the goats are moving. Five sites per plot (50 cm x 50 cm) under vegetation cover and five sites over the path with bare soil were sampled (0-7,5 and 7,5-15 cm depth). The results showed that soil macroaggregate stability (equivalent diameter of aggregates >0,25 mm) was significantly higher (p<0,05 %) in soil with vegetation cover and BSC compared with bare soil. Sealing index, as a measure of aggregate stability, determined in laboratory under simulated rain and expressed as hydraulic conductivity of soil surface sealing (Kse), decreased with decreasing soil vegetation cover and the presence of BSC. However, Ksei (i: inicial) and Ksef (f: final) were significantly greater in soil with more than 75 % of BSC in comparison to bare soils. The sealing index it is used to for to estimate changes in soil water losses. As the sealing index increases, the susceptibility of the soil to undergo surface sealing or slaking decrease. These results suggested that soil physical properties are potential indicators of soil quality with regard to soil erodibility and showed that soils under vegetation cover had higher quality level than bare soils. Some predictive regression equation had a high R2 value and was a useful tool for to evaluate the risk of extreme climatic changes and to mitigate their detrimental effects. We conclude that the global climatic change (CCG) will have a negative effect on these agroecosystems functions, mainly in soil and water conservation, carbon sequestration, and productivity. Natural recovery of soil physical properties from treading damage of pastoral soils will be possible in the future with the implementation of soil management strategies, mainly through re-vegetation and recuperation of the BSC. Key word: Soil structure; aggregate stability; soil sealing index; hydraulic conductivity of surface sealing.

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.

[Stabilization of Cadmium Contaminated Soils by Ferric Ion Modified Attapulgite (Fe/ATP)--Characterizations and Stabilization Mechanism].

PubMed

Rong, Yang; Li, Rong-bo; Zhou, Yong-li; Chen, Jing; Wang, Lin-ling; Lu, Xiao-hua

2015-08-01

Ferric ion modified attapulgite (Fe/ATP) was prepared by impregnation and its structure and morphology were characterized. The toxicity characteristic leaching procedure (TCLP) was used to evaluate the effect of Cadmium( Cd) stabilization in soil with the addition of attapulgite (ATP) and Fe/ATP. The stabilization mechanism of Cd was further elucidated by comparing the morphologies and structure of ATP and Fe/ATP before and after Cd adsorption. Fe/ATP exhibited much better adsorption capacity than ATP, suggesting different adsorption mechanisms occurred between ATP and Fe/ATP. The leaching concentrations of Cd in soil decreased by 45% and 91% respectively, with the addition of wt. 20% ATP and Fe/ATP. The former was attributed to the interaction between Cd2 and --OH groups by chemical binding to form inner-sphere complexes in ATP and the attachment between Cd2+ and the defect sites in ATP framework. Whereas Cd stabilization with Fe/ATP was resulted from the fact that the active centers (--OH bonds or O- sites) on ATP could react with Fe3+ giving Fe--O--Cd-- bridges, which helped stabilize Cd in surface soil. What'more, the ferric oxides and metal hydroxides on the surface of ATP could interact with Cd, probably by the formation of cadmium ferrite. In conclusion, Fe/ATP, which can be easily prepared, holds promise as a potential low-cost and environmental friendly stabilizing agent for remediation of soil contaminated with heavy metals.

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.

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.

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.

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.

Carbon stabilization and microbial growth in acidic mine soils after addition of different amendments for soil reclamation

NASA Astrophysics Data System (ADS)

Zornoza, Raúl; Acosta, Jose; Ángeles Muñoz, María; Martínez-Martínez, Silvia; Faz, Ángel; Bååth, Erland

2016-04-01

The extreme soil conditions in metalliferous mine soils have a negative influence on soil biological activity and therefore on soil carbon estabilization. Therefore, amendments are used to increase organic carbon content and activate microbial communities. In order to elucidate some of the factors controlling soil organic carbon stabilization in reclaimed acidic mine soils and its interrelationship with microbial growth and community structure, we performed an incubation experiment with four amendments: pig slurry (PS), pig manure (PM) and biochar (BC), applied with and without marble waste (MW; CaCO3). Results showed that PM and BC (alone or together with MW) contributed to an important increment in recalcitrant organic C, C/N ratio and aggregate stability. Bacterial and fungal growths were highly dependent on pH and labile organic C. PS supported the highest microbial growth; applied alone it stimulated fungal growth, and applied with MW it stimulated bacterial growth. BC promoted the lowest microbial growth, especially for fungi, with no significant increase in fungal biomass. MW+BC increased bacterial growth up to values similar to PM and MW+PM, suggesting that part of the biochar was degraded, at least in short-term mainly by bacteria rather than fungi. PM, MW+PS and MW+PM supported the highest microbial biomass and a similar community structure, related with the presence of high organic C and high pH, with immobilization of metals and increased soil quality. BC contributed to improved soil structure, increased recalcitrant organic C, and decreased metal mobility, with low stimulation of microbial growth.

Jatropha curcas L. Root Structure and Growth in Diverse Soils

PubMed Central

Valdés-Rodríguez, Ofelia Andrea; Sánchez-Sánchez, Odilón; Pérez-Vázquez, Arturo; Caplan, Joshua S.; Danjon, Frédéric

2013-01-01

Unlike most biofuel species, Jatropha curcas has promise for use in marginal lands, but it may serve an additional role by stabilizing soils. We evaluated the growth and structural responsiveness of young J. curcas plants to diverse soil conditions. Soils included a sand, a sandy-loam, and a clay-loam from eastern Mexico. Growth and structural parameters were analyzed for shoots and roots, although the focus was the plasticity of the primary root system architecture (the taproot and four lateral roots). The sandy soil reduced the growth of both shoot and root systems significantly more than sandy-loam or clay-loam soils; there was particularly high plasticity in root and shoot thickness, as well as shoot length. However, the architecture of the primary root system did not vary with soil type; the departure of the primary root system from an index of perfect symmetry was 14 ± 5% (mean ± standard deviation). Although J. curcas developed more extensively in the sandy-loam and clay-loam soils than in sandy soil, it maintained a consistent root to shoot ratio and root system architecture across all types of soil. This strong genetic determination would make the species useful for soil stabilization purposes, even while being cultivated primarily for seed oil. PMID:23844412

Jatropha curcas L. root structure and growth in diverse soils.

PubMed

Valdés-Rodríguez, Ofelia Andrea; Sánchez-Sánchez, Odilón; Pérez-Vázquez, Arturo; Caplan, Joshua S; Danjon, Frédéric

2013-01-01

Unlike most biofuel species, Jatropha curcas has promise for use in marginal lands, but it may serve an additional role by stabilizing soils. We evaluated the growth and structural responsiveness of young J. curcas plants to diverse soil conditions. Soils included a sand, a sandy-loam, and a clay-loam from eastern Mexico. Growth and structural parameters were analyzed for shoots and roots, although the focus was the plasticity of the primary root system architecture (the taproot and four lateral roots). The sandy soil reduced the growth of both shoot and root systems significantly more than sandy-loam or clay-loam soils; there was particularly high plasticity in root and shoot thickness, as well as shoot length. However, the architecture of the primary root system did not vary with soil type; the departure of the primary root system from an index of perfect symmetry was 14 ± 5% (mean ± standard deviation). Although J. curcas developed more extensively in the sandy-loam and clay-loam soils than in sandy soil, it maintained a consistent root to shoot ratio and root system architecture across all types of soil. This strong genetic determination would make the species useful for soil stabilization purposes, even while being cultivated primarily for seed oil.

Effect of acid rain pH on leaching behavior of cement stabilized lead-contaminated soil.

PubMed

Du, Yan-Jun; Wei, Ming-Li; Reddy, Krishna R; Liu, Zhao-Peng; Jin, Fei

2014-04-30

Cement stabilization is a practical approach to remediate soils contaminated with high levels of lead. However, the potential for leaching of lead out of these stabilized soils under variable acid rain pH conditions is a major environmental concern. This study investigates the effects of acid rain on the leaching characteristics of cement stabilized lead contaminated soil under different pH conditions. Clean kaolin clay and the same soil spiked with 2% lead contamination are stabilized with cement contents of 12 and 18% and then cured for 28 days. The soil samples are then subjected to a series of accelerated leaching tests (or semi-dynamic leaching tests) using a simulated acid rain leachant prepared at pH 2.0, 4.0 or 7.0. The results show that the strongly acidic leachant (pH ∼2.0) significantly altered the leaching behavior of lead as well as calcium present in the soil. However, the differences in the leaching behavior of the soil when the leachant was mildly acidic (pH ∼4.0) and neutral (pH ∼7.0) prove to be minor. In addition, it is observed that the lead contamination and cement content levels can have a considerable impact on the leaching behavior of the soils. Overall, the leachability of lead and calcium is attributed to the stability of the hydration products and their consequent influence on the soil buffering capacity and structure. Copyright © 2014 Elsevier B.V. All rights reserved.

Impact of monovalent cations on soil structure. Part II. Results of two Swiss soils

NASA Astrophysics Data System (ADS)

Farahani, Elham; Emami, Hojat; Keller, Thomas

2018-01-01

In this study, we investigated the impact of adding solutions with different potassium and sodium concentrations on dispersible clay, water retention characteristics, air permeability, and soil shrinkage behaviour using two agricultural soils from Switzerland with different clay content but similar organic carbon to clay ratio. Three different solutions (including only Na, only K, and the combination of both) were added to soil samples at three different cation ratio of soil structural stability levels, and the soil samples were incubated for one month. Our findings showed that the amount of readily dispersible clay increased with increasing Na concentrations and with increasing cation ratio of soil structural stability. The treatment with the maximum Na concentration resulted in the highest water retention and in the lowest shrinkage capacity. This was was associated with high amounts of readily dispersible clay. Air permeability generally increased during incubation due to moderate wetting and drying cycles, but the increase was negatively correlated with readily dispersible clay. Readily dispersible clay decreased with increasing K, while readily dispersible clay increased with increasing K in Iranian soil (Part I of our study). This can be attributed to the different clay mineralogy of the studied soils (muscovite in Part I and illite in Part II).

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.

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

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.

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.

Visual soil evaluation - future research requirements

NASA Astrophysics Data System (ADS)

Emmet-Booth, Jeremy; Forristal, Dermot; Fenton, Owen; Ball, Bruce; Holden, Nick

2017-04-01

A review of Visual Soil Evaluation (VSE) techniques (Emmet-Booth et al., 2016) highlighted their established utility for soil quality assessment, though some limitations were identified; (1) The examination of aggregate size, visible intra-porosity and shape forms a key assessment criterion in almost all methods, thus limiting evaluation to structural form. The addition of criteria that holistically examine structure may be desirable. For example, structural stability can be indicated using dispersion tests or examining soil surface crusting, while the assessment of soil colour may indirectly indicate soil organic matter content, a contributor to stability. Organic matter assessment may also indicate structural resilience, along with rooting, earthworm numbers or shrinkage cracking. (2) Soil texture may influence results or impeded method deployment. Modification of procedures to account for extreme texture variation is desirable. For example, evidence of compaction in sandy or single grain soils greatly differs to that in clayey soils. Some procedures incorporate separate classification systems or adjust deployment based on texture. (3) Research into impacts of soil moisture content on VSE evaluation criteria is required. Criteria such as rupture resistance and shape may be affected by moisture content. It is generally recommended that methods are deployed on moist soils and quantification of influences of moisture variation on results is necessary. (4) Robust sampling strategies for method deployment are required. Dealing with spatial variation differs between methods, but where methods can be deployed over large areas, clear instruction on sampling is required. Additionally, as emphasis has been placed on the agricultural production of soil, so the ability of VSE for exploring structural quality in terms of carbon storage, water purification and biodiversity support also requires research. References Emmet-Booth, J.P., Forristal. P.D., Fenton, O., Ball, B.C. & Holden, N.M. 2016. A review of visual soil evaluation techniques for soil structure. Soil Use and Management, 32, 623-634.

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

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.

Soil stability characteristics of mulberry lands at hydro-fluctuation belt in the Three Gorges Reservoir area, China.

PubMed

Jiang, Ping; Shi, Dongmei; Hu, Xueqin; Huang, Xianzhi; Li, Yexin; Guo, Tianlei

2015-10-01

The hydro-fluctuation belt in the Three Gorges Reservoir area is a typical seasonal and artificial wetland system and ecologically fragile zone. Using the widely existing mulberry forest lands in the hydro-fluctuation belt as an example and the 180-m water-level forest land as a control, this paper analyzes the soil stability of mulberry forestlands at different water levels in the hydro-fluctuation belt by analyzing and comparing the changes between soil physical and mechanical properties. The results indicated that (1) water-level changes, such as rising, flooding, draining, and exposure, affect the soil structure in mulberry forestlands. The soil agglomeration statuses for the soil layers decreased from 180 > 175 > 170 > 165 m, and the soil agglomeration statuses at a depth of 0∼20 cm decreased by 43.79, 44.95, and 57.45% compared with the control. (2) The soil water stability index decreased as follows: 180 > 170 > 175 > 165 m, which only accounted for 50.00, 47.73, and 40.91% of the control. In addition, the soil water stability indexes for the topsoils at various water levels were 1.87 (180 m), 1.67 (175 m), 2.92 (170 m), and 1.86 (165 m) times greater than those of the subsoils; thus, the resistance to hydraulic dispersion and disintegration were greater in the topsoil than in the subsoil. (3) The soil aggregate stability index decreased from 180 > 165 > 170 > 175 m and by 22.75, 23.53, and 35.29% compared with the control. (4) The soil shear strengths (composed of the cohesive force C and the internal friction angle φ) of the topsoils at water levels of 175, 170, and 165 m were significantly lower than in the control, and the internal friction angles decreased by 10.52, 19.08, and 43.25% and the cohesive force decreased by 9.88, 16.36, and 27.51%, respectively. The stability of the soil structure was greatly influenced by the soil clay content, soil organic matter content, and waterlogging duration. The study results could provide scientific support for soil and water conservation in the hydro-fluctuation belt and for biological filter construction in the Three Gorges Reservoir area to control the transport of sediment and non-point source pollutants.

Land use Effects on Storage, Stability and Structure of Organic Carbon in Soil Density Fractions Revealed by 13C Natural Abundance and CPMAS 13C NMR

NASA Astrophysics Data System (ADS)

Flessa, H.; Helfrich, M.; John, B.; Yamashita, T.; Ludwig, B.

2004-12-01

The type of land use and soil cultivation are important factors controlling organic carbon storage (SOC) in soils and they can also influence the relative importance, the structure, and the stability of different SOC pools. The objectives of our study were: i) to quantify the SOC stocks in different density fractions (mineral-associated soil organic matter > 2 g cm-3 (Mineral-SOM), free particulate organic matter < 1.6 g cm-3 (free POM), light occluded particulate organic matter < 1.6 g cm-3 (occluded POM<1.6) and dense occluded particulate organic matter 1.6 to 2.0 g cm-3 (occluded POM1.6-2.0)) of silty soils under different land use (spruce forest, grassland, maize, wheat), ii) to determine the structure of these SOC fractions by CPMAS 13C NMR spectroscopy, and iii) to analyse the stability of these SOC fractions in the maize soil on the basis of the stable isotope composition of SOC. The SOC concentration in the A horizon increased in the order wheat (12.7 g kg-1) < maize (13.0 g kg-1) < grassland (24.5 g kg-1) < spruce (40.5 g kg-1). The major part (86-91%) of the SOC was associated with the heavy mineral fraction at the grassland, maize and wheat site. In the A horizon of the spruce soil, the particulate organic matter accounted for 52% of the total SOC content. The chemical structure of the soil organic matter (SOM) was influenced by litter quality, the intensity of litter decomposition and the related production and storage of microbially-derived substances. SOM of the acid forest soil was characterized by large amounts of POM with a high content of spruce litter-derived alkyl C. In the biologically more active grassland and maize soil, litter-derived POM was decomposed more rapidly and SOC stocks were dominated by mineral-associated SOM which contained greater proportions of aryl and carbonyl C. The cultivation of the grassland soil induced enhanced mineralization of POM and in particular of mineral-associated SOM. The faster SOC turnover was associated with a relative accumulation of aromatic and carbonyl C structures in the mineral-bound SOM. In all soils, the free particulate organic matter had a smaller proportion of alkyl C and a larger proportion of O-alkyl C than the particulate organic matter occluded in aggregates. The mean age of the SOM in the density fractions of the maize soil increased with increasing aromaticity in the order free POM (22 yr) < occluded POM1.6-2.0 (49 yr) < mineral-associated SOM (63 yr). The results showed that the type of land use influenced the distribution pattern of litter carbon to functionally different SOM pools which represented different stages of SOM decomposition and humification. Additionally, the type of land use influenced the chemical structure of SOM in soil density fractions. Thus, the effect of land use on SOM storage should not only be assessed in terms of total C stocks but also with respect to changes of SOC structure, stability and function.

Carbon cycle confidence and uncertainty: Exploring variation among soil biogeochemical models

DOE PAGES

Wieder, William R.; Hartman, Melannie D.; Sulman, Benjamin N.; ...

2017-11-09

Emerging insights into factors responsible for soil organic matter stabilization and decomposition are being applied in a variety of contexts, but new tools are needed to facilitate the understanding, evaluation, and improvement of soil biogeochemical theory and models at regional to global scales. To isolate the effects of model structural uncertainty on the global distribution of soil carbon stocks and turnover times we developed a soil biogeochemical testbed that forces three different soil models with consistent climate and plant productivity inputs. The models tested here include a first-order, microbial implicit approach (CASA-CNP), and two recently developed microbially explicit models thatmore » can be run at global scales (MIMICS and CORPSE). When forced with common environmental drivers, the soil models generated similar estimates of initial soil carbon stocks (roughly 1,400 Pg C globally, 0–100 cm), but each model shows a different functional relationship between mean annual temperature and inferred turnover times. Subsequently, the models made divergent projections about the fate of these soil carbon stocks over the 20th century, with models either gaining or losing over 20 Pg C globally between 1901 and 2010. Single-forcing experiments with changed inputs, tem- perature, and moisture suggest that uncertainty associated with freeze-thaw processes as well as soil textural effects on soil carbon stabilization were larger than direct temper- ature uncertainties among models. Finally, the models generated distinct projections about the timing and magnitude of seasonal heterotrophic respiration rates, again reflecting structural uncertainties that were related to environmental sensitivities and assumptions about physicochemical stabilization of soil organic matter. Here, by providing a computationally tractable and numerically consistent framework to evaluate models we aim to better understand uncertainties among models and generate insights about fac- tors regulating the turnover of soil organic matter.« less

Carbon cycle confidence and uncertainty: Exploring variation among soil biogeochemical models

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

Wieder, William R.; Hartman, Melannie D.; Sulman, Benjamin N.

Emerging insights into factors responsible for soil organic matter stabilization and decomposition are being applied in a variety of contexts, but new tools are needed to facilitate the understanding, evaluation, and improvement of soil biogeochemical theory and models at regional to global scales. To isolate the effects of model structural uncertainty on the global distribution of soil carbon stocks and turnover times we developed a soil biogeochemical testbed that forces three different soil models with consistent climate and plant productivity inputs. The models tested here include a first-order, microbial implicit approach (CASA-CNP), and two recently developed microbially explicit models thatmore » can be run at global scales (MIMICS and CORPSE). When forced with common environmental drivers, the soil models generated similar estimates of initial soil carbon stocks (roughly 1,400 Pg C globally, 0–100 cm), but each model shows a different functional relationship between mean annual temperature and inferred turnover times. Subsequently, the models made divergent projections about the fate of these soil carbon stocks over the 20th century, with models either gaining or losing over 20 Pg C globally between 1901 and 2010. Single-forcing experiments with changed inputs, tem- perature, and moisture suggest that uncertainty associated with freeze-thaw processes as well as soil textural effects on soil carbon stabilization were larger than direct temper- ature uncertainties among models. Finally, the models generated distinct projections about the timing and magnitude of seasonal heterotrophic respiration rates, again reflecting structural uncertainties that were related to environmental sensitivities and assumptions about physicochemical stabilization of soil organic matter. Here, by providing a computationally tractable and numerically consistent framework to evaluate models we aim to better understand uncertainties among models and generate insights about fac- tors regulating the turnover of soil organic matter.« less

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.

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.

The role of Soil Water Retention Curve in slope stability analysis in unsaturated and heterogeneous soils.

NASA Astrophysics Data System (ADS)

Antinoro, Chiara; Arnone, Elisa; Noto, Leonardo V.

2015-04-01

The mechanisms of rainwater infiltration causing slope instability had been analyzed and reviewed in many scientific works. Rainwater infiltration into unsaturated soil increases the degree of saturation, hence affecting the shear strength properties and thus the probability of slope failure. It has been widely proved that the shear strength properties change with the soil water suction in unsaturated soils; therefore, the accuracy to predict the relationship between soil water content and soil water suction, parameterized by the soil-water characteristic curve, has significant effects on the slope stability analysis. The aim of this study is to investigate how the characterization of SWRC of differently structured unsaturated soils affects the slope stability on a simple infinite slope. In particular, the unimodal and bimodal distributions of the soil pore size were compared. Samples of 40 soils, highly different in terms of structure and texture, were collected and used to calibrate two bimodal SWRCs, i.e. Ross and Smettem (1993) and Dexter et al., (2008). The traditional unimodal van Genuchten (1980) model was also applied for comparison. Slope stability analysis was conducted in terms of Factor of Safety (FS) by applying the infinite slope model for unsaturated soils. In the used formulation, the contribution of the suction effect is tuned by a parameter 'chi' in a rate proportional to the saturation conditions. Different parameterizations of this term were also compared and analyzed. Results indicated that all three SWRC models showed good overall performance in fitting the sperimental SWRCs. Both the RS and DE models described adequately the water retention data for soils with a bimodal behavior confirmed from the analysis of pore size distribution, but the best performance was obtained by DE model confirmed. In terms of FS, the tree models showed very similar results as soil moisture approached to the saturated condition; however, within the residual zone, the DE model denoted an anomalous behavior depending on the used formulation for the 'chi' parameter, with decreasing FS as soil moisture decreases.

Geophysical methods for monitoring soil stabilization processes

NASA Astrophysics Data System (ADS)

Saneiyan, Sina; Ntarlagiannis, Dimitrios; Werkema, D. Dale; Ustra, Andréa

2018-01-01

Soil stabilization involves methods used to turn unconsolidated and unstable soil into a stiffer, consolidated medium that could support engineered structures, alter permeability, change subsurface flow, or immobilize contamination through mineral precipitation. Among the variety of available methods carbonate precipitation is a very promising one, especially when it is being induced through common soil borne microbes (MICP - microbial induced carbonate precipitation). Such microbial mediated precipitation has the added benefit of not harming the environment as other methods can be environmentally detrimental. Carbonate precipitation, typically in the form of calcite, is a naturally occurring process that can be manipulated to deliver the expected soil strengthening results or permeability changes. This study investigates the ability of spectral induced polarization and shear-wave velocity for monitoring calcite driven soil strengthening processes. The results support the use of these geophysical methods as soil strengthening characterization and long term monitoring tools, which is a requirement for viable soil stabilization projects. Both tested methods are sensitive to calcite precipitation, with SIP offering additional information related to long term stability of precipitated carbonate. Carbonate precipitation has been confirmed with direct methods, such as direct sampling and scanning electron microscopy (SEM). This study advances our understanding of soil strengthening processes and permeability alterations, and is a crucial step for the use of geophysical methods as monitoring tools in microbial induced soil alterations through carbonate precipitation.

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.

Application of soil nails to the stability of mine waste slopes

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

Tant, C.R.; Drumm, E.C.; Mauldon, M.

1996-12-31

The traditional soil nailed structure incorporates grouted or driven nails, and a wire mesh reinforced shotcrete facing to increase the stability of a slope or wall. This paper describes the construction and monitoring of a full-scale demonstration of nailing to stabilize coal mine spoil. The purpose of the investigation is to evaluate the performance of nailed slopes in mine spoil using methods proven for the stabilization of soil walls and slopes. The site in eastern Tennessee is a 12 meter high slope of dumped fill, composed of weathered shale chips, sandstone, and coal. The slope was formed by {open_quotes}pre-regulatory{close_quotes} contourmore » surface mining operations and served as a work bench during mining. The material varies in size from silt to boulders, and has a small amount of cohesion. Portions of the mine spoil slope have experienced slope instability and erosion which have hampered subsequent reclamation activities. Three different nail spacings and three different nail lengths were used in the design. The 12 meter high structure is instrumented to permit measurement of nail strain, and vertical inclinometer readings and survey measurements will be used for the detection of ground movement. The results of this study will aid in the development of design recommendations and construction guidelines for the application of soil nailing to stabilize mine spoil.« less

A regionally-adapted implementation of conservation agriculture delivers rapid improvements to soil properties associated with crop yield stability.

PubMed

Williams, Alwyn; Jordan, Nicholas R; Smith, Richard G; Hunter, Mitchell C; Kammerer, Melanie; Kane, Daniel A; Koide, Roger T; Davis, Adam S

2018-05-31

Climate models predict increasing weather variability, with negative consequences for crop production. Conservation agriculture (CA) may enhance climate resilience by generating certain soil improvements. However, the rate at which these improvements accrue is unclear, and some evidence suggests CA can lower yields relative to conventional systems unless all three CA elements are implemented: reduced tillage, sustained soil cover, and crop rotational diversity. These cost-benefit issues are important considerations for potential adopters of CA. Given that CA can be implemented across a wide variety of regions and cropping systems, more detailed and mechanistic understanding is required on whether and how regionally-adapted CA can improve soil properties while minimizing potential negative crop yield impacts. Across four US states, we assessed short-term impacts of regionally-adapted CA systems on soil properties and explored linkages with maize and soybean yield stability. Structural equation modeling revealed increases in soil organic matter generated by cover cropping increased soil cation exchange capacity, which improved soybean yield stability. Cover cropping also enhanced maize minimum yield potential. Our results demonstrate individual CA elements can deliver rapid improvements in soil properties associated with crop yield stability, suggesting that regionally-adapted CA may play an important role in developing high-yielding, climate-resilient agricultural systems.

Application of Soil Nailing Technique for Protection and Preservation Historical Buildings

NASA Astrophysics Data System (ADS)

Kulczykowski, Marek; Przewłócki, Jarosław; Konarzewska, Bogusława

2017-10-01

Soil nailing is one of the recent in situ techniques used for soil improvement and in stabilizing slopes. The process of soil nailing consists of reinforcing the natural ground with relatively small steel bars or metal rods, grouted in the pre-drilled holes. This method has a wide range of applications for stabilizing deep excavations and steep slopes. Soil nailing has recently become a very common method of slope stabilisation especially where situated beneath or adjacent to historical buildings. Stabilisation by nails drilled into existing masonry structures such as failing retaining walls abutments, provide long term stability without demolition and rebuilding costs. Two cases of soil nailing technology aimed at stabilising slopes beneath old buildings in Poland are presented in this paper. The first concerns application of this technology to repair a retaining wall supporting the base of the dam at the historic hydroelectric power plant in Rutki. The second regards a concept of improving the slope of the Castle Hill in Sandomierz. An analysis of the slope stability for the latter case, using stabilisation technique with the piling system and soil nailing was performed. Some advantages of soil nailing especially for protection of historical buildings, are also underlined. And, the main results of an economic comparison analysis are additionally presented.

Long-Term benefits of stabilizing soil subgrades.

DOT National Transportation Integrated Search

2002-06-01

The main intent of this study was an attempt to address questions concerning bearing strengths, longevity, durability, structural credit, economics, and performance of pavements resting on soil subgrades mixed with chemical admixtures. In-depth field...

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.

Transformations in soil organic matter and aggregate stability after conversion of Mediterranean forest to agriculture

NASA Astrophysics Data System (ADS)

Recio Vázquez, Lorena; Almendros, Gonzalo; Carral, Pilar; Knicker, Heike; González Pérez, José Antonio; González Vila, Francisco Javier

2013-04-01

Conversion of forest ecosystems into croplands often leads to severe decrease of the soil organic matter (SOM) levels with the concomitant deterioration of soil structure. The present research focuses on the effects of cultivation on the stability of soil macroaggregates, as well as on the total quantity and quality of SOM. Three representative soils from central Spain (i.e., Petric Calcisol, Cutanic Luvisol and Calcic Vertisol) were sampled. Each site had natural vegetation (NV) dominated either by characteristic Mediterranean forest (dehesa) or cereal crops (CC) under conventional tillage. For each site, three spatial replicates of the NV and CC were sampled. Soil aggregate stability was measured by the wet sieving method. The structural stability index was then calculated as the mass of aggregated soil (>250 μm) remaining after wet sieving, as a percent of total aggregate weight. The analytical characterization of the SOM was carried out after chemical fractionation for quantifying the different organic pools: free organic matter (FOM), humic acids (HA), fulvic acids (FA) and humin (H). Furthermore, whole soil samples pretreated with 10 % HF solution were analyzed by CP-MAS 13C NMR and the purified HA fraction was characterized by elementary analysis, visible and infrared spectroscopies and Py-GC/MS. A marked reduction in the proportion of stable aggregates when the natural ecosystem was converted to agriculture was observed. Values of the structural stability index (%) changed over from 96.2 to 38.1, 95.1 to 83.7 and 98.5 to 60.6 for the Calcisol, Luvisol and Vertisol respectively. Comparatively higher contents of SOM were found in the soils under NV (11.69 to 0.93, 3.29 to 2.72 and 9.51 to 0.79 g C100 g-1soil) even though a quantitative rearrangement of the SOM pools was noticed. In all sites, the relative contribution of the labile C (FOM) to the total SOM content decreased when the forest soils were converted into croplands, whereas the proportion of both HA and FA increased in the cultivated soils. Considering the differences in molecular characteristics of the HAs, cultivation increased aromaticity and humification degree, reflected in the reduction of the H/C atomic ratio and the increase of the E465 nm optical density of the HAs. The 13C NMR spectra of the whole soils showed increased signal intensity in the alkyl and O-alkyl regions in NV sites compared to agricultural systems. Infrared spectroscopy displayed a less conspicuous pattern in HAs from CC sites. Moreover, the major aromatic pyrolytic products in CC soils were alkylphenols, naphthalenes, benzenes, pyrenes and N-compounds (pyrroles, indoles...), with lower abundance of methoxyphenols regarding NV sites. Cultivation reduced SOM concentration and macroaggregate stability in the studied soils. The loss of organic C mainly affected labile pools of SOM, which could be partly explained as the organic debris (fungal hyphae, fine roots, polysaccharides) are the main binding agents, so the breakdown of macroaggregates with the tillage exposes the fresh organic materials to microbial degradation. The final consequence is an enrichment on recalcitrant C fractions in the cultivated soils.

Evaluation of the effectiveness of olive cake residue as an expansive soil stabilizer

NASA Astrophysics Data System (ADS)

Nalbantoglu, Zalihe; Tawfiq, Salma

2006-08-01

The quantity of the by-product olive cake residue generated in most parts of the Mediterranean countries continues to increase and expected to double in amount within 10 15 years. This increase intensifies the problems associated with the disposal of this by-product. Olive cake residue has a potential for use as a soil stabilizer and large volumes can be beneficially used. This study is directed toward determining if olive cake residue can be utilized to increase the strength and stability of expansive soils which constitute a costly natural hazard to lightweight structures on shallow foundations. A series of laboratory tests using engineering properties, such as Atterberg limits, moisture-density relationship (compaction), swell, unconfined compressive strength were undertaken to evaluate the effectiveness and performance of the olive cake residue as a soil stabilizer. Test results indicate that an addition of only 3% burned olive waste into the soil causes a reduction in plasticity, volume change and an increase in the unconfined compressive strength. However, it was observed that the presence of burned olive waste in the soil greater than 3% caused an increase in the compressibility and a decrease in the unconfined compressive strength. Test results indicate that the use of olive waste in soil stabilization gives greater benefits to the environment than simply disposing of the by-product, olive cake residue.

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.

Belowground rhizomes in paleosols: The hidden half of an Early Devonian vascular plant

NASA Astrophysics Data System (ADS)

Xue, Jinzhuang; Deng, Zhenzhen; Huang, Pu; Huang, Kangjun; Benton, Michael J.; Cui, Ying; Wang, Deming; Liu, Jianbo; Shen, Bing; Basinger, James F.; Hao, Shougang

2016-08-01

The colonization of terrestrial environments by rooted vascular plants had far-reaching impacts on the Earth system. However, the belowground structures of early vascular plants are rarely documented, and thus the plant-soil interactions in early terrestrial ecosystems are poorly understood. Here we report the earliest rooted paleosols (fossil soils) in Asia from Early Devonian deposits of Yunnan, China. Plant traces are extensive within the soil and occur as complex network-like structures, which are interpreted as representing long-lived, belowground rhizomes of the basal lycopsid Drepanophycus. The rhizomes produced large clones and helped the plant survive frequent sediment burial in well-drained soils within a seasonal wet-dry climate zone. Rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants. Predating the appearance of trees with deep roots in the Middle Devonian, plant rhizomes have long functioned in the belowground soil ecosystem. This study presents strong, direct evidence for plant-soil interactions at an early stage of vascular plant radiation. Soil stabilization by complex rhizome systems was apparently widespread, and contributed to landscape modification at an earlier time than had been appreciated.

Belowground rhizomes in paleosols: The hidden half of an Early Devonian vascular plant.

PubMed

Xue, Jinzhuang; Deng, Zhenzhen; Huang, Pu; Huang, Kangjun; Benton, Michael J; Cui, Ying; Wang, Deming; Liu, Jianbo; Shen, Bing; Basinger, James F; Hao, Shougang

2016-08-23

The colonization of terrestrial environments by rooted vascular plants had far-reaching impacts on the Earth system. However, the belowground structures of early vascular plants are rarely documented, and thus the plant-soil interactions in early terrestrial ecosystems are poorly understood. Here we report the earliest rooted paleosols (fossil soils) in Asia from Early Devonian deposits of Yunnan, China. Plant traces are extensive within the soil and occur as complex network-like structures, which are interpreted as representing long-lived, belowground rhizomes of the basal lycopsid Drepanophycus The rhizomes produced large clones and helped the plant survive frequent sediment burial in well-drained soils within a seasonal wet-dry climate zone. Rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants. Predating the appearance of trees with deep roots in the Middle Devonian, plant rhizomes have long functioned in the belowground soil ecosystem. This study presents strong, direct evidence for plant-soil interactions at an early stage of vascular plant radiation. Soil stabilization by complex rhizome systems was apparently widespread, and contributed to landscape modification at an earlier time than had been appreciated.

Belowground rhizomes in paleosols: The hidden half of an Early Devonian vascular plant

PubMed Central

Xue, Jinzhuang; Deng, Zhenzhen; Huang, Pu; Huang, Kangjun; Benton, Michael J.; Cui, Ying; Wang, Deming; Liu, Jianbo; Shen, Bing; Basinger, James F.; Hao, Shougang

2016-01-01

The colonization of terrestrial environments by rooted vascular plants had far-reaching impacts on the Earth system. However, the belowground structures of early vascular plants are rarely documented, and thus the plant−soil interactions in early terrestrial ecosystems are poorly understood. Here we report the earliest rooted paleosols (fossil soils) in Asia from Early Devonian deposits of Yunnan, China. Plant traces are extensive within the soil and occur as complex network-like structures, which are interpreted as representing long-lived, belowground rhizomes of the basal lycopsid Drepanophycus. The rhizomes produced large clones and helped the plant survive frequent sediment burial in well-drained soils within a seasonal wet−dry climate zone. Rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants. Predating the appearance of trees with deep roots in the Middle Devonian, plant rhizomes have long functioned in the belowground soil ecosystem. This study presents strong, direct evidence for plant−soil interactions at an early stage of vascular plant radiation. Soil stabilization by complex rhizome systems was apparently widespread, and contributed to landscape modification at an earlier time than had been appreciated. PMID:27503883

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.

Biomimetic Hydrogel Composites for Soil Stabilization and Contaminant Mitigation.

PubMed

Zhao, Zhi; Hamdan, Nasser; Shen, Li; Nan, Hanqing; Almajed, Abdullah; Kavazanjian, Edward; He, Ximin

2016-11-15

We have developed a novel method to synthesize a hyper-branched biomimetic hydrogel network across a soil matrix to improve the mechanical strength of the loose soil and simultaneously mitigate potential contamination due to excessive ammonium. This method successfully yielded a hierarchical structure that possesses the water retention, ion absorption, and soil aggregation capabilities of plant root systems in a chemically controllable manner. Inspired by the robust organic-inorganic composites found in many living organisms, we have combined this hydrogel network with a calcite biomineralization process to stabilize soil. Our experiments demonstrate that poly(acrylic acid) (PAA) can work synergistically with enzyme-induced carbonate precipitation (EICP) to render a versatile, high-performance soil stabilization method. PAA-enhanced EICP provides multiple benefits including lengthening of water supply time, localization of cementation reactions, reduction of harmful byproduct ammonium, and achievement of ultrahigh soil strength. Soil crusts we have obtained can sustain up to 4.8 × 10 3 kPa pressure, a level comparable to cementitious materials. An ammonium removal rate of 96% has also been achieved. These results demonstrate the potential for hydrogel-assisted EICP to provide effective soil improvement and ammonium mitigation for wind erosion control and other applications.

Evaluation and field verification of strength and structural improvement of chemically stabilized subgrade soil.

DOT National Transportation Integrated Search

2008-07-01

Often subgrade soils exhibit properties, particularly strength and/or volume change properties that limit their performance as a support element for pavements. : Typical problems include shrink-swell, settlement, collapse, erosion or simply insuffici...

Effect of Lime on characteristics of consolidation, strength, swelling and plasticity of fine grained soil

NASA Astrophysics Data System (ADS)

Estabragh, A. R.; Bordbar, A. T.; Parsaee, B.; Eskandari, Gh.

2009-04-01

Using Lime as an additive material to clayey soil is one of the best effective technique in building the soil structures to get some purposes such as soil stabilization, soil reinforcement and decreasing soil swelling. In this research the effect of Lime on geotechnical characteristics of a clayey soil was investigated. Soil specimen types used in this study were consisted of clayey soil as the control treatment and clay mixed with different weight fractions of lime, 4, 6, 8 & 10 percent. Some experiments such as CBR, atterburg limits, compaction, consolidation and swelling was conducted on specimens. Results revealed that adding lime to soil would change its physical and mechanical properties. Adding lime increase the compression strength and consolidation coefficient and decrease swelling potential and maximum dry density. According to the results, Atterburg experiments show that presence of lime in soil increase the liquid limit of low plasticity soil and decrease the liquid limit of high plasticity soil, but totally it decreases the plasticity index of soils. Key words: soil stabilization, lime, compression strength, swelling, atterburg limits, compaction

Assessing agricultural management effects on structure related soil hydraulic properties by tension infiltrometry

NASA Astrophysics Data System (ADS)

Bodner, G.; Loiskandl, W.; Kaul, H.-P.

2009-04-01

Soil structure is a dynamic property subject to numerous natural and human influences. It is recognized as fundamental for sustainable functioning of soil. Therefore knowledge of management impacts on the sensitive structural states of soil is decisive in order to avoid soil degradation. The stabilization of the soil's (macro)pore system and eventually the improvement of its infiltrability are essential to avoid runoff and soil erosion, particularly in view of an increasing probability of intense rainfall events. However structure-related soil properties generally have a high natural spatiotemporal variability that interacts with the potential influence of agricultural land use. This complicates a clear determination of management vs. environmental effects and requires adequate measurement methods, allowing a sufficient spatiotemporal resolution to estimate the impact of the targeted management factors within the natural dynamics of soil structure. A common method to assess structure-related soil hydraulic properties is tension infiltrometry. A major advantage of tension infiltrometer measurements is that no or only minimum soil disturbance is necessary and several structure-controlled water transmission properties can readily be derived. The method is more time- and cost-efficient compared to laboratory measurements of soil hydraulic properties, thus enabling more replications. Furthermore in situ measurements of hydraulic properties generally allow a more accurate reproduction of field soil water dynamics. The present study analyses the impact of two common agricultural management options on structure related hydraulic properties based on tension infiltrometer measurements. Its focus is the identification of the role of management within the natural spatiotemporal variability, particularly in respect to seasonal temporal dynamics. Two management approaches are analysed, (i) cover cropping as a "plant-based" agro-environmental measure, and (ii) tillage with different intensities including conventional tillage with a mouldboard plough, reduced tillage with a chisel plough and no-tillage. The results showed that the plant-based management measure of cover cropping had only minor influence on near-saturated hydraulic conductivity (kh) and flow weighted mean pore radius (λm). Substantial over-winter changes were found with a significant increase in kh and a reduction in the pore radius. A spatial trend in soil texture along the cover cropped slope resulted in a higher kh at lower pressure heads at the summit with higher fractions of coarse particles, while kh tended to be highest at the toeslope towards saturation. Cover crop management accounted for a maximum of 9.7% of the total variability in kh, with a decreasing impact towards the unsaturated range. A substantial difference to bare soil in the cover cropped treatments could be identified in relation to a stabilization of macro-pores over winter. The different tillage treatments had a substantial impact on near-saturated kh and pore radius. Although conventional tillage showed the highest values in kh and λm, settling of the soil after the ploughing event tended to reduce differences over time compared to the other tillage methods. The long-term no-tillage (10 years) however had the lowest values of kh at all measurement dates. The high contents of silt and fine sand probably resulted in soil densification that was not counterbalanced sufficiently by biological structure forming agents. The study could show that soil structure related hydraulic properties are subject to a substantial seasonal variability. A comprehensive assessment of agricultural measures such as tillage or cover cropping requires an estimate of these temporal dynamics and their interaction with the management strategies. Particularly for plant-based management measures such as cover cropping, which represent a less intense intervention in the structural states of the soil compared to tillage, this was evident, as the main mechanism revealed for this measure was structure stabilization over time. While spatial variability is mostly controlled in designed experiments, the role of temporal variability is often underestimated. From our study we concluded that (i) a proper understanding of processes involved in management effects on soil structure must take into consideration the dynamic nature of the respective soil properties, (ii) experimental planning for studies regarding management impacts on soil structure should allow an estimation of temporal variability, and (iii) for this purpose tension infiltrometry provides an efficient measurement tool to assess structure related soil hydraulic properties.

Carbon Flux and Isotopic Character of Soil and Soil Gas in Stabilized and Active Thaw Slumps in Northwest Alaska

NASA Astrophysics Data System (ADS)

Jensen, A.; Crosby, B. T.; Mora, C. I.; Lohse, K. A.

2012-12-01

Permafrost soils store nearly half the world's global carbon. Warming of arctic landscape results in permafrost thaw which causes ground subsidence or thermokarst. On hillslopes, these features rapidly and dramatically alter soil structure, temperature, and moisture, as well as the content and quality of soil organic matter. These changes alter both the rate and mechanism of carbon cycling in permafrost soils, making frozen soils available to both anaerobic and aerobic decomposition. In order to improve our predictive capabilities, we use a chronosequence thaw slumps to examine how fluxes from active and stabilized features differ. Our study site is along the Selawik River in northwest Alaska where a retrogressive thaw slump initiated in the spring of 2004. It has grown to a surface area of 50,000 m2. Products of the erosion are stored on the floor of the feature, trapped on a fan or flushed into the Selawik River. North of slump is undisturbed tundra and adjacent to the west is a slump feature that stabilized and is now covered with a second generation of spruce trees. In this 2 year study, we use measurements of CO2 efflux, δC13 in soil profiles and CO2 and CH4 abundance to constrain the response of belowground carbon emissions. We also focused on constraining which environmental factors govern C emissions within each of the above ecosystems. To this end, we measured soil temperature, and moisture, abundance and quality of soil organic carbon (SOC), water content, and bulk carbon compositions. Preliminary data from the summer of 2011 suggest that vegetation composition and soil temperature exert the strong control on CO2 efflux. The floor of the active slump and fan are bare mineral soils and are generally 10 to 15°C warmer than the tundra and stabilized slump. Consistently decreasing δC13 soil gas profiles in the recovered slump confirm that this region is a well-drained soil dominated by C3 vegetation. The δC13 gas profiles for the tundra, active slump floor, and active fan tend to be more variable as a consequence of less consistently structured soils. This could be due to either the predominance of older carbon being recycled within these profiles or a skewed balance between anaerobic vs. aerobic respiration.

What do Boletus, Chanterelle and Co. have in common with Eco engineering?

NASA Astrophysics Data System (ADS)

Graf, F.; Burri, K.; Böll, A.

2009-04-01

A major goal of eco engineering is its contribution to slope stability. The carefully selected plant and technical construction material are an indispensable requirement but not necessarily sufficient in view of long-term success. For that purpose, plant growth and the development of a functional vegetation cover are essential. However, particularly under extreme climatic and environmental conditions even pioneer plants reach their limits in bridging the gap between their proper needs and the effective yield of the soil degraded by erosion or sliding processes. Besides the conventional solutions that are the application of artificial fertiliser and soil conditioners, a competitive option is to be found in the "Kingdom of Fungi". Under natural conditions, as good as every plant species used in eco engineering lives in a symbiotic relationship with fungi, called mycorrhiza with Boletus and Chanterelle as two prominent representatives. Within these partnerships, the fungi take charge of the host's water and nutrient supply; considerably increasing its efficiency compared to non-mycorrhized roots. Consequently, plant growth, in particular root performance, and survival are significantly improved as is shown in a restoration experiment on an alpine ski slope in the Swiss mountains and has been demonstrated many times elsewhere. In addition to this indirect contribution to the restoration and re-stabilisation process, the mycorrhizal fungi provide more direct functions related to the development of a stable soil structure starting from a severely degraded soil material. The mycelia producing fungi assemble and stabilise micro- and macro-aggregates out of smallest organic and inorganic soil particles. The formation and stabilisation of the soil structure proceed at different spatial scales directly by electrostatic charge, adhesive and enmeshment mechanisms. Numerous investigations prove that, on the one hand, the sole application of mycorrhizal fungi to loose soil material may result in an increase of aggregate stability but, on the other hand, demonstrate its species specific dependency. Furthermore, mycorrhizal fungi support the soil aggregate stability by serving as a distribution vector for associated micro-organisms, mainly bacteria and archaea, some of them soil stabilising alike. A positive correlation was found between soil aggregate stability and dry unit weight, based on laboratory as well as field samples. Such a correlation is known for the shear strength parameters - particularly for the angle of internal friction Φ' - of the Mohr-Coulomb failure criterion on which most of the conventionally used models for soil and slope stability calculations are based. Moreover, evidence was provided that the aggregate stability of soil at low dry unit weight (~15.5 kN/m3) added with plants and mycorrhizal fungi corresponds to that of untreated soil material at high dry unit weight (~19.5 kN/m3) a feature found for the angle of internal friction Φ' too. Conclusively, based on these relationships, effects of plants and mycorrhizal fungi on soil stability may be interpreted as a virtual increase in dry unit weight and a real increase in the angle of internal friction Φ', respectively. The effect of plants and fungi on soil stability is, however, not restricted to withstand erosion and sliding processes induced by water. Recent experiments in a wind tunnel reveal the potential of this symbiosis related to wind erosion and, therefore, in view of combating desertification. Experiments with differently dense planted soil confirmed the negative correlation with the amount of sediment transport and health threatening fine dust (PM10) emission. The "mycorrhiza network" including and connecting plants, soil aggregate stability, and the angle of internal friction Φ' is of special meaning in view of soil stabilisation and the development of degraded soil. Carefully selected fungus-plant combinations shorten the delicate phase of re-colonisation and the development of a functional vegetation cover at simultaneous amelioration of the site specific conditions - representing the essential requirements for long-term success of eco engineering measures.

Experimental datasets on engineering properties of expansive soil treated with common salt.

PubMed

Durotoye, Taiwo O; Akinmusuru, Joseph O; Ogundipe, Kunle E

2018-06-01

Construction of highway pavements or high rise structures over the expansive soils are always problematic due to failures of volume change or swelling characteristic experienced in the water permeability of the soil. The data in this article represented summary of (Durotoye et al., 2016; Durotoye, 2016) [1], [2]. The data explored different percentages of sodium chloride as additive in stabilizing the engineering properties of expansive soil compared with other available stabilizer previously worked on. Experimental procedures carried out on expansive soil include: (Liquid limit, Plastic limit, Plasticity index, Shrinkage limit, Specific gravity Free swell index and Optimum water content) to determine the swelling parameters and (maximum dry density, California bearing ratio and unconfined compressive strength) to determine the strength parameters. The results of the experiment were presented in pie charts.

Black Carbon (Biochar) In Water/Soil Environments: Molecular Structure, Sorption, Stability, and Potential Risk.

PubMed

Lian, Fei; Xing, Baoshan

2017-12-05

Black carbon (BC) is ubiquitous in the environments and participates in various biogeochemical processes. Both positive and negative effects of BC (especially biochar) on the ecosystem have been identified, which are mainly derived from its diverse physicochemical properties. Nevertheless, few studies systematically examined the linkage between the evolution of BC molecular structure with the resulted BC properties, environmental functions as well as potential risk, which is critical for understanding the BC environmental behavior and utilization as a multifunctional product. Thus, this review highlights the molecular structure evolution of BC during pyrolysis and the impact of BC physicochemical properties on its sorption behavior, stability, and potential risk in terrestrial and aqueous ecosystems. Given the wide application of BC and its important role in biogeochemical processes, future research should focus on the following: (1) establishing methodology to more precisely predict and design BC properties on the basis of pyrolysis and phase transformation of biomass; (2) developing an assessment system to evaluate the long-term effect of BC on stabilization and bioavailability of contaminants, agrochemicals, and nutrient elements in soils; and (3) elucidating the interaction mechanisms of BC with plant roots, microorganisms, and soil components.

Soil erosion-runoff relationships: insights from laboratory studies

NASA Astrophysics Data System (ADS)

Mamedov, Amrakh; Warrington, David; Levy, Guy

2016-04-01

Understanding the processes and mechanisms affecting runoff generation and subsequent soil erosion in semi-arid regions is essential for the development of improved soil and water conservation management practices. Using a drip type laboratory rain simulator, we studied runoff and soil erosion, and the relationships between them, in 60 semi-arid region soils varying in their intrinsic properties (e.g., texture, organic matter) under differing extrinsic conditions (e.g., rain properties, and conditions prevailing in the field soil). Both runoff and soil erosion were significantly affected by the intrinsic soil and rain properties, and soil conditions within agricultural fields or watersheds. The relationship between soil erosion and runoff was stronger when the rain kinetic energy was higher rather than lower, and could be expressed either as a linear or exponential function. Linear functions applied to certain limited cases associated with conditions that enhanced soil structure stability, (e.g., slow wetting, amending with soil stabilizers, minimum tillage in clay soils, and short duration exposure to rain). Exponential functions applied to most of the cases under conditions that tended to harm soil stability (e.g., fast wetting of soils, a wide range of antecedent soil water contents and rain kinetic energies, conventional tillage, following biosolid applications, irrigation with water of poor quality, consecutive rain simulations). The established relationships between runoff and soil erosion contributed to a better understanding of the mechanisms governing overland flow and soil loss, and could assist in (i) further development of soil erosion models and research techniques, and (ii) the design of more suitable management practices for soil and water conservation.

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.

Impact of natural and calcined starfish (Asterina pectinifera) on the stabilization of Pb, Zn and As in contaminated agricultural soil.

PubMed

Lim, Jung Eun; Sung, Jwa Kyung; Sarkar, Binoy; Wang, Hailong; Hashimoto, Yohey; Tsang, Daniel C W; Ok, Yong Sik

2017-04-01

Metal stabilization using soil amendments is an extensively applied, economically viable and environmentally friendly remediation technique. The stabilization of Pb, Zn and As in contaminated soils was evaluated using natural starfish (NSF) and calcined starfish (CSF) wastes at different application rates (0, 2.5, 5.0 and 10.0 wt%). An incubation study was conducted over 14 months, and the efficiency of stabilization for Pb, Zn and As in soil was evaluated by the toxicity characteristic leaching procedure (TCLP) test. The TCLP-extractable Pb was reduced by 76.3-100 and 91.2-100 % in soil treated with NSF and CSF, respectively. The TCLP-extractable Zn was also reduced by 89.8-100 and 93.2-100 % in soil treated with NSF and CSF, respectively. These reductions could be associated with the increased metal adsorption and the formation of insoluble metal precipitates due to increased soil pH following application of the amendments. However, the TCLP-extractable As was increased in the soil treated with NSF, possibly due to the competitive adsorption of phosphorous. In contrast, the TCLP-extractable As in the 10 % CSF treatment was not detectable because insoluble Ca-As compounds might be formed at high pH values. Thermodynamic modeling by visual MINTEQ predicted the formation of ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ·26H 2 O) and portlandite (Ca(OH) 2 ) in the 10 % CSF-treated soil, while SEM-EDS analysis confirmed the needle-like structure of ettringite in which Pb was incorporated and stabilized in the 10 % CSF treatment.

Revisiting classic water erosion models in drylands: The strong impact of biological soil crusts

USGS Publications Warehouse

Bowker, M.A.; Belnap, J.; Bala, Chaudhary V.; Johnson, N.C.

2008-01-01

Soil erosion and subsequent degradation has been a contributor to societal collapse in the past and is one of the major expressions of desertification in arid regions. The revised universal soil loss equation (RUSLE) models soil lost to water erosion as a function of climate erosivity (the degree to which rainfall can result in erosion), topography, soil erodibility, and land use/management. The soil erodibility factor (K) is primarily based upon inherent soil properties (those which change slowly or not at all) such as soil texture and organic matter content, while the cover/management factor (C) is based on several parameters including biological soil crust (BSC) cover. We examined the effect of two more precise indicators of BSC development, chlorophyll a and exopolysaccharides (EPS), upon soil stability, which is closely inversely related to soil loss in an erosion event. To examine the relative influence of these elements of the C factor to the K factor, we conducted our investigation across eight strongly differing soils in the 0.8 million ha Grand Staircase-Escalante National Monument. We found that within every soil group, chlorophyll a was a moderate to excellent predictor of soil stability (R2 = 0.21-0.75), and consistently better than EPS. Using a simple structural equation model, we explained over half of the variance in soil stability and determined that the direct effect of chlorophyll a was 3?? more important than soil group in determining soil stability. Our results suggest that, holding the intensity of erosive forces constant, the acceleration or reduction of soil erosion in arid landscapes will primarily be an outcome of management practices. This is because the factor which is most influential to soil erosion, BSC development, is also among the most manageable, implying that water erosion in drylands has a solution. ?? 2008 Elsevier Ltd.

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.

Response surface method in geotechnical/structural analysis, phase 1

NASA Astrophysics Data System (ADS)

Wong, F. S.

1981-02-01

In the response surface approach, an approximating function is fit to a long running computer code based on a limited number of code calculations. The approximating function, called the response surface, is then used to replace the code in subsequent repetitive computations required in a statistical analysis. The procedure of the response surface development and feasibility of the method are shown using a sample problem in slop stability which is based on data from centrifuge experiments of model soil slopes and involves five random soil parameters. It is shown that a response surface can be constructed based on as few as four code calculations and that the response surface is computationally extremely efficient compared to the code calculation. Potential applications of this research include probabilistic analysis of dynamic, complex, nonlinear soil/structure systems such as slope stability, liquefaction, and nuclear reactor safety.

Landuse legacies of old-field succession and soil structure at the Calhoun Criticl Zone Observatory in SC, USA.

NASA Astrophysics Data System (ADS)

Brecheisen, Z. S.; Richter, D. D., Jr.; Callaham, M.; Carrera-Martinez, R.; Heine, P.

2017-12-01

The pre-colonial Southern Piedmont was an incredibly stable CZ with erosion rates between 0.35-3m/Myr on a 4th order interfluve. With soils and saprolite weathered up to 30m in total depth bedrock with multi-million year residence times under continual forest cover prior to widespread agricultural disturbance. With this biogeomorphic stability came time for soil macroporosity and soil structure to be established and maintained by the activities of soil fauna, plant root growth and death, and tree-fall tip-up events serving to continually mix and aerate the soil. Greatly accelerated surficial agricultural erosion (ca. 1750-1930) has fundamentally altered the Calhoun Critical Zone Observatory forest community dynamics aboveground and the soil structure, hydrology, and biogeochemistry belowground. The arrival of the plow to the Southern Piedmont marked the destruction of soil structure, macropore networks, and many of the macroinvertebrate soil engineers. This transformation came via forest clearing, soil tilling, compaction, and wholesale soil erosion, with the region having lost an estimated average of 18cm of soil across the landscape. In the temporal LULC progression from hardwood forests, to cultivated farms, to reforestation, secondary forest soil structure is expected to remain altered compared to the reference hardwood ecosystems. The research presented herein seeks to quantify CZ soil structure regeneration in old-field pine soil profiles' Ksat, aggregation, texture, macro-invertebrates, and direct measurements of topsoil porosity using X-ray computed tomography analysis on 15cm soil cores.

Quality of Irrigation Water Affects Soil Functionality and Bacterial Community Stability in Response to Heat Disturbance.

PubMed

Frenk, Sammy; Hadar, Yitzhak; Minz, Dror

2018-02-15

Anthropogenic activities alter the structure and function of a bacterial community. Furthermore, bacterial communities structured by the conditions the anthropogenic activities present may consequently reduce their stability in response to an unpredicted acute disturbance. The present mesocosm-scale study exposed soil bacterial communities to different irrigation water types, including freshwater, fertilized freshwater, treated wastewater, and artificial wastewater, and evaluated their response to a disturbance caused by heat. These effectors may be considered deterministic and stochastic forces common in agricultural operations of arid and semiarid regions. Bacterial communities under conditions of high mineral and organic carbon availability (artificial wastewater) differed from the native bacterial community and showed a proteobacterial dominance. These bacterial communities had a lower resistance to the heat treatment disturbance than soils under conditions of low resource availability (high-quality treated wastewater or freshwater). The latter soil bacterial communities showed a higher abundance of operational taxonomic units (OTUs) classified as Bacilli These results were elucidated by soil under conditions of high resource availability, which lost higher degrees of functional potential and had a greater bacterial community composition change. However, the functional resilience, after the disturbance ended, was higher under a condition of high resource availability despite the bacterial community composition shift and the decrease in species richness. The functional resilience was directly connected to the high growth rates of certain Bacteroidetes and proteobacterial groups. A high stability was found in samples that supported the coexistence of both resistant OTUs and fast-growing OTUs. IMPORTANCE This report presents the results of a study employing a hypothesis-based experimental approach to reveal the forces involved in determining the stability of a soil bacterial community to disturbance. The resultant postdisturbance bacterial community composition dynamics and functionality were analyzed. The paper demonstrates the relatedness of community structure and stability under cultivation conditions prevalent in an arid area under irrigation with water of different qualities. The use of common agricultural practices to demonstrate these features has not been described before. The combination of a fundamental theoretical issue in ecology with common and concerning disturbances caused by agricultural practice makes this study unique. Furthermore, the results of the present study have applicable importance regarding soil conservation, as it enables a better characterization and monitoring of stressed soil bacterial communities and possible intervention to reduce the stress. It will also be of valued interest in coming years, as fresh water scarcity and the use of alternative water sources are expected to rise globally. Copyright © 2018 American Society for Microbiology.

Dual, differential isotope labeling shows the preferential movement of labile plant constituents into mineral-bonded soil organic matter.

PubMed

Haddix, Michelle L; Paul, Eldor A; Cotrufo, M Francesca

2016-06-01

The formation and stabilization of soil organic matter (SOM) are major concerns in the context of global change for carbon sequestration and soil health. It is presently believed that lignin is not selectively preserved in soil and that chemically labile compounds bonding to minerals comprise a large fraction of the SOM. Labile plant inputs have been suggested to be the main precursor of the mineral-bonded SOM. Litter decomposition and SOM formation are expected to have temperature sensitivity varying with the lability of plant inputs. We tested this framework using dual (13) C and (15) N differentially labeled plant material to distinguish the metabolic and structural components within a single plant material. Big Bluestem (Andropogon gerardii) seedlings were grown in an enriched (13) C and (15) N environment and then prior to harvest, removed from the enriched environment and allowed to incorporate natural abundance (13) C-CO2 and (15) N fertilizer into the metabolic plant components. This enabled us to achieve a greater than one atom % difference in (13) C between the metabolic and structural components within the plant litter. This differentially labeled litter was incubated in soil at 15 and 35 °C, for 386 days with CO2 measured throughout the incubation. After 14, 28, 147, and 386 days of incubation, the soil was subsequently fractionated. There was no difference in temperature sensitivity of the metabolic and structural components with regard to how much was respired or in the amount of litter biomass stabilized. Only the metabolic litter component was found in the sand, silt, or clay fraction while the structural component was exclusively found in the light fraction. These results support the stabilization framework that labile plant components are the main precursor of mineral-associated organic matter. © 2016 John Wiley & Sons Ltd.

Soil Tillage Conservation and its Effect on Soil Properties Bioremediation and Sustained Production of Crops

NASA Astrophysics Data System (ADS)

Rusu, Teodor; Ioana Moraru, Paula; Muresan, Liliana; Andriuca, Valentina; Cojocaru, Olesea

2017-04-01

Soil Tillage Conservation (STC) is considered major components of agricultural technology for soil conservation strategies and part of Sustainable Agriculture (SA). Human action upon soil by tillage determines important morphological, physical-chemical and biological changes, with different intensities and evaluative directions. Nowadays, internationally is unanimous accepted the fact that global climatic changes are the results of human intervention in the bio-geo-chemical water and material cycle, and the sequestration of carbon in soil is considered an important intervention to limit these changes. STC involves reducing the number of tillage's (minimum tillage) to direct sowing (no-tillage) and plant debris remains at the soil surface in the ratio of at least 30%. Plant debris left on the soil surface or superficial incorporated contributes to increased biological activity and is an important source of carbon sequestration. STC restore soil structure and improve overall soil drainage, allowing more rapid infiltration of water into soil. The result is a soil bioremediation, more productive, better protected against wind and water erosion and requires less fuel for preparing the germinative bed. Carbon sequestration in soil is net advantageous, improving the productivity and sustainability. We present the influence of conventional plough tillage system on soil, water and organic matter conservation in comparison with an alternative minimum tillage (paraplow, chisel plow and rotary harrow) and no-tillage system. The application of STC increased the organic matter content 0.8 to 22.1% and water stabile aggregate content from 1.3 to 13.6%, in the 0-30 cm depth, as compared to the conventional system. For the organic matter content and the wet aggregate stability, the statistical analysis of the data showed, increasing positive significance of STC. While the soil fertility and the wet aggregate stability were initially low, the effect of conservation practices on the soil features resulted in a positive impact on the water permeability of the soil. Availability of soil moisture during the crop growth resulted in better plant water status. Subsequent release of conserved soil water regulated proper plant water status, soil structure, and lowered soil penetrometer resistance. Productions obtained at STC did not have significant differences for the wheat and maize crop but were higher for soybean. The advantages of minimum soil tillage systems for Romanian pedo-climatic conditions can be used to improve methods in low producing soils with reduced structural stability on sloped fields, as well as measures of water and soil conservation on the whole agroecosystem. Presently, it is necessary to make a change concerning the concept of conservation practices and to consider a new approach regarding the good agricultural practice. We need to focus on an upper level concerning conservation by focusing on soil quality. Carbon management is necessary for a complexity of matters including soil, water management, field productivity, biological fuel and climatic change. In conclusion a Sustainable Agriculture includes a range of complementary agricultural practices: (i) minimum soil tillage (through a system of reduced tillage or no-tillage) to preserve the structure, fauna and soil organic matter; (ii) permanent soil cover (cover crops, residues and mulches) to protect the soil and help to remove and control weeds; (iii) various combinations and rotations of the crops which stimulate the micro-organisms in the soil and controls pests, weeds and plant diseases. Acknowledgements: This paper was performed under the frame of the Partnership in priority domains - PNII, developed with the support of MEN-UEFISCDI, project no. PN-II-PT-PCCA-2013-4-0015: Expert System for Risk Monitoring in Agriculture and Adaptation of Conservative Agricultural Technologies to Climate Change, and International Cooperation Program - Sub-3.1. Bilateral AGROCEO c. no. 21BM/2016, PN-III-P3-3.1-PM-RO-MD-2016-0034: The comparative evaluation of conventional and conservative tillage systems regarding carbon sequestration and foundation of sustainable agroecosystems.

Road Maintenance Experience Using Polyurethane (PU) Foam Injection System and Geocrete Soil Stabilization as Ground Rehabilitation

NASA Astrophysics Data System (ADS)

Fakhar, A. M. M.; Asmaniza, A.

2016-07-01

There are many types of ground rehabilation and improvement that can be consider and implement in engineering construction works for soil improvement in order to prevent road profile deformation in later stage. However, when comes to road maintenance especially on operated expressways, not all method can be apply directly as it must comply to opreation's working window and lane closure basis. Key factors that considering ideal proposal for ground rehabilitation are time, cost, quality and most importantly practicality. It should provide long lifespan structure in order to reduce continuous cycle of maintenance. Thus, this paper will present two approaches for ground rehabilitation, namely Polyurethane (PU) Foam Injection System and Geocrete Soil Stabilization. The first approach is an injection system which consists two-parts chemical grout of Isocynate and Polyol when mixed together within soil structure through injection will polymerized with volume expansion. The strong expansion of grouting causes significant compression and compacting of the surrounding soil and subsequently improve ground properties and uplift sunken structure. The later is a cold in-place recyclying whereby mixture process that combines in-situ soil materials, cement, white powder (alkaline) additive and water to produce hard yet flexible and durable ground layer that act as solid foundation with improved bearing capacity. The improvement of the mechanical behaviour of soil through these two systems is investigated by an extensive testing programme which includes in-situ and laboratory test in determining properties such as strength, stiffness, compressibility, bearing capacity, differential settlement and etc.

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.

Influence of management practices on C stabilization pathways in agricultural volcanic ash soils (Canary Islands, Spain)

NASA Astrophysics Data System (ADS)

Hernandez, Zulimar; María Álvarez, Ana; Carral, Pilar; de Figueiredo, Tomas; Almendros, Gonzalo

2014-05-01

Although C stabilization mechanisms in agricultural soils are still controversial [1], a series of overlapped pathways has been suggested [2] such as: i) insolubilization of low molecular weight precursors of soil organic matter (SOM) with reactive minerals through physical and chemical bonding, ii) selective accumulation of biosynthetic substances which are recalcitrant because of its inherent chemical composition, and iii) preservation and furter diagenetic transformation of particulate SOM entrapped within resistant microaggregates, where diffusion of soil enzymes is largely hampered. In some environments where carbohydrate and N compounds are not readily biodegraded, e.g., with water saturated micropores, an ill-known C stabilization pathway may involve the formation of Maillard's reaction products [3]. In all cases, these pathways converge in the formation of recalcitrant macromolecular substances, sharing several properties with the humic acid (HA) fraction [4]. In template forests, the selective preservation and further microbial reworking of plant biomass has been identified as a prevailing mechanism in the accumulation of recalcitrant SOM forms [5]. However, in volcanic ash soils with intense organomineral interactions, condensation reactions of low molecular weight precursors with short-range minerals may be the main mechanism [6]. In order to shed some light about the effect of agricultural management on soil C stabilization processes on volcanic ash soils, the chemical composition of HA and some structural proxies of SOM informing on its origin and potential resistance to biodegradation, were examined in 30 soils from Canary Islands (Spain) by visible, infrared (IR) and 13C nuclear magnetic resonance (NMR) spectroscopies, elementary analysis and pyrolytic techniques. The results of multivariate treatments, suggested at least three simultaneous C stabilization biogeochemical trends: i) diagenetic alteration of plant biomacromolecules in soils receiving periodical inputs of manures. This includes accumulation of slightly transformed material in scenarios of high C mineralization rates, such are in vitrandic soils. ii) Accumulation of resilient organo-mineral complexes in non andic-soils with crystalline minerals and probable inputs of pyrogenic C in the past. Finally, iii) accumulation of aliphatic structures, such as carbohydrate- and N-rich macromolecules, leading to HAs with characteristics in common with those formed in aquatic environments. The formation of these HAs could be favoured by microbial activity in andic Anthrosols, and would define a specific type of soil C stabilization mechanism of aliphatic compounds encapsulated in nanoparticle-size soil pores, where persistent hydromorphic conditions were favoured by amorphous gels in volcanic ash soils. [1] Lal, R., 2004. Mitigation and Adaptation Strategies for Global Change 12, 303-322. [2] Stevenson, F.J., 1994. Humus Chemistry: Genesis, composition, reactions. 2nd ed. Wiley, New York. [3] Ellis, G.P., 1959. Advances in Carbohydrate Chemistry 14, 63-134. [4] Almendros, G., 2008. Humic substances. In: Cheswort, W. (Ed.), Encyclopedia of Soil Science, Springer, Dordretch, pp. 97-99. [5] Kögel-Knabner, I., Hatcher, P.G., Tegelaar, E.W., de Leeuw J.W., 1992. The Science of the Total Environment 113, 89-105. [6] Hernández, Z., Almendros, G., Carral, P., Álvarez, A., Knicker, H., Pérez-Trujillo, J.P., 2012. European Journal of Soil Science 63, 603-615.

Influence of Poorly Crystalline Metal Oxides on Soil Organic Matter Stability in Four Eastern Deciduous Forest Soils

NASA Astrophysics Data System (ADS)

Porras, R. C.; Torn, M. S.; McFarlane, K. J.

2011-12-01

Association with mineral surfaces is suggested as one mechanism underlying the long-term stabilization of organic matter in soils. Several recent studies have demonstrated a positive correlation between short range ordered soil Fe and Al concentrations and soil OM or radiocarbon based residence time. The positive correlation between poorly crystalline Fe and Al and 14C-based residence times suggests that mineral associated OM persists over much longer time scales. Suggested mechanisms include encapsulation within iron oxide microaggregate structures or adsorption to highly reactive metal oxide mineral surfaces both of which have been shown to reduce the bioavailabilty of toxicant species in soil and aquatic environments. We utilized radiocarbon measurements coupled with selective chemical dissolution techniques to investigate the relationship between the concentration of short range order Fe and Al oxides and the stability of soil organic matter across four deciduous forest sites in the eastern U.S.comprising three different soil orders. Preliminary results indicate that SRO Fe and Al slow the turnover of SOM, with a significant linear relationship between computed radiocarbon turnover time and SRO Al and Fe overall (R2= 0.60,P=0.0001,CL=95%). Piecewise regression analysis on turnover time vs. metal oxide concentration for all four sites shows an apparent metal oxide threshold value at 5g kg-1. Sites with SRO Al and Fe content below this value showed no statistically significant influence on SOM stability presumably because they are present in insufficient quantity to exert a measureable influence on the decomposability of organic inputs. Among individual sites, Harvard Forest had the highest extractable metal oxide concentrations and exhibited the strongest influence of SRO Fe and Al oxides on 14C based turnover times (R2=0.91, P=0.0001,CL=95%); in this soil, poorly crystalline metal oxides are quantitatively important in stabilizing organic inputs against decomposition. Although more fundamental geochemical research will be necessary to obtain a truly mechanistic description of the specific processes responsible for organic matter stabilization in soil, an empirical approach consisting of selective chemical dissolution coupled with 14C measurements does permit useful insights into the relationship between SOM stability and SRO metal oxide content for the soils under study which may in turn be used to inform model parameterizations.

Changes of microbial activities and soil aggregation in rhizosphere soil of lettuce plants by drought and the possible influence of inoculation with AM fungi and/or PGPR

NASA Astrophysics Data System (ADS)

Kohler, J.; Caravaca, F.; Roldán, A.

2009-04-01

The effect of different arbuscular mycorrhizal (AM) fungi, Glomus intraradices (Schenk & Smith) or Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe, and plant growth-promoting rhizobacteria (PGPR) (Pseudomonas mendocina Palleroni), alone or in combination, on structural stability and microbial activity in the rhizosphere soil of Lactuca sativa L. was assessed under well-watered conditions and two levels of drought. Desiccation caused an increase in aggregate stability and water-soluble and total carbohydrates but there were no significant differences among treated soils and the control soil. The glomalin-related soil protein (GRSP) levels in both the <2 mm and 0.2-4 mm soil fractions increased with medium water stress, whereas under severe water stress they did not differ with respect to those of well-watered soils. The values of GRSP in soils inoculated with PGPR and AM fungi were higher than in the control or fertilised soil under well-watered and severe-drought conditions, while under medium-drought conditions all soils showed similar GRSP values. Soils inoculated with AM fungi and PGPR generally presented higher dehydrogenase and phosphatase activities than the control soil, independent of the water regime.

Linking measurements of biodegradability, thermal stability and chemical composition to evaluate the effects of management on soil organic matter

NASA Astrophysics Data System (ADS)

Gregorich, Ed; Gillespie, Adam; Beare, Mike; Curtin, Denis; Sanei, Hamed; Yanni, Sandra

2015-04-01

The stability of soil organic matter (SOM) as it relates to resistance to microbial degradation has important implications for nutrient cycling, emission of greenhouse gases, and C sequestration. Hence, there is interest in developing new ways to accurately quantify and characterise the labile and stable forms of soil organic C. Our objectives in this study were to evaluate and describe relationships among the biodegradability, thermal stability and chemistry of SOM in soil under widely contrasting management regimes. Samples from the same soil under permanent pasture, an arable cropping rotation, and chemical fallow were fractionated (sand: 2000-50 μm; silt: 50-5 μm, and clay: < 5 μm). Biodegradability of the SOM in size fractions and whole soils was assessed in a laboratory mineralization study. The chemical composition of SOM was characterized by X-ray absorption near-edge structure (XANES) spectroscopy at the K-edge and its thermal stability was determined by analytical pyrolysis using a Rock-Eval pyrolyser. The mineralization bioassay showed that whole soils and soil fractions under fallow were less susceptible to biodegradation than other managements and that sand-associated organic matter was significantly more susceptible than that in the silt or clay fractions. Analysis by XANES showed accumulation of carboxylates and strong depletion of amides (protein) and aromatics in the fallow whole soil. Moreover, protein depletion was most significant in the sand fraction of the fallow soil. Sand fractions in fallow and cropped soils were, however, enriched in plant-derived phenols, aromatics and carboxylates compared to the sand fraction of pasture soils. In contrast, ketones, which have been identified as products of microbially-processed organic matter, were slightly enriched in the silt fraction of the pasture soil. These data suggest reduced inputs and cropping restrict the decomposition of plant residues and, without supplemental N additions, protein-N in native SOM is significantly mineralized in fallow systems to meet microbial C mineralization demands. Analytical pyrolysis showed distinct differences in the thermal stability of SOM among the size fractions and management treatments; it also showed that the loss of SOM generally involved dehydrogenation. The temperature at which half of the C was pyrolyzed showed strong correlation with mineralizable C and thus provides solid evidence for a link between the biological and thermal stability of SOM.

Exploratory Research on Bearing Characteristics of Confined Stabilized Soil

NASA Astrophysics Data System (ADS)

Wu, Shuai Shuai; Gao, Zheng Guo; Li, Shi Yang; Cui, Wen Bo; Huang, Xin

2018-06-01

The performance of a new kind of confined stabilized soil (CSS) was investigated which was constructed by filling the stabilized soil, which was made by mixing soil with a binder containing a high content of expansive component, into an engineering plastic pipe. Cube compressive strength of the stabilized soil formed with constraint and axial compression performance of stabilized soil cylinders confined with the constraint pipe were measured. The results indicated that combining the constraint pipe and the binder containing expansion component could achieve such effects: higher production of expansive hydrates could be adopted so as to fill more voids in the stabilized soil and improve its strength; at the same time compressive prestress built on the core stabilized soil, combined of which hoop constraint provided effective radial compressive force on the core stabilized soil. These effects made the CSS acquire plastic failure mode and more than twice bearing capacity of ordinary stabilized soil with the same binder content.

76 FR 57957 - Notice of Availability of a Draft Supplemental Environmental Impact Statement for Replacement of...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-19

... a geohazard soil stabilization system, structural upgrade to remaining structures, and other site... effects to the human environment. The No-Action Alternative was analyzed and assumes the newly proposed...

Effect of Humic Acids and pesticides on Agricultural Soil Structure and Stability and Its Implication on Soil Quality

NASA Astrophysics Data System (ADS)

Gaonkar, O. D.; Nambi, I. M.; G, S. K.

2016-12-01

The functional and morphological aspects of soil structure determine the soil quality. The dispersion of colloidal soil particles, especially the clay fraction and rupture of soil aggregates, both of which play an important role in soil structure development, lead to degradation of soil quality. The main objective of this work was to determine the effect of behaviour of soil colloids on the agricultural soil structure and quality. The effect of commercial humic acid, organophosphate pesticides and soil natural organic matter on the electrical and structural properties of the soil colloids was also studied. Agricultural soil, belonging to the sandy loam texture class from northern part of India was considered in this study. In order to understand the changes in the soil quality in the presence and absence of humic acids, the soil fabric and structure was analyzed by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM). Electrical properties of natural soil colloids in aqueous suspensions were assessed by zeta potential measurements at varying pH values with and without the presence of humic acids and pesticides. The influence of natural organic matter was analyzed by oxidizing the natural soil organic matter with hydrogen peroxide. The zeta potential of the soil colloids was found to be negative in the pH range studied. The results indicated that hydrogen peroxide treatment lead to deflocculation of colloidal soil particles. In addition, the humic acids undergoes effective adsorption onto the soil surface imparting more negative zeta potential to the colloidal soil particles. The soil hydrophilicity decreased in the presence of humic acids which was confirmed by surface free energy determination. Thus, it can be concluded that the presence of humic acids altered the soil fabric and structure, thereby affecting the soil quality. This study assumes significance in understanding the soil aggregation and the interactions at soil solid-liquid interface.

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.

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.

Enhanced stabilization of Pb, Zn, and Cd in contaminated soils using oxalic acid-activated phosphate rocks.

PubMed

Zhang, Zhuo; Guo, Guanlin; Wang, Mei; Zhang, Jia; Wang, Zhixin; Li, Fasheng; Chen, Honghan

2018-01-01

Phosphate amendments, especially phosphate rock (PR), are one of the most commonly used materials to stabilize heavy metals in contaminated soils. However, most of PR reserve consists of low-grade ore, which limits the efficiency of PR for stabilizing heavy metals. This study was to enhance the stabilization of heavy metals through improving the available phosphorous (P) release of PR by oxalic acid activation. Raw PR and activated PR (APR) were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analysis, and laser diffraction to determine the changes of structure and composition of APR. The stabilization effectiveness of lead (Pb), zinc (Zn), and cadmium (Cd) in soils by APR was investigated through toxicity leaching test and speciation analysis. The results indicated that after treatment by oxalic acid, (1) the crystallinity of the fluorapatite phase of PR transformed into the weddellite phase; (2) the surface area of PR increased by 37%; (3) the particle size of PR became homogenized (20-70 μm); and (4) the available P content in PR increased by 22 times. These changes of physicochemical characteristics of PR induced that APR was more effective to transform soil heavy metals from the non-residual fraction to the residual fraction and enhance the stabilization efficiency of Pb, Zn, and Cd than PR. These results are significant for the future use of low-grade PR to stabilize heavy metals.

Restoring the biological crust cover of soils across biomes in arid North America

NASA Astrophysics Data System (ADS)

Garcia-Pichel, Ferran; Antoninka, Anita; Bowker, Matthew; Giraldo Silva, Ana; Nelson, Corey; Velasco Ayuso, Sergio; Barger, Nichole; Belnap, Jayne; Reed, Sasha; Duniway, Michael

2015-04-01

Biological soil crust communities provide important ecosystem services to arid lands, particularly regarding soil fertility and stability against erosion. In North America, and in many other areas of the globe, increasingly intense human activities, ranging from cattle grazing to military training, have resulted in the significant deterioration of biological soil surface cover of soils. With the intent of attaining sustainable land use practices, we are conducting a 5-year, multi-institutional research effort to develop feasible soil crusts restoration strategies for US military lands. We are including field sites of varying climatic regions (warm and cold deserts, in the Chihuahuan Desert and in the Great Basin, respectively) and varying edaphic characteristics (sandy and silty soils in each). We have multiple aims. First, we aim to establishing effective "biocrust nurseries" that produce viable and pedigreed inoculum, as a supply center for biocrust restoration and for research and development. Second, we aim to develop optimal field application methods of biocrust inoculum in a series of field trials. Currently in our second year of research, we will be reporting on significant advances made on optimizing methodologies for the large-scale supply of inoculum based on a) pedigreed laboratory cultures that match the microbial community structure of the original sites, and b) "in soil" biomass enhancement, whereby small amounts of local crusts are nursed under greenhouse conditions to yield hundred-fold increases in biomass without altering significantly community structure. We will also report on field trials for methodologies in field application, which included shading, watering, application of chemical polymers, and soil surface roughening. In a soon-to-be-initiated effort we also aim to evaluate soil and plant responses to biocrust restoration with respect to plant community structure, soil fertility, and soil stability, in multi-factorial field experiments. An important part of the plan will be to construct effective channels for sharing challenges and solutions in biocrust restoration with military and federal land managers.

Distribution of chloride, pH, resistivity, and sulfate levels in backfill for mechanically-stabilized earth walls and implications for corrosion testing : [summary].

DOT National Transportation Integrated Search

2015-04-01

Road construction projects often require mechanically stabilized earth (MSE), earthwork : construction in which soil is retained by walls and reinforced with wire mesh, metal strips, : and structural geosynthetics (geotextile or geogrid). The fill so...

How far can we prevent further physical soil degradation in the future?

NASA Astrophysics Data System (ADS)

Horn, Rainer

2017-04-01

Arable as well as forest soils are exposed to increasing external stresses, which coincide with a further and deeper reaching soil degradation, which may result in an aggravation of hydraulic, gaseous, thermal but also physicochemical and chemical soil functions. The decline coincides with a simultaneous reduction in useable land areas and worsens food production amongst others. Therefore, it is mandatory, that stable soil structure from the surface down to depth prevents soil compaction, sustains water infiltration, reduces rates of soil erosion by water and wind in each case to the minimum possible under the soil, terrain, land use, and climatic conditions in which the soils occur. It improves organic carbon storage in soils and optimizes microbial activity and functions. These benefits coincide with sustainable soil properties and soil management systems, which prevent - deep mechanical stress propagation which can cause irreversible soil deformation, - loss of surface soil layers with coinciding organic and mineral nutrient pool available for microbial processing and plant uptake, - Truncation of soil horizons, or damage on private and public infrastructures (roads, houses) and downstream fields. In order to prevent negative impacts on soils, it is recommended, that A) concerning prevention of soil compaction - stresses applied to soils shall not exceed the mechanical soil stability to maintain the actual functioning of chemical, physical and biological processes and to utilize their resilience (i.e. the elasticity), - land use management strategies have to be related to the actual soil properties in order to optimize plant growth, yield, filtering and buffering of infiltrating water, and carbon sequestration. B) soil erosion by - water, wind, and tillage is counteracted by an adequate surface soil stability including a site specific residue management (e.g. conservation tillage), controlled traffic and harvesting, ecological grassland use strategies (e.g. fodder production and harvesting, adequate animal grazing), - wind is furthermore minimized by adequate hedgerow plantations, continuous cover crop growth, optimized particle bindings by water, infiltrating organic acids, appropriate grazing intensity. Agroforestry can be considered as an additional positive measure to reduce soil erosion risks generally and to ameliorate degraded sites. C) -plant cover on slopes remains untouched, overgrazing and consecutive soil homogenization especially under moist climatic conditions must be prevented but adjusted to the actual structure stability of the hillsides. The communication of these findings followed by application of such measures can help farmers and foresters as well as landowners to prevent (further) physical soil degradation in the future.

Temporal and spatial influences incur reconfiguration of Arctic heathland soil bacterial community structure.

PubMed

Hill, Richard; Saetnan, Eli R; Scullion, John; Gwynn-Jones, Dylan; Ostle, Nick; Edwards, Arwyn

2016-06-01

Microbial responses to Arctic climate change could radically alter the stability of major stores of soil carbon. However, the sensitivity of plot-scale experiments simulating climate change effects on Arctic heathland soils to potential confounding effects of spatial and temporal changes in soil microbial communities is unknown. Here, the variation in heathland soil bacterial communities at two survey sites in Sweden between spring and summer 2013 and at scales between 0-1 m and, 1-100 m and between sites (> 100 m) were investigated in parallel using 16S rRNA gene T-RFLP and amplicon sequencing. T-RFLP did not reveal spatial structuring of communities at scales < 100 m in any site or season. However, temporal changes were striking. Amplicon sequencing corroborated shifts from r- to K-selected taxon-dominated communities, influencing in silico predictions of functional potential. Network analyses reveal temporal keystone taxa, with a spring betaproteobacterial sub-network centred upon a Burkholderia operational taxonomic unit (OTU) and a reconfiguration to a summer sub-network centred upon an alphaproteobacterial OTU. Although spatial structuring effects may not confound comparison between plot-scale treatments, temporal change is a significant influence. Moreover, the prominence of two temporally exclusive keystone taxa suggests that the stability of Arctic heathland soil bacterial communities could be disproportionally influenced by seasonal perturbations affecting individual taxa. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.

Long-Term Grazing Exclusion Improves the Composition and Stability of Soil Organic Matter in Inner Mongolian Grasslands

PubMed Central

Wang, Chunyan; He, Nianpeng; Zhang, Jinjing; Lv, Yuliang; Wang, Li

2015-01-01

Alteration of the composition of soil organic matter (SOM) in Inner Mongolian grassland soils associated with the duration of grazing exclusion (GE) has been considered an important index for evaluating the restoring effects of GE practice. By using five plots from a grassland succession series from free grazing to 31-year GE, we measured the content of soil organic carbon (SOC), humic acid carbon (HAC), fulvic acid carbon (FAC), humin carbon (HUC), and humic acid structure to evaluate the changes in SOM composition. The results showed that SOC, HUC, and the ratios of HAC/FAC and HAC/extractable humus carbon (C) increased significantly with prolonged GE duration, and their relationships can be well fitted by positive exponential equations, except for FAC. In contrast, the HAC content increased logarithmically with prolonged GE duration. Long-term GE enhanced the content of SOC and soil humification, which was obvious after more than 10 years of GE. Solid-state 13C nuclear magnetic resonance spectroscopy showed that the ratios of alkyl C/O-alkyl C first decreased, and then remained stable with prolonged GE. Alternately, the ratios of aromaticity and hydrophobicity first increased, and then were maintained at relatively stable levels. Thus, a decade of GE improved the composition and structure of SOM in semiarid grassland soil and made it more stable. These findings provide new evidence to support the positive effects of long-term GE on soil SOC sequestration in the Inner Mongolian grasslands, in view of the improvement of SOM structure and stability. PMID:26057249

Long-Term Grazing Exclusion Improves the Composition and Stability of Soil Organic Matter in Inner Mongolian Grasslands.

PubMed

Wang, Chunyan; He, Nianpeng; Zhang, Jinjing; Lv, Yuliang; Wang, Li

2015-01-01

Alteration of the composition of soil organic matter (SOM) in Inner Mongolian grassland soils associated with the duration of grazing exclusion (GE) has been considered an important index for evaluating the restoring effects of GE practice. By using five plots from a grassland succession series from free grazing to 31-year GE, we measured the content of soil organic carbon (SOC), humic acid carbon (HAC), fulvic acid carbon (FAC), humin carbon (HUC), and humic acid structure to evaluate the changes in SOM composition. The results showed that SOC, HUC, and the ratios of HAC/FAC and HAC/extractable humus carbon (C) increased significantly with prolonged GE duration, and their relationships can be well fitted by positive exponential equations, except for FAC. In contrast, the HAC content increased logarithmically with prolonged GE duration. Long-term GE enhanced the content of SOC and soil humification, which was obvious after more than 10 years of GE. Solid-state 13C nuclear magnetic resonance spectroscopy showed that the ratios of alkyl C/O-alkyl C first decreased, and then remained stable with prolonged GE. Alternately, the ratios of aromaticity and hydrophobicity first increased, and then were maintained at relatively stable levels. Thus, a decade of GE improved the composition and structure of SOM in semiarid grassland soil and made it more stable. These findings provide new evidence to support the positive effects of long-term GE on soil SOC sequestration in the Inner Mongolian grasslands, in view of the improvement of SOM structure and stability.

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.

Influence of Soil Organic Matter Stabilization Mechanisms on Temperature Sensitivity of Soil Respiration

NASA Astrophysics Data System (ADS)

Gillabel, J.; de Gryze, S.; Six, J.; Merckx, R.

2007-12-01

Knowledge on the sensitivity of soil organic matter (SOM) respiration to changes in temperature is crucial for predicting future impacts of climate change on soil C stocks. Temperature sensitivity of respiration is determined by the chemical structure of the compound to be decomposed and by the availability of the organic matter for decomposers. Biochemically recalcitrant SOM has a higher temperature sensitivity than biochemically labile SOM. However, it is hypothesized that the stabilization of SOM by interaction with the soil matrix could be an important attenuating control on temperature sensitivity. We investigated the effect of different SOM stabilization mechanisms on temperature sensitivity of SOM respiration. Two main mechanisms were considered: chemical interactions of SOM with clay and silt particles, and physical protection inside aggregates. Soil samples from an agricultural silt loam soil were fractionated by wet-sieving into macroaggregates, microaggregates and silt+clay fractions. SOM stabilization in the silt+clay fraction occurs mainly chemically, whereas in aggregates physical protection of SOM is more important. Samples of each fraction and of bulk soil were incubated at two temperatures (20°C and 30°C) for one month. After 2% of total soil carbon was respired, temperature sensitivity was determined for respiration of the next 0.5% of total soil carbon. This was done by calculating a Q10 value as the ratio of the times needed at each temperature to respire that fraction of the soil C. This method allows determination of temperature sensitivity independent of C quality. Calculated Q10 values decreased in the order bulk soil > macroaggregates > microaggregates > silt+clay, with the difference between macroaggregate Q10 and silt+clay Q10 being the only significant difference. These results indicate that protection of SOM attenuates temperature sensitivity, with chemical protection (silt+clay) having a larger effect than physical protection (aggregates).

Seasonal Effects on the Relationships Between Soil Water Content, Pore Water Pressure and Shear Strength and Their Implications for Slope Stability

NASA Astrophysics Data System (ADS)

Hughes, P. N.

2015-12-01

A soil's shear resistance is mainly dependent upon the magnitude of effective stress. For small to medium height slopes (up to 10m) in clay soils the total stress acting along potential failure planes will be low, therefore the magnitude of effective stress (and hence soil shear strength) will be dominated by the pore-water pressure. The stability of slopes on this scale through periods of increased precipitation is improved by the generation of negative pore pressures (soil suctions) during preceding, warmer, drier periods. These negative pore water pressures increase the effective stress within the soil and cause a corresponding increase in shearing resistance. The relationships between soil water content and pore water pressure (soil water retention curves) are known to be hysteretic, but for the purposes of the majority of slope stability assessments in partially saturated clay soils, these are assumed to be consistent with time. Similarly, the relationship between shear strength and water content is assumed to be consistent over time. This research presents a laboratory study in which specimens of compacted Glacial Till (typical of engineered slopes within the UK) were subjected to repeated cycles of wetting and drying to simulate seasonal cycles. At predetermined water contents, measurements of soil suction were made using tensiometer and dewpoint potentiometer methods. The undrained shear strength of the specimens was then measured using triaxial strength testing equipment. Results indicate that repeated wetting and drying cycles caused a change in the soil water retention behaviour. A reduction in undrained shear strength at corresponding water contents along the wetting and drying paths was also observed. The mechanism for the change in the relationship is believed to be a deterioration in the soil physical structure due to shrink/swell induced micro-cracking. The non-stationarity of these relationships has implications for slope stability assessment.

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

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.

Plant diversity and root traits benefit physical properties key to soil function in grasslands.

PubMed

Gould, Iain J; Quinton, John N; Weigelt, Alexandra; De Deyn, Gerlinde B; Bardgett, Richard D

2016-09-01

Plant diversity loss impairs ecosystem functioning, including important effects on soil. Most studies that have explored plant diversity effects belowground, however, have largely focused on biological processes. As such, our understanding of how plant diversity impacts the soil physical environment remains limited, despite the fundamental role soil physical structure plays in ensuring soil function and ecosystem service provision. Here, in both a glasshouse and a long-term field study, we show that high plant diversity in grassland systems increases soil aggregate stability, a vital structural property of soil, and that root traits play a major role in determining diversity effects. We also reveal that the presence of particular plant species within mixed communities affects an even wider range of soil physical processes, including hydrology and soil strength regimes. Our results indicate that alongside well-documented effects on ecosystem functioning, plant diversity and root traits also benefit essential soil physical properties. © 2016 The Authors Ecology Letters published by CNRS and John Wiley & Sons Ltd.

Possibilities of the particle finite element method for fluid-soil-structure interaction problems

NASA Astrophysics Data System (ADS)

Oñate, Eugenio; Celigueta, Miguel Angel; Idelsohn, Sergio R.; Salazar, Fernando; Suárez, Benjamín

2011-09-01

We present some developments in the particle finite element method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the solid domains (the later including soil/rock and structures). A mesh connects the particles (nodes) defining the discretized domain where the governing equations for each of the constituent materials are solved as in the standard FEM. The stabilization for dealing with an incompressibility continuum is introduced via the finite calculus method. An incremental iterative scheme for the solution of the non linear transient coupled FSSI problem is described. The procedure to model frictional contact conditions and material erosion at fluid-solid and solid-solid interfaces is described. We present several examples of application of the PFEM to solve FSSI problems such as the motion of rocks by water streams, the erosion of a river bed adjacent to a bridge foundation, the stability of breakwaters and constructions sea waves and the study of landslides.

Do anaerobic digestates promote dispersion, acidification and water repellency in soils?

NASA Astrophysics Data System (ADS)

Voelkner, Amrei; Holthusen, Dörthe; Horn, Rainer

2014-05-01

Digestates are used as organic fertilizer on agricultural land due to their high amounts of nutrients (e.g. potassium, sodium). It is commonly expected that the application of sludge derived from anaerobic digestion can influence the soil structure and soil stability. Due to the fact that digestates contain large quantities of monovalent salts and long-chained fatty acids, the consequence of sludge amendment can be soil degradation caused by acidification, dispersion and increased water-repellency. Thus, water infiltration can be impeded which results in a preservation of stable soil aggregates. However, a diminished water infiltration can support water erosion and preferential flow of easy soluble nutrients into the groundwater. Our research was conducted with different digestates derived from maize, wheat and sugar beet to examine occurring processes in soils of two different textures after the application of anaerobic sludges. Particularly, we focused on the wetting properties of the soil. For this purpose, the wetting behavior was investigated by determining the sorptivity-based Repellency Index with moist samples and the contact angle with homogenized, air-dried soil material. Further surveys were carried out to assess the flow behavior of digestates application and the deformation of the particle-to-particle association by microscaled shearing. Additionally, the acidification process in the soil as a result of sludge application was investigated. To account for the dispersive impact of digestates, the turbidity of soil suspensions was ascertained. We summarize from the results that the digestates have a clear impact on the water repellency of the soil. We recognized a shift to more hydrophobic conditions. Partially, the pH remains on a high level due to the alkaline digestate, but several samples show a decline of pH, depending on the soil texture, respectively. However, soil structure was weakened as was shown by an increase of turbidity. As a conclusion, we point out the necessity to take into account the impact which anaerobic digestates might have on soil structure and stability in addition to their fertilizing effect to sustain the soil in a good state.

Untangling the biological contributions to soil stability in semiarid shrublands

USGS Publications Warehouse

Chaudhary, V. Bala; Bowker, Matthew A.; O'Dell, Thomas E.; Grace, James B.; Redman, Andrea E.; Rillig, Matthias C.; Johnson, Nancy C.

2009-01-01

Communities of plants, biological soil crusts (BSCs), and arbuscular mycorrhizal (AM) fungi are known to influence soil stability individually, but their relative contributions, interactions, and combined effects are not well understood, particularly in arid and semiarid ecosystems. In a landscape-scale field study we quantified plant, BSC, and AM fungal communities at 216 locations along a gradient of soil stability levels in southern Utah, USA. We used multivariate modeling to examine the relative influences of plants, BSCs, and AM fungi on surface and subsurface stability in a semiarid shrubland landscape. Models were found to be congruent with the data and explained 35% of the variation in surface stability and 54% of the variation in subsurface stability. The results support several tentative conclusions. While BSCs, plants, and AM fungi all contribute to surface stability, only plants and AM fungi contribute to subsurface stability. In both surface and subsurface models, the strongest contributions to soil stability are made by biological components of the system. Biological soil crust cover was found to have the strongest direct effect on surface soil stability (0.60; controlling for other factors). Surprisingly, AM fungi appeared to influence surface soil stability (0.37), even though they are not generally considered to exist in the top few millimeters of the soil. In the subsurface model, plant cover appeared to have the strongest direct influence on soil stability (0.42); in both models, results indicate that plant cover influences soil stability both directly (controlling for other factors) and indirectly through influences on other organisms. Soil organic matter was not found to have a direct contribution to surface or subsurface stability in this system. The relative influence of AM fungi on soil stability in these semiarid shrublands was similar to that reported for a mesic tallgrass prairie. Estimates of effects that BSCs, plants, and AM fungi have on soil stability in these models are used to suggest the relative amounts of resources that erosion control practitioners should devote to promoting these communities. This study highlights the need for system approaches in combating erosion, soil degradation, and arid-land desertification.

Response of soil biota to vineyard interrow soil cultivation can be altered by the surrounding landscape

NASA Astrophysics Data System (ADS)

Zaller, Johann; Buchholz, Jacob; Querner, Pascal; Paredes, Daniel; Kratschmer, Sophie; Schwantzer, Martina; Winter, Silvia; Strauss, Peter; Bauer, Thomas; Burel, Françoise; Guernion, Muriel; Scimia, Jennifer; Nicolai, Annegret; Cluzeau, Daniel

2017-04-01

Ecosystem services provided by viticultural landscapes result from interactions between management intensity, soil properties, organisms inhabiting these landscapes, and the diversity and structure of the surrounding landscape. However, there is actually very little known to what extent these different factors influence the abundance and diversity of various soil biota. In this study we examined (i) to what extent different soil management intensities of interrows affect the activity and diversity of soil biota (earthworms, Collembola, litter decomposition), (ii) the role of soil properties in influencing these effects and (iii) whether the surrounding landscape structure is altering these interactions. We collected data in 16 vineyards in Austria embedded in landscapes with varying structure (i.e. from structurally simple to complex) and assessed earthworms (hand sorting), Collembola (pitfall trapping and soil coring), litter decomposition (tea bag method). Additionally, soil physical (water infiltration, aggregate stability, porosity, bulk density, soil texture) and chemical (pH, soil carbon content, cation exchange capacity, potassium, phosphorus) parameters were assessed. The landscape surrounding our vineyards within a radius of 750 m was assessed by field mapping using a geographical information system. Results showed that different soil biota/processes are differently affected by soil cultivation intensity and soil properties. Parameters describing the surrounding landscape interacted more with the responses of Collembola to soil cultivation than with earthworms or litter decomposition. These investigations are part of the transdisciplinary BiodivERsA project VineDivers (www.vinedivers.eu) and will ultimately lead into management recommendations for various stakeholders.

[Soil microbial community structure of monoculture and mixed plantation stands of native tree species in south subtropical China].

PubMed

Luo, Da; Shi, Zuo-Min; Tang, Jing-Chao; Liu, Shi-Rong; Lu, Li-Hua

2014-09-01

The effects of three plantation stands, Erythrophleumf ordii (EF), Pinus massoniana (PM), and their mixed plantation (MP), on soil microbial biomass and microbial community structure in south subtropical China were studied by the method of phospholipid fatty acids (PLFAs) analysis. The results showed that the amounts of microbial total PLFAs and PLFAs of each microbial group in these three plantation stand soils were significantly higher in dry season than in rainy season. In dry season, the amounts of microbial total PLFAs, bacteria PLFAs, fungi PLFAs, and actinomycetes PLFAs were the highest in the PM soil, moderate in the MP soil, and the lowest in the EF soil. But in rainy season, the amounts of microbial total PLFAs, bacteria PLFAs, fungi PLFAs, and arbuscular mycorrhizal fungi (AMF) PLFAs in the EF soil were higher than in the MP soil, and were significantly higher than in the PM soil. Principal component analysis (PCA) indicated that the variations in soil microbial community structure composition were affected by both plantation types and seasons. Redundancy analysis (RDA) of soil microbial community structure and environmental factors showed that soil temperature and moisture, pH, total nitrogen content, and ammonium nitrogen content had significant correlations with PLFA signatures. In addition, the ratio of fungi PLFAs to bacteria PLFAs in the MP soil was the highest among the three stand soils within the whole year, indicating that mixed plantation stands could facilitate the stability of the soil ecosystem.

Assessment of soil organic matter persistence under different land uses applying a physical fractionation procedure

NASA Astrophysics Data System (ADS)

Giannetta, Beatrice; Plaza, César; López-de-Sá, Esther G.; Vischetti, Costantino; Zaccone, Claudio

2017-04-01

The understanding of the mechanisms involved in the build-up of soil organic matter (SOM) pools with long residence time is tightly linked to the comprehension of C dynamics. Organo-mineral associations are known to be strongly correlated with the accumulation of selective preserved C forms. Adsorption to minerals, as well as occlusion within aggregates, may affect SOM protection in different ways depending on its molecular structure and pedo-climatic conditions. In this research, we investigated changes in quantity and quality of SOM pools characterized by different protection mechanisms in coniferous and broadleaved forest soils, grassland soils, technosols and an agricultural soil with different organic amendments, in order to evaluate the influence of both land use and organic matter nature on physical and/or chemical stabilization of SOM. In particular, free (FR), intra-macroaggregate (MA), intra-microaggregate (MI), and mineral-associated (Min) fractions were separated in order to define physical and chemical mechanisms responsible for the SOM protection against degradation. All these SOM fractions were analyzed for organic C and total N concentration, and their stability assessed by thermogravimetric analysis (TD-TGA). Preliminary data show that, for all land uses, most of the organic C (40-60%) is found in the Min pool, followed by FR (20-40%)>MI MA. With the only exception of the FR, no significant correlations were found between the C/N ratio and a thermal stability index (H550-400/400-250) of each fraction; at the same time, a highly significant and positive correlation was found between these two parameters in all fractions isolated from agricultural soils. In particular, the thermal stability index measured in all Min fractions may be related to the more marked presence of labile compounds in this pool relative to recalcitrant compounds. Conversely, FR OM could not always represent a fresh and readily decomposable fraction.Furthermore, OM associated with soil minerals exhibits a low C/N ratio, possibly attributed to the association of proteins and peptides with the mineral phase. Future research steps will allow a better understanding of the role of molecular structure on SOM stabilization mechanisms, with a particular focus on the description of C and N compounds in organo-mineral associations.

Can we manipulate root system architecture to control soil erosion?

NASA Astrophysics Data System (ADS)

Ola, A.; Dodd, I. C.; Quinton, J. N.

2015-03-01

Soil erosion is a major threat to soil functioning. The use of vegetation to control erosion has long been a topic for research. Much of this research has focused on the above ground properties of plants, demonstrating the important role that canopy structure and cover plays in the reduction of water erosion processes. Less attention has been paid to plant roots. Plant roots are a crucial yet under-researched factor for reducing water erosion through their ability to alter soil properties, such as aggregate stability, hydraulic function and shear strength. However, there have been few attempts to manipulate plant root system properties to reduce soil erosion. Therefore, this review aims to explore the effects that plant roots have on soil erosion and hydrological processes, and how plant root architecture might be manipulated to enhance its erosion control properties. We clearly demonstrate the importance of root system architecture for the control of soil erosion. We also demonstrate that some plant species respond to nutrient enriched patches by increasing lateral root proliferation. The soil response to root proliferation will depend upon its location: at the soil surface dense mats of roots may block soil pores thereby limiting infiltration, enhancing runoff and thus erosion; whereas at depth local increases in shear strength may reinforce soils against structural failure at the shear plane. Additionally, in nutrient deprived regions, root hair development may be stimulated and larger amounts of root exudates released, thereby improving aggregate stability and decreasing erodibility. Utilising nutrient placement at depth may represent a potentially new, easily implemented, management strategy on nutrient poor agricultural land or constructed slopes to control erosion, and further research in this area is needed.

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...

[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.

[Study on mechanism of SOM stabilization of paddy soils under long-term fertilizations].

PubMed

Luo, Lu; Zhou, Ping; Tong, Cheng-Li; Shi, Hui; Wu, Jin-Shui; Huang, Tie-Ping

2013-02-01

Fourier transform infrared spectroscopy (FTIR) was applied to study the structure of soil organic matter (SOM) of paddy soils under long-term different fertilization treatments. The aim was to clarify the different distribution of SOM between different fertilization methods and between topsoil and subsoil, and to explore the stability mechanism of SOM under different fertilization treatments. The results showed that the content of topsoil organic carbon (SOC) was the highest under organic-inorganic fertilizations, with the increment of SOC by 18.5%, 12.9% and 18.4% under high organic manure (HOM), low organic manure (LOM) and straw returning (STW) respectively compared with no fertilization treatment (CK). The long-term fertilizations also changed the chemical structure of SOM. As compared with CK, different fertilization treatments increased the functional group absorbing intensity of chemical resistance compounds (aliphatic, aromaticity), carbohydrate and organo-silicon compounds, which was the most distinctive under treatments of HOM, LOM and STW. For example, the absorbing intensity of alkyl was 0.30, 0.25 and 0.29 under HOM, LOM and STW, respectively. These values were increased by 87% , 56% and 81% as compared with that under CK treatment. The functional group absorbing intensity of SOM in the topsoil was stronger than that in the subsoil, with the most distinctive difference under HOM, LOM and STW treatments. The present research indicated that the enhanced chemical resistance of functional group of SOM may contribute to the high contents of SOC in the paddy soils under long-term organic-inorganic fertilizations, which also suggested a chemical stabilization mechanism of SOM in the paddy soils.

Stress-Strain State of a Combinational Soil Half-Space During Reconstruction

NASA Astrophysics Data System (ADS)

Prusov, D. E.

2014-03-01

A method for studying the stress-strain state of soil-retaining structures is proposed. It is based on the nonlinear theory of elasticity and plasticity of soils and allows for geometrical and physical nonlinearities. Numerical and analytical results on the stability of a retaining wall are compared. The influence of an inhomogeneous soil half-space on the stress-strain state of a deep-ditch wall is analyzed numerically. A scientific rationale for the redevelopment of densely built-up residential areas under adverse geological engineering conditions is recommended.

Soil Tillage as a Factor of Soil Conservation

NASA Astrophysics Data System (ADS)

Sherer, D. V.; Chumanova, N. N.

2017-05-01

The work describes the question of the soil treatment system influence on agro-physical and microbiological properties of gray forest soils, and yield of barley in Western Siberia. Research works were carried out in 2013-2014 in Yaya region of the Kemerovo region. Tillage affects soil structure. The water stability in zero tillage conditions was poor (15.7%). Soil density corresponding to the optimum rate for barley is formed by the zonal processing system, while at the zero tillage soil remains solid. The best indicators of phosphataze, catalysis and amylase activity are formed with minimum processing system. In the experiment the highest yield of barley was obtained with minimum tillage - 12.1 c/ha.

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

Stability of Soil Organic Matter in Alpine Ecosystems: No Relationship with Vegetation

NASA Astrophysics Data System (ADS)

Matteodo, M.; Sebag, D.; Vittoz, P.; Verrecchia, E. P.

2016-12-01

There is an emerging understanding of mechanisms governing soil organic matter (SOM) stability, which is challenging the historical view of carbon persistence1. According to this alternative vision, SOM stability is not directly regulated by the molecular structure of plant inputs (i.e. the historical view), but the biotic and abiotic conditions of the surrounding environment which play a major role and mediate the influence of compound chemistry. The persistence of SOM is thus influenced by ecological conditions, controlling the access and activity of decomposers' enzymes and being ecosystem-dependent. In this study, we investigated differences of (1) carbon content, and (2) stability of organic matter in litter and organomineral layers from the most widespread plant communities at the subalpine-alpine level of the Swiss Alps. For this purpose, 230 samples from 47 soil profiles have been analysed across seven plant communities, along a subalpine-alpine elevation gradient. Both calcareous and siliceous grasslands were studied, as well as snowbed and ridge communities. Aboveground litter and A horizons were sampled and analysed using Rock-Eval Pyrolysis, a proxy-technique commonly used for the investigation of organic matter composition and stability2,3. Results show that the litter layers of the seven plant communities are significantly different in terms of total organic carbon (TOC) content, but slightly variable in terms of stability. The situation is radically different in the organomineral horizons where the amount of organic carbon is interestingly homogeneous, as well as the SOM stability. In mineral horizons, the amount and stability of SOM are mainly driven by the geological settings, and therefore vary in the different plant communities. These results show a clear disconnection between organic, organomineral, and mineral horizons in terms of factors governing soil organic matter stability. Consistent with the recent view of the carbon balance, plant input seems to influence the litter C dynamics (qualitatively and quantitatively) but not the SOM stability in A and mineral horizons. References 1Schmidt MWI, et al. (2011) Nature 478, 49-56. 2Disnar JR, et al. (2003) Org. Geochem. 34, 327-343. 3Sebag D, et al. (2006) Eur. J. of Soil Sci. 57, 344-355.

HDMR methods to assess reliability in slope stability analyses

NASA Astrophysics Data System (ADS)

Kozubal, Janusz; Pula, Wojciech; Vessia, Giovanna

2014-05-01

Stability analyses of complex rock-soil deposits shall be tackled considering the complex structure of discontinuities within rock mass and embedded soil layers. These materials are characterized by a high variability in physical and mechanical properties. Thus, to calculate the slope safety factor in stability analyses two issues must be taken into account: 1) the uncertainties related to structural setting of the rock-slope mass and 2) the variability in mechanical properties of soils and rocks. High Dimensional Model Representation (HDMR) (Chowdhury et al. 2009; Chowdhury and Rao 2010) can be used to carry out the reliability index within complex rock-soil slopes when numerous random variables with high coefficient of variations are considered. HDMR implements the inverse reliability analysis, meaning that the unknown design parameters are sought provided that prescribed reliability index values are attained. Such approach uses implicit response functions according to the Response Surface Method (RSM). The simple RSM can be efficiently applied when less than four random variables are considered; as the number of variables increases, the efficiency in reliability index estimation decreases due to the great amount of calculations. Therefore, HDMR method is used to improve the computational accuracy. In this study, the sliding mechanism in Polish Flysch Carpathian Mountains have been studied by means of HDMR. The Southern part of Poland where Carpathian Mountains are placed is characterized by a rather complicated sedimentary pattern of flysh rocky-soil deposits that can be simplified into three main categories: (1) normal flysch, consisting of adjacent sandstone and shale beds of approximately equal thickness, (2) shale flysch, where shale beds are thicker than adjacent sandstone beds, and (3) sandstone flysch, where the opposite holds. Landslides occur in all flysch deposit types thus some configurations of possible unstable settings (within fractured rocky-soil masses) resulting in sliding mechanisms have been investigated in this study. The reliability indices values drawn from the HDRM method have been compared with conventional approaches as neural networks: the efficiency of HDRM is shown in the case studied. References Chowdhury R., Rao B.N. and Prasad A.M. 2009. High-dimensional model representation for structural reliability analysis. Commun. Numer. Meth. Engng, 25: 301-337. Chowdhury R. and Rao B. 2010. Probabilistic Stability Assessment of Slopes Using High Dimensional Model Representation. Computers and Geotechnics, 37: 876-884.

Influence of Water Content on Pullout Behaviour of Geogrid

NASA Astrophysics Data System (ADS)

Chen, Rong; Song, Yang-yang; Hao, Dong-xue; Gao, Yu-cong

2017-06-01

The interaction between geogrid and soil is fundamental and crucial factor on safety and stability of geogrid-reinforced earth structure. Therefore, the interface index between geogrid and soil is of vital importance in the design of reinforced earth structures. The pullout behaviour of geogrid in soil is studied, an experimental investigation is conducted using geogrid in four groups of soil with 20%, 24%, 28%, 32% water contents, which correspond to normal stresses of 50, 100, 200 and 300 kPa respectively. The results indicate that the geogrid embedded in soil mainly represents pullout failure, and the ultimate pullout force is sensitive to water content. It decreases with the increase of the water content firstly. Besides, the water content influences the process of the pullout behaviour. The increase of water content leads to the ultimate pullout force soon.

Relating microbial community structure to functioning in forest soil organic carbon transformation and turnover.

PubMed

You, Yeming; Wang, Juan; Huang, Xueman; Tang, Zuoxin; Liu, Shirong; Sun, Osbert J

2014-03-01

Forest soils store vast amounts of terrestrial carbon, but we are still limited in mechanistic understanding on how soil organic carbon (SOC) stabilization or turnover is controlled by biotic and abiotic factors in forest ecosystems. We used phospholipid fatty acids (PLFAs) as biomarker to study soil microbial community structure and measured activities of five extracellular enzymes involved in the degradation of cellulose (i.e., β-1,4-glucosidase and cellobiohydrolase), chitin (i.e., β-1,4-N-acetylglucosaminidase), and lignin (i.e., phenol oxidase and peroxidase) as indicators of soil microbial functioning in carbon transformation or turnover across varying biotic and abiotic conditions in a typical temperate forest ecosystem in central China. Redundancy analysis (RDA) was performed to determine the interrelationship between individual PFLAs and biotic and abiotic site factors as well as the linkage between soil microbial structure and function. Path analysis was further conducted to examine the controls of site factors on soil microbial community structure and the regulatory pathway of changes in SOC relating to microbial community structure and function. We found that soil microbial community structure is strongly influenced by water, temperature, SOC, fine root mass, clay content, and C/N ratio in soils and that the relative abundance of Gram-negative bacteria, saprophytic fungi, and actinomycetes explained most of the variations in the specific activities of soil enzymes involved in SOC transformation or turnover. The abundance of soil bacterial communities is strongly linked with the extracellular enzymes involved in carbon transformation, whereas the abundance of saprophytic fungi is associated with activities of extracellular enzymes driving carbon oxidation. Findings in this study demonstrate the complex interactions and linkage among plant traits, microenvironment, and soil physiochemical properties in affecting SOC via microbial regulations.

Effect of Ionic Soil Stabilizers on Soil-Water Characteristic of Special Clay

NASA Astrophysics Data System (ADS)

Cui, D.; Xiang, W.

2011-12-01

The engineering properties of special clay are conventionally improved through the use of chemical additive such as ionic soil stabilizer (ISS). Such special clays are often referred to as stabilized or treated clays. The soil-water characteristic curves (SWCC) of special clays from Henan province and Hubei province were measured both in natural and stabilized conditions using the pressure plate apparatus in the suction range of 0-500 kPa. The SWCC results are used to interpret the special clays behavior due to stabilizer treatment. In addition, relationships were developed between the basic clay and stabilized properties such as specific surface area and pore size distribution. The analysis showed that specific surface area decreases, cumulative pore volume and average pore size diameter decrease, dehydration rate slows and the thickness of water film thins after treatment with Ionic Soil Stabilizer. The research data and interpretation analysis presented here can be extended to understand the water film change behaviors influencing the mechanical and physical properties of stabilized special clay soils. KEY WORDS: ionic soil stabilizer, special clay, pore size diameter, specific surface area, soil water characteristic curve, water film

Short-term incubation studies on degradation of biochar in soil

NASA Astrophysics Data System (ADS)

Lanza, Giacomo; Wirth, Stephan; Geßler, Arthur; Kern, Jürgen; Mumme, Jan

2014-05-01

Biochar is considered a stable, recalcitrant substance, which holds potential to store carbon in soils for prolonged time and therefore would provide a long-term carbon sink. Furthermore, biochar is discussed to enhance soil fertility and plant productivity, and may improve water and nutrient holding capacity. However, mineralisation to CO2 may occur, as for any soil organic carbon pool, depending on char composition, soil properties and environmental conditions. Therefore, it is important to gain insight into the stability of its carbon structure and the dynamics of decay processes in soil. The evaluation of biochar stability in soil is complicated by the impact of external factors thus as soil moisture and temperature, soil nutrient status and moreover by extended decay timescales. To overcome these difficulties, we performed dynamic incubation experiments under laboratory conditions, using a multi-channel, automated infra-red gas analysis system at 20°C for up to 10 days to detect CO2 emission over time. Our aim was to compare the decay dynamics of different biochar preparations added to soil, i.e. HTC-char and pyrochar from maize silage with and without biological post-processing (anaerobic digestion), as compared to unmodified maize straw. Digestate from a maize silage-fed anaerobic biogas reactor was also tested. As a result, the addition of charred or digested materials to soil resulted in much lower CO2 emission rates as compared to the unmodified maize straw, proving stability of biochar carbon compounds. Pyrochar showed to be the most stable of all substrates added, as the CO2 emission was hardly distinguishable from that of the control soil. Soil enriched with HTC-char emitted significantly more CO2 compared to soil enriched with pyrochar, but the post-processing was effective in reducing the emissions. Furthermore, HTC-char showed a two-step decay kinetics, which cannot apparently be explained with a simple double-pool model. In conclusion, the short-term incubation approach was effective to highlight differences in decomposition dynamics between the considered substrates in soil, and confirmed the effectiveness of the charring process to increase the stability of organic substrates in soil. More investigations are necessary to reveal the impact of readily available substrates and nutrients on degradation of biochar in soil, and to clarify the mechanisms responsible for the observed kinetics in order to derive a suitable process model.

Effects of spent mushroom compost application on the physicochemical properties of a degraded soil

NASA Astrophysics Data System (ADS)

Gümüş, İlknur; Şeker, Cevdet

2017-11-01

Under field and laboratory conditions, the application of organic amendments has generally shown an improvement in soil physicochemical properties. Here, spent mushroom compost (SMC) is proposed as a suitable organic amendment for soil structure restoration. Our study assessed the impact of SMC on the physicochemical properties of a weak-structured and physically degraded soil. The approach involved the establishment of a pot experiment with SMC applications into soil (control, 0.5, 1, 2, 4 and 8 %). Soils were incubated at field capacity (-33 kPa) for 21, 42, and 62 days under laboratory conditions. SMC applications into the soil significantly increased the aggregate stability (AS) and decreased the modulus of rupture. The application of SMC at rates of 1, 2, 4, and 8 % significantly increased the total nitrogen and soil organic carbon contents of the degraded soil at all incubation periods (p < 0.05). The results obtained in this study indicate that the application of SMC can improve soil physicochemical properties, which may benefit farmers, land managers, and mushroom growers.

Root architecture and wind-firmness of mature Pinus pinaster.

PubMed

Danjon, Frédéric; Fourcaud, Thierry; Bert, Didier

2005-11-01

This study aims to link three-dimensional coarse root architecture to tree stability in mature timber trees with an average of 1-m rooting depth. Undamaged and uprooted trees were sampled in a stand damaged by a storm. Root architecture was measured by three-dimensional (3-D) digitizing. The distribution of root volume by root type and in wind-oriented sectors was analysed. Mature Pinus pinaster root systems were organized in a rigid 'cage' composed of a taproot, the zone of rapid taper of horizontal surface roots and numerous sinkers and deep roots, imprisoning a large mass of soil and guyed by long horizontal surface roots. Key compartments for stability exhibited strong selective leeward or windward reinforcement. Uprooted trees showed a lower cage volume, a larger proportion of oblique and intermediate depth horizontal roots and less wind-oriented root reinforcement. Pinus pinaster stability on moderately deep soils is optimized through a typical rooting pattern and a considerable structural adaptation to the prevailing wind and soil profile.

Effect of cement injection on sandy soil slope stability, case study: slope in Petang district, Badung regency

NASA Astrophysics Data System (ADS)

Arya, I. W.; Wiraga, I. W.; GAG Suryanegara, I.

2018-01-01

Slope is a part of soil topography formed due to elevation difference from two soil surface. Landslides is frequently occur in natural slope, it is because shear force is greater than shear strength in the soil. There are some factor that influence slope stability such as: rain dissipation, vibration from earthquake, construction and crack in the soil. Slope instability can cause risk in human activity or even threaten human lives. Every years in rainy season, landslides always occur in Indonesia. In 2016, there was some landslide occurred in Bali. One of the most damaging is landslide in Petang district, Badung regency. This landslide caused main road closed entirely. In order to overcome and prevent landslide, a lot of method have been practiced and still looking for more sophisticated method for forecasting slope stability. One of the method to strengthen soil stability is filling the soil pores with some certain material. Cement is one of the material that can be used to fill the soil pores because when it is in liquid form, it can infiltrate into soil pores and fill the gap between soil particles. And after it dry, it can formed a bond with soil particle so that soil become stronger and the slope as well. In this study, it will use experimental method, slope model in laboratory to simulate a real slope behavior in the field. The first model is the slope without any addition of cement. This model will be become a benchmark for the other models. The second model is a slope with improved soil that injects the slope with cement. Injection of cement is done with varying interval distance of injection point is 5 cm and 10 cm. Each slope model will be given a load until the slope collapses. The slope model will also be analyzed with slope stability program. The test results on the improved slope models will be compared with unimproved slope. In the initial test will consist of 3 model. First model is soil without improvement or cement injection, second model is soil with cement injection interval 5 cm and third model is soil with cement injection interval 10 cm. The result is the shear strength (ϕ value) the soil is increase from 32.02° to 47.57°. The increase value of internal friction angle (ϕ) shows that an increase in shear strength of the cement improved soil. While, the value of cohesion (c) is zero indicating there is no cohesion in the soil. This is common for sand soil or sandy soil. The calculation of safety factor with GeoStructural Analysis obtained an increase of safety factor from 0.78 if the soil without cement injection to 1.07 and 1.17 if the soil is injected with cement at a distance of 10 cm and 5 cm.

Uncertainty in Ecohydrological Modeling in an Arid Region Determined with Bayesian Methods

PubMed Central

Yang, Junjun; He, Zhibin; Du, Jun; Chen, Longfei; Zhu, Xi

2016-01-01

In arid regions, water resources are a key forcing factor in ecosystem circulation, and soil moisture is the critical link that constrains plant and animal life on the soil surface and underground. Simulation of soil moisture in arid ecosystems is inherently difficult due to high variability. We assessed the applicability of the process-oriented CoupModel for forecasting of soil water relations in arid regions. We used vertical soil moisture profiling for model calibration. We determined that model-structural uncertainty constituted the largest error; the model did not capture the extremes of low soil moisture in the desert-oasis ecotone (DOE), particularly below 40 cm soil depth. Our results showed that total uncertainty in soil moisture prediction was improved when input and output data, parameter value array, and structure errors were characterized explicitly. Bayesian analysis was applied with prior information to reduce uncertainty. The need to provide independent descriptions of uncertainty analysis (UA) in the input and output data was demonstrated. Application of soil moisture simulation in arid regions will be useful for dune-stabilization and revegetation efforts in the DOE. PMID:26963523

36 CFR 219.19 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... response to climate change. Conservation. The protection, preservation, management, or restoration of... structure and/or function and changes resources, substrate availability, or the physical environment... carbon; climate regulation; water filtration, purification, and storage; soil stabilization; flood...

36 CFR 219.19 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-07-01

... response to climate change. Conservation. The protection, preservation, management, or restoration of... structure and/or function and changes resources, substrate availability, or the physical environment... carbon; climate regulation; water filtration, purification, and storage; soil stabilization; flood...

36 CFR 219.19 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... response to climate change. Conservation. The protection, preservation, management, or restoration of... structure and/or function and changes resources, substrate availability, or the physical environment... carbon; climate regulation; water filtration, purification, and storage; soil stabilization; flood...

How to interpret rheometry, an innovative technique in soil physicochemistry, correctly - explained by critical users

NASA Astrophysics Data System (ADS)

Holthusen, Dörthe; Paulus, Eloi; Pértile, Patricia; Reichert, José Miguel; José Reinert, Dalvan; Horn, Rainer

2015-04-01

In soil physics some new methods were developed in the past years, e.g. with regard to observe soil structure non-invasively by means of micro-computed tomography, while the range of methods that investigate a soil's behavior in motion, e.g. under the impact of mechanic stresses, was enlarged by rheometry. The adjustment to the specific conditions of soil as a relatively dry and heterogeneous media opened a new field compared to the materials under investigations till then, like concrete or clay dispersions. The potential of this methodology is not fully appreciated yet which we would like to change with the help of our findings and the deduced guidelines. Rheology itself has been making part of soil science already for many years; however, the technical investigation was mostly done at a large scale, by means of triaxial shear or shear frame or compression tests etc. The corresponding measuring device, the rheometer, hence was tested and developed by and for the industries of food, cosmetics, paintings and coatings and only quite recently found to be applicable to soil also. The most interesting aspect was the possibility to combine soil physics with soil chemistry, namely to relate the behavior of soil under mechanical stresses to chemical interactions like e.g. particle charge and friction between single particles by means of an amplitude sweep test. Meanwhile, many different soils of different texture, organic matter and oxides and hydroxides content, and fertilization levels have been investigated at different matric potentials and allowed for a comparatively broad classification system. Therewith, the microstructural stability of a given soil by means of stiffness degradation during an amplitude sweep test can be categorized as a function of texture and matric potential. The micro scale soil stability furthermore influences the processes and thus soil structural stability at larger scales, which supports the investigations of relationships between different scales. Transferability to field situations is given due to the character of the mechanic stress which equals those appearing e.g. under a tractor tire exerting vibrating, compressing and shearing forces. Unfortunately, the multiple results of this single test can impede the use of rheometry as their interpretation requires intensive data analysis. By pointing out the single results and their meaning for soil structure, we aim at facilitating the use of rheometry. We also suggest moderate alterations to take into account more strongly the vertical compression of soil for a more comprehensive implementation of a micro shear test. Additionally, we point out further uses of a rheometer in soil physics, which is the viscosity, i. e. the ability of a fluid to penetrate into a porous system and to be relocated within. Herewith, quite complex fluid characteristics, e.g. of animal manure, anaerobic digestates, but also pesticides in aqueous solution, root mucilage etc. can be determined and applied as improved, because more detailed, model parameters in soil water transport. As a conclusion, our contribution aims at further promoting a promising method for investigating the fundamentals of soil physics at the interface to soil chemistry.

Pyrosequencing Based Microbial Community Analysis of Stabilized Mine Soils

NASA Astrophysics Data System (ADS)

Park, J. E.; Lee, B. T.; Son, A.

2015-12-01

Heavy metals leached from exhausted mines have been causing severe environmental problems in nearby soils and groundwater. Environmental mitigation was performed based on the heavy metal stabilization using Calcite and steel slag in Korea. Since the soil stabilization only temporarily immobilizes the contaminants to soil matrix, the potential risk of re-leaching heavy metal still exists. Therefore the follow-up management of stabilized soils and the corresponding evaluation methods are required to avoid the consequent contamination from the stabilized soils. In this study, microbial community analysis using pyrosequencing was performed for assessing the potential leaching of the stabilized soils. As a result of rarefaction curve and Chao1 and Shannon indices, the stabilized soil has shown lower richness and diversity as compared to non-contaminated negative control. At the phyla level, as the degree of contamination increases, most of phyla decreased with only exception of increased proteobacteria. Among proteobacteria, gamma-proteobacteria increased against the heavy metal contamination. At the species level, Methylobacter tundripaludum of gamma-proteobacteria showed the highest relative portion of microbial community, indicating that methanotrophs may play an important role in either solubilization or immobilization of heavy metals in stabilized soils.

Interactions between soil texture, water, and nutrients control patterns of biocrusts abundance and structure

NASA Astrophysics Data System (ADS)

Young, Kristina; Bowker, Matthew; Reed, Sasha; Howell, Armin

2017-04-01

Heterogeneity in the abiotic environment structures biotic communities by controlling niche space and parameters. This has been widely observed and demonstrated in vascular plant and other aboveground communities. While soil organisms are presumably also strongly influenced by the physical and chemical dimensions of the edaphic environment, there are fewer studies linking the development, structure, productivity or function of surface soil communities to specific edaphic gradients. Here, we use biological soil crusts (biocrusts) as a model system to determine mechanisms regulating community structure of soil organisms. We chose soil texture to serve as an edaphic gradient because of soil texture's influence over biocrust distribution on a landscape level. We experimentally manipulated texture in constructed soil, and simultaneously manipulated two main outcomes of texture, water and nutrient availability, to determine the mechanism underlying texture's influence on biocrust abundance and structure. We grew biocrust communities from a field-sourced inoculum on four different soil textures, sieved from the same parent soil material, manipulating watering levels and nutrient additions across soil textures in a full-factorial design over a 5-month period of time. We measured abundance and structure of biocrusts over time, and measured two metrics of function, N2 fixation rates and soil stabilization, at the conclusion of the experiment. Our results showed finer soil textures resulted in faster biocrust community development and dominance by mosses, whereas coarser textures grew more slowly and had biocrust communities dominated by cyanobacteria and lichen. Additionally, coarser textured soils contained cyanobacterial filaments significantly deeper into the soil profile than fine textured soils. N2-fixation values increased with increasing moss cover and decreased with increasing cyanobacterial cover, however, the rate of change depended on soil texture and water amount. Soil shear resistance was highest on finer textured soil with the highest watering treatment, whereas compression resistance was highest on the coarsest textured soils with the highest watering amounts. Nutrient addition did not influence total cover or biocrust function, but did decrease lichen cover. Taken together, these results suggest that interactions between soil texture, water, and to a lesser degree nutrients, create predictable patterns in biocrust assemblage and offers a mechanistic understanding of edaphic controls over biocrust abundance and structure. These insights add to our increasing understanding of how edaphic gradients structure soil communities.

Effects of freeze-thaw on characteristics of new KMP binder stabilized Zn- and Pb-contaminated soils.

PubMed

Wei, Ming-Li; Du, Yan-Jun; Reddy, Krishna R; Wu, Hao-Liang

2015-12-01

For viable and sustainable reuse of solidified/stabilized heavy metal-contaminated soils as roadway subgrade materials, long-term durability of these soils should be ensured. A new binder, KMP, has been developed for solidifying/stabilizing soils contaminated with high concentrations of heavy metals. However, the effects of long-term extreme weather conditions including freeze and thaw on the leachability and strength of the KMP stabilized contaminated soils have not been investigated. This study presents a systematic investigation on the impacts of freeze-thaw cycle on leachability, strength, and microstructural characteristics of the KMP stabilized soils spiked with Zn and Pb individually and together. For comparison purpose, Portland cement is also tested as a conventional binder. Several series of tests are conducted including the toxicity characteristic leaching procedure (TCLP), modified European Community Bureau of Reference (BCR) sequential extraction procedure, unconfined compression test (UCT), and mercury intrusion porosimetry (MIP). The results demonstrate that the freeze-thaw cycles have much less impact on the leachability and strength of the KMP stabilized soils as compared to the PC stabilized soils. After the freeze-thaw cycle tests, the KMP stabilized soils display much lower leachability, mass loss, and strength loss. These results are assessed based on the chemical speciation of Zn and Pb, and pore size distribution of the soils. Overall, this study demonstrates that the KMP stabilized heavy metal-contaminated soils perform well under the freeze-thaw conditions.

Persistence of soil organic matter as an ecosystem property.

PubMed

Schmidt, Michael W I; Torn, Margaret S; Abiven, Samuel; Dittmar, Thorsten; Guggenberger, Georg; Janssens, Ivan A; Kleber, Markus; Kögel-Knabner, Ingrid; Lehmann, Johannes; Manning, David A C; Nannipieri, Paolo; Rasse, Daniel P; Weiner, Steve; Trumbore, Susan E

2011-10-05

Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily--and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.

Persistence of soil organic matter as an ecosystem property

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

Schmidt, M.W.; Torn, M. S.; Abiven, S.

2011-08-15

Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.

Soil stabilization by biological soil crusts in arid Tunisia

NASA Astrophysics Data System (ADS)

Guidez, Sabine; Couté, Alain; Bardat, Jacques

2015-04-01

As part of the fight against desertification (LCD) in arid Tunisia, we have been able to highlight the important role played by biological soil crusts (BSC) in soil stabilization. The identification of the major species of cyanobacteria, lichens and bryophytes, their adaptation and terrestrial colonization strategies in this high climatic constraints area through their morpho-anatomical criteria have been set. In addition to their biological composition, their internal arrangement (i.e. texture and microstructure) reflects the structural stability of BSC against erosion. Precisely, the aggregative power of cyanobacteria and their ways of moving inside a soil, the capacity of mosses to grow through the sediments and lichens ability to bind at particles on surface, thus stabilizing the substrate have been demonstrated. Then, the three biological components ability to capture soil particles has been widely illustrated, proving the major environmental contribution of BSC in arid areas biological crusts formation, providing that soils will experience an increase of organic matter and fine particles rates subsequently gaining faster and better stability. Although the thickness and the morphology of crusts are related to the cover rates of these different biological components, the water properties of the latter, studied at the environmental SEM, illustrate their important role in altering the water cycle. Thus, the mixed crusts, i.e. with good presence of three biological components, cause the highest runoff rates by their ability to retain the water and spread on the surface. In spite of a swelling coefficient in presence of water higher than cryptogams, the cyanobacterial crusts located in newly stabilized areas of our studied region, remain finally insufficiently dense to impact surface hydrology. But, we showed after all that the cyanobacteria, pioneer species, have a certain environmental role. The lichen crusts cause a increased runoff because the lichens have a ability to extend them horizontally on the soil surface. Despite the water capture for their metabolism, the water flows; it isn't released in the depth. The moss crusts show an opposite process with an increased infiltration thanks to the possibility of a vertical transit of water through their sheets, stem and roots. So, in relation to bare soils, a crust with a good microbial and cryptogamic development causes more runoff. As part of the fight against the desertification in arid Tunisia, hydrological impact of BSC may lead to elaborate some ecosystem strategies in water and soils management. Indeed, climate aridity is not synonymous with edaphic aridity.

Biological soil crusts as soil stabilizers: Chapter 16

USGS Publications Warehouse

Belnap, Jayne; Buedel, Burkhard; Weber, Bettina; Buedel, Burkhard; Belnap, Jayne

2016-01-01

Soil erosion is of particular concern in dryland regions, as the sparse cover of vascular plants results in large interspaces unprotected from the erosive forces of wind and water. Thus, most of these soil surfaces are stabilized by physical or biological soil crusts. However, as drylands are extensively used by humans and their animals, these crusts are often disturbed, compromising their stabilizing abilities. As a result, approximately 17.5% of the global terrestrial lands are currently being degraded by wind and water erosion. All components of biocrusts stabilize soils, including green algae, cyanobacteria, fungi, lichens, and bryophytes, and as the biomass of these organisms increases, so does soil stability. In addition, as lichens and bryophytes live atop the soil surface, they provide added protection from raindrop impact that cyanobacteria and fungi, living within the soil, cannot. Much research is still needed to determine the relative ability of individual species and suites of species to stabilize soils. We also need a better understanding of why some individuals or combination of species are better than others, especially as these organisms become more frequently used in restoration efforts.

Filtration stability of living brush mattresses at navigable waterways

NASA Astrophysics Data System (ADS)

Sokopp, Manuel

2017-04-01

According to the guidelines of the Federal Waterways Engineering and Research Institute in Germany, waterway construction buildings, which include soil bioengineering structures, must be stable against soil displacements. Therefore, willow brush mattresses were tested for their filtration stability in a specially developed process which is based on the testing of geotextiles and armourstones used for navigable waterway constructions. In March 2016 willow brush mattresses made of white (Salix alba L.) or basket willows (Salix viminalis L.) were planted in 16 sample boxes, each with a cross-section area of 30x30 cm. For the tests on filtration stability, the upper 20 cm of the box were separated and placed upside down into a device in which the sample box could be flowed through from below. When a water column of 50 cm above the sample was reached, the water outlet was opened so the water flowed through the sample in the opposite direction, thus simulating drawdown. By the measurements of the pressure sensors above and below the sample, the coefficient of permeability k of the rooted soil during drawdown could be calculated. After this hydropeaking cycle, the soil material that was rinsed out through the willow branches was collected, weighed after drying until weight constancy, and compared with the dry mass of the retained soil material to calculate the share of the total mass. These filtration stability tests were carried out directly after planting the sample boxes, as well as one, three and six months afterwards, each test series with four reruns per willow species. Over time, the increasing root penetration resulted in a significant reduction in the permeability and in more retained soil material.

The effect of simulated acid rain on the stabilization of cadmium in contaminated agricultural soils treated with stabilizing agents.

PubMed

Zhu, Hao; Wu, Chunfa; Wang, Jun; Zhang, Xumei

2018-04-16

Stabilization technology is one of widely used remediation technologies for cadmium (Cd)-contaminated agricultural soils, but stabilized Cd in soil may be activated again when external conditions such as acid rain occurred. Therefore, it is necessary to study the effect of acid rain on the performance of different stabilizing agents on Cd-polluted agriculture soils. In this study, Cd-contaminated soils were treated with mono-calcium phosphate (MCP), mono-ammonium phosphate (MAP), and artificial zeolite (AZ) respectively and incubated 3 months. These treatments were followed by two types of simulated acid rain (sulfuric acid rain and mixed acid rain) with three levels of acidity (pH = 3.0, 4.0, and 5.6). The chemical forms of Cd in the soils were determined by Tessier's sequential extraction procedure, and the leaching toxicities of Cd in the soils were assessed by toxicity characteristic leaching procedure (TCLP). The results show that the three stabilizing agents could decrease the mobility of Cd in soil to some degree with or without simulated acid rain (SAR) treatment. The stabilization performances followed the order of AZ < MAP < MCP. Acid rain soaking promoted the activation of Cd in stabilized soil, and both anion composition and pH of acid rain were two important factors that influenced the stabilization effect of Cd.

Soil-Water Characteristic Curves of Red Clay treated by Ionic Soil Stabilizer

NASA Astrophysics Data System (ADS)

Cui, D.; Xiang, W.

2009-12-01

The relationship of red clay particle with water is an important factor to produce geological disaster and environmental damage. In order to reduce the role of adsorbed water of red clay in WuHan, Ionic Soil Stabilizer (ISS) was used to treat the red clay. Soil Moisture Equipment made in U.S.A was used to measure soil-water characteristic curve of red clay both in natural and stabilized conditions in the suction range of 0-500kPa. The SWCC results were used to interpret the red clay behavior due to stabilizer treatment. In addition, relationship were compared between the basic soil and stabilizer properties such as water content, dry density, liquid limit, plastic limit, moisture absorption rate and stabilizer dosages. The analysis showed that the particle density and specific surface area increase, the dehydration rate slows and the thickness of water film thins after treatment with Ionic Soil Stabilizer. After treatment with the ISS, the geological disasters caused by the adsorbed water of red clay can be effectively inhibited.

[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.

[Responses of forest soil carbon pool and carbon cycle to the changes of carbon input].

PubMed

Wang, Qing-kui

2011-04-01

Litters and plant roots are the main sources of forest soil organic carbon (C). This paper summarized the effects of the changes in C input on the forest soil C pool and C cycle, and analyzed the effects of these changes on the total soil C, microbial biomass C, dissoluble organic C, and soil respiration. Different forests in different regions had inconsistent responses to C input change, and the effects of litter removal or addition and of root exclusion or not differed with tree species and regions. Current researches mainly focused on soil respiration and C pool fractions, and scarce were about the effects of C input change on the changes of soil carbon structure and stability as well as the response mechanisms of soil organisms especially soil fauna, which should be strengthened in the future.

Lead Speciation and In Vitro Bioaccessibility of Compost-Amended Urban Garden Soils

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

Attanayake, Chammi P.; Hettiarachchi, Ganga M.; Ma, Qing

In situ soil amendments can modify the Pb bioavailability by changing soil Pb speciation. Urban soils from three vegetable gardens containing different total Pb concentrations were used. The study evaluated how compost amendment and aging of soil-compost mixture in situ affected the following: (i) soil Pb speciation in the field and (ii) change of soil Pb speciation during an in vitro bioaccessibility extraction mimicking gastric phase dissolution at pH 2.5. X-ray absorption fine structure spectroscopy was used to determine Pb speciation in amended and nonamended soils and residues left after in vitro bioaccessibility extraction of those soils. Compost amendment andmore » aging of compost in the field had a negligible effect on Pb bioaccessibility in the soils. Major Pb species in the soils were Pb sorbed to Fe oxy(hydr)oxide (Pb-Fh) and to soil organic C (Pb-Org). The fraction of Pb-Org was increased as soil-compost mixture aged in the field. During the in vitro extraction, the fraction of Pb-Fh was decreased, the fraction of Pb-Org was increased, and hydroxypyromorphite was formed in both amended and nonamended soils. Freshly incorporated compost enhanced the dissolution of Pb-Fh during the extraction. As soil-compost mixture aged in the field, the dissolution of Pb-Fh was low, demonstrating more stability of the Pb-Fh during the extraction. Compost amendment showed potential to contribute to reduced bioaccessibility of Pb as compost aged in the soil by increasing Pb-Org fraction in the field and stability of Pb-Fh during the in vitro bioaccessibility extraction.« less

Interactions Between Wind Erosion, Vegetation Structure, and Soil Stability in Groundwater Dependent Plant Communities

NASA Astrophysics Data System (ADS)

Vest, K. R.; Elmore, A. J.; Okin, G. S.

2009-12-01

Desertification is a human induced global phenomenon causing a loss of biodiversity and ecosystem productivity. Semi-arid grasslands are vulnerable to anthropogenic impacts (i.e., groundwater pumping and surface water diversion) that decrease vegetation cover and increase bare soil area leading to a greater probability of soil erosion, potentially enhancing feedback processes associated with desertification. To enhance our understanding of interactions between anthropogenic, physical, and biological factors causing desertification, this study used a combination of modeling and field observations to examine the relationship between chronic groundwater pumping and vegetation cover change and its effects on soil erosion and stability. The work was conducted in Owens Valley California, where a long history of groundwater pumping and surface water diversion has lead to documented vegetation changes. The work examined hydrological, ecological and biogeochemical factors across thirteen sites in Owens Valley. We analyzed soil stability, vegetation and gap size, soil organic carbon, and we also installed Big Spring Number Eight (BSNE) catchers to calculate mass transport of aeolian sediment across sites. Mass transport calculations were used to validate a new wind erosion model that represents the effect of porous vegetation on surface windshear velocity. Results across two field seasons show that the model can be used to predict mass transport, and areas with increased groundwater pumping show a greater susceptibility to erosion. Sediment collected in BSNE catchers was positively correlated with site gap size. Additionally, areas with larger gap sizes have a greater threshold shear velocity and soil stability, yet mass transport was greater at these sites than at sites with smaller gap sizes. Although modeling is complicated by spatial variation in multiple model parameters (e.g., gap size, threshold shear velocity in gaps), our results support the hypothesis that soils with high organic matter are being eroded following the loss of vegetation cover due to groundwater decline leaving behind bare soil surfaces with less fertility hampering vegetation reestablishment. Desertification in this system is apparently easily initiated through groundwater decline due to the high friability of these meadow soils.

Coir geotextile for slope stabilization and cultivation - A case study in a highland region of Kerala, South India

NASA Astrophysics Data System (ADS)

Vishnudas, Subha; Savenije, Hubert H. G.; Van der Zaag, Pieter; Anil, K. R.

A sloping field is not only vulnerable to soil erosion it may also suffer from soil moisture deficiency. Farmers that cultivate on slopes everywhere face similar problems. Conservation technologies may reduce soil and nutrient losses, and thus enhance water holding capacity and soil fertility. But although these technologies promote sustainable crop production on steep slopes, the construction of physical structure such as bench terraces are often labour intensive and expensive to the farmers, since construction and maintenance require high investments. Here we studied the efficiency of coir geotextile with and without crop cultivation in reducing soil moisture deficiency on marginal slopes in Kerala, India. From the results it is evident that the slopes treated with geotextile and crops have the highest moisture retention capacity followed by geotextiles alone, and that the control plot has the lowest moisture retention capacity. As the poor and marginal farmers occupy the highland region, this method provides an economically viable option for income generation and food security along with slope stabilization.

Spatial arrangement of organic compounds on a model mineral surface: implications for soil organic matter stabilization.

PubMed

Petridis, Loukas; Ambaye, Haile; Jagadamma, Sindhu; Kilbey, S Michael; Lokitz, Bradley S; Lauter, Valeria; Mayes, Melanie A

2014-01-01

The complexity of the mineral-organic carbon interface may influence the extent of stabilization of organic carbon compounds in soils, which is important for global climate futures. The nanoscale structure of a model interface was examined here by depositing films of organic carbon compounds of contrasting chemical character, hydrophilic glucose and amphiphilic stearic acid, onto a soil mineral analogue (Al2O3). Neutron reflectometry, a technique which provides depth-sensitive insight into the organization of the thin films, indicates that glucose molecules reside in a layer between Al2O3 and stearic acid, a result that was verified by water contact angle measurements. Molecular dynamics simulations reveal the thermodynamic driving force behind glucose partitioning on the mineral interface: The entropic penalty of confining the less mobile glucose on the mineral surface is lower than for stearic acid. The fundamental information obtained here helps rationalize how complex arrangements of organic carbon on soil mineral surfaces may arise.

Temporal pattern of soil matric suction in the unsaturated soil slope under different forest cover

NASA Astrophysics Data System (ADS)

Hayati, Elyas; Abdi, Ehsan; Mohseni Saravi, Mohsen; Nieber, John; Majnounian, Baris; Chirico, Giovanni

2017-04-01

In the vadose zone, usually, soils experience high matric suction during dry periods which results in a significant additional soil strength component (i.e., apparent cohesion) and thus plays a crucial role in the stability of unsaturated soil slopes. But, in the wet periods, when rain-water infiltrates into the soil, the matric suction of the soil dissipates partially or completely. It is a well-understood concept that vegetation can modify the hillslope hydrology and subsequent stability conditions by increasing soil matric suction through both interception of rainfall and depletion of soil water content via transpiration. Anthropogenic pressures, particularly clear-cutting and deforestation, affect many hydro-geomorphological processes including catchment and hillslope hydrology and stability. However, quantifying the changes in soil hydrologic conditions and the resulted stability of slopes due to these degrading activities remained an unresolved problem. To address this gap, a continuous measurement of soil water dynamics has been conducted at two adjacent hillslopes (one forested hillslope and one degraded hillslope) using PR2/6 profile probe for a 9-month period of time to demonstrate the forest cover-specific influence on the hillslope hydrology and stability during different seasons. The results have been then presented in terms of estimated soil matric suction to facilitate analyzing the resulted stability states due to the changes in soil water balance with time in the two studied hillslopes. The data were tested to check whether there are any differences between the forested and degraded hillslopes in terms of soil matric suction and augmented soil cohesion during different seasons. Finally, the response of soil hydrologic condition and the resulted slope stability for the 9-month period were analyzed and discussed for the different hillslopes.

Immobilization of metals in contaminated soils using natural polymer-based stabilizers.

PubMed

Tao, Xue; Li, Aimin; Yang, Hu

2017-03-01

Three low-cost natural polymer materials, namely, lignin (Ln), carboxymethyl cellulose, and sodium alginate, were used for soil amendment to immobilize lead and cadmium in two contaminated soil samples collected from a mining area in Nanjing, China. The remediation effects of the aforementioned natural polymers were evaluated by toxicity characteristic leaching procedure (TCLP) and sequential extractions. The stabilizers could lower the bioavailability of Pb and Cd in the contaminated soils, and the amount of the exchangeable forms of the aforementioned two metals were reduced evidently. TCLP results showed that the leaching concentrations of Pb and Cd were decreased by 5.46%-71.1% and 4.25%-49.6%, respectively, in the treated soils. The contents of the organic forms of the two metals both increased with the increase in stabilizer dose on the basis of the redistribution of metal forms by sequential extractions. These findings were due to the fact that the abundant oxygen-containing groups on the polymeric amendments were effective in chelating and immobilizing Pb and Cd, which have been further confirmed from the metal adsorptions in aqueous solutions. Moreover, Ln achieved the greatest effect among the three polymers under study because of the former's distinct three-dimensional molecular structure, showing the preferential immobilization of Pb over Cd in soils also. Thus, the above-mentioned natural polymers hold great application potentials for reducing metal ion entry into the food chain at a field scale. Copyright © 2016 Elsevier Ltd. All rights reserved.

Analysis of aggregate pier systems for stabilization of subgrade settlement.

DOT National Transportation Integrated Search

2014-12-01

Every year, ODOT undertakes numerous pavement patching/resurfacing projects to repair pavement : distress and structural failure due to soft and/or organic soils constituting the subgrade. Other than the : temporary solution of patching/resurfacing, ...

Assessing the variation in bund structure design and its impact on soil physical properties and hydrology in Koga catchment, Highlands of Ethiopia

NASA Astrophysics Data System (ADS)

Lakew, Walle; Baartman, Jantiene; Fleskens, Luuk; Selassie, Yihenew; Ritsema, Coen

2017-04-01

Prolonged soil drying and severe moisture stress during the dry season, and soil saturation and erosion during the short rainy season are critical problems in the Ethiopian highlands. Large-scale implementation of bund structures has been used as soil and water management (SWM) strategy to fight these problems and establish a sustainable land management (SLM) system. However, many SWM practices are implemented with design flaws or without proper design and maintenance, and do not match conservation requirements. The quality of implementation and effects of bund structures on soil physical properties is not yet documented. Therefore, in this study, field investigations and laboratory analysis were carried out to evaluate the variation in bund structure design and its impact on soil-water retention, bulk density, porosity and soil depth. Results show that the dimensions and stability of bund structures, and consequently, the impacts of bunds varied widely. The widths and heights of bunds, and slope gradients were significantly correlated with infiltration rate and available soil-water content. Water holding capacity was 24% higher compared to that on untreated farms. Bunds with larger dimensions of top width (>85 cm) and height (>75 cm) showed 17 and 18% higher water holding capacity compared to fields with bunds having lower dimensions. In addition, results exhibited that the porosity and soil depth were significantly affected by the dimensions of bund structures and increased with increasing widths and heights of bunds. A 14.2% increase in porosity; a 41.2% increase in infiltration rate; and a 17.5% decrease in bulk density was found in soils of treated farms compared to those of untreated farm plots. Differences in particle size distribution and soil erodibility among widths of the bunds were low. It can be concluded that bund structure design varied substantially throughout the study area, which had impacted soil-water storage and soil physical properties. Bund structure design should be adapted to local biophysical settings at catchment level to enhance on- and offsite impacts.

Expansive soil stabilization with coir waste and lime for flexible pavement subgrade

NASA Astrophysics Data System (ADS)

Narendra Goud, G.; Hyma, A.; Shiva Chandra, V.; Sandhya Rani, R.

2018-03-01

Expansive soil properties can be improved by various methods to make it suitable for construction of flexible pavement. The coir pith is the by-product (bio-waste) generated from coir industry during extraction of coir fiber from coconut husk. Openly disposed coir pith can make the surrounding areas unhygienic. This bio-waste can be one of the potential materials to stabilize the expansive soils. In the present study coir pith and lime are used as stabilizers. Different combinations of coir pith contents (1%, 2% and 3%) and lime contents (2%, 3% and 4%)are used to study the behavior of expansive soil. Unconfined compressive strength (UCS) of unstabilized and stabilized soils was determined. Optimum content of coir pith and lime are determined based on UCS of the soil. California bearing ratio of soil determined at optimum contents of coir pith and lime. Flexible pavement layer compositions for two levels of traffic using stabilized soil subgrade.

Using synthetic polymers to reduce soil erosion after forest fires in Mediterranean soils

NASA Astrophysics Data System (ADS)

Lado, Marcos; Ben-Hur, Meni; Inbar, Assaf

2010-05-01

Forest fires are a major environmental problem in the Mediterranean region because they result in a loss of vegetation cover, changes in biodiversity, increases in greenhouse gasses emission and a potential increase of runoff and soil erosion. The large increases in runoff and sediment yields after high severity fires have been attributed to several factors, among them: increase in soil water repellency; soil sealing by detached particles and by ash particles, and the loss of a surface cover. The presence of a surface cover increases infiltration, and decreases runoff and erosion by several mechanisms which include: rainfall interception, plant evapotranspiration, preservation of soil structure by increasing soil organic matter, and increasing surface roughness. The loss of vegetation cover as a result of fire leaves the surface of the soil exposed to the direct impact of the raindrops, and therefore the sensitivity of the soil to runoff generation and soil loss increases. In this work, we propose a new method to protect soils against post-fire erosion based on the application of synthetic polymers to the soil. Laboratory rainfall simulations and field runoff plots were used to analyze the suitability of the application of synthetic polymers to reduce soil erosion and stabilize soil structure in Mediterranean soils. The combination of these two processes will potentially favor a faster recovery of the vegetation structure. This method has been successfully applied in arable land, however it has not been tested in burnt forests. The outcome of this study may provide important managerial tools for forest management following fires.

30 CFR 817.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 30 Mineral Resources 3 2013-07-01 2013-07-01 false Revegetation: Mulching and other soil... STANDARDS-UNDERGROUND MINING ACTIVITIES § 817.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been...

30 CFR 817.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 30 Mineral Resources 3 2014-07-01 2014-07-01 false Revegetation: Mulching and other soil... STANDARDS-UNDERGROUND MINING ACTIVITIES § 817.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been...

30 CFR 816.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 30 Mineral Resources 3 2014-07-01 2014-07-01 false Revegetation: Mulching and other soil... STANDARDS-SURFACE MINING ACTIVITIES § 816.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been regraded and...

30 CFR 817.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 3 2010-07-01 2010-07-01 false Revegetation: Mulching and other soil... STANDARDS-UNDERGROUND MINING ACTIVITIES § 817.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been...

30 CFR 816.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 30 Mineral Resources 3 2012-07-01 2012-07-01 false Revegetation: Mulching and other soil... STANDARDS-SURFACE MINING ACTIVITIES § 816.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been regraded and...

30 CFR 816.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 30 Mineral Resources 3 2013-07-01 2013-07-01 false Revegetation: Mulching and other soil... STANDARDS-SURFACE MINING ACTIVITIES § 816.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been regraded and...

30 CFR 817.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 30 Mineral Resources 3 2012-07-01 2012-07-01 false Revegetation: Mulching and other soil... STANDARDS-UNDERGROUND MINING ACTIVITIES § 817.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been...

30 CFR 816.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 3 2010-07-01 2010-07-01 false Revegetation: Mulching and other soil... STANDARDS-SURFACE MINING ACTIVITIES § 816.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been regraded and...

30 CFR 817.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 3 2011-07-01 2011-07-01 false Revegetation: Mulching and other soil... STANDARDS-UNDERGROUND MINING ACTIVITIES § 817.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been...

30 CFR 816.114 - Revegetation: Mulching and other soil stabilizing practices.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 3 2011-07-01 2011-07-01 false Revegetation: Mulching and other soil... STANDARDS-SURFACE MINING ACTIVITIES § 816.114 Revegetation: Mulching and other soil stabilizing practices. Suitable mulch and other soil stabilizing practices shall be used on all areas that have been regraded and...

Changes in soil microbial community structure influenced by agricultural management practices in a mediterranean agro-ecosystem.

PubMed

García-Orenes, Fuensanta; Morugán-Coronado, Alicia; Zornoza, Raul; Cerdà, Artemi; Scow, Kate

2013-01-01

Agricultural practices have proven to be unsuitable in many cases, causing considerable reductions in soil quality. Land management practices can provide solutions to this problem and contribute to get a sustainable agriculture model. The main objective of this work was to assess the effect of different agricultural management practices on soil microbial community structure (evaluated as abundance of phospholipid fatty acids, PLFA). Five different treatments were selected, based on the most common practices used by farmers in the study area (eastern Spain): residual herbicides, tillage, tillage with oats and oats straw mulching; these agricultural practices were evaluated against an abandoned land after farming and an adjacent long term wild forest coverage. The results showed a substantial level of differentiation in the microbial community structure, in terms of management practices, which was highly associated with soil organic matter content. Addition of oats straw led to a microbial community structure closer to wild forest coverage soil, associated with increases in organic carbon, microbial biomass and fungal abundances. The microbial community composition of the abandoned agricultural soil was characterised by increases in both fungal abundances and the metabolic quotient (soil respiration per unit of microbial biomass), suggesting an increase in the stability of organic carbon. The ratio of bacteria:fungi was higher in wild forest coverage and land abandoned systems, as well as in the soil treated with oat straw. The most intensively managed soils showed higher abundances of bacteria and actinobacteria. Thus, the application of organic matter, such as oats straw, appears to be a sustainable management practice that enhances organic carbon, microbial biomass and activity and fungal abundances, thereby changing the microbial community structure to one more similar to those observed in soils under wild forest coverage.

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.

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.

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.

Plant exudates may stabilize or weaken soil depending on species, origin and time

PubMed Central

Naveed, M.; Brown, L. K.; Raffan, A. C.; George, T. S.; Bengough, A. G.; Roose, T.; Sinclair, I.; Koebernick, N.; Cooper, L.; Hackett, C. A.

2017-01-01

Summary We hypothesized that plant exudates could either gel or disperse soil depending on their chemical characteristics. Barley (Hordeum vulgare L. cv. Optic) and maize (Zea mays L. cv. Freya) root exudates were collected using an aerated hydroponic method and compared with chia (Salvia hispanica L.) seed exudate, a commonly used root exudate analogue. Sandy loam soil was passed through a 500‐μm mesh and treated with each exudate at a concentration of 4.6 mg exudate g−1 dry soil. Two sets of soil samples were prepared. One set of treated soil samples was maintained at 4°C to suppress microbial processes. To characterize the effect of decomposition, the second set of samples was incubated at 16°C for 2 weeks at −30 kPa matric potential. Gas chromatography–mass spectrometry (GC–MS) analysis of the exudates showed that barley had the largest organic acid content and chia the largest content of sugars (polysaccharide‐derived or free), and maize was in between barley and chia. Yield stress of amended soil samples was measured by an oscillatory strain sweep test with a cone plate rheometer. When microbial decomposition was suppressed at 4°C, yield stress increased 20‐fold for chia seed exudate and twofold for maize root exudate compared with the control, whereas for barley root exudate decreased to half. The yield stress after 2 weeks of incubation compared with soil with suppressed microbial decomposition increased by 85% for barley root exudate, but for chia and maize it decreased by 87 and 54%, respectively. Barley root exudation might therefore disperse soil and this could facilitate nutrient release. The maize root and chia seed exudates gelled soil, which could create a more stable soil structure around roots or seeds. Highlights Rheological measurements quantified physical behaviour of plant exudates and effect on soil stabilization.Barley root exudates dispersed soil, which could release nutrients and carbon.Maize root and chia seed exudates had a stabilizing effect on soil.Physical engineering of soil in contact with plant roots depends on the nature and origin of exudates. PMID:29263712

Probing the rhizosphere to define mineral organic relationships

NASA Astrophysics Data System (ADS)

Schulz, M. S.; Dohnalkova, A.; Stonestrom, D. A.

2016-12-01

Soil organic matter (SOM) accumulation and stabilization over time is an important process as soils are a large carbon reservoir in which feedbacks under changing climates are unclear. The association of SOM with poorly crystalline or short-range-ordered secondary minerals has been shown to be important for carbon stabilization. Commonly used soil extraction techniques display correlations of SOM with secondary phases but do not show causation. The fate of root exudates in soils and processes controlling exudate associations with mineral phases are as yet structurally undefined. Sub-micron exploration of in-situ relations provides valuable information on SOM-mineral interactions. Soils of the Santa Cruz (California) marine terrace chronosequence are used to illustrate changes in deep (> 1 m) rhizosphere through time. Cracks and soil ped faces are sites of high root density and organic matter (biofilm or mucilage) deposition. We employ a variety of scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) techniques for high resolution imaging and elemental analyses of deep rhizosphere and associated carbon mineral interactions. In these coastal prairie soils microscopy reveals secondary clay minerals associated with and possibly forming from organic-rich mucilage that occurs along the aforementioned rooting networks on fracture surfaces. We hypothesize that the production of secondary clays in the rhizosphere is an important mode of C incorporation into secondary minerals.

Effect of carbonation on leachability, strength and microstructural characteristics of KMP binder stabilized Zn and Pb contaminated soils.

PubMed

Du, Yan-Jun; Wei, Ming-Li; Reddy, Krishna R; Wu, Hao-liang

2016-02-01

This study presents a systematic investigation of effects of carbonation on the contaminant leachability and unconfined compressive strength of KMP stabilized contaminated soils. A field soil spiked with Zn and Pb individually and together is stabilized using a new KMP additive under standard curing conditions and also with carbonation. The KMP additive is composed of oxalic acid-activated phosphate rock, monopotassium phosphate and reactive magnesia. The stabilized soils are tested for acid neutralization capacity, toxic characteristics leaching characteristics, contaminant speciation and unconfined compression strength. X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy analyses are performed to assess reaction products. The results demonstrate that carbonation increases both acid buffer capacity index and unconfined compressive strength, but decreases leachability of KMP stabilized soils. These results are interpreted based on the changes in chemical speciation of Zn and Pb and also stability and solubility of the reaction products (metal phosphates and carbonates) formed in the soils. Overall, this study demonstrates that carbonation has positive effects on leachability and strength of the KMP stabilized soils. Copyright © 2015 Elsevier Ltd. All rights reserved.

[Nutrient contents and microbial populations of aeolian sandy soil in Sanjiangyuan region of Qinghai Province].

PubMed

Lin, Chao-feng; Chen, Zhan-quan; Xue, Quan-hong; Lai, Hang-xian; Chen, Lai-sheng; Zhang, Deng-shan

2007-01-01

Sanjiangyuan region (the headstream of three rivers) in Qinghai Province of China is the highest and largest inland alpine wetland in the world. The study on the nutrient contents and microbial populations of aeolian sandy soils in this region showed that soil organic matter content increased with the evolution of aeolian sand dunes from un-stabilized to stabilized state, being 5.9 and 3.8 times higher in stabilized sand dune than in mobile and semi-stabilized sand dunes, respectively. Soil nitrogen and phosphorus contents increased in line with the amount of organic matter, while potassium content and pH value varied slightly. The microbial populations changed markedly with the development of vegetation, fixing of mobile sand, and increase of soil nutrients. The quantities of soil bacteria, fungi and actinomycetes were 4.0 and 2.8 times, 19.6 and 6.3 times, and 12.4 and 2.6 times higher in stabilized and semi-stabilized sand dunes than in mobile sand dune, respectively, indicating that soil microbial bio-diversity was increased with the evolution of aeolian sand dunes from mobile to stabilized state. In addition, the quantities of soil microbes were closely correlated with the contents of soil organic matter, total nitrogen, and available nitrogen and phosphorus, but not correlated with soil total phosphorus, total and available potassium, or pH value.

The potential roles of biological soil crusts in dryland hydrologic cycles

USGS Publications Warehouse

Belnap, J.

2006-01-01

Biological soil crusts (BSCs) are the dominant living cover in many drylands of the world. They possess many features that can influence different aspects of local hydrologic cycles, including soil porosity, absorptivity, roughness, aggregate stability, texture, pore formation, and water retention. The influence of biological soil crusts on these factors depends on their internal and external structure, which varies with climate, soil, and disturbance history. This paper presents the different types of biological soil crusts, discusses how crust type likely influences various aspects of the hydrologic cycle, and reviews what is known and not known about the influence of biological crusts on sediment production and water infiltration versus runoff in various drylands around the world. Most studies examining the effect of biological soil crusts on local hydrology are done by comparing undisturbed sites with those recently disturbed by the researchers. Unfortunately, this greatly complicates interpretation of the results. Applied disturbances alter many soil features such as soil texture, roughness, aggregate stability, physical crusting, porosity, and bulk density in ways that would not necessarily be the same if crusts were not naturally present. Combined, these studies show little agreement on how biological crusts affect water infiltration or runoff. However, when studies are separated by biological crust type and utilize naturally occurring differences among these types, results indicate that biological crusts in hyperarid regions reduce infiltration and increase runoff, have mixed effects in and regions, and increase infiltration and reduce runoff in semiarid cool and cold drylands. However, more studies are needed before broad generalizations can be made on how biological crusts affect infiltration and runoff. We especially need studies that control for sub-surface soil features such as bulk density, micro- and macropores, and biological crust structure. Unlike the mixed effects of biological crusts on infiltration and runoff among regions, almost all studies show that biological crusts reduce sediment production, regardless of crust or dryland type.

The potential roles of biological soil crusts in dryland hydrologic cycles

NASA Astrophysics Data System (ADS)

Belnap, Jayne

2006-10-01

Biological soil crusts (BSCs) are the dominant living cover in many drylands of the world. They possess many features that can influence different aspects of local hydrologic cycles, including soil porosity, absorptivity, roughness, aggregate stability, texture, pore formation, and water retention. The influence of biological soil crusts on these factors depends on their internal and external structure, which varies with climate, soil, and disturbance history. This paper presents the different types of biological soil crusts, discusses how crust type likely influences various aspects of the hydrologic cycle, and reviews what is known and not known about the influence of biological crusts on sediment production and water infiltration versus runoff in various drylands around the world. Most studies examining the effect of biological soil crusts on local hydrology are done by comparing undisturbed sites with those recently disturbed by the researchers. Unfortunately, this greatly complicates interpretation of the results. Applied disturbances alter many soil features such as soil texture, roughness, aggregate stability, physical crusting, porosity, and bulk density in ways that would not necessarily be the same if crusts were not naturally present. Combined, these studies show little agreement on how biological crusts affect water infiltration or runoff. However, when studies are separated by biological crust type and utilize naturally occurring differences among these types, results indicate that biological crusts in hyperarid regions reduce infiltration and increase runoff, have mixed effects in arid regions, and increase infiltration and reduce runoff in semiarid cool and cold drylands. However, more studies are needed before broad generalizations can be made on how biological crusts affect infiltration and runoff. We especially need studies that control for sub-surface soil features such as bulk density, micro- and macropores, and biological crust structure. Unlike the mixed effects of biological crusts on infiltration and runoff among regions, almost all studies show that biological crusts reduce sediment production, regardless of crust or dryland type.

Land-use and land-management change: relationships with earthworm and fungi communities and soil structural properties.

PubMed

Spurgeon, David J; Keith, Aidan M; Schmidt, Olaf; Lammertsma, Dennis R; Faber, Jack H

2013-12-01

Change in land use and management can impact massively on soil ecosystems. Ecosystem engineers and other functional biodiversity in soils can be influenced directly by such change and this in turn can affect key soil functions. Here, we employ meta-analysis to provide a quantitative assessment of the effects of changes in land use and land management across a range of successional/extensification transitions (conventional arable → no or reduced tillage → grassland → wooded land) on community metrics for two functionally important soil taxa, earthworms and fungi. An analysis of the relationships between community change and soil structural properties was also included. Meta-analysis highlighted a consistent trend of increased earthworm and fungal community abundances and complexity following transitions to lower intensity and later successional land uses. The greatest changes were seen for early stage transitions, such as introduction of reduced tillage regimes and conversion to grassland from arable land. Not all changes, however, result in positive effects on the assessed community metrics. For example, whether woodland conversion positively or negatively affects community size and complexity depends on woodland type and, potentially, the changes in soil properties, such as pH, that may occur during conversion. Alterations in soil communities tended to facilitate subsequent changes in soil structure and hydrology. For example, increasing earthworm abundances and functional group composition were shown to be positively correlated with water infiltration rate (dependent on tillage regime and habitat characteristics); while positive changes in fungal biomass measures were positively associated with soil microaggregate stability. These findings raise the potential to manage landscapes to increase ecosystem service provision from soil biota in relation to regulation of soil structure and water flow.

Factors influencing the natural regeneration of the pioneering shrub Calligonum mongolicum in sand dune stabilization plantations in arid deserts of northwest China.

PubMed

Fan, Baoli; McHugh, Allen David; Guo, Shujiang; Ma, Quanlin; Zhang, Jianhui; Zhang, Xiaojuan; Zhang, Weixing; Du, Juan; Yu, Qiushi; Zhao, Changming

2018-03-01

Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air-filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations.

Finite Element analyses of soil bioengineered slopes

NASA Astrophysics Data System (ADS)

Tamagnini, Roberto; Switala, Barbara Maria; Sudan Acharya, Madhu; Wu, Wei; Graf, Frank; Auer, Michael; te Kamp, Lothar

2014-05-01

Soil Bioengineering methods are not only effective from an economical point of view, but they are also interesting as fully ecological solutions. The presented project is aimed to define a numerical model which includes the impact of vegetation on slope stability, considering both mechanical and hydrological effects. In this project, a constitutive model has been developed that accounts for the multi-phase nature of the soil, namely the partly saturated condition and it also includes the effects of a biological component. The constitutive equation is implemented in the Finite Element (FE) software Comes-Geo with an implicit integration scheme that accounts for the collapse of the soils structure due to wetting. The mathematical formulation of the constitutive equations is introduced by means of thermodynamics and it simulates the growth of the biological system during the time. The numerical code is then applied in the analysis of an ideal rainfall induced landslide. The slope is analyzed for vegetated and non-vegetated conditions. The final results allow to quantitatively assessing the impact of vegetation on slope stability. This allows drawing conclusions and choosing whenever it is worthful to use soil bioengineering methods in slope stabilization instead of traditional approaches. The application of the FE methods show some advantages with respect to the commonly used limit equilibrium analyses, because it can account for the real coupled strain-diffusion nature of the problem. The mechanical strength of roots is in fact influenced by the stress evolution into the slope. Moreover, FE method does not need a pre-definition of any failure surface. FE method can also be used in monitoring the progressive failure of the soil bio-engineered system as it calculates the amount of displacements and strains of the model slope. The preliminary study results show that the formulated equations can be useful for analysis and evaluation of different soil bio-engineering methods of slope stabilization.

[Soil humus differentiation and correlation with other soil biochemical properties in pure forests in semi-arid low-hilly area of Inner Mongolia, China].

PubMed

Zhang, Xiao-Xi; Liu, Zeng-Wen; Bing, Yuan-Hao; Zhu, Bo-Chao; Huang, Liang-Jia

2014-10-01

Whether the content and composition of soil humus in pure forest change due to its simple component of litter and specificity of single-species dominant community is a key problem for forest sustainable management. In this study, soils from 6 kind of pure forests in semi-arid low-hilly area of Inner Mongolia were collected and their humus and other biochemical properties were measured to investigate the differentiation of soil humus and the impact factors. The results showed that the soil of Picea asperata and Betula platyphylla pure forests had the highest contents of humus and better condensation degrees and stabilities, followed by that of Populus simonii, Larix principis-rupprechtii and Ulmus pumila pure forests, while the soil of Pinus tabuliformis pure forest had the lowest content of humus, condensation degree and stability. There were significant positive correlations between soil microorganism biomass, activity of phosphatase and the content and stability of soil humus. In contrast, the soil peroxidate, dehydrogenase activity and soil humus content showed significant negative correlations with each other. Furthermore, the enhancement of dehydrogenase activity might decrease the stability of humus. There were significant positive correlations between available N and the content and stability of soil humus, but total Cu, Zn and Fe had negative correlations with them, and total Cu and Fe might reduce the stability of humus as well. The particularity of pure forest environment and litter properties might be the key inducement to soil humus differentiation, thus reforming the pure forest through mixing with other tree species or planting understory vegetation would be the fundamental way to improve the soil humus composition and stability.

The Interacting controls of pyrolysis temperature and plant taxa on pyrogenic organic matter stability and decomposition in a Northern Michigan forest soil

NASA Astrophysics Data System (ADS)

Gibson, C. D.; Filley, T. R.; Bird, J. A.; Hatton, P. J.; Stark, R. E.; Nadelhoffer, K. J.

2017-12-01

Pyrogenic organic matter (PyOM) produced during forest fires is considered a large sink of stable soil organic matter (SOM) in boreal-temperate forest ecotones, where fire frequency and intensity is growing with changing climate. Understanding how changes in fire regime and predicted shifts in plant taxa will interact to affect PyOM dynamics in soil is imperative to assessing the impact of climate change on SOM maintenance. The stability of PyOM in soil may be co-determined by the physiochemical structure imparted on PyOM during pyrolysis and by its initial taxa-dependent wood chemistry and anatomy. To determine PyOM-C turnover rates in soil, we followed the fate of 13C-enriched wood or PyOM (200, 300, 450, or 600°C) derived from red maple (RM) or jack pine (JP) wood in soil from a recently burned forest in northern Michigan, USA. We found that pyrolysis temperature-controlled physiochemical changes influenced, with threshold dynamics, PyOM stability resulting in mean residence times of 2 (PyOM 200°C) to 450 years for both taxa, confirming that most PyOM (<600°C) turns over on the century, not millennial time scale. Water leachable C, carbohydrate and non-lignin phenol content correlated positively with early PyOM-C mineralization for both JP and RM, but the pyrolysis temperature at which this interaction was strongest differed with taxa reflecting the difference in thermal transition in which carbonization begins (300°C for JP and 450°C for RM). In contrast to previous studies, the addition of sucrose suggests that a co-metabolism mechanism of PyOM decomposition is minor in this soil. Our results show that while the first order control on PyOM stability in this soil is pyrolysis temperature, wood taxa did affect PyOM C MRT, in part due to differences in the amount of water soluble C released by PyOM during the initial decomposition dynamics in soil.

Aggregate stability and water retention near saturation characteristics as affected by soil texture, aggregate size and polyacrylamide application

USDA-ARS?s Scientific Manuscript database

Understanding the effects of soil intrinsic properties and extrinsic conditions on aggregate stability is essential for the development of effective soil and water conservation practices. Our objective was to evaluate the combined role of soil texture, aggregate size and application of a stabilizing...

Mapping fields of 137Cs contamination in soils in the context of their stability and hierarchical spatial structure

NASA Astrophysics Data System (ADS)

Korobova, E.; Romanov, S.

2009-04-01

Technogenic radioisotopes now dispersed in the environment are involved in natural and technogenic processes forming specific geochemical fields and serving as tracers of modern mass migration and geofield transformation. Cs-137 radioisotopes having a comparatively long life time are known for a fast fixation by the top soil layer; radiocesium activity can be measured in the surface layer in field conditions. This makes 137Cs rather convenient for the study and modeling a behavior of toxic elements in soils [1-3, 5] and for the investigation of relative stability and hierarchical fractal structures of the soil contamination of the atmospheric origin [2]. The objective of the experimental study performed on the test site in Bryansk region was to find and prove polycentric regularities in the structure of 137Cs contamination field formed after the Chernobyl accident in natural conditions. Such a character of spatial variability can be seen on the maps showing different soil parameters and chemical element distribution measured in grids [3-5]. The research was undertaken to support our idea of the regular patterns in the contamination field structure that enables to apply a mathematical theory of the field to the geochemical fields modeling on the basis of a limited number of direct measurements sufficient to reproduce the configuration and main parameters of the geochemical field structure on the level of the elementary landscape geochemical system (top-slope-bottom). Cs-137 field measurements were verified by a direct soil sampling. Soil cores dissected into subsamples with increments of 2, 5 and 10 cm, were taken to the depth of 40 cm at points with various surface activity located at different elements of relief. According to laboratory measurements 137Cs inventory in soils varied from 344 to 3448 kBq/m2 (983 kBq/m2 on the average). From 95,1% to 98,0% to of the total inventory was retained in the top 20-cm soil layer. This confirmed that field gamma spectrometry could be used to investigate patterns of 137Cs spatial redistribution in the top soil layers. The portion of 137Cs conserved in top layers corresponded to the meso- and micro relief elements. The character and stability of 137Cs spatial structure was studied by measuring its activity within nested plots with different steps of 5, 2, 1 and 0,2 m (the latter was a minimum resolution step for the field NaI detector). Performed measurements showed that the contamination field of 137Cs had a regular structure of polycentric character and exhibited a decrease in spatial variability of contamination with the decrease of the measured area. Repeated measurements of soil contamination in successive years of 2005-2008 along and cross the slopes provided with topographic survey proved the stability of contamination field (r=0, 915, n=121, r=0,912, n=30) and its relation to the meso- and microrelief features. Variation 137Cs activity in lateral direction (along the slopes and thalweg of the hollow)showed a regular character also. In our opinion the regularity in 137Cs spatial structure in the soil cover may result from radionuclide redistribution with the surface and subsurface water flow highly sensitive to the changes in elevation of different scale, and to the slope length and inclination. Cs-137 lateral distribution pattern was likely to reflect alternation of lateral and vertical water mass migration along the slopes. The performed study showing regularity in 137Cs redistribution seems to open new possibilities to develop the deterministic strategy in the study of contamination fields and modeling toxic elements spatial distribution in the soil cover on different scales. The authors are much obliged to Dr. V. Samsonov and Dr. F. Moiseenko for participation in the field work and to S. Kirov for the performance of the laboratory measurement of the soil and plant samples. References 1. Khomutinin, Yu.V., Kashparov, V.A., Zhebrovskaya, E.I., 2001. Optimization of sampling and measurement of the specimen for radioecological monitoring. UkrNIISKHR, Kiev. 2. Korobova, E.M., Romanov, S.L., Samsonov, V.L., Kirov, S.S., 2006. Experimental study of spatial 137Cs redistribution in paragenetic elementary landscapes, in: Kasimov, N.S. et al (Eds.), Geochemistry of biosphere (devoted to 90-th anniversary of A.I. Perelman), MSU, IGEM, RFFI, Moscow-Smolensk, pp.157-159. 3. Linnik, V.G., Saveliev, A.A., Govorun, A.P., Ivanitsky, O.M., Sokolov, A.V., 2006. Analysis of the Cs-137 contamination field on micro-landscape scale within the virgin meadows in the western part of the Bryansk region, in: Kasimov, N.S. et al (Eds.), Geochemistry of biosphere (devoted to 90-th anniversary of A.I. Perelman), MSU, IGEM, RFFI, Moscow-Smolensk, pp. 201-204. 4. Samsonova V.P. Spatial variability of the soil parameters. On example of soddy-podozolic soils. Moscow, LKI, 2008, 156 p. 5.Shcheglov, A.I., Tsvetnova, O.B., Klyashtorin, A.I., 2001. Biogeochemical migration of technogenic radionuclides in forest ecosystems. Nauka, Moscow.

Factors controlling soil organic carbon stability along a temperate forest altitudinal gradient

PubMed Central

Tian, Qiuxiang; He, Hongbo; Cheng, Weixin; Bai, Zhen; Wang, Yang; Zhang, Xudong

2016-01-01

Changes in soil organic carbon (SOC) stability may alter carbon release from the soil and, consequently, atmospheric CO2 concentration. The mean annual temperature (MAT) can change the soil physico-chemical characteristics and alter the quality and quantity of litter input into the soil that regulate SOC stability. However, the relationship between climate and SOC stability remains unclear. A 500-day incubation experiment was carried out on soils from an 11 °C-gradient mountainous system on Changbai Mountain in northeast China. Soil respiration during the incubation fitted well to a three-pool (labile, intermediate and stable) SOC decomposition model. A correlation analysis revealed that the MAT only influenced the labile carbon pool size and not the SOC stability. The intermediate carbon pool contributed dominantly to cumulative carbon release. The size of the intermediate pool was strongly related to the percentage of sand particle. The decomposition rate of the intermediate pool was negatively related to soil nitrogen availability. Because both soil texture and nitrogen availability are temperature independent, the stability of SOC was not associated with the MAT, but was heavily influenced by the intrinsic processes of SOC formation and the nutrient status. PMID:26733344

Warming reduces the growth and diversity of biological soil crusts in a semi-arid environment: implications for ecosystem structure and functioning

PubMed Central

Escolar, Cristina; Martínez, Isabel; Bowker, Matthew A.; Maestre, Fernando T.

2012-01-01

Biological soil crusts (BSCs) are key biotic components of dryland ecosystems worldwide that control many functional processes, including carbon and nitrogen cycling, soil stabilization and infiltration. Regardless of their ecological importance and prevalence in drylands, very few studies have explicitly evaluated how climate change will affect the structure and composition of BSCs, and the functioning of their constituents. Using a manipulative experiment conducted over 3 years in a semi-arid site from central Spain, we evaluated how the composition, structure and performance of lichen-dominated BSCs respond to a 2.4°C increase in temperature, and to an approximately 30 per cent reduction of total annual rainfall. In areas with well-developed BSCs, warming promoted a significant decrease in the richness and diversity of the whole BSC community. This was accompanied by important compositional changes, as the cover of lichens suffered a substantial decrease with warming (from 70 to 40% on average), while that of mosses increased slightly (from 0.3 to 7% on average). The physiological performance of the BSC community, evaluated using chlorophyll fluorescence, increased with warming during the first year of the experiment, but did not respond to rainfall reduction. Our results indicate that ongoing climate change will strongly affect the diversity and composition of BSC communities, as well as their recovery after disturbances. The expected changes in richness and composition under warming could reduce or even reverse the positive effects of BSCs on important soil processes. Thus, these changes are likely to promote an overall reduction in ecosystem processes that sustain and control nutrient cycling, soil stabilization and water dynamics. PMID:23045707

Fe-C interactions and soil organic matter stability in two tropical soils of contrasting parent materials

NASA Astrophysics Data System (ADS)

Coward, E.; Thompson, A.; Plante, A. F.

2014-12-01

The long residence time of soil organic matter (SOM) is a dynamic property, reflecting the diversity of stabilization mechanisms active within the soil matrix. Climate and ecosystem properties act at the broadest scale, while biochemical recalcitrance, physical occlusion and mineral association drive stability at the microscale. Increasing evidence suggests that the stability of SOM is dominated by organo-mineral interactions. However, the 2:1 clays that provide much of the stabilization capacity in temperate soils are typically absent in tropical soils due to weathering. In contrast, these soils may contain an abundance of iron and aluminium oxides and oxyhydroxides, known as short-range-order (SRO) minerals. These SRO minerals are capable of SOM stabilization through adsorption or co-precipitation, a faculty largely enabled by their high specific surface area (SSA). As such, despite their relatively small mass, SRO minerals may contribute substantially to the SOM stabilization capacity of tropical soils. The objective of this work is to characterize and quantify these Fe-C interactions. Surface (0-20 cm) soil samples were taken from 20 quantitative soil pits dug within the Luquillo Critical Zone Observatory in northeast Puerto Rico. Soils were stratified across granodiorite and volcaniclastic parent materials. Four extraction procedures were used to isolate three different forms of Fe-C interactions: sodium pyrophosphate to isolate organo-metallic complexes, hydroxylamine and oxalate to isolate SRO Fe- and Al-hydroxides, and dithionite to isolate crystalline Fe-oxyhydroxides. Extracts were analysed for DOC and Fe and Al concentrations to estimate the amount of SOM associated with each mineral type. Soils were subjected to SSA and solid-phase C analyses before and after extraction to determine the contribution of the various Fe mineral types to soil SSA, and therefore to potential stabilization capacity through organo-mineral complexation. Preliminary results suggest that extracts from granodiorite parent material contain on average twice the Fe than those from volcaniclastic parent material. The removal of SRO minerals reduced SSA in both soil types, and appear to contribute substantially to SOM stabilization compared to the bulk mineral matrix.

Laboratory Evaluation of the Effects of 3-Chloride Compounds on the Geotechnical Properties of an Expansive Subgrade Soil

NASA Astrophysics Data System (ADS)

Radhakrishnan, G.; Anjan Kumar, M.; Raju, G. V. R. Prasada

2017-12-01

Expansive soils are known to be problematic due to their nature and behavior. These soils show volume changes due to changes in moisture content, which cause distortions to structures constructed on them. Relentless efforts are being made all over the world to find solution to the problems of expansive soils. In the case of flexible pavements, unless the subgrade is appropriately treated during the construction stage, the maintenance cost will increase substantially due to deterioration. There are many methods of stabilising expansive subgrade soils. Chemical stabilisation is one such technique employed in improving the engineering properties of the expansive soil. Investigations on chemical stabilization of expansive soils revealed that conventionally used lime could be replaced by the chloride compound chemicals because of their ready dissolvability in water, ease of mixing with soil and supply of sufficient cations for ready cation exchange. The main objective of this work is to study the effectiveness of three chloride compound chemicals, ammonium chloride (NH4Cl), magnesium chloride (MgCl2) and aluminum chloride (AlCl3) on the geotechnical properties of an expansive soil. The chemicals content up to 2% were added to the soil and its effect on the index limits, swell pressure, compaction characteristics as well as California bearing ratio are studied. It was observed that aluminum chloride chemical content has a significantly higher influence than the other two chemicals and it could be recognized as an effective chemical stabilizer.

Change in physical structure of a phenol-spiked sapric histosol observed by Differential Scanning Calorimetry

NASA Astrophysics Data System (ADS)

Ondruch, Pavel; Kucerik, Jiri; Schaumann, Gabriele E.

2014-05-01

Interactions of pollutants with soil organic matter (SOM), their fate and transformation are crucial for understanding of soil functions and properties. In past, many papers dealing with sorption of organic and inorganic compounds have been published. However, their aim was almost exceptionally fo-cused on the pollutants themselves, determination of sorption isotherms and influence of external factors, while the change in SOM supramolecular structure was usually ignored. The SOM structure is, however, very important, since the adsorbed pollutant might have a significant influence on soil stability and functions. Differential scanning calorimetry (DSC) represents a technique, which has been successfully used to analyze the physical structure and physico-chemical aging of SOM. It has been found out that water molecules progressively stabilize SOM (water molecule bridge (WaMB)) (Schaumann & Bertmer 2008). Those bridges connect and stabilize SOM and can be disrupted at higher temperature (WaMB transition; (Kunhi Mouvenchery et al. 2013; Schaumann et al. 2013). In the same temperature region melting of aliphatic moieties can be observed (Hu et al. 2000; Chilom & Rice 2005; Kucerik et al. submitted 2013). In this work, we studied the effect of phenol on the physical structure of sapric histosol. Phenol was dissolved in various solvents (water, acetone, hexane, methanol) and added to soils. After the evaporation of solvents by air drying, the sample was equilibrated at 76% relative humidity for 3 weeks. Using DSC, we investigated the influence of phenol on histosol structure and time dependence of melting temperature of aliphatic moieties and WaMB transition. While addition of pure organic solvent only resulted in slightly increased transition temperatures, both melting temperature and WaMB transition temperature were significantly reduced in most cases if phenol was dissolved in these solvents. Water treatment caused a decrease in WaMB transition temperature but increased melting temperature. During the 150 days of physico-chemical aging, an increase in WaMB transition and melting temperature of aliphatic crystallites was was observed. Several types of treatments contrasting with this development were attributed to specific solvent -phenol interactions and will be discussed in this contribution. The results indicate that after introduction of phenol and during the consequent relaxation of the SOM structure, the re-formation of water molecule bridges is significantly reduced and decelerated. WaMB has been suggested as one SOM stabilizing mechanism (Schaumann & Bertmer 2008); the incorporation of phenol destabilizes the physical structure of SOM. It is assumed that phenol can penetrate into the WaMB hotspots, competes with water and/or disrupts WaMB or participate in WaMB formation. Simultaneously, phenol can penetrate and irreversibly change also the aliphatic crystallites, which are traditionally not considered being actively involved in sorption processes. It furthermore could compete with the organic matter for the hydration water. In this contribution, we will discuss these mechanisms. The results clearly demonstrate the potential of DSC to probe labile (physical) structures in soil organic matter and to elucidate interaction of organic chemicals with SOM moieties. References Chilom, G. & Rice, J.A. (2005). Glass transition and crystallite melting in natural organic matter. Organic Geochemistry, 36, 1339-1346. Hu, W.-G.; Mao, J.; Xing, B. & Schmidt-Rohr, K. (2000). Poly(methylene) crystallites in humic substances detected by Nuclear Magnetic Resonance. Environmental Science and Technology, 34, 530-534. Kucerik, J.; Schwarz, J.; Jaeger, A.; Bertmer, M. & Schaumann, G. (submitted 2013). Character of transitions causing physicochemical aging of a sapric histosol. Kunhi Mouvenchery, Y.; Jaeger, A.; Aquino, A.J.A.; Tunega, D.; Diehl, D.; Bertmer, M. & Schaumann, G.E. (2013). Restructuring of a peat in interaction with multivalent cations: Effect of cation type and aging time. PLoS ONE, 8, e65359. Schaumann, G.E. & Bertmer, M. (2008). Do water molecules bridge soil organic matter molecule segments? European Journal of Soil Science, 59, 423-429. Schaumann, G.E.; Gildemeister, D.; Kunhi Mouvenchery, Y.; Spielvogel, S. & Diehl, D. (2013). Interactions between cations and water molecule bridges in soil organic matter. Journal of Soils and Sediments, 13, 1579-1588.

Short-term responses and resistance of soil microbial community structure to elevated CO2 and N addition in grassland mesocosms.

PubMed

Simonin, Marie; Nunan, Naoise; Bloor, Juliette M G; Pouteau, Valérie; Niboyet, Audrey

2017-05-01

Nitrogen (N) addition is known to affect soil microbial communities, but the interactive effects of N addition with other drivers of global change remain unclear. The impacts of multiple global changes on the structure of microbial communities may be mediated by specific microbial groups with different life-history strategies. Here, we investigated the combined effects of elevated CO2 and N addition on soil microbial communities using PLFA profiling in a short-term grassland mesocosm experiment. We also examined the linkages between the relative abundance of r- and K-strategist microorganisms and resistance of the microbial community structure to experimental treatments. N addition had a significant effect on microbial community structure, likely driven by concurrent increases in plant biomass and in soil labile C and N. In contrast, microbial community structure did not change under elevated CO2 or show significant CO2 × N interactions. Resistance of soil microbial community structure decreased with increasing fungal/bacterial ratio, but showed a positive relationship with the Gram-positive/Gram-negative bacterial ratio. Our findings suggest that the Gram-positive/Gram-negative bacteria ratio may be a useful indicator of microbial community resistance and that K-strategist abundance may play a role in the short-term stability of microbial communities under global change. © FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

The impact of extreme environmental factors on the mineralization potential of the soil

NASA Astrophysics Data System (ADS)

Zinyakova, Natalia; Semenov, Vyacheslav

2016-04-01

Warming, drying, wetting are the prevalent disturbing natural impacts that affect the upper layers of uncultivated and arable soils. The effect of drying-wetting cycles act as a physiological stress for the soil microbial community and cause changes in its structure, the partial death or lysis of the microbial biomass. The mobilization of the SOM and the stabilization of the potentially mineralizable components lead to change of mineralization potential in the soil. To test the effects of different moisture regime on plant growth and soil biological properties, plot experiment with the gray forest soil including trials with plants (corn) and bare fallow was performed. Different regimes of soil moisture (conditionally optimal, relatively deficient soil moisture and repeated cycles of drying-wetting) were created. Control of soil moisture was taken every two or three days. Gas sampling was carried out using closed chambers. Soil samples were collected at the end of the pot experiment. The potentially mineralizable content of soil organic carbon (SOC) was measured by biokinetic method based on (1) aerobic incubation of soil samples under constant temperature and moisture conditions during 158 days, (2) quantitation of C-CO2, and (3) fitting of C-CO2 cumulative curve by a model of first-order kinetic. Total soil organic carbon was measured by Tyrin's wet chemical oxidation method. Permanent deficient moisture in the soil favored the preservation of potentially mineralizable SOC. Two repeated cycles of drying-wetting did not reduce the potentially mineralizable carbon content in comparison with control under optimal soil moisture during 90 days of experiment. The emission loss of C-CO2 from the soil with plants was 1.4-1.7 times higher than the decrease of potentially mineralizable SOC due to the contribution of root respiration. On the contrary, the decrease of potentially mineralized SOC in the soil without plants was 1.1-1.2 times larger than C-CO2 emissions from the soil as a result of stabilization processes. Thus, the alternation of drying-wetting cycles results in 1) the death of microbial biomass and recolonization of the soil microorganisms; 2) favors the splitting and degradation of soil aggregates, as well as the reaggregation and stabilization of aggregates; 3) contributes to the mobilization of the SOM and also 4) initiates the stabilization of the potentially mineralizable components. The effect of drying-wetting cycles is expressed not so much in the loss of the total soil organic carbon as in the degradation of the SOM quality with decreasing its mineralization potential. We can conclude that different soil moisture regimes lead to essential changes of mineralization potential in the gray forest soil. The amount of mineralization loss soil carbon via C-CO2 emission is directly associated with the decrease of potentially mineralizable carbon. Deficient moisture is a reason for temporarily sequestration of SOC potentially mineralizable under optimal moisture. This work was supported by RSF. Project number 14-14-00625

A new model for humic materials and their interactions with hydrophobic organic chemicals in soil-water or sediment-water systems

USGS Publications Warehouse

Wershaw, R. L.

1986-01-01

A generalized model of humic materials in soils and sediments, which is consistent with their observed properties, is presented. This model provides a means of understanding the interaction of hydrophobic pollutants with humic materials. In this model, it is proposed that the humic materials in soils and sediments consist of a number of different oligomers and simple compounds which result from the partial degradation of plant remains. These degradation products are stabilized by incorporation into humic aggregates bound together by weak bonding mechanisms, such as hydrogen bonding, pi bonding, and hydrophobic interactions. The resulting structures are similar to micelles or membranes, in which the interiors of the structures are hydrophobic and the exteriors are hydrophilic. Hydrophobic compounds will partition into the hydrophobic interiors of the humic micelles or "membrane-like" structures. ?? 1986.

Biology Notes.

ERIC Educational Resources Information Center

School Science Review, 1981

1981-01-01

Presents a computer program for analyzing diets, a game designed to supplement a topic on insects, a technique for demonstrating the role of ethene in fruit ripening, an apparatus for removing arthropods from soil samples, activities using cichlids, and an activity on bonds stabilizing protein structure. (JN)

Soil manganese redox cycling in suboxic zones: Effects on soil carbon stability

EPA Science Inventory

Suboxic soil environments contain a disproportionately higher concentration of highly reactive free radicals relative to the surrounding soil matrix, which may have significant implications for soil organic matter cycling and stabilization. This study investigated how Mn-ozidizin...

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.

A combination of ferric nitrate/EDDS-enhanced washing and sludge-derived biochar stabilization of metal-contaminated soils.

PubMed

Yoo, Jong-Chan; Beiyuan, Jingzi; Wang, Lei; Tsang, Daniel C W; Baek, Kitae; Bolan, Nanthi S; Ok, Yong Sik; Li, Xiang-Dong

2018-03-01

In this study, soil washing and stabilization as a two-step soil remediation strategy was performed to remediate Pb- and Cu-contaminated soils from shooting range and railway sites. Ferric nitrate (Fe(NO 3 ) 3 ) and [S,S]-ethylenediamine disuccinate (EDDS) were used as washing agents, whereas three types of sludge-derived biochars and phosphogypsum were employed as soil stabilizers. While Fe(NO 3 ) 3 extracted larger amounts of metals compared to EDDS (84% Pb and 64% Cu from shooting range soil; 30% Pb and 40% Cu from railway site soil), it caused severe soil acidification. Both Fe(NO 3 ) 3 and EDDS washing enhanced the mobility of residual metals in the two soils, which in most cases could be mitigated by subsequent 2-month stabilization by sludge-derived biochars or phosphogypsum. By contrast, the metal bioaccessibility could only be reduced by soil washing. Nutrient-rich sludge-derived biochar replenished available P and K in both soils, whereas Fe(NO 3 ) 3 washing provided available nitrogen (N). Soil amendment enhanced acid phosphatase activity but marginally improved soil dehydrogenase and urease activity in the treated soils, possibly due to the influence of residual metals. This study supported the integration of soil washing (by Fe(NO 3 ) 3 or EDDS) with soil stabilization (by sludge-derived biochars or phosphogypsum) for accomplishing the reduction of metal mobility and bioaccessibility, while restoring the environmental quality of the treated soils. Copyright © 2017 Elsevier B.V. All rights reserved.

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...

12 years of intensive management increases soil carbon stocks in Loblolly pine and Sweetgum stands

NASA Astrophysics Data System (ADS)

Sanchez, F. G.; Samuelson, L.; Johnsen, K.

2009-12-01

To achieve and maintain productivity goals, forest managers rely on intensive management strategies. These strategies have resulted in considerable gains in forest productivity. However, the impacts of these strategies on belowground carbon dynamics is less clear. Carbon dynamics are influenced by a multitude of factors including soil moisture, nutrient status, net primary productivity and carbon allocation patterns. In this study, we describe the impact of four management strategies on soil carbon and nitrogen stocks in 12-year-old loblolly pine and sweetgum plantations. The management strategies are: (1) complete understory control, (2) complete understory control + drip irrigation, (3) complete understory control + drip irrigation and fertilization and (4) complete understory control + drip irrigation and fertilization and pest control. These management strategies were replicated on 3 blocks in a randomized complete block design. After 12 years, soil carbon stocks increased with increasing management intensity for both tree species. This effect was consistent throughout the depth increments measured (0-10, 10-20, 20-30 cm). Alternatively, no significant effect was detected for soil nitrogen at any depth increment. Sweetgum had higher soil carbon and nitrogen stocks at each depth increment than loblolly pine. There was a greater difference in nitrogen stocks than carbon stocks between the two species resulting in lower soil C:N ratios in the sweetgum stands. These observations may be due to differences in net primary productivity, rooting structure and carbon allocation patterns of sweetgum compared with loblolly pine. To determine the relative stability of the carbon and nitrogen stocks for the different treatments and tree species, we sequentially fractionated the soil samples into six fractions of differing stability. Although soil carbon stocks for both species increased with management intensity, there was no detectable difference in the soil carbon fractions based on management intensity. Additionally, there was no difference between soil carbon fractions based on tree species. These observations suggest that although external inputs (i.e., moisture, carbon and nutrients) increase soil carbon stocks, they do not alter soil carbon stabilization mechanisms at these sites.

Landform position and charring conditions control decomposition of soil organic matter and pyrogenic carbon

NASA Astrophysics Data System (ADS)

Abney, R.; Jin, L.; Berhe, A. A.

2017-12-01

Wildfire is a significant global control on both ecosystem properties and biogeochemical cycling, and wildfires are projected to increase in both size and severity with continued climate change. Post-fire, charred biomass, or pyrogenic carbon, is left behind as a significant, relatively slow-cycling component of the soil organic matter pool. Pyrogenic carbon has a turnover time on the centennial scale, and previous research has demonstrated that it is highly susceptible to erosion. However, the interaction of the roles of landform position and combustion temperature remains unexplored. We collected live Pinus jeffreyi bark and charred it under combustion conditions at three temperatures (200°C, 350°C, and 500°C). The charred bark was mixed with soil collected from both eroding and depositional landform positions and incubated for six months. Throughout this incubation, microbial respiration was monitored via collection of CO2, and cumulative respiration was fitted using both single- and multi-pool exponential models. Overall, respiration was highest in soil and char mixtures in the depositional landform positions. Pyrogenic carbon concentrations, as determined by the Kurth Mackenzie Deluca method, declined only slightly in the 200°C char mixed with the depositional soil. Scanning electron microscopy images of the chars before and after incubation illustrate some incorporation of soil organic matter into the structures of the char, and some breakdown of the physical structures of the char. Altogether, the lower temperature chars mixed with the soil from the depositional landform position had the highest decomposition rates, which suggests the role that landform position may play on the stability of pyrogenic carbon at the landscape scale. Furthermore, this implies that the post-fire erosional re-distribution of pyrogenic carbon may act as a significant control of its long-term stabilization in soil and landscape-scale soil carbon stocks.

Changes in soil carbon eight years after the death of mesquite, Prosopis velutina, in an arid environment

NASA Astrophysics Data System (ADS)

DeMarco, J.; Filley, T. R.; Throop, H. L.

2012-12-01

Encroachment of woody plants into grasslands is one of the major global land cover changes of the past century. Woody encroachment in semi-arid and arid ecosystems ("drylands") is of particular concern because these systems cover almost half of the global land surface and account for 30-35% of terrestrial net primary production. Understanding how C cycling is altered with shrub encroachment in drylands is therefore essential for understanding whether these systems will be a source or sink to regional or global C cycling. Little is known about how shrub encroachment influences the input source and stability of C in the soil. Shrub encroachment could lead to a shift in the source of aboveground litter and/or belowground inputs that can vary in their chemistry. These changes in inputs may influence the stability of soil C in the system. We used a chronosequence of shrub removal treatments and compared them to live shrubs and grass plots to assess changes in soil C sources and stability with time since shrub death. Our objectives were to 1) quantify whether soil C concentrations change with shrub encroachment, 2) quantify how woody encroachment alters the source and stability of soil C, and 3) to investigate how the source and stability of soil C changes with shrub death. We assessed changes in soil C following shrub encroachment and death in the Sonoran Desert by comparing soil from grassy areas, under live velvet mesquite (Prosopis velutina) canopies, and under mesquite skeletons that died 8 years prior to the study. Soils were collected at two depths (0-5 cm and 5-20 cm) and were measured for total organic C and total N. The lignin and cutin composition of the soils and the dominant plants in this system were also analyzed to assess the relative source and stability of C in these soils. The composition of lignin and cutin in plants are characteristic of major plant groups (grasses versus woody plants) and are preserved in the soil allowing assessment of the relative source contribution to soil C. Lignin is composed of the derivatives of three basic structural classes: vanillyls, syringyls, and cinnamyls. By analyzing the ratios of cinnamyls to vanillyls (C/V) and syringyls to vanillyls (S/V) the relative contribution of grasses versus shrub inputs present in soil can be determined. We found that C and N concentrations for shallow soils under live and dead shrubs were at least twice as high compared to grass plots (Treatment-%N: F3, 20 = 12.8, p < 0.0001; %C: F3,20= 1.2, p < 0.0001) and deeper soils across all treatments (Depth-%N: F1, 20 = 74.9, p < 0.0001; %C: F1, 20 = 2.2, p < 0.001). There were no significant differences in C and N concentrations among vegetation types for the deeper depth. Shallow soil ratios of C/V were higher in grass soils compared to live shrub soils (F3,12 = 3.5, p = 0.05) while ratios of S/V were greater in shrub soils compared to grass soils (F3,12 = 24.7, p < 0.0001). Neither C/V nor S/V ratios differed between live and dead shrubs. In contrast, cutin yields (mg 100 mg-1 C) were significantly lower under dead shrubs and in grass plots than under live shrubs (F3,12 = 7.0, p < 0.001). Our preliminary data suggest that shrub encroachment in this system enhances soil C storage and may have long-term effects on soil C for at least 8 years after shrub mortality.

Select geotechnical properties of a lime stabilized expansive soil amended with bagasse ash and coconut shell powder

NASA Astrophysics Data System (ADS)

James, Jijo; Pandian, P. Kasinatha

2018-03-01

Lime stabilization has been and still is one of the most preferred methods for stabilization of expansive soils. However, in the recent times, utilization of solid waste materials in soil stabilization has gained prominence as an effective means to manage wastes generated from various sources. In this work, an attempt has been made to utilize waste materials from two sources as auxiliary additives to lime in the stabilization of an expansive soil. Bagasse ash (BA), a waste by-product from the sugar industry and Coconut shell powder (CSP), a processed waste obtained from left over coconut shells of oil extraction industry were used as auxiliary additives. An expansive soil obtained from a local field was subjected to chemical, mineral, microstructural and geotechnical characterization in the laboratory and stabilized using 3% lime. The waste materials were subjected to chemical, mineral and microstructural characterization. The stabilization process was amended with four different contents viz. 0.25%, 0.5%, 1% and 2% of BA and CSP separately and the effect of the amendment was studied on the unconfined compressive strength (UCS), plasticity, swell-shrink and microstructural characteristics of the expansive soil. The results of the study indicated that BA amendment of lime stabilization performed better than CSP in improving the UCS, plasticity, swell-shrink and microstructure of the lime stabilized expansive soil.

Divergent taxonomic and functional responses of microbial communities to field simulation of aeolian soil erosion and deposition.

PubMed

Ma, Xingyu; Zhao, Cancan; Gao, Ying; Liu, Bin; Wang, Tengxu; Yuan, Tong; Hale, Lauren; Nostrand, Joy D Van; Wan, Shiqiang; Zhou, Jizhong; Yang, Yunfeng

2017-08-01

Aeolian soil erosion and deposition have worldwide impacts on agriculture, air quality and public health. However, ecosystem responses to soil erosion and deposition remain largely unclear in regard to microorganisms, which are the crucial drivers of biogeochemical cycles. Using integrated metagenomics technologies, we analysed microbial communities subjected to simulated soil erosion and deposition in a semiarid grassland of Inner Mongolia, China. As expected, soil total organic carbon and plant coverage were decreased by soil erosion, and soil dissolved organic carbon (DOC) was increased by soil deposition, demonstrating that field simulation was reliable. Soil microbial communities were altered (p < .039) by both soil erosion and deposition, with dramatic increase in Cyanobacteria related to increased stability in soil aggregates. amyA genes encoding α-amylases were specifically increased (p = .01) by soil deposition and positively correlated (p = .02) to DOC, which likely explained changes in DOC. Surprisingly, most of microbial functional genes associated with carbon, nitrogen, phosphorus and potassium cycling were decreased or unaltered by both erosion and deposition, probably arising from acceleration of organic matter mineralization. These divergent responses support the necessity to include microbial components in evaluating ecological consequences. Furthermore, Mantel tests showed strong, significant correlations between soil nutrients and functional structure but not taxonomic structure, demonstrating close relevance of microbial function traits to nutrient cycling. © 2017 John Wiley & Sons Ltd.

Andic soils : mineralogical effect onto organic matter dynamics, organic matter effect onto mineral dynamics, or both?

NASA Astrophysics Data System (ADS)

Basile-Doelsch, Isabelle; Amundson, Ronald; Balesdent, Jérome; Borschneck, Daniel; Bottero, Jean-Yves; Colin, Fabrice; de Junet, Alexis; Doelsch, Emmanuel; Legros, Samuel; Levard, Clément; Masion, Armand; Meunier, Jean-Dominique; Rose, Jérôme

2014-05-01

From a strictly mineralogical point of view, weathering of volcanic glass produces secondary phases that are short range ordered alumino-silicates (SRO-AlSi). These are imogolite tubes (2 to 3 nm of diameter) and allophane supposedly spheres (3.5 to 5 nm). Their local structure is composed of a curved gibbsite Al layer and Si tetrahedra in the vacancies (Q0). Proto-imogolites have the same local structure but are roof-shape nanoparticles likely representing the precursors of imogolite and allophanes (Levard et al. 2010). These structures and sizes give to the SRO-AlSi large specific surfaces and high reactivities. In some natural sites, imogolites and allophanes are formed in large quantities. Aging of these phases may lead to the formation of more stable minerals (halloysite, kaolinite and gibbsite) (Torn et al 1997). In natural environments, when the weathering of volcanic glass is associated with the establishment of vegetation, the soils formed are generally andosols. These soils are particularly rich in organic matter (OM), which is explained by the high ability of SRO-AlSi mineral phases to form bonds with organic compounds. In a first order "bulk" approach, it is considered that these bonds strongly stabilize the organic compounds as their mean age can reach more than 10 kyrs in some studied sites (Basile-Doelsch et al. 2005; Torn et al. 1997). However, the structure of the mineral phases present in andosols deserves more attention. Traditionally, the presence in the SRO-AlSi andosols was shown by selective dissolution approaches by oxalate and pyrophosphate. Using spectroscopic methods, mineralogical analysis of SRO-AlSi in andosols samples showed that these mineral phases were neither imogolites nor allophanes as originally supposed, but only less organized structures remained in a state of proto-imogolites (Basile-Doelsch al. 2005 ; Levard et al., 2012). The presence of OM would have an inhibitory effect on the formation of secondary mineral phases, by blocking the crystal growth of SRO-AlSi. Conversely, the effect of minerals on the dynamics of organic compounds also deserves to be studied in greater detail. If the "bulk" approaches showed that proto-imogolites involve long-term stabilized OM, other approaches such as densimetric fractionation and C3/C4 chronosequences (Basile-Doelsch et al. 2007; De Junet et al. 2013) led us to consider a new model involving two types of organo-mineral interactions: (1) OM stabilized by strong bonds to proto-imogolite, leading to a slow OM turnover and (2) OM retained within the porosity of the 3D structure formed by the proto-imogolite (similar to a gel structure), leading to a faster OM turnover. Understanding the mechanisms of organo-mineral interactions in andosols will open new research directions for understanding the mechanisms of stabilization of OM in any type of soil (Bonnard et al. 2012). Basile-Doelsch et al., Geoderma, 137, 477-489, 2007. Basile-Doelsch et al., European Journal of Soil Science, 56, 689-703, 2005. Bonnard et al., European Journal of Soil Science, 63, 5, 625-636, 2012. de Junet, et al., Journal of Analytical and Applied Pyrolysis, 99, 92-10, 2013, Levard et al, Geoderma, 183-184, 100-108, 2012. Levard et al. Chemistry Of Materials, 22, 2466-2473, 2010 Torn et al. Nature, London, 389, 170-173, 1997.

Natural succession on abandoned cropland effectively decreases the soil erodibility and improves the fungal diversity.

PubMed

Zhang, Chao; Liu, Guobin; Song, Zilin; Qu, Dong; Fang, Linchuan; Deng, Lei

2017-10-01

Changes in plants and soils during natural succession have been evaluated, but little is known about the effects of succession on the activities of soil microbes and their interactions with soil erodibility. We conducted a field study on the Chinese Loess Plateau, typical of this semiarid area, to determine the effect of secondary succession on the stability of soil structure against erosion and on the composition of soil fungal communities. Characteristics of plant, soil, and fungal communities were assessed across a 30-yr chronosequence of grassland developed from abandoned cropland. The diversity and composition of the fungal communities were determined using high-throughput sequencing of the internal transcribed spacer. Six grasslands were selected to represent different successional age classes: 0 (cropland), 5, 10, 15, 20, and 30 yr. Short-term decreases (initial 5 yr) in the amounts of soil organic carbon, total nitrogen, available phosphorus, and fungal biomass and in fungal diversity had returned to original levels (i.e., cropland) within 15 yr and were much higher after continued succession. Abandoning cropland for succession caused the soil erodibility (K) decrease and the aboveground coverage, soil nutrient levels, content of larger (>5 mm) water-stable aggregate, mean aggregate weight diameter, and diversity of the fungal communities improvement including arbuscular mycorrhizas (AMF), ectomycorrhizas (EMF), and saprotrophs. The fungal communities were dominated by Ascomycota, Zygomycota, Basidiomycota, and Glomeromycota during the succession. The successional patterns of the plant and fungal communities were similar, although distinct fungal communities were not observed in the two initial stages, suggesting that fungal succession may develop more slowly than plant succession. Plant root biomass, EMF, and soil organic carbon content accounted for most of the variation of soil erodibility (28.6%, 19.5%, and 11.8%, respectively), indicating their importance in shaping soil structure to prevent erosion. Our results demonstrated that abandoning cropland for natural succession could decrease soil erodibility and increase fungal diversity. EMF plays an important role in soil stability against erosion in the Loess Plateau. Abandoning cropland for natural succession should be recommended for alleviating soil erosion and improving the degraded soils in this area. © 2017 by the Ecological Society of America.

A study of the effectiveness of the use of gypsum and volcanic ash against the stability of clay soil in terms of UCT and CBR values

NASA Astrophysics Data System (ADS)

Roesyanto; Iskandar, R.; Hastuty, IP; Lubis, AIU

2018-02-01

Soil stabilization is an effort to improve engineering properties of soil. The conventional soil stabilization is by adding additives to the soil such as Portland cement, lime, and bitumen. The clay stabilization research was done by adding gypsum and volcanic ash. The research purposes were to find out the value of engineering properties of clay due to the addition of 2% gypsum and 2% - 15% volcanic ash. The soil was classified as Clay - Low Plasticity (CL) based on USCS and was classified as A-7-6 (10) based on AASHTO classification system. The UCT values of original soil and original soil plus 2% gypsum were 1.40 kg/cm2 and 1.66 kg/cm2 respectively. The CBR soaked and unsoaked values of original soil were 4.44% and 6.28% correspondingly. Meanwhile, CBR soaked and CBR unsoaked values of original soil plus 2% gypsum were 6.74% and 8.02% respectively. The research results showed that the additives materials of gypsum and volcanic ash improved the engineering properties of clay. The UCT result from the stabilized soil by 2% gypsum and 10% volcanic ash gave value of 2.79 kg/cm2 (increased 99.28% from original soil). For CBR test, the most effective mixture were in variation of 2% gypsum and 9% volcanic ash which gave value of 9.07% (104.27% increase from original soil) for CBR soaked and 10.29% (63.85% increase from original soil) for CBR unsoaked. The stabilized soil with 2% gypsum and 9% volcanic ash was classified as CL based on USCS and was classified as A-6 (4) based on AASHTO classification system.

Multiple tuned mass damper based vibration mitigation of offshore wind turbine considering soil-structure interaction

NASA Astrophysics Data System (ADS)

Hussan, Mosaruf; Sharmin, Faria; Kim, Dookie

2017-08-01

The dynamics of jacket supported offshore wind turbine (OWT) in earthquake environment is one of the progressing focuses in the renewable energy field. Soil-structure interaction (SSI) is a fundamental principle to analyze stability and safety of the structure. This study focuses on the performance of the multiple tuned mass damper (MTMD) in minimizing the dynamic responses of the structures objected to seismic loads combined with static wind and wave loads. Response surface methodology (RSM) has been applied to design the MTMD parameters. The analyses have been performed under two different boundary conditions: fixed base (without SSI) and flexible base (with SSI). Two vibration modes of the structure have been suppressed by multi-mode vibration control principle in both cases. The effectiveness of the MTMD in reducing the dynamic response of the structure is presented. The dynamic SSI plays an important role in the seismic behavior of the jacket supported OWT, especially resting on the soft soil deposit. Finally, it shows that excluding the SSI effect could be the reason of overestimating the MTMD performance.

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.

The Effects of Various Amendments on Trace Element Stabilization in Acidic, Neutral, and Alkali Soil with Similar Pollution Index

PubMed Central

Kim, Min-Suk; Min, Hyun-Gi; Lee, Sang-Hwan; Kim, Jeong-Gyu

2016-01-01

Many studies have examined the application of soil amendments, including pH change-induced immobilizers, adsorbents, and organic materials, for soil remediation. This study evaluated the effects of various amendments on trace element stabilization and phytotoxicity, depending on the initial soil pH in acid, neutral, and alkali conditions. As in all types of soils, Fe and Ca were well stabilized on adsorption sites. There was an effect from pH control or adsorption mechanisms on the stabilization of cationic trace elements from inorganic amendments in acidic and neutral soil. Furthermore, acid mine drainage sludge has shown great potential for stabilizing most trace elements. In a phytotoxicity test, the ratio of the bioavailable fraction to the pseudo-total fraction significantly affected the uptake of trace elements by bok choy. While inorganic amendments efficiently decreased the bioavailability of trace elements, significant effects from organic amendments were not noticeable due to the short-term cultivation period. Therefore, the application of organic amendments for stabilizing trace elements in agricultural soil requires further study. PMID:27835687

Study on stability of rake teeth inserting soil of chain rake type mulching film recovery machine based on Adams

NASA Astrophysics Data System (ADS)

Guo, Wensong; Jian, Jianming; San, Yunlong; Lui, Rui; Li, Gang; Hou, Shulin

2017-08-01

Traditional rake type mulching film recycling machine has the problem of difficulty in unloading and packing film, poor continuity of the work. In order to solve such problems, this paper designs a kind of chain rake type mulching film recycling machine which can realize continuous raking film, collecting film, transporting film, shaking off soil, unloading film. Rake teeth is the basic part of chain rake mulching recycling machine. The stability of rake teeth's inserting soil is an important factor to ensure recovery efficiency of the plastic film recovery. By virtual prototype simulation, this paper study the influence of different factors on the stability of rake teeth inserting soil. The results are as follows: The speed of chain rake has no significant effect on the stability of rake teeth inserting soil; Reducing resistance of rake teeth in the process of working, is conducive to improve the stability of rake teeth inserting soil; Appropriate increasing elastic modulus of chain rake, is helpful to enhance the stability of rake teeth inserting soil.

The Effects of Various Amendments on Trace Element Stabilization in Acidic, Neutral, and Alkali Soil with Similar Pollution Index.

PubMed

Kim, Min-Suk; Min, Hyun-Gi; Lee, Sang-Hwan; Kim, Jeong-Gyu

2016-01-01

Many studies have examined the application of soil amendments, including pH change-induced immobilizers, adsorbents, and organic materials, for soil remediation. This study evaluated the effects of various amendments on trace element stabilization and phytotoxicity, depending on the initial soil pH in acid, neutral, and alkali conditions. As in all types of soils, Fe and Ca were well stabilized on adsorption sites. There was an effect from pH control or adsorption mechanisms on the stabilization of cationic trace elements from inorganic amendments in acidic and neutral soil. Furthermore, acid mine drainage sludge has shown great potential for stabilizing most trace elements. In a phytotoxicity test, the ratio of the bioavailable fraction to the pseudo-total fraction significantly affected the uptake of trace elements by bok choy. While inorganic amendments efficiently decreased the bioavailability of trace elements, significant effects from organic amendments were not noticeable due to the short-term cultivation period. Therefore, the application of organic amendments for stabilizing trace elements in agricultural soil requires further study.

Denudational slope processes on weathered basalt in northern California: 130 ka history of soil development, periods of slope stability and colluviation, and climate change

NASA Astrophysics Data System (ADS)

McDonald, Eric; Harrison, Bruce; Baldwin, John; Page, William; Rood, Dylan

2017-04-01

The geomorphic history of hillslope evolution is controlled by multiple types of denudational processes. Detailed analysis of hillslope soil-stratigraphy provides a means to identify the timing of periods of slope stability and non-stability, evidence of the types of denudational processes, and possible links to climatic drivers. Moreover, the degree of soil formation and the presence of buried or truncated soils provide evidence of the relative age of alternating periods of colluviation and stability. We use evaluation of soil stratigraphy, for a small forested hillslope (<500 m of slope length) located in the Cascades of northern California, to elucidate both the timing and processes controlling 130 ka of hillslope evolution. The soils and slope colluvium are derived from highly weathered basalt. Stratigraphic interpretation is reinforced with soil profile development index (PDI) derived age estimates, tephrochronology, luminescence ages on colluvium, and He3 nuclide exposure dates. Soils formed along hilltop ridges are well developed and reflect deep (>2-3 m) in-situ weathering of the basalt bedrock. PDI age estimates and He3 exposure dates indicate that these hilltop soils had been in place for 100-130 ka, implying a long period of relative surface stability. At about 40-30 ka, soil stratigraphy indicates the onset of 3 distinct cycles of denudation of the hilltop and slopes. Evidence for changes in stability and onset of soil erosion is the presence of several buried soils formed in colluvium downslope of the hilltop. These buried soils have formed in sediment derived from erosion of the hilltop soils (i.e. soil parent material of previously weathered soil matrix and basalt cobbles). The oldest buried soil indicates that slope stability was re-established between 32-23 ka, with stability and soil formation lasting to about 10 ka. Soil-stratigraphy indicates that two additional intervals of downslope transport of sediment between 6-10 ka, and 2-5 ka. Soil properties indicate that the primary method of downslope transport is largely due to tree throw and faunal burrowing. Onset of slope instability at 40-30 ka appears to be related to changes in vegetation with establishment of a pine dominated forest (increase in tree throw) and/or onset of local faulting. By comparison, slope stability from 30-10 ka appears to be a related to the formation of a shrub dominated steppe and a decrease in tree throw. The two periods of slope erosion after 10 ka appear related to regional periods of pronounced channel incision. Results indicate that soil stratigraphy can provide a key record of slope evolution and related paleoenvironmental changes.

Aggregate stability, root length and root thickness influenced by a mycorrhizal inoculum? - Results from a three-year eco-engineering field experiment on an alpine slope.

NASA Astrophysics Data System (ADS)

Bast, Alexander; Wilcke, Wolfgang; Lüscher, Peter; Graf, Frank; Gärtner, Holger

2014-05-01

In mountain environments many slopes are covered by coarse grained, glacial-, periglacial- or/and denudation-derived substrate. These slopes show a high geomorphic activity and are susceptible for erosional processes, shallow landslides or debris flows, which can result in a high socio-economic hazard potential. This is especially true for steep slopes, lacking a protecting vegetation cover. Regarding hazard prevention, eco-engineering gained in importance because related techniques provide a sustainable measure to protect erosion-prone hillslopes. The idea of using plants for sustainable erosion control and protection against shallow landslides, demands some essential requirements, as e.g., a stable seedbed providing appropriate water and nutrient supply. However, degraded alpine slopes are often unstable and the coarse-grained material shows a low retention capacity of water and nutrients. Extreme conditions like this hamper a fast and sustainable development of a protecting vegetation cover even if pioneer plants are used to stabilize the slopes. Thus, the question arises what needs to be done to give planted saplings within eco-engineering projects maximum support developing their above- and belowground structures to promote slope stabilization. Laboratory experiments using potted plants have shown a positive impact of mycorrhizal fungi inoculation plant development and soil structure, i.e. the formation of (stable) aggregates within several months. Soil aggregate stability is an integrating parameter, reflecting several aspects of the plant-soil system and for this also an indicator of soil development and soil stability. Because of this and based on the promising laboratory results, we intended to apply this approach in a field-experiment We established (i) mycorrhizal and (ii) non-mycorrhizal treated eco-engineered research plots on a field experimental scale, covering a total area of approx. 1000 m2 on an ENE exposed slope (coarse morainic and denudation-derived substrate; inclination ~40 - 45 °; elevation 1220 - 1360 m a.s.l.) located in the Eastern Swiss Alps, where many environmental parameters can be seen as homogeneous. Soil aggregate stability, the formation of water stable aggregates and the fine-root development was quantified at the end of three consecutively vegetation periods. Our results show, that an impact of the mycorrhizal inoculum on aggregate stability was not traceable after one vegetation period, which contradicts our expectations and former laboratory experiments. At the mycorrhizal inoculated site, fine roots showed indeed a lower root length density compared to the non-mycorrhizal treated site, but the proportion of roots with thicker diameters tended to be higher. At the end of the third vegetation period this pattern changed. Aggregate stability is then highest at the inoculated site and root length density increased showing the highest values as well. The tendency to thicker root diameters at the mycorrhizal treated site can be confirmed. Our findings show that studies on a field experimental scale are inevitable. Laboratory experiments and field studies complement each other, and lead to a better understanding, having regard to a successful application of sustainable eco-engineering measures on erosion-prone slopes in alpine environments.

Four millennia of woodland structure and dynamics at the Arctic treeline of eastern Canada.

PubMed

Auger, Sarah; Payette, Serge

2010-05-01

Paleoecological analysis using complementary indicators of vegetation and soil can provide spatially explicit information on ecological processes influencing trajectories of long-term ecosystem change. Here we document the structure and dynamics of an old-growth woodland before and after its inception 1000 years ago. We infer vegetation and soil characteristics from size and age distributions of black spruce (Picea mariana (Mill.) B.S.P.), soil properties, plant fossils, and paleosols. Radiocarbon ages of charcoal on the ground and in the soil indicate that the fire return interval was approximately 300 years between 2750 and 1000 cal. yr BP. No fire evidence was found before and after this period despite the presence of spruce since 4200 cal. yr BP. The size structures of living and dead spruce suggest that the woodland is in equilibrium with present climate in absence of fire. Tree establishment and mortality occurred regularly since the last fire event around 950 cal. yr BP. Both layering and occasional seeding have contributed to stabilize the spatial distribution of spruce over the past 1000 years. Since initial afforestation, soil development has been homogenized by the changing spatial distribution of spruce following each fire. We conclude that the history of the woodland is characterized by vegetation shifts associated with fire and soil disturbances and by millennial-scale maintenance of the woodland's structure despite changing climatic conditions.

[Effects of soil properties on the stabilization process of cadmium in Cd alone and Cd-Pb contaminated soils].

PubMed

Wu, Man; Xu, Ming-Gang; Zhang, Wen-Ju; Wu, Hai-Wen

2012-07-01

In order to clarify the effects of soil properties on the stabilization process of the cadmium (Cd) added, 11 different soils were collected and incubated under a moisture content of 65%-70% at 25 degrees C. The changes of available Cd contents with incubation time (in 360 days) in Cd and Cd-Pb contaminated treatments were determined. The stabilization process was simulated using dynamic equations. The results showed that after 1.0 mg x kg(-1) Cd or 500 mg x kg(-1) Pb + 1.0 mg x kg(-1) Cd were added into the soil, the available Cd content decreased rapidly during the first 15 days, and then the decreasing rate slowed down, with an equilibrium content reached after 60 days' incubation. In Cd-Pb contaminated soils, the presence of Pb increased the content of available Cd. The stabilization process of Cd could be well described by the second-order equation and the first order exponential decay; meanwhile, dynamic parameters including equilibrium content and stabilization velocity were used to characterize the stabilization process of Cd. These two key dynamic parameters were significantly affected by soil properties. Correlation analysis and stepwise regression suggested that high pH and high cation exchange capacity (CEC) significantly retarded the availability of Cd. High pH had the paramount effect on the equilibrium content. The stabilization velocity of Cd was influenced by the soil texture. It took shorter time for Cd to get stabilized in sandy soil than in the clay.

Differential effects of fine root morphology on water dynamics in the root-soil interface

NASA Astrophysics Data System (ADS)

DeCarlo, K. F.; Bilheux, H.; Warren, J.

2017-12-01

Soil water uptake form plants, particularly in the rhizosphere, is a poorly understood question in the plant and soil sciences. Our study analyzed the role of belowground plant morphology on soil structural and water dynamics of 5 different plant species (juniper, grape, maize, poplar, maple), grown in sandy soils. Of these, the poplar system was extended to capture drying dynamics. Neutron radiography was used to characterize in-situ dynamics of the soil-water-plant system. A joint map of root morphology and soil moisture was created for the plant systems using digital image processing, where soil pixels were connected to associated root structures via minimum distance transforms. Results show interspecies emergent behavior - a sigmoidal relationship was observed between root diameter and bulk/rhizosphere soil water content difference. Extending this as a proxy for extent of rhizosphere development with root age, we observed a logistic growth pattern for the rhizosphere: minimal development in the early stages is superceded by rapid onset of rhizosphere formation, which then stabilizes/decays with the likely root suberization. Dynamics analysis of water content differences between the root/rhizosphere, and rhizosphere/bulk soil interface highlight the persistently higher water content in the root at all water content and root size ranges. At the rhizosphere/bulk soil interface, we observe a shift in soil water dynamics by root size: in super fine roots, we observe that water content is primarily lower in the rhizosphere under wetter conditions, which then gradually increases to a relatively higher water content under drier conditions. This shifts to a persistently higher rhizosphere water content relative to bulk soil in both wet/dry conditions with increased root size, suggesting that, by size, the finest root structures may contribute the most to total soil water uptake in plants.

Comparative research on tillable properties of diatomite-improved soils in the Yangtze River Delta region, China.

PubMed

Qu, Ji-Li; Zhao, Dong-Xue

2016-10-15

To improve soil texture and structure, techniques associated with physical, biological or chemical aspects are generally adopted, among which diatomite is an important soil conditioner. However, few studies have been conducted to investigate the physical, hydraulic and tillage performance of diatomite-improved soils. Consistency limits and compaction properties were investigated in this study, and several performance indicators were compared, such as the liquid limit, plastic limit and compactability, of silt, silt loam and silty-clay loam soils to which diatomite was added at volumetric ratios of 0%, 10%, 20%, and 30%. The results showed that diatomite significantly (p<0.05) improved the consistency limits, with the most preferred effects in the silt soil. The liquid limits were increased by 53.9%, 27.3%, and 14.7%, in the silt, silt loam and silty-clay loam soils, respectively, when the volumetric ratio was 30%. While diatomite lowered the maximum dry bulk density (MBD) of the classified soils, the optimum moisture content (OMC) was increased overall. The trend was consistent with the proportion of diatomite, and MBD decreased by 8.7%, 10.3%, and 13.2% in the silt, silt loam and silty-clay loam soils when 30% diatomite was mixed, whereas OMC increased by 28.7%, 22.4%, and 25.3%, respectively. Additionally, aggregate stability was negatively correlated with MBD but positively correlated with OMC. Diatomite exerts positive effects on soil mechanical strength, suggesting that soils from sludge farms are more tillable with a larger stabilized and workable matrix. Copyright © 2016 Elsevier B.V. All rights reserved.

Investigating local controls on soil moisture temporal stability using an inverse modeling approach

NASA Astrophysics Data System (ADS)

Bogena, Heye; Qu, Wei; Huisman, Sander; Vereecken, Harry

2013-04-01

A better understanding of the temporal stability of soil moisture and its relation to local and nonlocal controls is a major challenge in modern hydrology. Both local controls, such as soil and vegetation properties, and non-local controls, such as topography and climate variability, affect soil moisture dynamics. Wireless sensor networks are becoming more readily available, which opens up opportunities to investigate spatial and temporal variability of soil moisture with unprecedented resolution. In this study, we employed the wireless sensor network SoilNet developed by the Forschungszentrum Jülich to investigate soil moisture variability of a grassland headwater catchment in Western Germany within the framework of the TERENO initiative. In particular, we investigated the effect of soil hydraulic parameters on the temporal stability of soil moisture. For this, the HYDRUS-1D code coupled with a global optimizer (DREAM) was used to inversely estimate Mualem-van Genuchten parameters from soil moisture observations at three depths under natural (transient) boundary conditions for 83 locations in the headwater catchment. On the basis of the optimized parameter sets, we then evaluated to which extent the variability in soil hydraulic conductivity, pore size distribution, air entry suction and soil depth between these 83 locations controlled the temporal stability of soil moisture, which was independently determined from the observed soil moisture data. It was found that the saturated hydraulic conductivity (Ks) was the most significant attribute to explain temporal stability of soil moisture as expressed by the mean relative difference (MRD).

[Distribution characteristics of soil nematodes in reclaimed land of copper-mine-tailings in different plant associations].

PubMed

Zhu, Yong-heng; Li, Ke-zhong; Zhang, Heng; Han, Fei; Zhou, Ju-hua; Gao, Ting-ting

2015-02-01

A survey was carried out to investigate soil nematode communities in the plant associations of gramineae (Arthraxon lanceolatus, AL; Imperata cylindrica, IC) and leguminosae (Glycine soja, GS) in reclaimed land of copper-mine-tailings and in the plant associations of gramineae (Digitaria chrysoblephara, DC-CK) of peripheral control in Fenghuang Mountain, Tongling City. A total of 1277 nematodes were extracted and sorted into 51 genera. The average individual density of the nematodes was 590 individuals · 100 g(-1) dry soil. In order to analyze the distribution character- istics of soil nematode communities in reclaimed land of copper-mine-tailings, Shannon community diversity index and soil food web structure indices were applied in the research. The results showed that the total number of nematode genus and the Shannon community diversity index of soil nematode in the three plant associations of AL, IC and GS were less than that in the plant associations of DC-CK. Compared with the ecological indices of soil nematode communities among the different plant associations in reclaimed land of copper-mine-tailings and peripheral natural habitat, we found that the structure of soil food web in the plant associations of GS was more mature, with bacterial decomposition being dominant in the soil organic matter decomposition, and that the soil ecosystem in the plant associations of GS was not stable with low interference. This indicated that the soil food web in the plant associations of leguminosae had a greater development potential to improve the ecological stability of the reclaimed land of copper-mine-tailings. On the other hand, the structure of soil food web in the plant associations of AL and IC were relatively stable in a structured state with fungal decomposition being dominant in the decomposition of soil organic matter. This indicated that the soil food web in the plant associations of gramineae was at a poor development level.

Structure, composition and metagenomic profile of soil microbiomes associated to agricultural land use and tillage systems in Argentine Pampas.

PubMed

Carbonetto, Belén; Rascovan, Nicolás; Álvarez, Roberto; Mentaberry, Alejandro; Vázquez, Martin P

2014-01-01

Agriculture is facing a major challenge nowadays: to increase crop production for food and energy while preserving ecosystem functioning and soil quality. Argentine Pampas is one of the main world producers of crops and one of the main adopters of conservation agriculture. Changes in soil chemical and physical properties of Pampas soils due to different tillage systems have been deeply studied. Still, not much evidence has been reported on the effects of agricultural practices on Pampas soil microbiomes. The aim of our study was to investigate the effects of agricultural land use on community structure, composition and metabolic profiles on soil microbiomes of Argentine Pampas. We also compared the effects associated to conventional practices with the effects of no-tillage systems. Our results confirmed the impact on microbiome structure and composition due to agricultural practices. The phyla Verrucomicrobia, Plactomycetes, Actinobacteria, and Chloroflexi were more abundant in non cultivated soils while Gemmatimonadetes, Nitrospirae and WS3 were more abundant in cultivated soils. Effects on metabolic metagenomic profiles were also observed. The relative abundance of genes assigned to transcription, protein modification, nucleotide transport and metabolism, wall and membrane biogenesis and intracellular trafficking and secretion were higher in cultivated fertilized soils than in non cultivated soils. We also observed significant differences in microbiome structure and taxonomic composition between soils under conventional and no-tillage systems. Overall, our results suggest that agronomical land use and the type of tillage system have induced microbiomes to shift their life-history strategies. Microbiomes of cultivated fertilized soils (i.e. higher nutrient amendment) presented tendencies to copiotrophy while microbiomes of non cultivated homogenous soils appeared to have a more oligotrophic life-style. Additionally, we propose that conventional tillage systems may promote copiotrophy more than no-tillage systems by decreasing soil organic matter stability and therefore increasing nutrient availability.

Structure, Composition and Metagenomic Profile of Soil Microbiomes Associated to Agricultural Land Use and Tillage Systems in Argentine Pampas

PubMed Central

Carbonetto, Belén; Rascovan, Nicolás; Álvarez, Roberto; Mentaberry, Alejandro; Vázquez, Martin P.

2014-01-01

Agriculture is facing a major challenge nowadays: to increase crop production for food and energy while preserving ecosystem functioning and soil quality. Argentine Pampas is one of the main world producers of crops and one of the main adopters of conservation agriculture. Changes in soil chemical and physical properties of Pampas soils due to different tillage systems have been deeply studied. Still, not much evidence has been reported on the effects of agricultural practices on Pampas soil microbiomes. The aim of our study was to investigate the effects of agricultural land use on community structure, composition and metabolic profiles on soil microbiomes of Argentine Pampas. We also compared the effects associated to conventional practices with the effects of no-tillage systems. Our results confirmed the impact on microbiome structure and composition due to agricultural practices. The phyla Verrucomicrobia, Plactomycetes, Actinobacteria, and Chloroflexi were more abundant in non cultivated soils while Gemmatimonadetes, Nitrospirae and WS3 were more abundant in cultivated soils. Effects on metabolic metagenomic profiles were also observed. The relative abundance of genes assigned to transcription, protein modification, nucleotide transport and metabolism, wall and membrane biogenesis and intracellular trafficking and secretion were higher in cultivated fertilized soils than in non cultivated soils. We also observed significant differences in microbiome structure and taxonomic composition between soils under conventional and no- tillage systems. Overall, our results suggest that agronomical land use and the type of tillage system have induced microbiomes to shift their life-history strategies. Microbiomes of cultivated fertilized soils (i.e. higher nutrient amendment) presented tendencies to copiotrophy while microbiomes of non cultivated homogenous soils appeared to have a more oligotrophic life-style. Additionally, we propose that conventional tillage systems may promote copiotrophy more than no-tillage systems by decreasing soil organic matter stability and therefore increasing nutrient availability. PMID:24923965

Visually assessing the level of development and soil surface stability of cyanobacterially dominated biological soil crusts

USGS Publications Warehouse

Belnap, J.; Phillips, S.L.; Witwicki, D.L.; Miller, M.E.

2008-01-01

Biological soil crusts (BSCs) are an integral part of dryland ecosystems and often included in long-term ecological monitoring programs. Estimating moss and lichen cover is fairly easy and non-destructive, but documenting cyanobacterial level of development (LOD) is more difficult. It requires sample collection for laboratory analysis, which causes soil surface disturbance. Assessing soil surface stability also requires surface disturbance. Here we present a visual technique to assess cyanobacterial LOD and soil surface stability. We define six development levels of cyanobacterially dominated soils based on soil surface darkness. We sampled chlorophyll a concentrations (the most common way of assessing cyanobacterial biomass), exopolysaccharide concentrations, and soil surface aggregate stability from representative areas of each LOD class. We found that, in the laboratory and field, LOD classes were effective at predicting chlorophyll a soil concentrations (R2=68-81%), exopolysaccharide concentrations (R2=71%), and soil aggregate stability (R2=77%). We took representative photos of these classes to construct a field guide. We then tested the ability of field crews to distinguish these classes and found this technique was highly repeatable among observers. We also discuss how to adjust this index for the different types of BSCs found in various dryland regions.

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.

Evaluation Criteria and Results of Full Scale Testing of Bridge Abutment Made from Reinforced Soil

NASA Astrophysics Data System (ADS)

Hildebrand, Maciej; Rybak, Jarosław

2017-10-01

Structures made of reinforced soil can be evaluated for their safety based on a load testing. Measurement results are essentially evaluated by displacements of surcharge (mainly in vertical direction) and facing elements (mainly in horizontal direction). Displacements are within several tenths to several millimetres and they can be taken by common geodetic equipment. Due to slow soil consolidation (progress of displacements) under constant load, observations should be made over several days or even weeks or months. A standard procedure of heating of geotextiles, used in laboratory conditions to simulate long term behaviour cannot be used in a natural scale. When the load is removed, the soil unloading occurs. Both the progress of displacements and soil unloading after unloading of the structure are the key presumptions for evaluating its safety (stability). Assessment of measuring results must be preceded by assuming even the simplest model of the structure, so as it could be possible to estimate the expected displacements under controlled load. In view of clearly random nature of soil parameters of retaining structure composed of reinforced soil and due to specific erection technology of reinforced soil structure, the assessment of its condition is largely based on expert’s judgment. It is an essential and difficult task to interpret very small displacements which are often enough disturbed by numerous factors like temperature, insolation, precipitation, vehicles, etc. In the presented paper, the authors tried to establish and juxtapose some criteria for a load test of a bridge abutment and evaluate their suitability for decision making. Final remarks are based on authors experience from a real full scale load test.

Agriculturization in the Argentinean Northern Humid Pampas: the Impact on Soil Structure and Runoff

NASA Astrophysics Data System (ADS)

Sasal, M. C.; Léonard, J.; Andriulo, A.; Wilson, M. G.

2012-04-01

Argentina is among the countries with the largest cropped area under no-tillage (NT). No tillage was adopted in the northern Humid Pampas to reduce the widespread soil degradation by water erosion. With the advent of genetically modified soybean varieties, NT has developed exponentially. This evolution, combined with the influence of the international market trend, has resulted in large changes in crop sequence composition toward the disappearance of pastures and the expansion of soybean monoculture. The aim of this work was to evaluate the long-term consequences of these changes on the topsoil structure and the way in which the evolution of soil structure relates to the simplification of the crop sequence and to runoff at a regional scale. We analyzed the topsoil structure of 25 sites with Argiudolls having 4 to 29 consecutive years of NT using the cultural profile approach. An intensification sequence index (ISI) was calculated as the ratio between the length of the growth period and the length of the year. Fifteen natural-rainfall runoff plots (100 m2) with 3.5% slope were used to analyze the relationship between soil structural state, crop sequence and runoff for four years. Four types of soil structures were identified and a general pattern of vertical soil structure organization was revealed. The top centimeters of 72% of the sites were dominated by a granular structure. Platy soil structure development was omnipresent: all sites exhibited a horizontal platy structure (<10 cm thick) developing either directly from the soil surface or from below the granular structure. Below the platy structure layer, a gamma soil structure (with visible structural porosity) was observed in all sites (30-75% of the A horizon), while compacted delta soil structure was detected in localized zones. A significant parabolic relationship (R2=0.60) was found between the number of consecutive years under NT and the proportion of platy structure in the A horizon. The proportion of platy structure increased during the first 15 years of NT, and then the extension of platy structure tended to stabilize and even to decrease after 20 to 25 years. The development of platy soil structure was negatively related to the ISI (R2=0.57) and runoff increased as the proportion of platy structure increased and the proportion of granular structure decreased (R2=0.85). We concluded that high soybean frequency in cropping systems under NT favors the extension of platy soil structure and increases runoff. More than 70% of the agricultural area of the northern Humid Pampas region is currently covered by soybean cultivation, mostly as a single annual crop (ISI=0.38). Our results thus suggest that promoting management practices such as the expansion of wheat/soybean double crop (ISI=0.83) could limit soil structure degradation and reduce runoff and the associated environmental risks.

Effects of corn cob ash on lime stabilized lateritic soil

NASA Astrophysics Data System (ADS)

Nnochiri, Emeka Segun

2018-03-01

This study assesses the effects of Corn Cob Ash (CCA) on lime-stabilized lateritic soil. Preliminary tests were carried out on the natural soil sample for purpose of identification and classification. Lime being the main stabilizing material was thoroughly mixed with the soil sample to determine the optimum lime requirement of the sample as a basis for evaluating the effects of the CCA. The optimum lime requirement was 10%. The CCA was thereafter added to the lime stabilized soil in varying proportions of 2, 4, 6, 8 and 10%. Unsoaked CBR increased from 83% at 0% CCA to highest value of 94% at 4% CCA. Unconfined Compressive Strength (UCS) values increased from 1123kN/m2 at 0% CCA to highest value of 1180kN/m2 at 4% CCA. It was therefore concluded that CCA can serve as a good complement for lime stabilization in lateritic soil.

ENVIRONMENTAL EVALUATION FOR UTILIZATION OF ASH IN SOIL STABILIZATION

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

David J. Hassett; Loreal V. Heebink

2001-08-01

The Minnesota Pollution Control Agency (MPCA) approved the use of coal ash in soil stabilization, indicating that environmental data needed to be generated. The overall project goal is to evaluate the potential for release of constituents into the environment from ash used in soil stabilization projects. Supporting objectives are: (1) To ensure sample integrity through implementation of a sample collection, preservation, and storage protocol to avoid analyte concentration or loss. (2) To evaluate the potential of each component (ash, soil, water) of the stabilized soil to contribute to environmental release of analytes of interest. (3) To use laboratory leaching methodsmore » to evaluate the potential for release of constituents to the environment. (4) To facilitate collection of and to evaluate samples from a field runoff demonstration effort. The results of this study indicated limited mobility of the coal combustion fly ash constituents in laboratory tests and the field runoff samples. The results presented support previous work showing little to negligible impact on water quality. This and past work indicates that soil stabilization is an environmentally beneficial CCB utilization application as encouraged by the U.S. Environmental Protection Agency. This project addressed the regulatory-driven environmental aspect of fly ash use for soil stabilization, but the demonstrated engineering performance and economic advantages also indicate that the use of CCBs in soil stabilization can and should become an accepted engineering option.« less

Assessment of water-soluble thiourea-formaldehyde (WTF) resin for stabilization/solidification (S/S) of heavy metal contaminated soils.

PubMed

Liu, She-Jiang; Jiang, Jia-Yu; Wang, Shen; Guo, Yu-Peng; Ding, Hui

2018-03-15

Stabilization/Solidification (S/S) can be regarded as necessary for remediation of heavy metal contaminated soil. There is, however, solid agent is not very convenient to use. Water-soluble thiourea-formaldehyde (WTF) is a novel chelating agent, which has more practical applications. The process of WTF resin for S/S process of heavy metal contaminated soils was studied. Laboratory-prepared slurries, made of field soils spiked with Cd 2+ and Cr 6+ were treated with WTF resin. The toxicity characteristic leaching procedure (TCLP) showed that with 2 wt% WTF, in the neutral condition of soil after treatment for 7 d, the leaching concentrations of Cd 2+ and Cr 6+ in contaminated soil were decreased by 80.3% and 92.6% respectively. Moreover, Tessier sequence extraction procedure showed WTF resin reduced the leaching concentration by transforming heavy metal from exchange form to organic form. The structure of WTF is obtained according to elemental analysis result and reaction mechanism. Through analysis of the infrared spectrogram of WTF and WTF heavy mental chelating precipitation, WTF can form stable chelate with heavy mental through coordination. The significant groups are hydroxyl, nitrogen and sulphur function groups in WTF mainly. Toxicology test revealed that the WTF resin is nontoxic to microorganism in the soils. Copyright © 2017 Elsevier B.V. All rights reserved.

Long-term efficiency of soil stabilization with apatite and Slovakite: the impact of two earthworm species (Lumbricus terrestris and Dendrobaena veneta) on lead bioaccessibility and soil functioning.

PubMed

Tica, D; Udovic, M; Lestan, D

2013-03-01

Remediation soil is exposed to various environmental factors over time that can affect the final success of the operation. In the present study, we assessed Pb bioaccessibility and microbial activity in industrially polluted soil (Arnoldstein, Austria) stabilized with 5% (w/w) of Slovakite and 5% (w/w) of apatite soil after exposure to two earthworm species, Lumbricus terrestris and Dendrobaena veneta, used as model environmental biotic soil factors. Stabilization resulted in reduced Pb bioaccessibility, as assessed with one-step extraction tests and six-step sequential extraction, and improved soil functioning, mirrored in reduced β-glucosidase activity in soil. Both earthworm species increased Pb bioaccessibility, thus decreasing the initial stabilization efficacy and indicating the importance of considering the long-term fate of remediated soil. The earthworm species had different effects on soil enzyme activity, which can be attributed to species-specific microbial populations in earthworm gut acting on the ingested soil. Copyright © 2012 Elsevier Ltd. All rights reserved.

[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.

Integrating plant litter quality, soil organic matter stabilization, and the carbon saturation concept.

PubMed

Castellano, Michael J; Mueller, Kevin E; Olk, Daniel C; Sawyer, John E; Six, Johan

2015-09-01

Labile, 'high-quality', plant litters are hypothesized to promote soil organic matter (SOM) stabilization in mineral soil fractions that are physicochemically protected from rapid mineralization. However, the effect of litter quality on SOM stabilization is inconsistent. High-quality litters, characterized by high N concentrations, low C/N ratios, and low phenol/lignin concentrations, are not consistently stabilized in SOM with greater efficiency than 'low-quality' litters characterized by low N concentrations, high C/N ratios, and high phenol/lignin concentrations. Here, we attempt to resolve these inconsistent results by developing a new conceptual model that links litter quality to the soil C saturation concept. Our model builds on the Microbial Efficiency-Matrix Stabilization framework (Cotrufo et al., 2013) by suggesting the effect of litter quality on SOM stabilization is modulated by the extent of soil C saturation such that high-quality litters are not always stabilized in SOM with greater efficiency than low-quality litters. © 2015 John Wiley & Sons Ltd.

A Dynamic Hydrology-Critical Zone Framework for Rainfall-triggered Landslide Hazard Prediction

NASA Astrophysics Data System (ADS)

Dialynas, Y. G.; Foufoula-Georgiou, E.; Dietrich, W. E.; Bras, R. L.

2017-12-01

Watershed-scale coupled hydrologic-stability models are still in their early stages, and are characterized by important limitations: (a) either they assume steady-state or quasi-dynamic watershed hydrology, or (b) they simulate landslide occurrence based on a simple one-dimensional stability criterion. Here we develop a three-dimensional landslide prediction framework, based on a coupled hydrologic-slope stability model and incorporation of the influence of deep critical zone processes (i.e., flow through weathered bedrock and exfiltration to the colluvium) for more accurate prediction of the timing, location, and extent of landslides. Specifically, a watershed-scale slope stability model that systematically accounts for the contribution of driving and resisting forces in three-dimensional hillslope segments was coupled with a spatially-explicit and physically-based hydrologic model. The landslide prediction framework considers critical zone processes and structure, and explicitly accounts for the spatial heterogeneity of surface and subsurface properties that control slope stability, including soil and weathered bedrock hydrological and mechanical characteristics, vegetation, and slope morphology. To test performance, the model was applied in landslide-prone sites in the US, the hydrology of which has been extensively studied. Results showed that both rainfall infiltration in the soil and groundwater exfiltration exert a strong control on the timing and magnitude of landslide occurrence. We demonstrate the extent to which three-dimensional slope destabilizing factors, which are modulated by dynamic hydrologic conditions in the soil-bedrock column, control landslide initiation at the watershed scale.

Soil Communities Promote Temporal Stability and Species Asynchrony in Experimental Grassland Communities

PubMed Central

Pellkofer, Sarah; van der Heijden, Marcel G. A.; Schmid, Bernhard; Wagg, Cameron

2016-01-01

Background Over the past two decades many studies have demonstrated that plant species diversity promotes primary productivity and stability in grassland ecosystems. Additionally, soil community characteristics have also been shown to influence the productivity and composition of plant communities, yet little is known about whether soil communities also play a role in stabilizing the productivity of an ecosystem. Methodology/Principal Findings Here we use microcosms to assess the effects of the presence of soil communities on plant community dynamics and stability over a one-year time span. Microcosms were filled with sterilized soil and inoculated with either unaltered field soil or field soil sterilized to eliminate the naturally occurring soil biota. Eliminating the naturally occurring soil biota not only resulted in lower plant productivity, and reduced plant species diversity, and evenness, but also destabilized the net aboveground productivity of the plant communities over time, which was largely driven by changes in abundance of the dominant grass Lolium perenne. In contrast, the grass and legumes contributed more to net aboveground productivity of the plant communities in microcosms where soil biota had been inoculated. Additionally, the forbs exhibited compensatory dynamics with grasses and legumes, thus lowering temporal variation in productivity in microcosms that received the unaltered soil inocula. Overall, asynchrony among plant species was higher in microcosms where an unaltered soil community had been inoculated, which lead to higher temporal stability in community productivity. Conclusions/Significance Our results suggest that soil communities increase plant species asynchrony and stabilize plant community productivity by equalizing the performance among competing plant species through potential antagonistic and facilitative effects on individual plant species. PMID:26829481

Seismic Response of Steel Braced Building Frame Considering Soil Structure Interaction (SSI): An Experimental Study

NASA Astrophysics Data System (ADS)

Hirave, Vivek; Kalyanshetti, Mahesh

2018-02-01

Conventional fixed-base analysis ignoring the effect of soil-flexibility may result in unsafe design. Therefore, to evaluate the realistic behavior of structure the soil structure interaction (SSI) effect shall be incorporated in the analysis. In seismic analysis, provision of bracing system is one of the important option for the structure to have sufficient strength with adequate stiffness to resist lateral forces. The different configuration of these bracing systems alters the response of buildings, and therefore, it is important to evaluate the most effective bracing systems in view point of stability against SSI effect. In present study, three RC building frames, G+3, G+5 and G+7 and their respective scaled down steel model with two types of steel bracing system incorporating the effect of soil flexibility is considered for experimental and analytical study. The analytical study is carried out using Elastic continuum approach and the experimental study is carried out using Shake Table. The influence of SSI on various seismic parameters is presented. The study reveals that, steel bracing system is beneficial to control SSI effect and it is observed that V bracing is more effective, in resisting seismic load considering SSI.

Can we manipulate root system architecture to control soil erosion?

NASA Astrophysics Data System (ADS)

Ola, A.; Dodd, I. C.; Quinton, J. N.

2015-09-01

Soil erosion is a major threat to soil functioning. The use of vegetation to control erosion has long been a topic for research. Much of this research has focused on the above-ground properties of plants, demonstrating the important role that canopy structure and cover plays in the reduction of water erosion processes. Less attention has been paid to plant roots. Plant roots are a crucial yet under-researched factor for reducing water erosion through their ability to alter soil properties, such as aggregate stability, hydraulic function and shear strength. However, there have been few attempts to specifically manipulate plant root system properties to reduce soil erosion. Therefore, this review aims to explore the effects that plant roots have on soil erosion and hydrological processes, and how plant root architecture might be manipulated to enhance its erosion control properties. We demonstrate the importance of root system architecture for the control of soil erosion. We also show that some plant species respond to nutrient-enriched patches by increasing lateral root proliferation. The erosional response to root proliferation will depend upon its location: at the soil surface dense mats of roots may reduce soil erodibility but block soil pores thereby limiting infiltration, enhancing runoff. Additionally, in nutrient-deprived regions, root hair development may be stimulated and larger amounts of root exudates released, thereby improving aggregate stability and decreasing erodibility. Utilizing nutrient placement at specific depths may represent a potentially new, easily implemented, management strategy on nutrient-poor agricultural land or constructed slopes to control erosion, and further research in this area is needed.

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.

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.

Subgrade stabilization alternatives to lime and cement.

DOT National Transportation Integrated Search

2010-04-15

This project involved four distinct research activities, (1) the influence of temperature on lime-stabilized soils, (2) the influence of temperature on cement-stabilized soils (3) temperature modeling of stabilized subgrade and (4) use of calcium chl...

Long-term Stabilization of Disturbed Slopes Resulting from Construction Operations

DOT National Transportation Integrated Search

2018-01-01

Highway construction disturbs soil, which must be stabilized to prevent migration of soil particles into water bodies. Stabilization is enforced by law, regulation, and a permit system. Stabilization is most efficiently attained by reestablishment of...

Relationships between stability, maturity, water-extractable organic matter of municipal sewage sludge composts and soil functionality.

PubMed

Sciubba, Luigi; Cavani, Luciano; Grigatti, Marco; Ciavatta, Claudio; Marzadori, Claudio

2015-09-01

Compost capability of restoring or enhancing soil quality depends on several parameters, such as soil characteristics, compost carbon, nitrogen and other nutrient content, heavy metal occurrence, stability and maturity. This study investigated the possibility of relating compost stability and maturity to water-extractable organic matter (WEOM) properties and amendment effect on soil quality. Three composts from municipal sewage sludge and rice husk (AN, from anaerobic wastewater treatment plants; AE, from aerobic ones; MIX, from both anaerobic and aerobic ones) have been analysed and compared to a traditional green waste compost (GM, from green manure, solid waste and urban sewage sludge). To this aim, WEOMs were characterized through chemical analysis; furthermore, compost stability was evaluated through oxygen uptake rate calculation and maturity was estimated through germination index determination, whereas compost impact on soil fertility was studied, in a lab-scale experiment, through indicators as inorganic nitrogen release, soil microbial biomass carbon, basal respiration rate and fluorescein di-acetate hydrolysis. The obtained results indicated that WEOM characterization could be useful to investigate compost stability (which is related to protein and phenol concentrations) and maturity (related to nitrate/ammonium ratio and degree of aromaticity) and then compost impact on soil functionality. Indeed, compost stability resulted inversely related to soil microbial biomass, basal respiration rate and fluorescein di-acetate hydrolysis when the products were applied to the soil.

Calcium-based stabilizer induced heave in Oklahoma sulfate-bearing soils.

DOT National Transportation Integrated Search

2011-06-01

The addition of lime stabilizers can create problems in soils containing sulfates. In most cases, lime is mixed with expansive soils rendering them non-expansive; however, when a certain amount of sulfate is present naturally in expansive soils, the ...

Apparatus for treatment of soils contaminated with organic pollutants

DOEpatents

Wickramanayake, Godage B.

1993-01-01

An apparatus for treating soil contaminated by organic compounds wherein an ozone containing gas is treated with acid to increase the stability of the ozone in the soil environment and the treated ozone applied to the contaminated soil in a manner adapted to decompose the organic compounds; one embodiment of the apparatus comprises a means to supply ozone as a gas-ozone mixture, a stability means to treat ozone obtained from the supply and distribution means to apply the stabilized gas-ozone to soil. The soil may be treated in situ or may be removed for treatment and refilled.

Investigation of Stabilised Batu Pahat Soft Soil Pertaining on its CBR and Permeability Properties for Road Construction

NASA Astrophysics Data System (ADS)

Mohd Idrus, M. M.; Singh, J. S. M.; Musbah, A. L. A.; Wijeyesekera, D. C.

2016-07-01

Soil stabilization by adding materials such as cement, lime and bitumen is one of the effective methods for improving the geotechnical properties of soils [11] Nano-particle is one of the newest additives and many studies about using nano-particle in soil improvement has been done but it was given less attention when soft clay soils stabilization is concerned. To evaluate the strength characteristics of stabilized Batu Pahat soft clay, laboratory investigation on early strength gained by the stabilized soil must be conducted to formulate a suitable and economical mix design [10]. To achieve such purpose, the study examined the effect of NanoClay on the California Bearing Ratio and the Permeability of soft clay. The results gained shows that the Nano-Clay is able to increase the strength of the soft clay [9]. The California Bearing Ratio of the soil is increase significantly where the results for the highest percentage of admixture is 14.4% while the permeability of the soil decreases significantly with increasing Nano-Clay whereby the results of the highest percentage of admixture is 2.0187x10-11 m/s. After doing this research, it is proven that Nano-clay can contribute towards better soil stabilization and enhance the quality of soil as subgrade and foundation at large.

Temperature responses of individual soil organic matter components

NASA Astrophysics Data System (ADS)

Feng, Xiaojuan; Simpson, Myrna J.

2008-09-01

Temperature responses of soil organic matter (SOM) remain unclear partly due to its chemical and compositional heterogeneity. In this study, the decomposition of SOM from two grassland soils was investigated in a 1-year laboratory incubation at six different temperatures. SOM was separated into solvent extractable compounds, suberin- and cutin-derived compounds, and lignin-derived monomers by solvent extraction, base hydrolysis, and CuO oxidation, respectively. These SOM components have distinct chemical structures and stabilities and their decomposition patterns over the course of the experiment were fitted with a two-pool exponential decay model. The stability of SOM components was also assessed using geochemical parameters and kinetic parameters derived from model fitting. Compared with the solvent extractable compounds, a low percentage of lignin monomers partitioned into the labile SOM pool. Suberin- and cutin-derived compounds were poorly fitted by the decay model, and their recalcitrance was shown by the geochemical degradation parameter (ω - C16/∑C16), which was observed to stabilize during the incubation. The temperature sensitivity of decomposition, expressed as Q10, was derived from the relationship between temperature and SOM decay rates. SOM components exhibited varying temperature responses and the decomposition of lignin monomers exhibited higher Q10 values than the decomposition of solvent extractable compounds. Our study shows that Q10 values derived from soil respiration measurements may not be reliable indicators of temperature responses of individual SOM components.

Density functional theory study of phase stability and defect thermodynamics in iron-oxyhydroxide mineral materials

NASA Astrophysics Data System (ADS)

Pinney, Nathan Douglas

Due to their high surface area and reactivity toward a variety of heavy metal and oxyanion species of environmental concern, Fe-(oxyhydr)oxide materials play an important role in the geochemical fate of natural and anthropogenic contaminants in soils, aquifers and surface water environments worldwide. In this research, ab initio simulations describe the bulk structure, magnetic properties, and relative phase stability of major Fe-(oxyhydr)oxide materials, including hematite, goethite, lepidocrocite, and ferrihydrite.These bulk models are employed in further studies of point defect and alloy/dopant thermodynamics in these materials, allowing construction of a phase stability model that better replicates the structure and composition of real materials. Li + adsorption at the predominant goethite (101) surface is simulated using ab initio methods, offering energetic and structural insight into the binding mechanisms of metal cations over a range of surface protonation conditions.

Interactions in Natural Colloid Systems "Biosolids" - Soil and Plant

NASA Astrophysics Data System (ADS)

Kalinichenko, Kira V.; Nikovskaya, Galina N.; Ulberg, Zoya R.

2016-04-01

The "biosolids" are complex biocolloid system arising in huge amounts (mln tons per year) from biological municipal wastewater treatment. These contain clusters of nanoparticles of heavy metal compounds (in slightly soluble or unsoluble forms, such as phosphates, sulphates, carbonates, hydroxides, and etc.), cells, humic substances and so on, involved in exopolysaccharides (EPS) net matrix. One may consider that biosolids are the natural nanocomposite. Due to the presence of nitrogen, phosphorus, potassium and other macro- and microelements (heavy metals), vitamins, aminoacids, etc., the biosolids are a depot of bioelements for plant nutrition. Thus, it is generally recognized that most rationally to utilize them for land application. For this purpose the biocolloid process was developed in biosolids system by initiation of microbial vital ability followed by the synthesis of EPS, propagation of ecologically important microorganisms, loosening of the structure and weakening of the coagulation contacts between biosolids colloids, but the structure integrity maintaining [1,2]. It was demonstrated that the applying of biosolids with metabolizing microorganisms to soil provided the improving soil structure, namely the increasing of waterstable aggregates content (70% vs. 20%). It occurs due to flocculation ability of biosolids EPS. The experimental modelling of mutual interactions in systems of soils - biosolids (with metabolizing microorganisms) were realized and their colloid and chemical mechanisms were formulated [3]. As it is known, the most harmonious plant growth comes at a prolonged entering of nutrients under the action of plant roots exudates which include pool of organic acids and polysaccharides [4]. Special investigations showed that under the influence of exudates excreted by growing plants, the biosolids microelements can release gradually from immobilized state into environment and are able to absorb by plants. Thus, the biosolids can serve as an active component of soil substrate. Soil enrichment with biosolids nanocomposite resulted in an improving of its structures, a faster growth of plants and substantial harvest increase, as compared with control (unfertilized) soil. 1. Kalinichenko KV, Nikovskaya GN, and Ulberg ZR (2012) Bioextraction of heavy metals from colloidal sludge systems. Colloid Journ. 74(5): 553-557. 2. Kalinichenko KV, Nikovskaya GN, and Ulberg ZR (2013) Changes in the surface properties and stability of biocolloids of a sludge system upon extraction of heavy metals. Colloid Journ. 75(3): 274-278. 3. Nikovskaya GN, et al (2006) The influence of different reclamation agents and microorganisms on the aggregative stability of the colloidal fraction of meadow chernozem soil. Colloid Journal. 68 (3): 345-349. 4. Dakora FD, Phillips DA (2002) Root exudates as mediators of mineral acquisition in low-nutrient environments. Plant and Soil. 1: 35-47.

Centrifugal Modelling of Soil Structures. Part III. The Stability of River Banks and Flood Embankments.

DTIC Science & Technology

1978-10-01

mode Plate 3.6, and also electrically using a strain gauged diaphragm transducer. This transducer was mounted in a I" BSP plug and installed in a...manufactured by Druck Ltd of Leicester and have been described by Hird, 1974. The membrane is a single silicon crystal into which is diffused a strain gauge ...diaphragm strain gauge on the back. The transducers were very small and gave excellent results in the water line to the reservoir. In the soil, however

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...

Chapter D. The Loma Prieta, California, Earthquake of October 17, 1989 - Earth Structures and Engineering Characterization of Ground Motion

USGS Publications Warehouse

Holzer, Thomas L.

1998-01-01

This chapter contains two papers that summarize the performance of engineered earth structures, dams and stabilized excavations in soil, and two papers that characterize for engineering purposes the attenuation of ground motion with distance during the Loma Prieta earthquake. Documenting the field performance of engineered structures and confirming empirically based predictions of ground motion are critical for safe and cost effective seismic design of future structures as well as the retrofitting of existing ones.

Improvement of Expansive Soils Using Chemical Stabilizers

NASA Astrophysics Data System (ADS)

Ikizler, S. B.; Senol, A.; Khosrowshahi, S. K.; Hatipoğlu, M.

2014-12-01

The aim of this study is to investigate the effect of two chemical stabilizers on the swelling potential of expansive soil. A high plasticity sodium bentonite was used as the expansive soil. The additive materials including fly ash (FA) and lime (L) were evaluated as potential stabilizers to decrease the swelling pressure of bentonite. Depending on the type of additive materials, they were blended with bentonite in different percentages to assess the optimum state and approch the maximum swell pressure reduction. According to the results of swell pressure test, both fly ash and lime reduce the swelling potential of bentonite but the maximum improvement occurs using bentonite-lime mixture while the swelling pressure reduction approaches to 49%. The results reveal a significant reduction of swelling potential of expansive soil using chemical stabilizers. Keywords: Expansive soil; swell pressure; chemical stabilization; fly ash; lime

Physical soil quality indicators for monitoring British soils

NASA Astrophysics Data System (ADS)

Corstanje, Ron; Mercer, Theresa G.; Rickson, Jane R.; Deeks, Lynda K.; Newell-Price, Paul; Holman, Ian; Kechavarsi, Cedric; Waine, Toby W.

2017-09-01

Soil condition or quality determines its ability to deliver a range of functions that support ecosystem services, human health and wellbeing. The increasing policy imperative to implement successful soil monitoring programmes has resulted in the demand for reliable soil quality indicators (SQIs) for physical, biological and chemical soil properties. The selection of these indicators needs to ensure that they are sensitive and responsive to pressure and change, e.g. they change across space and time in relation to natural perturbations and land management practices. Using a logical sieve approach based on key policy-related soil functions, this research assessed whether physical soil properties can be used to indicate the quality of British soils in terms of their capacity to deliver ecosystem goods and services. The resultant prioritised list of physical SQIs was tested for robustness, spatial and temporal variability, and expected rate of change using statistical analysis and modelling. Seven SQIs were prioritised: soil packing density, soil water retention characteristics, aggregate stability, rate of soil erosion, depth of soil, soil structure (assessed by visual soil evaluation) and soil sealing. These all have direct relevance to current and likely future soil and environmental policy and are appropriate for implementation in soil monitoring programmes.

Improvement of physical, chemical, and biological properties of aridisol from Botswana by the incorporation of torrefied biomass

PubMed Central

Ogura, Tatsuki; Date, Yasuhiro; Masukujane, Masego; Coetzee, Tidimalo; Akashi, Kinya; Kikuchi, Jun

2016-01-01

Effective use of agricultural residual biomass may be beneficial for both local and global ecosystems. Recently, biochar has received attention as a soil enhancer, and its effects on plant growth and soil microbiota have been investigated. However, there is little information on how the physical, chemical, and biological properties of soil amended with biochar are affected. In this study, we evaluated the effects of the incorporation of torrefied plant biomass on physical and structural properties, elemental profiles, initial plant growth, and metabolic and microbial dynamics in aridisol from Botswana. Hemicellulose in the biomass was degraded while cellulose and lignin were not, owing to the relatively low-temperature treatment in the torrefaction preparation. Water retentivity and mineral availability for plants were improved in soils with torrefied biomass. Furthermore, fertilization with 3% and 5% of torrefied biomass enhanced initial plant growth and elemental uptake. Although the metabolic and microbial dynamics of the control soil were dominantly associated with a C1 metabolism, those of the 3% and 5% torrefied biomass soils were dominantly associated with an organic acid metabolism. Torrefied biomass was shown to be an effective soil amendment by enhancing water retentivity, structural stability, and plant growth and controlling soil metabolites and microbiota. PMID:27313139

Improvement of physical, chemical, and biological properties of aridisol from Botswana by the incorporation of torrefied biomass

NASA Astrophysics Data System (ADS)

Ogura, Tatsuki; Date, Yasuhiro; Masukujane, Masego; Coetzee, Tidimalo; Akashi, Kinya; Kikuchi, Jun

2016-06-01

Effective use of agricultural residual biomass may be beneficial for both local and global ecosystems. Recently, biochar has received attention as a soil enhancer, and its effects on plant growth and soil microbiota have been investigated. However, there is little information on how the physical, chemical, and biological properties of soil amended with biochar are affected. In this study, we evaluated the effects of the incorporation of torrefied plant biomass on physical and structural properties, elemental profiles, initial plant growth, and metabolic and microbial dynamics in aridisol from Botswana. Hemicellulose in the biomass was degraded while cellulose and lignin were not, owing to the relatively low-temperature treatment in the torrefaction preparation. Water retentivity and mineral availability for plants were improved in soils with torrefied biomass. Furthermore, fertilization with 3% and 5% of torrefied biomass enhanced initial plant growth and elemental uptake. Although the metabolic and microbial dynamics of the control soil were dominantly associated with a C1 metabolism, those of the 3% and 5% torrefied biomass soils were dominantly associated with an organic acid metabolism. Torrefied biomass was shown to be an effective soil amendment by enhancing water retentivity, structural stability, and plant growth and controlling soil metabolites and microbiota.

Improvement of physical, chemical, and biological properties of aridisol from Botswana by the incorporation of torrefied biomass.

PubMed

Ogura, Tatsuki; Date, Yasuhiro; Masukujane, Masego; Coetzee, Tidimalo; Akashi, Kinya; Kikuchi, Jun

2016-06-17

Effective use of agricultural residual biomass may be beneficial for both local and global ecosystems. Recently, biochar has received attention as a soil enhancer, and its effects on plant growth and soil microbiota have been investigated. However, there is little information on how the physical, chemical, and biological properties of soil amended with biochar are affected. In this study, we evaluated the effects of the incorporation of torrefied plant biomass on physical and structural properties, elemental profiles, initial plant growth, and metabolic and microbial dynamics in aridisol from Botswana. Hemicellulose in the biomass was degraded while cellulose and lignin were not, owing to the relatively low-temperature treatment in the torrefaction preparation. Water retentivity and mineral availability for plants were improved in soils with torrefied biomass. Furthermore, fertilization with 3% and 5% of torrefied biomass enhanced initial plant growth and elemental uptake. Although the metabolic and microbial dynamics of the control soil were dominantly associated with a C1 metabolism, those of the 3% and 5% torrefied biomass soils were dominantly associated with an organic acid metabolism. Torrefied biomass was shown to be an effective soil amendment by enhancing water retentivity, structural stability, and plant growth and controlling soil metabolites and microbiota.

Is it efficient to co-compost and co-vermicompost green waste with biochar and/or clay to reduce CO2 emissions? A short-term laboratory experiment on (vermi)composts with additives.

NASA Astrophysics Data System (ADS)

Barthod, Justine; Rumpel, Cornélia; Paradelo, Remigio; Dignac, Marie-France

2016-04-01

Intensive farming practices can lead to a depletion of soil organic matter, negatively impacting important soil properties such as structural stability, fertility and C storage. The addition of organic amendments such as compost and vermicompost, rich in carbon, helps maintaining soil organic matter levels or restoring degraded soils. Composting and vermicomposting are based on stabilization of organic matter through the mineralization of easily decomposable organic matter compounds, therefore releasing greenhouse gases, including CO2. The aim of this study was to evaluate the global potential reduction of such emissions by the use of additives (2:1 clay and/or biochar): during (vermi)composting processes and after use of the final products as soil amendments. We hypothesized that the interactions between the additives and organic matter may lead to carbon stabilization and that such interactions may be enhanced by the presence of worms (Eisenia). We added in different proportions clay (25% or 50%), biochar (10%) and a mixture of biochar (10%) with clay (25%) to pre-composted green waste. The CO2 emissions of the composting and vermicomposting processes were measured during 21 days. After that, the amendments were added to a loamy cambisol soil and the CO2 emissions were monitored during 30 days of a laboratory experiment. The most efficient treatments in terms of reducing global CO2 emissions were the co-vermicomposting process with 25% clay followed by co-composting with 50% clay and with 10% biochar plus 25% clay. In this treatment (vermicompost with 25% clay), the carbon emissions were decreased by up to 44% compared to regular compost. Addition of biochar reduced CO2 emissions only during composting. Co-composting with biochar could be a promising avenue to limit global CO2 emissions whereas in presence of worms clay additions are better suited. These findings suggest that the presence of worms increased the formation of organo-mineral associations and thus C protection up to a certain clay/organic matter ratio. This strategy could be used to enhance the stability of organic amendments and increase soil carbon sequestration.

Topsoil and Deep Soil Organic Carbon Concentration and Stability Vary with Aggregate Size and Vegetation Type in Subtropical China

PubMed Central

Fang, Xiang-Min; Chen, Fu-Sheng; Wan, Song-Ze; Yang, Qing-Pei; Shi, Jian-Min

2015-01-01

The impact of reforestation on soil organic carbon (OC), especially in deep layer, is poorly understood and deep soil OC stabilization in relation with aggregation and vegetation type in afforested area is unknown. Here, we collected topsoil (0–15 cm) and deep soil (30–45 cm) from six paired coniferous forests (CF) and broad-leaved forests (BF) reforested in the early 1990s in subtropical China. Soil aggregates were separated by size by dry sieving and OC stability was measured by closed-jar alkali-absorption in 71 incubation days. Soil OC concentration and mean weight diameter were higher in BF than CF. The cumulative carbon mineralization (Cmin, mg CO2-C kg-1 soil) varied with aggregate size in BF and CF topsoils, and in deep soil, it was higher in larger aggregates than in smaller aggregates in BF, but not CF. The percentage of soil OC mineralized (SOCmin, % SOC) was in general higher in larger aggregates than in smaller aggregates. Meanwhile, SOCmin was greater in CF than in BF at topsoil and deep soil aggregates. In comparison to topsoil, deep soil aggregates generally exhibited a lower Cmin, and higher SOCmin. Total nitrogen (N) and the ratio of carbon to phosphorus (C/P) were generally higher in BF than in CF in topsoil and deep soil aggregates, while the same trend of N/P was only found in deep soil aggregates. Moreover, the SOCmin negatively correlated with OC, total N, C/P and N/P. This work suggests that reforested vegetation type might play an important role in soil OC storage through internal nutrient cycling. Soil depth and aggregate size influenced OC stability, and deep soil OC stability could be altered by vegetation reforested about 20 years. PMID:26418563

Stability of organic carbon in deep soil layers controlled by fresh carbon supply.

PubMed

Fontaine, Sébastien; Barot, Sébastien; Barré, Pierre; Bdioui, Nadia; Mary, Bruno; Rumpel, Cornelia

2007-11-08

The world's soils store more carbon than is present in biomass and in the atmosphere. Little is known, however, about the factors controlling the stability of soil organic carbon stocks and the response of the soil carbon pool to climate change remains uncertain. We investigated the stability of carbon in deep soil layers in one soil profile by combining physical and chemical characterization of organic carbon, soil incubations and radiocarbon dating. Here we show that the supply of fresh plant-derived carbon to the subsoil (0.6-0.8 m depth) stimulated the microbial mineralization of 2,567 +/- 226-year-old carbon. Our results support the previously suggested idea that in the absence of fresh organic carbon, an essential source of energy for soil microbes, the stability of organic carbon in deep soil layers is maintained. We propose that a lack of supply of fresh carbon may prevent the decomposition of the organic carbon pool in deep soil layers in response to future changes in temperature. Any change in land use and agricultural practice that increases the distribution of fresh carbon along the soil profile could however stimulate the loss of ancient buried carbon.

The Hydromechanics of Vegetation for Slope Stabilization

NASA Astrophysics Data System (ADS)

Mulyono, A.; Subardja, A.; Ekasari, I.; Lailati, M.; Sudirja, R.; Ningrum, W.

2018-02-01

Vegetation is one of the alternative technologies in the prevention of shallow landslide prevention that occurs mostly during the rainy season. The application of plant for slope stabilization is known as bioengineering. Knowledge of the vegetative contribution that can be considered in bioengineering was the hydrological and mechanical aspects (hydromechanical). Hydrological effect of the plant on slope stability is to reduce soil water content through transpiration, interception, and evapotranspiration. The mechanical impact of vegetation on slope stability is to stabilize the slope with mechanical reinforcement of soils through roots. Vegetation water consumption varies depending on the age and density, rainfall factors and soil types. Vegetation with high ability to absorb water from the soil and release into the atmosphere through a transpiration process will reduce the pore water stress and increase slope stability, and vegetation with deep root anchoring and strong root binding was potentially more significant to maintain the stability of the slope.

Estimating Vegetation Structure in African Savannas using High Spatial Resolution Imagery

NASA Astrophysics Data System (ADS)

Axelsson, C.; Hanan, N. P.

2016-12-01

High spatial resolution satellite imagery allows for detailed mapping of trees in savanna landscapes, including estimates of woody cover, tree densities, crown sizes, and the spatial pattern of trees. By linking these vegetation parameters to rainfall and soil properties we gain knowledge of how the local environment influences vegetation. A thorough understanding of the underlying ecosystem processes is key to assessing the future productivity and stability of these ecosystems. In this study, we have processed and analyzed hundreds of sites sampled from African savannas across a wide range of rainfall and soil conditions. The vegetation at each site is classified using unsupervised classification with manual assignment into woody, herbaceous and bare cover classes. A crown delineation method further divides the woody areas into individual tree crowns. The results show that rainfall, soil, and topography interactively influence vegetation structure. We see that both total rainfall and rainfall seasonality play important roles and that soil type influences woody cover and the sizes of tree crowns.

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 phosphate-based binder for stabilization of soils contaminated with heavy metals: leaching, strength and microstructure characterization.

PubMed

Du, Yan-Jun; Wei, Ming-Li; Reddy, Krishna R; Jin, Fei; Wu, Hao-Liang; Liu, Zhi-Bin

2014-12-15

Cement stabilization is used extensively to remediate soils contaminated with heavy metals. However, previous studies suggest that the elevated zinc (Zn) and lead (Pb) concentrations in the contaminated soils would substantially retard the cement hydration, leading to the deterioration of the performance of cement stabilized soils. This study presents a new binder, KMP, composed of oxalic acid-activated phosphate rock, monopotassium phosphate and reactive magnesia. The effectiveness of stabilization using this binder is investigated on soils spiked with Zn and Pb, individually and together. Several series of tests are conducted including toxicity characteristic leaching (TCLP), ecotoxicity in terms of luminescent bacteria test and unconfined compressive strength. The leachability of a field Zn- and Pb- contaminated soil stabilized with KMP is also evaluated by TCLP leaching test. The results show that the leached Zn concentrations are lower than the China MEP regulatory limit except when Zn and Pb coexist and for the curing time of 7 days. On the other hand, the leached Pb concentrations for stabilized soils with Pb alone or mixed Zn and Pb contamination are much lower than the China MEP or USEPA regulatory limit, irrespective of the curing time. The luminescent bacteria test results show that the toxicity of the stabilized soils has been reduced considerably and is classified as slightly toxic class. The unconfined compressive strength of the soils decrease with the increase in the Zn concentration. The stabilized soils with mixed Zn and Pb contaminants exhibit notably higher leached Zn concentration, while there is lower unconfined compressive strength relative to the soils when contaminated with Zn alone. The X-ray diffraction and scanning electron microscope analyses reveal the presence of bobierrite (Mg3(PO4)2·8H2O) and K-struvite (MgKPO4·6H2O) as the main products formed in the KMP stabilized uncontaminated soils; the formation of hopeite (Zn3(PO4)2·4H2O), scholzite (CaZn2(PO4)2·2H2O), zinc hydroxide (Zn(OH)2), and fluoropyromorphite (Pb5(PO4)3F) in the soils are the main mechanisms for immobilization of Zn and Pb with the KMP binder. The change in the relative quantities of the formed phosphate-based products, with respect to the Zn concentration and presence of mixed Zn and Pb contaminants, can well explain the measured impact of the Zn concentration levels and presence of both Zn and Pb contaminants on the unconfined compressive strength of the KMP stabilized soils. Copyright © 2014 Elsevier Ltd. All rights reserved.

Superfund Innovative Technology Evaluation - Demonstration Bulletin: In-Situ Soil Stabilization

EPA Science Inventory

In-situ stabilization technology immobilizes organics and inorganic compounds in wet or dry soils by using reagents (additives) to polymerize with the soils and sludges producing a cement-like mass. Two basic components of this technology are the Geo-Con/DSM Deep Soil Mixing Sy...

Concurrent temporal stability of the apparent electrical conductivity and soil water content

USDA-ARS?s Scientific Manuscript database

Knowledge of spatio-temporal soil water content (SWC) variability within agricultural fields is useful to improve crop management. Spatial patterns of soil water contents can be characterized using the temporal stability analysis, however high density sampling is required. Soil apparent electrical c...

Influence of biochar on the physical, chemical and retention properties of an amended sandy soil

NASA Astrophysics Data System (ADS)

Baiamonte, Giorgio; De Pasquale, Claudio; Parrino, Francesco; Crescimanno, Giuseppina

2017-04-01

Soil porosity plays an important role in soil-water retention and water availability to crops, potentially affecting both agricultural practices and environmental sustainability. The pore structure controls fluid flow and transport through the soil, as well as the relationship between the properties of individual minerals and plants. Moreover, the anthropogenic pressure on soil properties has produced numerous sites with extensive desertification process close to residential areas. Biochar (biologically derived charcoal) is produced by pyrolysis of biomasses under low oxygen conditions, and it can be applied for recycling organic waste in soils and increase soil fertility, improving soil structure and enhancing soil water storage and soil water movement. Soil application of biochar might have agricultural, environmental and sustainability advantages over the use of organic manures or compost, as it is a porous material with a high inner surface area. The main objectives of the present study were to investigate the possible application of biochar from forest residues, derived from mechanically chipped trunks and large branches of Abies alba M., Larix decidua Mill., Picea excelsa L., Pinus nigra A. and Pinus sylvestris L. pyrolysed at 450 °C for 48h, to improve soil structural and hydraulic properties (achieving a stabilization of soil). Different amount of biochar were added to a desertic sandy soil, and the effect on soil porosity water retention and water available to crops were investigated. The High Energy Moisture Characteristic (HEMC) technique was applied to investigate soil-water retention at high-pressure head levels. The adsorption and desorption isotherms of N2 on external surfaces were also determined in order to investigate micro and macro porosity ratio. Both the described model of studies on adsorption-desorption experiments with the applied isotherms model explain the increasing substrate porosity with a particular attention to the macro and micro porosity, respectively.

Root tensile strength of grey alder and mountain maple grown on a coarse grained eco-engineered slope in the Swiss Alps related to wood anatomical features

NASA Astrophysics Data System (ADS)

Kink, Dimitri; Bast, Alexander; Meyer, Christine; Meier, Wolfgang; Egli, Markus; Gärtner, Holger

2014-05-01

Steep, vegetation free slopes are a common feature in alpine areas. The material covering these slopes is prone to all kind of erosional processes, resulting in a high risk potential for population and infrastructure. This risk potential is likely to increase with the predicted change in the spatiotemporal distribution of precipitation events. A potential increase in extreme precipitation events will also result in a higher magnitude and frequency of erosional processes. In the Swiss Alps as in many other mountainous areas, there is a need to stabilize these slopes to reduce their direct or indirect hazard potential. In this regard, eco-engineering is a very promising and sustainable approach for slope stabilization. Planting trees and shrubs is a central task in eco-engineering. A developing vegetation cover will on one hand reduce the mechanical effects of rainfall by an increased interception, on the other hand, the root systems cause modifications of soil properties. Roots not only provide anchorage for the plants, they also promote soil aggregation and are able to penetrate possible shear horizons. Overall, anchorage of plants is at the same extend also stabilizing the near subsurface. When rainfall occurs, the saturated soil exerts downhill pressure to a tree or shrub. As long as the root distribution supports anchorage, the respective slope area remains stable. At this point, the tensile strength of the roots is a critical measure, because it is more likely that the supporting roots break than the entire root system being pulled out of the soil completely. As a consequence, root tensile strength is an important parameter in characterizing the soil stabilization potential of trees and shrubs. It is known that tree roots show a high variability in their anatomical structure depending on their depth below soil surface as well as their distance to the main stem. Therefore, we assume that these structural changes affect the tensile strength of every single root. In order to confirm this assumption and possibly find more important root properties which have an influence on soil stabilization, the root systems of seven trees (three grey alder, four mountain maple) were excavated and analyzed. The study site is a catchment, where shallow landslides are common. It is located in the Prättigau valley in the Eastern Swiss Alps and was eco-engineered in 1997. The substrate is coarse-grained morainic material, mean annual air temperature reaches 4.64°C, average precipitation is 1170 mm, and the altitude is about 1000 m a.s.l.. The root system of each tree was uncovered carefully by hand to keep the roots undamaged, before removal it was photographed in situ to document the root distribution. The root systems were then cut into single root pieces of about 20 cm length and the position of each sample was documented. The root samples were then hierarchically classified in several root classes. The tensile strength of more than 500 samples was determined. In addition, the values for age, diameter, and root moisture were ascertained. Since it was assumed, that the cellular structure of the roots has an influence on the tensile strength, two microscopic thin-sections were prepared from all successfully tested root samples. The microscopic analysis focused on anatomical parameters such as the size and number of vessels, their distribution as well as their conductivity. The results for the final correlation between the anatomical characteristics and the root's tensile strength are presented for both tree species.

Stockpiling hydrated lime-soil mixtures.

DOT National Transportation Integrated Search

2007-06-01

The concept and feasibility of stockpiling and reusing hydrated lime-soil mixtures to stabilize particular areas on stabilization projects after the mixing contractor has departed were examined. In chemical stabilization of subgrades, situations ofte...

Solubility of lead and copper in biochar-amended small arms range soils: influence of soil organic carbon and pH.

PubMed

Uchimiya, Minori; Bannon, Desmond I

2013-08-14

Biochar is often considered a strong heavy metal stabilizing agent. However, biochar in some cases had no effects on, or increased the soluble concentrations of, heavy metals in soil. The objective of this study was to determine the factors causing some biochars to stabilize and others to dissolve heavy metals in soil. Seven small arms range soils with known total organic carbon (TOC), cation exchange capacity, pH, and total Pb and Cu contents were first screened for soluble Pb and Cu concentrations. Over 2 weeks successive equilibrations using weak acid (pH 4.5 sulfuric acid) and acetate buffer (0.1 M at pH 4.9), Alaska soil containing disproportionately high (31.6%) TOC had nearly 100% residual (insoluble) Pb and Cu. This soil was then compared with sandy soils from Maryland containing significantly lower (0.5-2.0%) TOC in the presence of 10 wt % (i) plant biochar activated to increase the surface-bound carboxyl and phosphate ligands (PS450A), (ii) manure biochar enriched with soluble P (BL700), and (iii) unactivated plant biochars produced at 350 °C (CH350) and 700 °C (CH500) and by flash carbonization (corn). In weak acid, the pH was set by soil and biochar, and the biochars increasingly stabilized Pb with repeated extractions. In pH 4.9 acetate buffer, PS450A and BL700 stabilized Pb, and only PS450A stabilized Cu. Surface ligands of PS450A likely complexed and stabilized Pb and Cu even under acidic pH in the presence of competing acetate ligand. Oppositely, unactivated plant biochars (CH350, CH500, and corn) mobilized Pb and Cu in sandy soils; the putative mechanism is the formation of soluble complexes with biochar-borne dissolved organic carbon. In summary, unactivated plant biochars can inadvertently increase dissolved Pb and Cu concentrations of sandy, low TOC soils when used to stabilize other contaminants.

Activity and stability of a complex bacterial soil community under simulated Martian conditions

NASA Astrophysics Data System (ADS)

Hansen, Aviaja Anna; Merrison, Jonathan; Nørnberg, Per; Aagaard Lomstein, Bente; Finster, Kai

2005-04-01

A simulation experiment with a complex bacterial soil community in a Mars simulation chamber was performed to determine the effect of Martian conditions on community activity, stability and survival. At three different depths in the soil core short-term effects of Martian conditions with and without ultraviolet (UV) exposure corresponding to 8 Martian Sol were compared. Community metabolic activities and functional diversity, measured as glucose respiration and versatility in substrate utilization, respectively, decreased after UV exposure, whereas they remained unaffected by Martian conditions without UV exposure. In contrast, the numbers of culturable bacteria and the genetic diversity were unaffected by the simulated Martian conditions both with and without UV exposure. The genetic diversity of the soil community and of the colonies grown on agar plates were evaluated by denaturant gradient gel electrophoresis (DGGE) on DNA extracts. Desiccation of the soil prior to experimentation affected the functional diversity by decreasing the versatility in substrate utilization. The natural dominance of endospores and Gram-positive bacteria in the investigated Mars-analogue soil may explain the limited effect of the Mars incubations on the survival and community structure. Our results suggest that UV radiation and desiccation are major selecting factors on bacterial functional diversity in terrestrial bacterial communities incubated under simulated Martian conditions. Furthermore, these results suggest that forward contamination of Mars is a matter of great concern in future space missions.

In-tank precipitation facility (ITP) and H-Tank Farm (HTF) geotechnical report, WSRC-TR-95-0057, Revision 0, Volume 5

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

NONE

A geotechnical study has been completed in H-Area for the In-Tank Precipitation Facility (ITP) and the balance of the H-Area Tank Farm (HTF) at the Savannah River Site (SRS) in South Carolina. The study consisted of subsurface field exploration, field and laboratory testing, and engineering analyses. The purpose of these investigations is to evaluate the overall stability of the H-Area tanks under static and dynamic conditions. The objectives of the study are to define the site-specific geological conditions at ITP and HTF, obtain engineering properties for the assessment of the stability of the native soils and embankment under static andmore » dynamic loads (i.e., slope stability, liquefaction potential, and potential settlements), and derive properties for soil-structure interaction studies. This document (Volume 5) contains the laboratory test results for the In-Tank Precipitation Facility (ITP) and H-Tank Farm (HTF) Geotechnical Report.« less

Accelerated decay rates drive soil organic matter persistence and storage in temperate forests via greater mineral stabilization of microbial residues.

NASA Astrophysics Data System (ADS)

Phillips, R.; Craig, M.; Turner, B. L.; Liang, C.

2017-12-01

Climate predicts soil organic matter (SOM) stocks at the global scale, yet controls on SOM stocks at finer spatial scales are still debated. A current hypothesis predicts that carbon (C) and nitrogen (N) storage in soils should be greater when decomposition is slow owing to microbial competition for nutrients or the recalcitrance of organic substrates (hereafter the `slow decay' hypothesis). An alternative hypothesis predicts that soil C and N storage should be greater in soils with rapid decomposition, owing to the accelerated production of microbial residues and their stabilization on soil minerals (hereafter the `stabilization hypothesis'). To test these alternative hypotheses, we quantified soil C and N to 1-m depth in temperate forests across the Eastern and Midwestern US that varied in their biotic, climatic, and edaphic properties. At each site, we sampled (1) soils dominated by arbuscular mycorrhizal (AM) tree species, which typically have fast decay rates and accelerated N cycling, (2) soils dominated by ectomycorrhizal (ECM) tree species, which generally have slow decay rates and slow N cycling, and (3) soils supporting both AM and ECM trees. To the extent that trees and theor associated microbes reflect and reinforce soil conditions, support for the slow decay hypothesis would be greater SOM storage in ECM soils, whereas support for the stabilization hypothesis would be greater SOM storage in AM soils. We found support for both hypotheses, as slow decomposition in ECM soils increased C and N storage in topsoil, whereas fast decomposition in AM soils increased C and N storage in subsoil. However, at all sites we found 57% greater total C and N storage in the entire profile in AM- soils (P < 0.0001), supporting the stabilization hypothesis. Amino sugar biomarkers (an indicator of microbial necromass) and particle size fractionation revealed that the greater SOM storage in AM soils was driven by an accumulation of microbial residues on clay minerals and metal oxides. Taken together, our results indicate that tree species influence soil C and N storage owing to how differences in decay rates affect mineral stabilization of organic matter. Further, our findings indicate that slow decay promotes soil C and N stocks at the soil surface, whereas fast decay promotes greater soil C and N stocks at depth.

[Stabilization and long-term effect of chromium contaminated soil].

PubMed

Wang, Jing; Luo, Qi-Shi; Zhang, Chang-Bo; Tan, Liang; Li, Xu

2013-10-01

Short-term (3 d and 28 d) and long-term (1 a) stabilization effects of Cr contaminated soil were investigated through nature curing, using four amendments including ferrous sulfide, ferrous sulfate, zero-valent iron and sodium dithionite. The results indicated that ferrous sulfide and zero-valent iron were not helpful for the stabilization of Cr(VI) when directly used because of their poor solubility and immobility. Ferrous sulfate could effectively and rapidly decrease total leaching Cr and Cr(VI) content. The stabilization effect was further promoted by the generation of iron hydroxides after long-term curing. Sodium dithionite also had positive effect on soil stabilization. Appropriate addition ratio of the two chemicals could help maintain the soil pH in range of 6-8.

Long-term rice cultivation stabilizes soil organic carbon and promotes soil microbial activity in a salt marsh derived soil chronosequence

PubMed Central

Wang, Ping; Liu, Yalong; Li, Lianqing; Cheng, Kun; Zheng, Jufeng; Zhang, Xuhui; Zheng, Jinwei; Joseph, Stephen; Pan, Genxing

2015-01-01

Soil organic carbon (SOC) sequestration with enhanced stable carbon storage has been widely accepted as a very important ecosystem property. Yet, the link between carbon stability and bio-activity for ecosystem functioning with OC accumulation in field soils has not been characterized. We assessed the changes in microbial activity versus carbon stability along a paddy soil chronosequence shifting from salt marsh in East China. We used mean weight diameter, normalized enzyme activity (NEA) and carbon gain from straw amendment for addressing soil aggregation, microbial biochemical activity and potential C sequestration, respectively. In addition, a response ratio was employed to infer the changes in all analyzed parameters with prolonged rice cultivation. While stable carbon pools varied with total SOC accumulation, soil respiration and both bacterial and fungal diversity were relatively constant in the rice soils. Bacterial abundance and NEA were positively but highly correlated to total SOC accumulation, indicating an enhanced bio-activity with carbon stabilization. This could be linked to an enhancement of particulate organic carbon pool due to physical protection with enhanced soil aggregation in the rice soils under long-term rice cultivation. However, the mechanism underpinning these changes should be explored in future studies in rice soils where dynamic redox conditions exist. PMID:26503629

Long-term rice cultivation stabilizes soil organic carbon and promotes soil microbial activity in a salt marsh derived soil chronosequence

NASA Astrophysics Data System (ADS)

Wang, Ping; Liu, Yalong; Li, Lianqing; Cheng, Kun; Zheng, Jufeng; Zhang, Xuhui; Zheng, Jinwei; Joseph, Stephen; Pan, Genxing

2015-10-01

Soil organic carbon (SOC) sequestration with enhanced stable carbon storage has been widely accepted as a very important ecosystem property. Yet, the link between carbon stability and bio-activity for ecosystem functioning with OC accumulation in field soils has not been characterized. We assessed the changes in microbial activity versus carbon stability along a paddy soil chronosequence shifting from salt marsh in East China. We used mean weight diameter, normalized enzyme activity (NEA) and carbon gain from straw amendment for addressing soil aggregation, microbial biochemical activity and potential C sequestration, respectively. In addition, a response ratio was employed to infer the changes in all analyzed parameters with prolonged rice cultivation. While stable carbon pools varied with total SOC accumulation, soil respiration and both bacterial and fungal diversity were relatively constant in the rice soils. Bacterial abundance and NEA were positively but highly correlated to total SOC accumulation, indicating an enhanced bio-activity with carbon stabilization. This could be linked to an enhancement of particulate organic carbon pool due to physical protection with enhanced soil aggregation in the rice soils under long-term rice cultivation. However, the mechanism underpinning these changes should be explored in future studies in rice soils where dynamic redox conditions exist.

Long-term rice cultivation stabilizes soil organic carbon and promotes soil microbial activity in a salt marsh derived soil chronosequence.

PubMed

Wang, Ping; Liu, Yalong; Li, Lianqing; Cheng, Kun; Zheng, Jufeng; Zhang, Xuhui; Zheng, Jinwei; Joseph, Stephen; Pan, Genxing

2015-10-27

Soil organic carbon (SOC) sequestration with enhanced stable carbon storage has been widely accepted as a very important ecosystem property. Yet, the link between carbon stability and bio-activity for ecosystem functioning with OC accumulation in field soils has not been characterized. We assessed the changes in microbial activity versus carbon stability along a paddy soil chronosequence shifting from salt marsh in East China. We used mean weight diameter, normalized enzyme activity (NEA) and carbon gain from straw amendment for addressing soil aggregation, microbial biochemical activity and potential C sequestration, respectively. In addition, a response ratio was employed to infer the changes in all analyzed parameters with prolonged rice cultivation. While stable carbon pools varied with total SOC accumulation, soil respiration and both bacterial and fungal diversity were relatively constant in the rice soils. Bacterial abundance and NEA were positively but highly correlated to total SOC accumulation, indicating an enhanced bio-activity with carbon stabilization. This could be linked to an enhancement of particulate organic carbon pool due to physical protection with enhanced soil aggregation in the rice soils under long-term rice cultivation. However, the mechanism underpinning these changes should be explored in future studies in rice soils where dynamic redox conditions exist.

Biochemical activity and chemical-structural properties of soil organic matter after 17 years of amendments with olive-mill pomace co-compost.

PubMed

Aranda, V; Macci, C; Peruzzi, E; Masciandaro, G

2015-01-01

This study evaluates soil fertility, biochemical activity and the soil's ability to stabilize organic matter after application of composted olive-mill pomace. This organic amendment was applied in two different olive groves in southern Spain having different soil typologies (carbonated and silicic). Olive grove soils after 17 years of organic management with application of olive-mill pomace co-compost were of higher quality than those with conventional management where no co-compost had been applied. The main chemical parameters studied (total organic carbon, total nitrogen, available phosphorus, exchangeable bases, cation exchange capacity, total extractable carbon (TEC), and humic-to-fulvic acids ratio), significantly increased in soils treated with the organic amendment. In particular, the more resistant pool of organic matter (TEC) enhanced by about six and eight fold in carbonated and silicic soils, respectively. Moreover, the amended silicic soils showed the most significant increases in enzyme activities linked to C and P cycles (β-glucosidase twenty-five fold higher and phosphatase seven fold higher). Organic management in both soils induced higher organic matter mineralization, as shown by the higher pyrrole/phenol index (increasing 40% and 150% in carbonated and silicic soils, respectively), and lower furfural/pyrrole index (decreasing 27% and 71% in carbonated and silicic soils, respectively). As a result of mineralization, organic matter incorporated was also more stable as suggested by the trend of the aliphatic/aromatic index (decreasing 36% and 30% in carbonated and silicic soils, respectively). Therefore, management system and soil type are key factors in increasing long-term C stability or sequestration in soils. Thus application of olive-oil extraction by-products to soils could lead to important mid-to -long-term agro-environmental benefits, and be a valuable alternative use for one of the most widespread polluting wastes in the Mediterranean region. Copyright © 2014 Elsevier Ltd. All rights reserved.

Detecting Below-Ground Processes, Diversity, and Ecosystem Function in a Savanna Ecosystem Using Spectroscopy Across Different Vegetation Layers

NASA Astrophysics Data System (ADS)

Cavender-Bares, J.; Schweiger, A. K.; Madritch, M. D.; Gamon, J. A.; Hobbie, S. E.; Montgomery, R.; Townsend, P. A.

2017-12-01

Above-and below-ground plant traits are important for substrate input to the rhizosphere. The substrate composition of the rhizosphere, in turn, affects the diversity of soil organisms, influences soil biochemistry, and water content, and resource availability for plant growth. This has substantial consequences for ecosystem functions, such as above-ground productivity and stability. Above-ground plant chemical and structural traits can be linked to the characteristics of other plant organs, including roots. Airborne imaging spectroscopy has been successfully used to model and predict chemical and structural traits of the above-ground vegetation. However, remotely sensed images capture, almost exclusively, signals from the top of the canopy, providing limited direct information about understory vegetation. Here, we use a data set collected in a savanna ecosystem consisting of spectral measurements gathered at the leaf, the whole plant, and vegetation canopy level to test for hypothesized linkages between above- and below-ground processes that influence root biomass, soil biochemistry, and the diversity of the soil community. In this environment, consisting of herbaceous vegetation intermixed with shrubs and trees growing at variable densities, we investigate the contribution of different vegetation strata to soil characteristics and test the ability of imaging spectroscopy to detect these in plant communities with contrasting vertical structure.

Long lasting effects of the conversion from natural forest to poplar plantation on soil microbial communities.

PubMed

Vitali, Francesco; Mastromei, Giorgio; Senatore, Giuliana; Caroppo, Cesarea; Casalone, Enrico

2016-01-01

In this study, we evaluate the long-lasting effects on soil microbial communities of a change within a single land-use category, specifically the conversion from natural forest to forest plantation. To minimize the effects of impacts other than land-use (i.e., climatic and anthropogenic), we chose three sites within a Natural Park, with homogeneous orographic and soil texture characteristics. We compared microbial diversity in a total of 156 soil samples from two natural mixed forests and a similar forest converted to poplar plantation about thirty years ago. The diversity and structure of bacterial and fungal communities were investigated by terminal restriction fragments length polymorphism (T-RFLP) analysis of the 16S-rRNA gene and the ITS-rDNA regions, respectively. Bacterial and fungal communities from the forest plantation, compared to those from natural forest soils, showed different community structure and lower α-diversity values, consistently with the significantly higher pH values and lower organic matter content of those soils. β-diversity values, the number of measured and estimated dominant OTUs, and their distribution among the three sites showed that microbial communities from the two natural forests were much more similar to each other than they were to communities from the poplar plantation, suggesting an effect of the forest conversion on the composition and diversity of soil microbial communities. α-diversity in cultivated forest soils had narrower temporal fluctuations than in natural forest soils, suggesting higher temporal stability of microbial communities. Overall, we demonstrated that the conversion from natural forest to forest plantation altered soil microbial communities, changing their structure, lowering their diversity, and causing a spatial and temporal homogenization. Copyright © 2015 Elsevier GmbH. All rights reserved.

Soil physical properties changed induced by dry-wet cycles in the water-level fluctuation zone of Three Gorges Reservoir region, China

NASA Astrophysics Data System (ADS)

Cui, Junfang; Tang, Xiangyu; Zhang, Wei

2017-04-01

In southwest China, a grand hydraulic engineering called Three Gorges Dam (TGD) was completed and under full power run since 2009, making a total area of 349 km2 along Yangtze River exposing the dry-wet cycles by its impounding of water step by step from the elevations of 135 m in summer season to 175 m in winter season at each year. As populated area, the environmental issues aroused by the TGR have centered on water quality, biodiversity, sedimentation, downstream riverbed erosion and pollutants (both heavy metals and organic pollutants) transportation. All these are regulated or affected by soil structure and pore network, directly or indirectly. Thus, the study of soil physical quality changed induced by these seasonal dry-wet cycles is crucial. The objective of this study is: (1) to describe soil structural status in WLF zone of TGR by combination of laboratory measures and visual evaluation method; (2) to describe the pore system in this zone by both SWRC and CT images; and (3) to address the changes of soil physical quality changed by seasonal dry-wet cycles. Our results showed a deterioration of soil structure (indicated by a high Sq score in VESS) and soil aggregate stability (indicated by low MWD and the mass fractal dimension Dm) in lower land of TGR. The data from both soil water retention curve and micro-CT image demonstrates a going -worse of soil physical quality by decreasing of soil pore number and porosity as well as a shift of drainable micro-pores (0.1 < r < 125 µm) to non-drainable micro-pores (r < 0.1 µm) in the lower land of TGR.

Stabilization of heavy metals in soil using two organo-bentonites.

PubMed

Yu, Kai; Xu, Jian; Jiang, Xiaohong; Liu, Cun; McCall, Wesley; Lu, Jinlong

2017-10-01

Stabilization of Cu, Zn, Cd, Hg, Cr and As in soil using tetramethylammonium (TMA) and dodecyltrimethylammonium (DTMA) modified bentonites (T-Bents and D-Bents) as amendments was investigated. Toxicity characteristic leaching procedure (TCLP) was used to quantify the metal mobility after soil treatment. The structural parameters of modified bentonites, including the BET surface area, basal spacing and zeta potential were obtained as a function of the TMA and DTMA loading at 40, 80, 120, 160 and 200% of the bentonite's cation exchange capacity, respectively. The results indicated that the characteristics of the organo-bentonites fundamentally varied depending on the species and concentration of modifiers loaded on bentonite. T-Bents and D-Bents manifested distinct immobilization effectiveness towards various metals. In association with the organo-bentonite characteristics, the main interactive mechanisms for Cu, Zn and Cd proceeded via cation exchange, Hg proceeded via physical adsorption and partitioning, Cr and As proceeded via specific adsorption and electrostatic attraction, respectively. This study provided operational and mechanistic basis for optimizing the organic clay synthesis and selecting as the appropriate amendment for remediation of heavy metal contaminated soils. Copyright © 2017 Elsevier Ltd. All rights reserved.

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.

Effects of Dissolved Organic Matter Properties on Formation and Composition of Mineral-Organic Co-Precipitates at the Nanometer Scale

NASA Astrophysics Data System (ADS)

Possinger, A. R.; Zachman, M.; Lehmann, J.

2016-12-01

An important, yet largely overlooked case of soil organic carbon (SOC) stabilization through mineral-organic associations is the co-precipitation of dissolved organic matter (DOM) into mineral precipitates as they form. The contribution of co-precipitated DOM to the mineral-stabilized SOC pool is expected to be greatest in soil environments with frequent mineral dissolution and precipitation processes. Compared to surface adsorption, properties of mineral-organic co-precipitates are expected to differ at both the particle scale (e.g., total carbon (C) content and composition) and the molecular scale (e.g., impurities in mineral structure), with potential implications for stability and C turnover; additionally, these properties vary across C sources, amounts, and forms. Consequently, high-resolution visualization and characterization combined with bulk chemical measurements is needed to provide a more complete understanding of co-precipitate formation processes and properties, especially as a function of C co-precipitant characteristics. In this study, we evaluate the effect of model C compound and DOM chemical properties (e.g., iron-binding affinity) on the formation, structure, and chemical properties of ferrihydrite (Fh) (Fe3+3O2 •0.5H2O) co-precipitates. Salicylic acid (SA), sucrose and water-extractable DOM from coniferous or deciduous-dominated organic soils were either adsorbed to pre-formed Fh or co-precipitated with Fh. At a C/Fe ratio 10, the amount of co-precipitated C differed among all organic compounds, and for DOM, was more than 2X greater for co-precipitation than adsorption, suggesting a greater capacity for C retention. To probe the molecular-scale C spatial distribution of Fh-SA particles, we obtained Scanning Transmission Electron Microscopy with Electron Energy Loss Spectroscopy (STEM-EELS) maps at a nanometer-scale spatial pixel resolution. Additionally, we will present chemical characteristics of organic-Fh co-precipitates and adsorption complexes investigated in bulk using C Near-Edge X-ray Absorption Fine Structure (NEXAFS) and Fourier Transform Infrared (FT-IR) spectroscopy. Ultimately, these observations of model co-precipitation systems will be used to better interpret observations of putative co-precipitated OM in natural soils.

Induced polarization for characterizing and monitoring soil stabilization processes

NASA Astrophysics Data System (ADS)

Saneiyan, S.; Ntarlagiannis, D.; Werkema, D. D., Jr.

2017-12-01

Soil stabilization is critical in addressing engineering problems related to building foundation support, road construction and soil erosion among others. To increase soil strength, the stiffness of the soil is enhanced through injection/precipitation of a chemical agents or minerals. Methods such as cement injection and microbial induced carbonate precipitation (MICP) are commonly applied. Verification of a successful soil stabilization project is often challenging as treatment areas are spatially extensive and invasive sampling is expensive, time consuming and limited to sporadic points at discrete times. The geophysical method, complex conductivity (CC), is sensitive to mineral surface properties, hence a promising method to monitor soil stabilization projects. Previous laboratory work has established the sensitivity of CC on MICP processes. We performed a MICP soil stabilization projects and collected CC data for the duration of the treatment (15 days). Subsurface images show small, but very clear changes, in the area of MICP treatment; the changes observed fully agree with the bio-geochemical monitoring, and previous laboratory experiments. Our results strongly suggest that CC is sensitive to field MICP treatments. Finally, our results show that good quality data alone are not adequate for the correct interpretation of field CC data, at least when the signals are low. Informed data processing routines and the inverse modeling parameters are required to produce optimal results.

Modified granulation of red mud by weak gelling and its application to stabilization of Pb.

PubMed

Luo, Hui-li; Huang, Sheng-sheng; Luo, Lin; Wu, Gen-yi; Liu, Yan

2012-08-15

This study presents a novel modification of red mud (RM) with cementitious materials by rotary drum granulation under partial hydration. Admixtures and surfactants were applied to improve the microspore structure of red mud-based granules in order to stabilize Pb steadily. Through XRD and SEM-EDS analyses, it was demonstrated that calcite, the main alkali in RM, was partially concreted and coated. Compared to pH 12.47 for RM, the lowest pH of the granules was 10.66 implying that the release of OH(-) from hydrolysis and decomposition was decreased. Based on stabilization of Pb, influence on soil properties and forming qualities, composition of the optimum granule PSP was determined as 5% cement, 5% gypsum, 1% rice straw, and 0.1% emulsifier OP-10. Within a 90 d remediation, immobilization of ionic Pb in a 500 mg kg(-1) Pb-contaminated artificial soil was 9.85 mg kg(-1) at day 30 with 5% PSP2 as substitute. Furthermore, the reverse increase diminished as the final concentration was 11.13 mg kg(-1) while it was 14.25 mg kg(-1) by RM. The increase of residual Pb was 122.61%, which was better than the 83.92% of RM. Particularly, the highest pH in mine soil was 11.09 at day 1 with RM, but the decrease of ionic Pb was 46.26%. Meanwhile, a significant deviation from the control soil zeta-potential lasted longer and the recovery was more difficult, as compared to the granules. Therefore, a granulated modification of RM is shown to be very important when aiming at steady release of OH(-) to improve the later stabilization of Pb. Copyright © 2012 Elsevier B.V. All rights reserved.

The stability of clay using mount Sinabung ash with unconfined compression test (uct) value

NASA Astrophysics Data System (ADS)

Puji Hastuty, Ika; Roesyanto; Hutauruk, Ronny; Simanjuntak, Oberlyn

2018-03-01

The soil has a important role as a highway’s embankment material (sub grade). Soil conditions are very different in each location because the scientifically soil is a very complex and varied material and the located on the field is very loose or very soft, so it is not suitable for construction, then the soil should be stabilized. The additive material commonly used for soil stabilization includes cement, lime, fly ash, rice husk ash, and others. This experiment is using the addition of volcanic ash. The purpose of this study was to determine the Index Properties and Compressive Strength maximum value with Unconfined Compression Test due to the addition of volcanic ash as a stabilizing agent along with optimum levels of the addition. The result showed that the original soil sample has Water Content of 14.52%; the Specific Weight of 2.64%; Liquid limit of 48.64% and Plasticity Index of 29.82%. Then, the Compressive Strength value is 1.40 kg/cm2. According to USCS classification, the soil samples categorized as the (CL) type while based on AASHTO classification, the soil samples are including as the type of A-7-6. After the soil is stabilized with a variety of volcanic ash, can be concluded that the maximum value occurs at mixture variation of 11% Volcanic Ash with Unconfined Compressive Strength value of 2.32 kg/cm2.

Growth and nutrient content of herbaceous seedlings associated with biological soil crusts

Treesearch

R. L. Pendleton; B. K. Pendleton; G. L. Howard; S. D. Warren

2003-01-01

Biological soil crusts of arid and semiarid lands contribute significantly to ecosystem stability by means of soil stabilization, nitrogen fixation, and improved growth and establishment of vascular plant species. In this study, we examined growth and nutrient content of Bromus tectorum, Elymus elymoides, Gaillardia pulchella, and Sphaeralcea munroana grown in soil...

Impact of pilling and long-term topsoil storage on the potential 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. Natural gas mining involves removal of the topsoil, including surface crust, and storage of ...

Contribution of plant lignin to the soil organic matter formation and stabilization

USDA-ARS?s Scientific Manuscript database

Lignin is the third most abundant plant constituent after cellulose and hemicellulose and thought to be one of the building blocks for soil organic matter formation. Lignin can be used as a predictor for long-term soil organic matter stabilization and C sequestration. Soils and humic acids from fo...

Landslides Zonation Hazard: relation between geological structures and landslides occurrence in hilly tropical regions of Brazil.

PubMed

Cerri, Rodrigo I; Reis, Fábio A G V; Gramani, Marcelo F; Giordano, Lucilia C; Zaine, José Eduardo

2017-01-01

This paper presents a new approach of landslides zonation hazard studies, based on an integrated study of structural data along with geomorphological and external factors, in a hilly regions of Brazil, covered by a tropical humid rain-forest, called Serra do Mar. The Serra do Mar consists of a hilly region along the east coast of Brazil, with high slopes and many geological structures in a gneiss - migmatitic terrain. In contrast to traditional approaches, this method proposes that structural data (foliation, fractures and bedding planes) and its relation with the slope geometry, is important to be consider in the landslide zonation hazard, along with declivity, relative relief, soil and rock properties, land use and vegetation cover and hydrogeological and climate factors. Results show that slopes with high hazard have the same dip direction of geological structures. Landslide zonation hazard using structural data contributes to a better understanding of how these structures, preserved in tropical residual soils, influence on slope stability and generates landslides.

DNA in soil: adsorption, genetic transformation, molecular evolution and genetic microchip.

PubMed

Trevors, J T

1996-07-01

This review examines interactions between DNA and soil with an emphasis on the persistence and stability of DNA in soil. The role of DNA in genetic transformation in soil microorganisms will also be discussed. In addition, a postulated mechanism for stabilization and elongation/assembly of primitive genetic material and the role of soil particles, salt concentrations, temperature cycling and crystal formation is examined.

GeoMo 2007 : subgrade stabilization--foundations & pavements

DOT National Transportation Integrated Search

2007-08-01

One day seminar given by two of the leading authorities on the soil stabilization. Course participants will gain familiarity with the concepts and related topics for optimization of soil stabilization and pavement design. The recently published TRB c...

[Environmental behavior and effect of biomass-derived black carbon in soil: a review].

PubMed

Liu, Yu-Xue; Liu, Wei; Wu, Wei-Xiang; Zhong, Zhe-Ke; Chen, Ying-Xu

2009-04-01

Biomass-derived black carbon, also named biochar, has the characteristics of high stability against decay and high capability of adsorption, and can affect the environment through its interactions with climate and geology, playing a significant role in global climate change, carbon biogeochemical cycle, and environmental system. In recent years, more and more researchers in the fields of atmospheric sciences, geology, and environmental science focused on the environmental behavior and effect of biochar. As one possible source of the components with high aromatic structure in soil humus, biochar is of great importance in increasing soil carbon storage and improving soil fertility, and in maintaining the balance of soil ecosystem. This paper offered the latest information regarding the characteristics and biotic and abiotic oxidation mechanisms of biochar, its effects on global climate change, and the environmental effect of biochar in soil. Research prospects were briefly discussed on the environmental behavior and effect of biochar in soil ecosystem.

Variation of Soil Aggregation along the Weathering Gradient: Comparison of Grain Size Distribution under Different Disruptive Forces.

PubMed

Wei, Yujie; Wu, Xinliang; Xia, Jinwen; Shen, Xue; Cai, Chongfa

2016-01-01

The formation and stabilization of soil aggregates play a key role in soil functions. To date, few studies have been performed on the variation of soil aggregation with increasing soil weathering degree. Here, soil aggregation and its influencing factors along the weathering gradient were investigated. Six typical zonal soils (derived from similar parent materials) were sampled from temperate to tropical regions. Grain size distribution (GSD) in aggregate fragmentation with increasing disruptive forces (air-dried, water dispersion and chemical dispersion) was determined by laser diffraction particle size analyzer. Different forms of sesquioxides were determined by selective chemical extraction and their contributions to soil aggregation were identified by multiple stepwise regression analysis. The high variability of sesquioxides in different forms appeared with increasing free oxide content (Fed and Ald) from the temperate to tropical soils. The transformation of GSD peak to small size varied with increasing disruptive forces (p<0.05). Although in different weathering degrees, zonal soils showed a similar fragmentation process. Aggregate water stability generally increased with increasing soil weathering (p<0.01), with higher stability in eluvium (A) horizon than in illuvium (B) horizon (p<0.01). Crystalline oxides and amorphous iron oxides (Feo), especially (Fed-Feo) contributed to the formation of air-dried macroaggregates and their stability against slaking (R2 = 55%, p<0.01), while fine particles (<50μm) and Feo (excluding the complex form Fep) played a positive role in the formation of water stable aggregates (R2 = 93%, p<0.01). Additionally, water stable aggregates (including stability, size distribution and specific surface area) were closely related with pH, organic matter, cation exchange capacity (CEC), bulk density (BD), and free oxides (including various forms) (p<0.05). The overall results indicate that soil aggregation conforms to aggregate hierarchy theory to some extent along the weathering gradient and different forms of sesquioxides perform their specific roles in the formation and stabilization of different size aggregates.

Variation of Soil Aggregation along the Weathering Gradient: Comparison of Grain Size Distribution under Different Disruptive Forces

PubMed Central

Wu, Xinliang; Xia, Jinwen; Shen, Xue; Cai, Chongfa

2016-01-01

The formation and stabilization of soil aggregates play a key role in soil functions. To date, few studies have been performed on the variation of soil aggregation with increasing soil weathering degree. Here, soil aggregation and its influencing factors along the weathering gradient were investigated. Six typical zonal soils (derived from similar parent materials) were sampled from temperate to tropical regions. Grain size distribution (GSD) in aggregate fragmentation with increasing disruptive forces (air-dried, water dispersion and chemical dispersion) was determined by laser diffraction particle size analyzer. Different forms of sesquioxides were determined by selective chemical extraction and their contributions to soil aggregation were identified by multiple stepwise regression analysis. The high variability of sesquioxides in different forms appeared with increasing free oxide content (Fed and Ald) from the temperate to tropical soils. The transformation of GSD peak to small size varied with increasing disruptive forces (p<0.05). Although in different weathering degrees, zonal soils showed a similar fragmentation process. Aggregate water stability generally increased with increasing soil weathering (p<0.01), with higher stability in eluvium (A) horizon than in illuvium (B) horizon (p<0.01). Crystalline oxides and amorphous iron oxides (Feo), especially (Fed-Feo) contributed to the formation of air-dried macroaggregates and their stability against slaking (R2 = 55%, p<0.01), while fine particles (<50μm) and Feo (excluding the complex form Fep) played a positive role in the formation of water stable aggregates (R2 = 93%, p<0.01). Additionally, water stable aggregates (including stability, size distribution and specific surface area) were closely related with pH, organic matter, cation exchange capacity (CEC), bulk density (BD), and free oxides (including various forms) (p<0.05). The overall results indicate that soil aggregation conforms to aggregate hierarchy theory to some extent along the weathering gradient and different forms of sesquioxides perform their specific roles in the formation and stabilization of different size aggregates. PMID:27529618

Old and stable soil organic matter is not necessarily chemically recalcitrant: Implications for modeling concepts and temperature sensitivity

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

Kleber, M.; Nico, P.S.; Plante, A.

2010-03-01

Soil carbon turnover models generally divide soil carbon into pools with varying intrinsic decomposition rates. Although these decomposition rates are modified by factors such as temperature, texture, and moisture, they are rationalized by assuming chemical structure is a primary controller of decomposition. In the current work, we use near edge X-ray absorption fine structure (NEXAFS) spectroscopy in combination with differential scanning calorimetry (DSC) and alkaline cupric oxide (CuO) oxidation to explore this assumption. Specifically, we examined material from the 2.3-2.6 kg L{sup -1} density fraction of three soils of different type (Oxisol, Alfisol, Inceptisol). The density fraction with the youngestmore » {sup 14}C age (Oxisol, 107 years) showed the highest relative abundance of aromatic groups and the lowest O-alkyl C/aromatic C ratio as determined by NEXAFS. Conversely, the fraction with the oldest C (Inceptisol, 680 years) had the lowest relative abundance of aromatic groups and highest O-alkyl C/aromatic C ratio. This sample also had the highest proportion of thermally labile materials as measured by DSC, and the highest ratio of substituted fatty acids to lignin phenols as indicated by CuO oxidation. Therefore, the organic matter of the Inceptisol sample, with a {sup 14}C age associated with 'passive' pools of carbon (680 years), had the largest proportion of easily metabolizable organic molecules with low thermodynamic stability, whereas the organic matter of the much younger Oxisol sample (107 years) had the highest proportion of supposedly stable organic structures considered more difficult to metabolize. Our results demonstrate that C age is not necessarily related to molecular structure or thermodynamic stability, and we suggest that soil carbon models would benefit from viewing turnover rate as codetermined by the interaction between substrates, microbial actors, and abiotic driving variables. Furthermore, assuming that old carbon is composed of complex or 'recalcitrant' compounds will erroneously attribute a greater temperature sensitivity to those materials than they may actually possess.« less

Interactions of Zn(II) Ions with Humic Acids Isolated from Various Type of Soils. Effect of pH, Zn Concentrations and Humic Acids Chemical Properties.

PubMed

Boguta, Patrycja; Sokołowska, Zofia

2016-01-01

The main aim of this study was the analysis of the interaction between humic acids (HAs) from different soils and Zn(II) ions at wide concentration ranges and at two different pHs, 5 and 7, by using fluorescence and FTIR spectroscopy, as well as potentiometric measurements. The presence of a few areas of HAs structures responsible for Zn(II) complexing was revealed. Complexation at α-sites (low humified structures of low-molecular weight and aromatic polycondensation) and β-sites (weakly humified structures) was stronger at pH 7 than 5. This trend was not observed for γ-sites (structures with linearly-condensed aromatic rings, unsaturated bonds and large molecular weight). The amount of metal complexed at pH5 and 7 by α and γ-structures increased with a decrease in humification and aromaticity of HAs, contrary to β-areas where complexation increased with increasing content of carboxylic groups. The stability of complexes was higher at pH 7 and was the highest for γ-structures. At pH 5, stability decreased with C/N increase for α-areas and -COOH content increase for β-sites; stability increased with humification decrease for γ-structures. The stability of complexes at α and β-areas at pH 7 decreased with a drop in HAs humification. FTIR spectra at pH 5 revealed that the most-humified HAs tended to cause bidentate bridging coordination, while in the case of the least-humified HAs, Zn caused bidentate bridging coordination at low Zn additions and bidentate chelation at the highest Zn concentrations. Low Zn doses at pH 7 caused formation of unidentate complexes while higher Zn doses caused bidentate bridging. Such processes were noticed for HAs characterized by high oxidation degree and high oxygen functional group content; where these were low, HAs displayed bidentate bridging or even bidentate chelation. To summarize, the above studies have showed significant impact of Zn concentration, pH and some properties of HAs on complexation reactions of humic acids with zinc.

Interactions of Zn(II) Ions with Humic Acids Isolated from Various Type of Soils. Effect of pH, Zn Concentrations and Humic Acids Chemical Properties

PubMed Central

Boguta, Patrycja; Sokołowska, Zofia

2016-01-01

The main aim of this study was the analysis of the interaction between humic acids (HAs) from different soils and Zn(II) ions at wide concentration ranges and at two different pHs, 5 and 7, by using fluorescence and FTIR spectroscopy, as well as potentiometric measurements. The presence of a few areas of HAs structures responsible for Zn(II) complexing was revealed. Complexation at α-sites (low humified structures of low-molecular weight and aromatic polycondensation) and β-sites (weakly humified structures) was stronger at pH 7 than 5. This trend was not observed for γ-sites (structures with linearly-condensed aromatic rings, unsaturated bonds and large molecular weight). The amount of metal complexed at pH5 and 7 by α and γ-structures increased with a decrease in humification and aromaticity of HAs, contrary to β-areas where complexation increased with increasing content of carboxylic groups. The stability of complexes was higher at pH 7 and was the highest for γ-structures. At pH 5, stability decreased with C/N increase for α-areas and -COOH content increase for β-sites; stability increased with humification decrease for γ-structures. The stability of complexes at α and β-areas at pH 7 decreased with a drop in HAs humification. FTIR spectra at pH 5 revealed that the most-humified HAs tended to cause bidentate bridging coordination, while in the case of the least-humified HAs, Zn caused bidentate bridging coordination at low Zn additions and bidentate chelation at the highest Zn concentrations. Low Zn doses at pH 7 caused formation of unidentate complexes while higher Zn doses caused bidentate bridging. Such processes were noticed for HAs characterized by high oxidation degree and high oxygen functional group content; where these were low, HAs displayed bidentate bridging or even bidentate chelation. To summarize, the above studies have showed significant impact of Zn concentration, pH and some properties of HAs on complexation reactions of humic acids with zinc. PMID:27077915

Immobilization of simulated radioactive soil waste containing cerium by self-propagating high-temperature synthesis

NASA Astrophysics Data System (ADS)

Mao, Xianhe; Qin, Zhigui; Yuan, Xiaoning; Wang, Chunming; Cai, Xinan; Zhao, Weixia; Zhao, Kang; Yang, Ping; Fan, Xiaoling

2013-11-01

A simulated radioactive soil waste containing cerium as an imitator element has been immobilized by a thermite self-propagating high-temperature synthesis (SHS) process. The compositions, structures, and element leaching rates of products with different cerium contents have been characterized. To investigate the influence of iron on the chemical stability of the immobilized products, leaching tests of samples with different iron contents with different leaching solutions were carried out. The results showed that the imitator element cerium mainly forms the crystalline phases CeAl11O18 and Ce2SiO5. The leaching rate of cerium over a period of 28 days was 10-5-10-6 g/(m2 day). Iron in the reactants, the reaction products, and the environment has no significant effect on the chemical stability of the immobilized SHS products.

Creating a Bio-Inspired Solution to Prevent Erosion

NASA Astrophysics Data System (ADS)

Reher, R.; Martinez, A.; Cola, J.; Frost, D.

2016-12-01

Through the study of geophysical sciences, lessons can be developed which allow for the introduction of bio-inspired design and art concepts to K-5 elementary students. Students are placed into an engineering mindset in which they must apply the concepts of bio-geotechnics to observe how we can use nature to prevent and abate erosion. Problems are staged for students using realistic engineering scenarios such as erosion prevention through biomimicry and the study of anchorage characteristics of root structures in regard to stability of soil. Specifically, a lesson is introduced where students research, learn, and present information about bio-inspired designs to understand these concepts. They lean how plant roots differ in size and shape to stabilize soil. In addition, students perform a series of hands-on experiments which demonstrate how bio-cements and roots can slow erosion.

Bacteria and fungi can contribute to nutrients bioavailability and aggregate formation in degraded soils.

PubMed

Rashid, Muhammad Imtiaz; Mujawar, Liyakat Hamid; Shahzad, Tanvir; Almeelbi, Talal; Ismail, Iqbal M I; Oves, Mohammad

2016-02-01

Intensive agricultural practices and cultivation of exhaustive crops has deteriorated soil fertility and its quality in agroecosystems. According to an estimate, such practices will convert 30% of the total world cultivated soil into degraded land by 2020. Soil structure and fertility loss are one of the main causes of soil degradation. They are also considered as a major threat to crop production and food security for future generations. Implementing safe and environmental friendly technology would be viable solution for achieving sustainable restoration of degraded soils. Bacterial and fungal inocula have a potential to reinstate the fertility of degraded land through various processes. These microorganisms increase the nutrient bioavailability through nitrogen fixation and mobilization of key nutrients (phosphorus, potassium and iron) to the crop plants while remediate soil structure by improving its aggregation and stability. Success rate of such inocula under field conditions depends on their antagonistic or synergistic interaction with indigenous microbes or their inoculation with organic fertilizers. Co-inoculation of bacteria and fungi with or without organic fertilizer are more beneficial for reinstating the soil fertility and organic matter content than single inoculum. Such factors are of great importance when considering bacteria and fungi inocula for restoration of degraded soils. The overview of presented mechanisms and interactions will help agriculturists in planning sustainable management strategy for reinstating the fertility of degraded soil and assist them in reducing the negative impact of artificial fertilizers on our environment. Copyright © 2015 Elsevier GmbH. All rights reserved.

How far are rheological parameters from amplitude sweep tests predictable using common physicochemical soil properties?

NASA Astrophysics Data System (ADS)

Stoppe, N.; Horn, R.

2017-01-01

A basic understanding of soil behavior on the mesoscale resp. macroscale (i.e. soil aggregates resp. bulk soil) requires knowledge of the processes at the microscale (i.e. particle scale), therefore rheological investigations of natural soils receive growing attention. In the present research homogenized and sieved (< 2 mm) samples from Marshland soils of the riparian zone of the River Elbe (North Germany) were analyzed with a modular compact rheometer MCR 300 (Anton Paar, Ostfildern, Germany) with a profiled parallel-plate measuring system. Amplitude sweep tests (AST) with controlled shear deformation were conducted to investigate the viscoelastic properties of the studied soils under oszillatory stress. The gradual depletion of microstructural stiffness during AST cannot only be characterized by the well-known rheological parameters G, G″ and tan δ but also by the dimensionless area parameter integral z, which quantifies the elasticity of microstructure. To discover the physicochemical parameters, which influences the microstructural stiffness, statistical tests were used taking the combined effects of these parameters into account. Although the influence of the individual factors varies depending on soil texture, the physicochemical features significantly affecting soil micro structure were identified. Based on the determined statistical relationships between rheological and physicochemical parameters, pedotransfer functions (PTF) have been developed, which allow a mathematical estimation of the rheological target value integral z. Thus, stabilizing factors are: soil organic matter, concentration of Ca2+, content of CaCO3 and pedogenic iron oxides; whereas the concentration of Na+ and water content represent structurally unfavorable factors.

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

Stabilization of Horseshoe Lake Road using Geofibers and Soil-Sement

DOT National Transportation Integrated Search

2012-04-03

One solution to reducing the cost of importing gravel in areas where available soils are predominately silts and : sands is to stabilize the local soils with geofibers and synthetic fluids. There have been several studies which : have evaluated impro...

Integrating EDDS-enhanced washing with low-cost stabilization of metal-contaminated soil from an e-waste recycling site.

PubMed

Beiyuan, Jingzi; Tsang, Daniel C W; Ok, Yong Sik; Zhang, Weihua; Yang, Xin; Baek, Kitae; Li, Xiang-Dong

2016-09-01

While chelant-enhanced soil washing has been widely studied for metal extraction from contaminated soils, there are concerns about destabilization and leaching of residual metals after remediation. This study integrated 2-h soil washing enhanced by biodegradable ethylenediaminedisuccinic acid (EDDS) and 2-month stabilization using agricultural waste product (soybean stover biochar pyrolyzed at 300 and 700 °C), industrial by-product (coal fly ash (CFA)), and their mixture. After integration with 2-month stabilization, the leachability and mobility of residual metals (Cu, Zn, and Pb) in the field-contaminated soil were significantly reduced, especially for Cu, in comparison with 2-h EDDS washing alone. This suggested that the metals destabilized by EDDS-washing could be immobilized by subsequent stabilization with biochar and CFA. Moreover, when the remediation performance was evaluated for phytoavailability and bioaccessibility, prior EDDS washing helped to achieve a greater reduction in the bioavailable fraction of metals than sole stabilization treatment. This was probably because the weakly-bound metals were first removed by EDDS washing before stabilization. Both individual and combined applications of biochar and CFA showed comparable effectiveness regardless of the difference in material properties, possibly due to the high level of amendments (150 ton ha(-1)). Based on the mobility and bioaccessibility results, the estimated human health risk (primarily resulting from Pb) could be mitigated to an acceptable level in water consumption pathway or reduced by half in soil ingestion pathway. These results suggest that an integration of EDDS washing with soil stabilization can alleviate post-remediation impacts of residual metals in the treated soil. Copyright © 2016 Elsevier Ltd. All rights reserved.

Alternative materials for the modification and stabilization of unstable subgrade soils

DOT National Transportation Integrated Search

1997-05-01

This study examines two lime by-products and two fly ashes for treatment of unstable (CBR<6) subgrade soils. The treatment methods include both modification and stabilization. Modification is temporily enhancing subgrade stability to improve construc...

Stabilization of As-, Pb-, and Cu-contaminated soil using calcined oyster shells and steel slag.

PubMed

Moon, Deok Hyun; Wazne, Mahmoud; Cheong, Kyung Hoon; Chang, Yoon-Young; Baek, Kitae; Ok, Yong Sik; Park, Jeong-Hun

2015-07-01

In this study, As-, Pb-, and Cu-contaminated soil was stabilized using calcined oyster shells (COS) and steel slag (SS). The As-contaminated soil was obtained from a timber mill site where chromate copper arsenate (CCA) was used as a preservative. On the other hand, Pb- and Cu-contaminated soil was obtained from a firing range. These two soils were thoroughly mixed to represent As-, Pb-, and Cu-contaminated soil. Calcined oyster shells were obtained by treating waste oyster shells at a high temperature using the calcination process. The effectiveness of stabilization was evaluated by 1-N HCl extraction for As and 0.1-N HCl extraction for Pb and Cu. The treatment results showed that As, Pb, and Cu leachability were significantly reduced upon the combination treatment of COS and SS. The sole treatment of SS (10 wt%) did not show effective stabilization. However, the combination treatment of COS and SS showed a significant reduction in As, Pb, and Cu leachability. The best stabilization results were obtained from the combination treatment of 15 wt% COS and 10 wt% SS. The SEM-EDX results suggested that the effective stabilization of As was most probably achieved by the formation of Ca-As and Fe-As precipitates. In the case of Pb and Cu, stabilization was most probably associated with the formation of pozzolanic reaction products such as CSHs and CAHs.

Divergent composition but similar function of soil food webs of individual plants: plant species and community effects.

PubMed

Bezemer, T M; Fountain, M T; Barea, J M; Christensen, S; Dekker, S C; Duyts, H; van Hal, R; Harvey, J A; Hedlund, K; Maraun, M; Mikola, J; Mladenov, A G; Robin, C; de Ruiter, P C; Scheu, S; Setälä, H; Smilauer, P; van der Putten, W H

2010-10-01

Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.

On the tree stability risk

NASA Astrophysics Data System (ADS)

Giambastiani, Yamuna; Preti, Federico; Errico, Alessandro; Penna, Daniele

2017-04-01

There is growing interest in developing models for predicting how root anchorage and tree bracing could influence tree stability. This work presents the results of different experiments aimed at evaluating the mechanical response of plate roots to pulling tests. Pulling tests have been executed with increasing soil water content and soil of different texture. Different types of tree bracing have been examined for evaluating its impact on plant stiffness. Root plate was anchored with different systems for evaluating the change in overturning resistance. The first results indicate that soil water content contributed to modify both the soil cohesion and the stabilizing forces. Wind effect, slope stability and root reinforcement could be better quantified by means of such a results.

Stabilization of marly soils with portland cement

NASA Astrophysics Data System (ADS)

Piskunov, Maksim; Karzin, Evgeny; Lukina, Valentina; Lukinov, Vitaly; Kholkin, Anatolii

2017-10-01

Stabilization of marlous soils with Portland cement will increase the service life of motor roads in areas where marl is used as a local road construction material. The result of the conducted research is the conclusion about the principal possibility of stabilization of marlous soils with Portland cement, and about the optimal percentage of the mineral part and the binding agent. When planning the experiment, a simplex-lattice plan was implemented, which makes it possible to obtain a mathematical model for changing the properties of a material in the form of polynomials of incomplete third order. Brands were determined for compressive strength according to GOST 23558-94 and variants of stabilized soils were proposed for road construction.

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.

Degradation of Biofumigant Isothiocyanates and Allyl Glucosinolate in Soil and Their Effects on the Microbial Community Composition

PubMed Central

Hanschen, Franziska S.; Yim, Bunlong; Winkelmann, Traud; Smalla, Kornelia; Schreiner, Monika

2015-01-01

Brassicales species rich in glucosinolates are used for biofumigation, a process based on releasing enzymatically toxic isothiocyanates into the soil. These hydrolysis products are volatile and often reactive compounds. Moreover, glucosinolates can be degraded also without the presence of the hydrolytic enzyme myrosinase which might contribute to bioactive effects. Thus, in the present study the stability of Brassicaceae plant-derived and pure glucosinolates hydrolysis products was studied using three different soils (model biofumigation). In addition, the degradation of pure 2-propenyl glucosinolate was investigated with special regard to the formation of volatile breakdown products. Finally, the influence of pure glucosinolate degradation on the bacterial community composition was evaluated using denaturing gradient gel electrophoresis of 16S rRNA gene amplified from total community DNA. The model biofumigation study revealed that the structure of the hydrolysis products had a significant impact on their stability in the soil but not the soil type. Following the degradation of pure 2-propenyl glucosinolate in the soils, the nitrile as well as the isothiocyanate can be the main degradation products, depending on the soil type. Furthermore, the degradation was shown to be both chemically as well as biologically mediated as autoclaving reduced degradation. The nitrile was the major product of the chemical degradation and its formation increased with iron content of the soil. Additionally, the bacterial community composition was significantly affected by adding pure 2-propenyl glucosinolate, the effect being more pronounced than in treatments with myrosinase added to the glucosinolate. Therefore, glucosinolates can have a greater effect on soil bacterial community composition than their hydrolysis products. PMID:26186695

Molecular C dynamics downstream: the biochemical decomposition sequence and its impact on soil organic matter structure and function.

PubMed

Grandy, A Stuart; Neff, Jason C

2008-10-15

Advances in spectroscopic and other chemical methods have greatly enhanced our ability to characterize soil organic matter chemistry. As a result, the molecular characteristics of soil C are now known for a range of ecosystems, soil types, and management intensities. Placing this knowledge into a broader ecological and management context is difficult, however, and remains one of the fundamental challenges of soil organic matter research. Here we present a conceptual model of molecular soil C dynamics to stimulate inter-disciplinary research into the ecological implications of molecular C turnover and its management- and process-level controls. Our model describes three properties of soil C dynamics: 1) soil size fractions have unique molecular patterns that reflect varying degrees of biological and physical control over decomposition; 2) there is a common decomposition sequence independent of plant inputs or other ecosystem properties; and 3) molecular decomposition sequences, although consistent, are not uniform and can be altered by processes that accelerate or slow the microbial transformation of specific molecules. The consequences of this model include several key points. First, lignin presents a constraint to decomposition of plant litter and particulate C (>53 microm) but exerts little influence on more stable mineral-associated soil fractions <53 microm. Second, carbon stabilized onto mineral fractions has a distinct composition related more to microbially processed organic matter than to plant-related compounds. Third, disturbances, such as N fertilization and tillage, which alter decomposition rates, can have "downstream effects"; that is, a disturbance that directly alters the molecular dynamics of particulate C may have a series of indirect effects on C stabilization in silt and clay fractions.

Peat Soil Stabilization using Lime and Cement

NASA Astrophysics Data System (ADS)

Zambri, Nadhirah Mohd; Ghazaly, Zuhayr Md.

2018-03-01

This paper presents a study of the comparison between two additive Lime and Cement for treating peat soil in term of stabilization. Peat and organic soils are commonly known for their high compressibility, extremely soft, and low strength. The aim of this paper is to determine the drained shear strength of treated peat soil from Perlis for comparison purposes. Direct Shear Box Test was conducted to obtain the shear strength for all the disturbed peat soil samples. The quick lime and cement was mixed with peat soil in proportions of 10% and 20% of the dry weight peat soil. The experiment results showed that the addition of additives had improved the strength characteristics of peat soil by 14% increment in shear strength. In addition, the mixture of lime with peat soil yield higher result in shear strength compared to cement by 14.07% and 13.5% respectively. These findings indicate that the lime and cement is a good stabilizer for peat soil, which often experienced high amount of moisture content.

The role of vegetation in the stability of forested slopes

Treesearch

Robert R. Ziemer

1981-01-01

Summary - Vegetation helps stabilize forested slopes by providing root strength and by modifying the saturated soil water regime. Plant roots can anchor through the soil mass into fractures in bedrock, can cross zones of weakness to more stable soil, and can provide interlocking long fibrous binders within a weak soil mass. In Mediterranean-type climates, having warm...

Role of biological soil crusts in desert hydrology and geomorphology: Implications for military training operations

Treesearch

Steven D. Warren

2014-01-01

Biological soil crusts, composed of soil surfaces stabilized by a consortium of cyanobacteria, algae, fungi, lichens, and/or bryophytes, are common in most deserts and perform functions of primary productivity, nitrogen fixation, nutrient cycling, water redistribution, and soil stabilization. The crusts are highly susceptible to disturbance. The degree of perturbation...

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.

Soil-covered strategy for ecological restoration alters the bacterial community structure and predictive energy metabolic functions in mine tailings profiles.

PubMed

Li, Yang; Sun, Qingye; Zhan, Jing; Yang, Yang; Wang, Dan

2017-03-01

Native soil amendment has been widely used to stabilize mine tailings and speed up the development of soil biogeochemical functions before revegetation; however, it remains poorly understood about the response of microbial communities to ecological restoration of mine tailings with soil-covered strategy. In this study, microbial communities along a 60-cm profile were investigated in mine tailings during ecological restoration of two revegetation strategies (directly revegetation and native soil covered) with different plant species. The mine tailings were covered by native soils as thick as 40 cm for more than 10 years, and the total nitrogen, total organic carbon, water content, and heavy metal (Fe, Cu, and Zn) contents in the 0-40 cm intervals of profiles were changed. In addition, increased microbial diversity and changed microbial community structure were also found in the 10-40 cm intervals of profiles in soil-covered area. Soil-covered strategy rather than plant species and soil depth was the main factor influencing the bacterial community, which explained the largest portion (29.96%) of the observed variation. Compared directly to revegetation, soil-covered strategy exhibited the higher relative abundance of Acidobacteria and Deltaproteobacteria and the lower relative abundance of Bacteroidetes, Gemmatimonadetes, Betaproteobacteria, and Gammaproteobacteria. PICRUSt analysis further demonstrated that soil-covered caused energy metabolic functional changes in carbon, nitrogen, and sulfur metabolism. Given all these, the soil-covered strategy may be used to fast-track the establishment of native microbial communities and is conducive to the rehabilitation of biogeochemical processes for establishing native plant species.

Effect of long-term organic fertilization on the soil pore characteristics of greenhouse vegetable fields converted from rice-wheat rotation fields.

PubMed

Xu, L Y; Wang, M Y; Shi, X Z; Yu, Q B; Shi, Y J; Xu, S X; Sun, W X

2018-08-01

The shift from rice-wheat rotation (RWR) to greenhouse vegetable soils has been widely practiced in China. Several studies have discussed the changes in soil properties with land-use changes, but few studies have sought to address the differences in soil pore properties, especially for fields based on long-term organic fertilization under greenhouse vegetable system from RWR fields. This study uses the X-ray computed tomography (CT) scanning and statistical analysis to compare the long-term effects of the conversion of organic greenhouse vegetable fields (over one year, nine years, and fourteen years) from RWR fields on the soil macropore structure as well as the influencing factors from samples obtained in Nanjing, Jiangsu, China, using the surface soil layer and triplicate samples. The results demonstrated that the macropore structure became more complex and stable, with a higher connectivity, fractal dimension (FD) and a lower degree of anisotropy (DA), as the greenhouse vegetable planting time increased. The total topsoil macroporosity increased considerably, but the rate of increase gradually decelerated with time. The transmission pores (round pores ranging from 50 to 500μm) increased with time, but the biopores (>2000μm) clearly decreased after nine years of use as greenhouse vegetable fields. Soil organic matter (OM) has a significant relationship with the soil pore structure characteristics, especially for the transmission pores. In addition, organic fertilization on the topsoil had a short-term effect on the pores, but the effect stabilized and had a weak influence on the pores over longer periods. These results suggested that organic fertilization was conducive for controlling soil degradation regarding it physical quality for water and oxygen availability in the short term. Copyright © 2018 Elsevier B.V. All rights reserved.

Earthworms are associated with subpopulations of Gammaproteobacteria irrespective of the total soil microbiota composition and stability.

PubMed

Fjøsne, Trine; Myromslien, Frøydis D; Wilson, Robert C; Rudi, Knut

2018-05-01

Soil represents one of the most complex microbial ecosystems on earth. It is well-known that invertebrates such as earthworms have a major impact on transformations of organic material in soil, while their effect on the soil microbiota remains largely unknown. The aim of our work was therefore to investigate the association of earthworms with temporal stability, composition and diversity in two soil microbiota experimental series. We found that earthworms were consistently associated with an increase in subgroups of Gammaproteobacteria, despite major differences in microbiota composition and temporal stability across the experimental series. Our results therefore suggest that earthworms can affect subpopulation dynamics in the soil microbiota, irrespective of the total microbiota composition. If the soil microbiota is comprised of independent microbiota components, this can contribute to our general understanding of the complexity of the soil microbiota.

Use of Biomass Ash as a stabilization agent for expansive marly soils (SE Spain)

NASA Astrophysics Data System (ADS)

Ureña, C.; Azañón, J. M.; Caro, J. M.; Irigaray, C.; Corpas, F.; Ramirez, A.; Rivas, F.; Salazar, L. M.; Mochón, I.

2012-04-01

In recent years, several biomass power plants have been installed in Southeastern Spain to reuse olive oil industry residues. This energy production tries to reduce the high costs associated with fossil fuels, but without entering into direct competition to traditional food crops. The waste management in these biomass energy plants is still an issue since there are non-flammable materials which remains after incineration in the form of ashes. In Southeastern Spain there is also a great amount of clayey and marly soils whose volume is very sensitive to changes in climate conditions, making them unsuitable for civil engineering. We propose the use of biomass ash (both fly ash and bottom ash) as a stabilization agent for expansive soils in order to improve the efficiency of construction processes by using locally available materials. In this work biomass ashes from a biomass power plant in Southeastern Spain have been used to stabilize 6 samples of local marly soil. Those 6 samples of expansive soil were mixed with different dosages of biomass ash (2%, 4% and 7%) to create 18 specimens of treated soil, which were submitted to Proctor, Atterberg Limits, pH and Free Swell Index tests, following Spanish Standards UNE by AENOR. X-Ray Diffraction (XRD) tests by powder method were also carried out, using a diffractometer Philips X'Pert-MPD. The results obtained for the original untreated marly soil were: PI = 34.6; Free Swell = 12.5; pH = 8. By adding biomass ash the value of the plasticity index (PI) became slightly lower although it was not low enough as to obtain a non-plastic soil (PI under 25). However, there were dramatical decreases of free swell index (FSI) after the stabilization treatment: FSI < 8.18 (2% biomass); FSI < 6.15 (4% biomass); FSI < 4.18 (7% biomass); These results suggest that treated soil is quite less susceptible than the original soil to moisture changes. The pH of the mixes after adding biomass ash rose from 8 to 11±1 leading to an alkaline environment which, as reviewed literature points out, helps to the development of pozzolanic reactions and stabilization process. Finally, XRD tests indicated a sharp decrease in the intensity of reflection of the Smectite peak, suggesting a reduction in the amount of this expansive mineral in treated soils. This positive and durable effect may be related to cation exchange from Na+ to smaller cations or even the formation of mixed-layered clay minerals. A further research must be conducted to determine the pozzolanic properties of biomass ash (i.e., its suitability for concrete composites), the optimum dosages, etc. The further research is also necessary to better understand the mineralogy changes occurred within the crystalline structure. Nevertheless, these first results let us infer that biomass ash from power plants has a high capacity to enhance mechanical properties of expansive soils. Given the widespread use of biomass in industry today, the secondary use of biomass ash might improve the sustainability and efficiency of the biomass generation, incineration and waste management process.

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.

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.

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.

Feasibility Study of Improved Methods for Riverbank Stabilization

DTIC Science & Technology

1964-11-01

hose materials which appear to be technically feasible for such applications are listed in Tables I - 1 and I - 2. I-9 Artificial Riprap...the uncompacted asphalt pavement. Those which 1-11 show the most potential for further study are soil cement, synthetic elastomer sheeting, and...uncompated asphalt pavement. Chemical soil stabilization and metal sheeting are too exp~nsive, and the quality of chemically stabilized soil protection is

Field investigation of geosynthetics used for subgrade stabilization : [project summary].

DOT National Transportation Integrated Search

2009-08-01

Roadways are commonly constructed on weak native soil deposits. When excavation and replacement of these soils is not cost effective, soil stabilization may be necessary to provide a working platform so that the base course gravel layer can be proper...

EVALUATION OF SOLIDIFICATION/STABILIZATION AS A BEST DEMONSTRATED AVAILABLE TECHNOLOGY FOR CONTAMINATED SOILS

EPA Science Inventory

This project involved the evaluation of solidification/stabilization technology as a BDAT for contaminated soil. Three binding agents were used on four different synthetically contaminated soils. Performance evaluation data included unconfined compressive strength (UCS) and the T...

Soil Water Holding Capacity Mitigates Downside Risk and Volatility in US Rainfed Maize: Time to Invest in Soil Organic Matter?

PubMed Central

Williams, Alwyn; Hunter, Mitchell C.; Kammerer, Melanie; Kane, Daniel A.; Jordan, Nicholas R.; Mortensen, David A.; Smith, Richard G.; Snapp, Sieglinde

2016-01-01

Yield stability is fundamental to global food security in the face of climate change, and better strategies are needed for buffering crop yields against increased weather variability. Regional- scale analyses of yield stability can support robust inferences about buffering strategies for widely-grown staple crops, but have not been accomplished. We present a novel analytical approach, synthesizing 2000–2014 data on weather and soil factors to quantify their impact on county-level maize yield stability in four US states that vary widely in these factors (Illinois, Michigan, Minnesota and Pennsylvania). Yield stability is quantified as both ‘downside risk’ (minimum yield potential, MYP) and ‘volatility’ (temporal yield variability). We show that excessive heat and drought decreased mean yields and yield stability, while higher precipitation increased stability. Soil water holding capacity strongly affected yield volatility in all four states, either directly (Minnesota and Pennsylvania) or indirectly, via its effects on MYP (Illinois and Michigan). We infer that factors contributing to soil water holding capacity can help buffer maize yields against variable weather. Given that soil water holding capacity responds (within limits) to agronomic management, our analysis highlights broadly relevant management strategies for buffering crop yields against climate variability, and informs region-specific strategies. PMID:27560666

Vegetation Influences on Long-Term Carbon Stabilization in Soils: a Coast Redwood-Prairie Comparison

NASA Astrophysics Data System (ADS)

Mambelli, S.; Burton, S. D.; McFarlane, K. J.; Torn, M. S.; Dawson, T. E.

2010-12-01

Complex interactions and feedbacks among soil, biota, climate, and parent material determine the long-term pathways and mechanisms of carbon persistence in soils. While it is well known that litter chemistry influences litter decay on annual-decadal timescales, its impact on long-term SOM storage is still under debate. We tested the role of the substrate available to decomposers in determining decomposition and sequestration of carbon by comparing two contrasting ecosystems representing end-members in terms of tissue lifespan and litter recalcitrance, an old-growth redwood forest and an adjacent tree-less prairie, at one site with identical climate, topography, and parent material. Solid-state CP MAS 13C NMR was applied to investigate the chemical structure of vegetation tissues (aboveground and belowground), and of soil fractions (particulate organic carbon free in the soil matrix and particulate organic carbon located inside soil aggregates, or free and occluded light fraction (LF), respectively) at different depths. In addition, the carbon stability of these soil density fractions was estimated based on radiocarbon modeling. Preliminary NMR results showed strong differences between redwood and prairie tissues, and between litters and surface soil fractions. On average, redwood litter contained more aromatic carbon (C and O substituted aryl C), more lipids (alkyl C) and fewer carbohydrates (O-alkyl C) than prairie litter. Under both vegetation types we found that the chemical structure changed consistently from litter to free LF, and from free LF to occluded LF. The alkyl C signal intensity increased, while the O-alkyl C fraction decreased, but more strongly at the redwood forest. The proportion of aromatic functional groups in the total organic matter (aromaticity) was always higher in the soil fractions compared with the original litters. Redwood soil fractions aromaticity was 0.32 (+80% from litter), while prairie soil fractions aromaticity varied from 0.17 (free LF) to 0.23 (occluded LF)(+40 and +90% from litter, respectively). The proportion of carbon in carbonyl groups (alkyl/O-alkyl ratio), an estimate of the degree of decomposition, increased from the free LF to the occluded LF at both ecosystems (0.30 to 0.75 in the redwood forest, 0.24 to 0.68 in the prairie, respectively). In summary, the similar decomposition stage of the redwood and prairie SOM and the higher aromaticity of the free LF in the redwood soil compared to the original litter suggest the preservation of recalcitrant redwood constituents but only in the free soil matrix. Further investigations at deeper soil depths are underway.

Investigating local controls on temporal stability of soil water content using sensor network data and an inverse modeling approach

NASA Astrophysics Data System (ADS)

Qu, W.; Bogena, H. R.; Huisman, J. A.; Martinez, G.; Pachepsky, Y. A.; Vereecken, H.

2013-12-01

Soil water content is a key variable in the soil, vegetation and atmosphere continuum with high spatial and temporal variability. Temporal stability of soil water content (SWC) has been observed in multiple monitoring studies and the quantification of controls on soil moisture variability and temporal stability presents substantial interest. The objective of this work was to assess the effect of soil hydraulic parameters on the temporal stability. The inverse modeling based on large observed time series SWC with in-situ sensor network was used to estimate the van Genuchten-Mualem (VGM) soil hydraulic parameters in a small grassland catchment located in western Germany. For the inverse modeling, the shuffled complex evaluation (SCE) optimization algorithm was coupled with the HYDRUS 1D code. We considered two cases: without and with prior information about the correlation between VGM parameters. The temporal stability of observed SWC was well pronounced at all observation depths. Both the spatial variability of SWC and the robustness of temporal stability increased with depth. Calibrated models both with and without prior information provided reasonable correspondence between simulated and measured time series of SWC. Furthermore, we found a linear relationship between the mean relative difference (MRD) of SWC and the saturated SWC (θs). Also, the logarithm of saturated hydraulic conductivity (Ks), the VGM parameter n and logarithm of α were strongly correlated with the MRD of saturation degree for the prior information case, but no correlation was found for the non-prior information case except at the 50cm depth. Based on these results we propose that establishing relationships between temporal stability and spatial variability of soil properties presents a promising research avenue for a better understanding of the controls on soil moisture variability. Correlation between Mean Relative Difference of soil water content (or saturation degree) and inversely estimated soil hydraulic parameters (log10(Ks), log10(α), n, and θs) at 5-cm, 20-cm and 50-cm depths. Solid circles represent parameters estimated by using prior information; open circles represent parameters estimated without using prior information.

Micro-x-ray fluorescence, micro-x-ray absorption spectroscopy, and micro-x-ray diffraction investigation of lead speciation after the addition of different phosphorus amendments to a smelter-contaminated soil.

PubMed

Baker, Lucas R; Pierzynski, Gary M; Hettiarachchi, Ganga M; Scheckel, Kirk G; Newville, Matthew

2014-03-01

The stabilization of Pb on additions of P to contaminated soils and mine spoil materials has been well documented. It is clear from the literature that different P sources result in different efficacies of Pb stabilization in the same contaminated material. We hypothesized that the differences in the efficacy of Pb stabilization in contaminated soils on fluid or granular P amendment addition is due to different P reaction processes in and around fertilizer granules and fluid droplets. We used a combination of several synchrotron-based techniques (i.e., spatially resolved micro-X-ray fluorescence, micro-X-ray absorption near-edge structure spectroscopy, and micro-X-ray diffraction) to speciate Pb at two incubation times in a smelter-contaminated soil on addition of several fluid and granular P amendments. The results indicated that the Pb phosphate mineral plumbogummite was an intermediate phase of pyromorphite formation. Additionally, all fluid and granular P sources were able to induce Pb phosphate formation, but fluid phosphoric acid (PA) was the most effective with time and distance from the treatment. Granular phosphate rock and triple super phosphate (TSP) amendments reacted to generate Pb phosphate minerals, with TSP being more effective at greater distances from the point of application. As a result, PA and TSP were the most effective P amendments at inducing Pb phosphate formation, but caution needs to be exercised when adding large amounts of soluble P to the environment. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

The Effect of Drying-Wetting Cycle’s Repetition to the Characteristic of Natural and Stabilization Residual Soils Jawa Timur - Indonesia

NASA Astrophysics Data System (ADS)

Muntaha, M.

2017-11-01

Indonesia, which located in tropical region, continuously undergoes wetting and drying cycles due to the changeable seasons. An important role in activating the clay minerals on tropical residual soils is the main factor that affects the static and dynamic properties, such as: volume change, soil suction and dynamic modulus. The purpose of this paper is to evaluate the effect of drying-wetting cycles repetition on volume change, soil suction and mechanical characteristics of natural and stabilization of residual soils from Jawa Timur - Indonesia. The natural undisturbed and stabilized residual soil sample was naturally and gradually dried up with air to 25%, 50%, 75%, and 100 % of the initial water content. The wetting processes were carried out with the gradual increment water content of 25 %(wsat - wi), 50 %(wsat - wi), 75 %(wsat - wi), up to 100 %(wsat - wi). The Direct Shear test is used to measure the mechanic properties, and Whatman filter paper No. 42 is used to measure the soil suction. The drying-wetting processes were carried out for 1, 2, 4, and 6 cycles. The laboratory test results showed that, the void ratio decreased, the unit weight, cohesion and the internal friction angle were increasing due to stabilization. Drying-wetting cycle repetition reduces void ratio, negative pore-water pressure, cohesion and internal friction angle of natural and stabilized soils. Briefly, the decreased of mechanical soil properties was proven from the physical properties change observation.

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

Tillage and crop residue management methods had minor effects on the stock and stabilization of topsoil carbon in a 30-year field experiment.

PubMed

Singh, Pooja; Heikkinen, Jaakko; Ketoja, Elise; Nuutinen, Visa; Palojärvi, Ansa; Sheehy, Jatta; Esala, Martti; Mitra, Sudip; Alakukku, Laura; Regina, Kristiina

2015-06-15

We studied the effects of tillage and straw management on soil aggregation and soil carbon sequestration in a 30-year split-plot experiment on clay soil in southern Finland. The experimental plots were under conventional or reduced tillage with straw retained, removed or burnt. Wet sieving was done to study organic carbon and soil composition divided in four fractions: 1) large macroaggregates, 2) small macroaggregates, 3) microaggregates and 4) silt and clay. To further estimate the stability of carbon in the soil, coarse particulate organic matter, microaggregates and silt and clay were isolated from the macroaggregates. Total carbon stock in the topsoil (equivalent to 200 kg m(-2)) was slightly lower under reduced tillage (5.0 kg m(-2)) than under conventional tillage (5.2 kg m(-2)). Reduced tillage changed the soil composition by increasing the percentage of macroaggregates and decreasing the percentage of microaggregates. There was no evidence of differences in the composition of the macroaggregates or carbon content in the macroaggregate-occluded fractions. However, due to the higher total amount of macroaggregates in the soil, more carbon was bound to the macroaggregate-occluded microaggregates in reduced tillage. Compared with plowed soil, the density of deep burrowing earthworms (Lumbricus terrestris) was considerably higher under reduced tillage and positively associated with the percentage of large macroaggregates. The total amount of microbial biomass carbon did not differ between the treatments. Straw management did not have discernible effects either on soil aggregation or soil carbon stock. We conclude that although reduced tillage can improve clay soil structure, generally the chances to increase topsoil carbon sequestration by reduced tillage or straw management practices appear limited in cereal monoculture systems of the boreal region. This may be related to the already high C content of soils, the precipitation level favoring decomposition and aggregate turnover in the winter with topsoil frost. Copyright © 2015. Published by Elsevier B.V.

Environmental impacts of different crop rotations in terms of soil compaction.

PubMed

Götze, Philipp; Rücknagel, Jan; Jacobs, Anna; Märländer, Bernward; Koch, Heinz-Josef; Christen, Olaf

2016-10-01

Avoiding soil compaction caused by agricultural management is a key aim of sustainable land management, and the soil compaction risk should be considered when assessing the environmental impacts of land use systems. Therefore this project compares different crop rotations in terms of soil structure and the soil compaction risk. It is based on a field trial in Germany, in which the crop rotations (i) silage maize (SM) monoculture, (ii) catch crop mustard (Mu)_sugar beet (SB)-winter wheat (WW)-WW, (iii) Mu_SM-WW-WW and (iv) SB-WW-Mu_SM are established since 2010. Based on the cultivation dates, the operation specific soil compaction risks and the soil compaction risk of the entire crop rotations are modelled at two soil depths (20 and 35 cm). To this end, based on assumptions of the equipment currently used in practice by a model farm, two scenarios are modelled (100 and 50% hopper load for SB and WW harvest). In addition, after one complete rotation, in 2013 and in 2014, the physical soil parameters saturated hydraulic conductivity (kS) and air capacity (AC) were determined at soil depths 2-8, 12-18, 22-28 and 32-38 cm in order to quantify the soil structure. At both soil depths, the modelled soil compaction risks for the crop rotations including SB (Mu_SB-WW-WW, SB-WW-Mu_SM) are higher (20 cm: medium to very high risks; 35 cm: no to medium risks) than for those without SB (SM monoculture, Mu_SM-WW-WW; 20 cm: medium risks; 35 cm: no to low risks). This increased soil compaction risk is largely influenced by the SB harvest in years where soil water content is high. Halving the hopper load and adjusting the tyre inflation pressure reduces the soil compaction risk for the crop rotation as a whole. Under these conditions, there are no to low soil compaction risks for all variants in the subsoil (soil depth 35 cm). Soil structure is mainly influenced in the topsoil (2-8 cm) related to the cultivation of Mu as a catch crop and WW as a preceding crop. Concerning kS, Mu_SB-WW-WW (240 cm d(-1)) and Mu_SM-WW-WW (196 cm d(-1)) displayed significantly higher values than the SM monoculture (67 cm d(-1)), indicating better structural stability and infiltration capacity. At other soil depths, and for the parameter AC, there are no systematic differences in soil structure between the variants. Under the circumstances described, all crop rotations investigated are not associated with environmental impacts caused by soil compaction. Copyright © 2016 Elsevier Ltd. All rights reserved.

Stabilization techniques for reactive aggregate in soil-cement base course : technical summary.

DOT National Transportation Integrated Search

2003-01-01

The objectives of this research are 1) to identify the mineralogical properties of soil-cement bases which have heaved or can potentially heave, 2) to simulate expansion of cement-stabilized soil in the laboratory, 3) to correlate expansion with the ...

Design and construction control guidance for chemically stabilized pavement base layers.

DOT National Transportation Integrated Search

2013-12-01

A laboratory and field study was conducted related to chemically stabilized pavement layers, which is also : referred to as soil-cement. Soil-cement practices within MDOT related to Class 9C soils used for base layers : were evaluated in this report....

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...

Crusts: biological

USGS Publications Warehouse

Belnap, Jayne; Elias, Scott A.

2013-01-01

Biological soil crusts, a community of cyanobacteria, lichens, mosses, and fungi, are an essential part of dryland ecosystems. They are critical in the stabilization of soils, protecting them from wind and water erosion. Similarly, these soil surface communities also stabilized soils on early Earth, allowing vascular plants to establish. They contribute nitrogen and carbon to otherwise relatively infertile dryland soils, and have a strong influence on hydrologic cycles. Their presence can also influence vascular plant establishment and nutrition.

Formation and Stability of Microbially Derived Soil Organic Matter

NASA Astrophysics Data System (ADS)

Waldrop, M. P.; Creamer, C.; Foster, A. L.; Lawrence, C. R.; Mcfarland, J. W.; Schulz, M. S.

2017-12-01

Soil carbon is vital to soil health, food security, and climate change mitigation, but the underlying mechanisms controlling the stabilization and destabilization of soil carbon are still poorly understood. There has been a conceptual paradigm shift in how soil organic matter is formed which now emphasizes the importance of microbial activity to build stable (i.e. long-lived) and mineral-associated soil organic matter. In this conceptual model, the consumption of plant carbon by microorganisms, followed by subsequent turnover of microbial bodies closely associated with mineral particles, produces a layering of amino acid and lipid residues on the surfaces of soil minerals that remains protected from destabilization by mineral-association and aggregation processes. We tested this new model by examining how isotopically labeled plant and microbial C differ in their fundamental stabilization and destabilization processes on soil minerals through a soil profile. We used a combination of laboratory and field-based approaches to bridge multiple spatial scales, and used soil depth as well as synthetic minerals to create gradients of soil mineralogy. We used Raman microscopy as a tool to probe organic matter association with mineral surfaces, as it allows for the simultaneous quantification and identification of living microbes, carbon, minerals, and isotopes through time. As expected, we found that the type of minerals present had a strong influence on the amount of C retained, but the stabilization of new C critically depends on growth, death, and turnover of microbial cells. Additionally, the destabilization of microbial residue C on mineral surfaces was little affected by flushes of DOC relative to wet-dry cycles alone. We believe this new insight into microbial mechanisms of C stabilization in soils will eventually lead to new avenues for measuring and modeling SOM dynamics in soils, and aid in the management of soil C to mediate global challenges.

Stabilizing effect of biochar on soil extracellular enzymes after a denaturing stress.

PubMed

Elzobair, Khalid A; Stromberger, Mary E; Ippolito, James A

2016-01-01

Stabilizing extracellular enzymes may maintain enzymatic activity while protecting enzymes from proteolysis and denaturation. A study determined whether a fast pyrolysis hardwood biochar (CQuest™) would reduce evaporative losses, subsequently stabilizing soil extracellular enzymes and prohibiting potential enzymatic activity loss following a denaturing stress (microwaving). Soil was incubated in the presence of biochar (0%, 1%, 2%, 5%, or 10% by wt.) for 36 days and then exposed to microwave energies (0, 400, 800, 1600, or 3200 J g(-1) soil). Soil enzymes (β-glucosidase, β-d-cellobiosidase, N-acetyl-β-glucosaminidase, phosphatase, leucine aminopeptidase, β-xylosidase) were analyzed by fluorescence-based assays. Biochar amendment reduced leucine aminopeptidase and β-xylosidase potential activity after the incubation period and prior to stress exposure. The 10% biochar rate reduced soil water loss at the lowest stress level (400 J microwave energy g(-1) soil). Enzyme stabilization was demonstrated for β-xylosidase; intermediate biochar application rates prevented a complete loss of this enzyme's potential activity after soil was exposed to 400 (1% biochar treatment) or 1600 (5% biochar treatment) J microwave energy g(-1) soil. Remaining enzyme potential activities were not affected by biochar, and activities decreased with increasing stress levels. We concluded that biochar has the potential to reduce evaporative soil water losses and stabilize certain extracellular enzymes where activity is maintained after a denaturing stress; this effect was biochar rate and enzyme dependent. While biochar may reduce the potential activity of certain soil extracellular enzymes, this phenomenon was not universal as the majority of enzymes assayed in this study were unaffected by exposure to biochar. Copyright © 2015 Elsevier Ltd. All rights reserved.

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.

Sustainable land management practices as providers of several ecosystem services under rainfed Mediterranean agroecosystems

NASA Astrophysics Data System (ADS)

Almagro, María; de Vente, Joris; Boix-Fayós, Carolina; García-Franco, Noelia; Melgares de Aguilar, Javier; González, David; Solé-Benet, Albert; Martínez-Mena, María

2015-04-01

Little is known about the multiple impacts of sustainable land management practices on soil and water conservation, carbon sequestration, mitigation of global warming, and crop yield productivity in semiarid Mediterranean agroecosystems. We hypothesized that a shift from intensive tillage to more conservative tillage management practices (reduced tillage optionally combined with green manure) leads to an improvement in soil structure and quality and will reduce soil erosion and enhance carbon sequestration in semiarid Mediterranean rainfed agroecosystems. To test the hypothesis, we assessed the effects of different tillage treatments (conventional (CT), reduced (RT), reduced tillage combined with green manure (RTG), and no tillage (NT)) on soil structure and soil water content, runoff and erosion control, soil CO2 emissions, crop yield and carbon sequestration in two semiarid agroecosystems with organic rainfed almond in the Murcia Region southeast Spain). It was found that reduction and suppression of tillage under almonds led to an increase in soil water content in both agroecosystems. Crop yields ranged from 775 to 1766 kg ha-1 between tillage 18 treatments, but we did not find a clear relation between soil water content and crop yield. RT and RTG treatments showed lower soil erosion rates and higher crop yields of almonds than under CT treatment. Overall, higher soil organic carbon contents and aggregate stability were observed under RTG treatment than under RT or CT treatment. It is concluded that conversion from CT to RTG is suitable to increase carbon inputs without enhancing soil CO2 emissions in semiarid Mediterranean agroecosystems.

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.

Valorisation of Sugarcane Bagasse Ash in the Manufacture of Lime-Stabilized Blocks

NASA Astrophysics Data System (ADS)

James, Jijo; Pandian, Pitchai Kasinatha

2016-06-01

The study investigated the potential of lime in the manufacture of stabilized soil blocks and the valorisation of a solid waste, Bagasse Ash (BA), in its manufacture. A locally available soil was collected from a field and characterized in the soil laboratory as a clay of intermediate plasticity. This soil was stabilized using lime, the quantity of which was determined from the Eades and Grim pH test. The soil was stabilized using this lime content, amended with various BA contents during mixing, and moulded into blocks of 19 cm x 9 cm x 9 cm. The blocks were then moist cured for a period of 28 days, following which they were subjected to compressive strength, water absorption and efflorescence tests. The results of the tests revealed that the addition of BA resulted in enhanced compressive strength of the blocks, increased the water absorption marginally, and resulted in no efflorescence in any of the combinations, although the limited combinations in the study could not produce enough strength to meet the specifications of the Bureau of Indian Standards. The study revealed that BA can be effectively valorised in the manufacture of stabilized soil blocks.

Characterizing Feedback Control Mechanisms in Nonlinear Microbial Models of Soil Organic Matter Decomposition by Stability Analysis

NASA Astrophysics Data System (ADS)

Georgiou, K.; Tang, J.; Riley, W. J.; Torn, M. S.

2014-12-01

Soil organic matter (SOM) decomposition is regulated by biotic and abiotic processes. Feedback interactions between such processes may act to dampen oscillatory responses to perturbations from equilibrium. Indeed, although biological oscillations have been observed in small-scale laboratory incubations, the overlying behavior at the plot-scale exhibits a relatively stable response to disturbances in input rates and temperature. Recent studies have demonstrated the ability of microbial models to capture nonlinear feedbacks in SOM decomposition that linear Century-type models are unable to reproduce, such as soil priming in response to increased carbon input. However, these microbial models often exhibit strong oscillatory behavior that is deemed unrealistic. The inherently nonlinear dynamics of SOM decomposition have important implications for global climate-carbon and carbon-concentration feedbacks. It is therefore imperative to represent these dynamics in Earth System Models (ESMs) by introducing sub-models that accurately represent microbial and abiotic processes. In the present study we explore, both analytically and numerically, four microbe-enabled model structures of varying levels of complexity. The most complex model combines microbial physiology, a non-linear mineral sorption isotherm, and enzyme dynamics. Based on detailed stability analysis of the nonlinear dynamics, we calculate the system modes as functions of model parameters. This dependence provides insight into the source of state oscillations. We find that feedback mechanisms that emerge from careful representation of enzyme and mineral interactions, with parameter values in a prescribed range, are critical for both maintaining system stability and capturing realistic responses to disturbances. Corroborating and expanding upon the results of recent studies, we explain the emergence of oscillatory responses and discuss the appropriate microbe-enabled model structure for inclusion in ESMs.

Structure and reactivity of ferrihydrite-soil organic carbon-calcium ternary complexes

NASA Astrophysics Data System (ADS)

Yang, Y.; Adhikari, D.; Sowers, T.; Stuckey, J.; Poulson, S.; Sparks, D. L.

2017-12-01

Complete understanding about the interactions between soil organic carbon (SOC) and minerals is important for predicting the stability of SOC and its response to climate change. Recent studies have shown the importance of calcium (Ca)-bearing minerals and iron (Fe) oxide in associating with and stabilizing SOC. In this study, we have investigated the formation and reactivity of ferrihydrite-SOC-Ca ternary complexes. During the co-precipitation of ferrihydrite with SOC in the presence of Ca2+, 60% of SOC can be co-precipitated with ferrihydrite at a C/Fe (molar ratio) of up to 10, whereas the Ca/Fe ratio was saturated at 0.2. Increasing amount of Ca2+ did not affect the co-precipitation of SOC with ferrihydrite or the lability of ferrihydrite-bound SOC. In addition, microbial reduction of ferrihydrite and reductive release of ferrihydrite-bound SOC were not influenced by the presence of Ca, but the pathway for Fe mineral transformation during the reduction was affected by Ca. In the meantime, Fe reduction selectively released carboxylic-enriched SOC. As a comparison, the presence of SOC increased the incorporation of Ca into the structure of ferrihydrite. Our results indicate the formation of ferrihydrite-SOC-Ca complexes, with organic carbon bridging the ferrihydrite and Ca. Such ternary complexes potentially play an important role in regulating the interactions between SOC and mineral phases in soil.

Stabilize lead and cadmium in contaminated soils using hydroxyapatite and potassium chloride.

PubMed

Wang, Li; Li, Yonghua; Li, Hairong; Liao, Xiaoyong; Wei, Binggan; Ye, Bixiong; Zhang, Fengying; Yang, Linsheng; Wang, Wuyi; Krafft, Thomas

2014-12-01

Combination of hydroxyapatite (HAP) and potassium chloride (KCl) was used to stabilize lead and cadmium in contaminated mining soils. Pot experiments of chilli (Capsicum annuum) and rape (Brassica rapachinensis) were used to evaluate the stabilization efficiency. The results were the following: (1) the optimal combination decreased the leachable lead by 83.3 and 97.27 %, and decreased leachable cadmium by 57.82 and 35.96% for soil HF1 and soil HF2, respectively; (2) the total lead and cadmium concentrations in both plants decreased 69 and 44 %, respectively; (3) The total lead and cadmium concentrations in the edible parts of both vegetables also decreased significantly. This study reflected that potassium chloride can improve the stabilization efficiency of hydroxyapatite, and the combination of hydroxyapatite and potassium chloride can be effectively used to remediate lead and cadmium contaminated mining soil.

TECHNOLOGY EVALUATION REPORT: SILICATE TECHNOLOGY CORPORATION - SOLIDIFICATION/STABILIZATION OF PCP AND INORGANIC CONTAMINANTS IN SOILS - SELMA, CA

EPA Science Inventory

This Technolgy Evaluation Report evaluates the solidification/stabilization process of Silicate Technology Corporation (STC) for the on-site treatment of contaminated soil The STC immobilization technology uses a proprietary product (FMS Silicate) to chemically stabilize and ...

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.

Annual Removal of Aboveground Plant Biomass Alters Soil Microbial Responses to Warming

PubMed Central

Xue, Kai; Yuan, Mengting M.; Xie, Jianping; Li, Dejun; Qin, Yujia; Wu, Liyou; Deng, Ye; He, Zhili; Van Nostrand, Joy D.; Luo, Yiqi; Tiedje, James M.

2016-01-01

ABSTRACT Clipping (i.e., harvesting aboveground plant biomass) is common in agriculture and for bioenergy production. However, microbial responses to clipping in the context of climate warming are poorly understood. We investigated the interactive effects of grassland warming and clipping on soil properties and plant and microbial communities, in particular, on microbial functional genes. Clipping alone did not change the plant biomass production, but warming and clipping combined increased the C4 peak biomass by 47% and belowground net primary production by 110%. Clipping alone and in combination with warming decreased the soil carbon input from litter by 81% and 75%, respectively. With less carbon input, the abundances of genes involved in degrading relatively recalcitrant carbon increased by 38% to 137% in response to either clipping or the combined treatment, which could weaken long-term soil carbon stability and trigger positive feedback with respect to warming. Clipping alone also increased the abundance of genes for nitrogen fixation, mineralization, and denitrification by 32% to 39%. Such potentially stimulated nitrogen fixation could help compensate for the 20% decline in soil ammonium levels caused by clipping alone and could contribute to unchanged plant biomass levels. Moreover, clipping tended to interact antagonistically with warming, especially with respect to effects on nitrogen cycling genes, demonstrating that single-factor studies cannot predict multifactorial changes. These results revealed that clipping alone or in combination with warming altered soil and plant properties as well as the abundance and structure of soil microbial functional genes. Aboveground biomass removal for biofuel production needs to be reconsidered, as the long-term soil carbon stability may be weakened. PMID:27677789

The synergetic effect of moisture protection, substrate quality and biotic acclimation on soil organic carbon persistence along a cultivated loamy hillslope

NASA Astrophysics Data System (ADS)

Wiaux, François; Vanclooster, Marnik; Cornelis, Jean-Thomas; Van Oost, Kristof

2014-05-01

The combination of hydrologic, geomorphic and biogeochemical approaches is required to determine organic carbon (OC) persistence and dynamics within landscapes. Here, we used soil in-situ surface heterotrophic respiration measurement as an indicator of OC persistence along a hillslope (crop field on the loess belt under temperate climate), characterized by an important erosion-induced OC stock colluvium downslope. Along this topographical gradient, we quantified the space-time structure of soil water and temperature, and soil OC amount and quality (from a chemical point of view based on NaOCl oxidation) in relation to CO2 fluxes. We used a Generalized Least Square (GLS) regression model to identify the role of each abiotic factor as well as their interactions on observed soil respiration rates, and to calculate time-average values of these CO2 fluxes at each studied slope positions. We observed significant differences between the observed respiration rates along the topographical gradient (up to 30% more CO2 emissions downslope and 50% backslope, relative to un-eroded summit position). Despite mean CO2 fluxes (standardized at 15°C) at the bottom of the slope are significantly higher (p<0.05) than at the top of the hillslope, this difference is lower than expected given the high OC stock found downslope (c.2 times higher than at the summit position). In the cultivated loamy hillslope, the soil OC persistence is mainly controlled by the stabilizing effect of the high moisture content, implying large amount of OC. This provides evidence that soil OC dynamic (sink or source) can be mainly governed by site-specific abiotic conditions (e.g. soil moisture). On the other hand, OC found downslope was showed to be especially vulnerable for OC mineralization (it would emit 26% to c.40% more CO2 in case of temperature increase), due to both (i) improved efficiency of soil-micro-organisms in stabilizing conditions, and (ii) high quality of OC stock (easy to decompose for soil micro-organisms). This leads to consider erosion-induced OC stocks in downslope colluviums as "delayed bombs", which may be reconnected to the atmosphere if the current stabilizing conditions of this specific pedo-climatic ecosystem would be changed.

Stabilization of enzymatically polymerized phenolic chemicals in a model soil organic matter-free geomaterial.

PubMed

Palomo, Mónica; Bhandari, Alok

2012-01-01

A variety of remediation methods, including contaminant transformation by peroxidase-mediated oxidative polymerization, have been proposed to manage soils and groundwater contaminated with chlorinated phenols. Phenol stabilization has been successfully observed during cross polymerization between phenolic polymers and soil organic matter (SOM) for soils with SOM >3%. This study evaluates peroxidase-mediated transformation and removal of 2,4-dichlorophenol (DCP) from an aqueous phase in contact with a natural geomaterial modified to contain negligible (<0.3%) SOM. The results are compared with those for soils with higher SOM. The SOM-free sorbent was generated by removing SOM using a NaOCl oxidation. When horseradish peroxidase (HRP) was used to induce polymerization of DCP, the soil-water phase distribution relationship (PDR) of DCP polymerization products (DPP) was complete within 1 d and PDRs did not significantly change over the 28 d of study. The conversion of DCP to DPP was close to 95% efficient. Extractable solute consisted entirely of DPP with 5% or less of unreacted DCP. The aqueous extractability of DPP from SOM-free geomaterial decreased at longer contact times and at smaller residual aqueous concentrations of DPP. DCP stabilization appeared to have resulted from a combination of sorption, precipitation, and ligand exchange between oligomeric products and the exposed mineral surfaces. Modification of the mineral surface through coverage with DPP enhanced the time-dependent retention of the oligomers. DPP stabilization in SOM-free geomaterial was comparable with that reported in the literature with soil containing SOM contents >1%. Results from this study suggest that the effectiveness of HRP-mediated stabilization of phenolic compounds not only depends on the cross-coupling with SOM, but also on the modification of the surface of the sorbent that can augment affinity with oligomers and enhance stabilization. Coverage of the mineral surface by phenolic oligomers may be analogous to SOM that can potentially sorb other xenobiotics. HRP- mediated reactions can be used to stabilize DCP associated with low SOM mineral soils or aquifer media, thereby restricting the transport of phenolic contaminants in the soil environment. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

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.

Field and lab evaluation of the use of lime fly ash to replace soil cement as a base course : final report.

DOT National Transportation Integrated Search

1997-09-01

This study evaluates the performance of lime/fly ash stabilized base as an alternative to soil cement stabilized base for flexible pavement systems on reconstructed highways in Louisiana. Louisiana has historically used soil cement for most flexible ...

Long term stability of microbial diversity and activity potential in severely disturbed arid lands of the southwest

USDA-ARS?s Scientific Manuscript database

Arid land cryptobiotic soil crusts govern water infiltration, soil aggregate stability and nutrient cycling between soil microbial communities and vascular plants. Surface mining involves removal of topsoil and associated crust and storage in mixed mounds for extended periods. The exposed subsoil an...

Identification and stabilization methods for problematic silt soils : a laboratory evaluation of modification and stabilization additives.

DOT National Transportation Integrated Search

2003-07-01

The instability and pumping response of non-plastic, high silt (and fine sand) soils was investigated. Common reagents, i.e., lime, lime-fly ash, Portland cement, and slag cement were included as admixtures with three high silt (and fine sand) soils....

Tree diversity and species identity effects on soil fungi, protists and animals are context dependent

PubMed Central

Tedersoo, Leho; Bahram, Mohammad; Cajthaml, Tomáš; Põlme, Sergei; Hiiesalu, Indrek; Anslan, Sten; Harend, Helery; Buegger, Franz; Pritsch, Karin; Koricheva, Julia; Abarenkov, Kessy

2016-01-01

Plant species richness and the presence of certain influential species (sampling effect) drive the stability and functionality of ecosystems as well as primary production and biomass of consumers. However, little is known about these floristic effects on richness and community composition of soil biota in forest habitats owing to methodological constraints. We developed a DNA metabarcoding approach to identify the major eukaryote groups directly from soil with roughly species-level resolution. Using this method, we examined the effects of tree diversity and individual tree species on soil microbial biomass and taxonomic richness of soil biota in two experimental study systems in Finland and Estonia and accounted for edaphic variables and spatial autocorrelation. Our analyses revealed that the effects of tree diversity and individual species on soil biota are largely context dependent. Multiple regression and structural equation modelling suggested that biomass, soil pH, nutrients and tree species directly affect richness of different taxonomic groups. The community composition of most soil organisms was strongly correlated due to similar response to environmental predictors rather than causal relationships. On a local scale, soil resources and tree species have stronger effect on diversity of soil biota than tree species richness per se. PMID:26172210

Tree diversity and species identity effects on soil fungi, protists and animals are context dependent.

PubMed

Tedersoo, Leho; Bahram, Mohammad; Cajthaml, Tomáš; Põlme, Sergei; Hiiesalu, Indrek; Anslan, Sten; Harend, Helery; Buegger, Franz; Pritsch, Karin; Koricheva, Julia; Abarenkov, Kessy

2016-02-01

Plant species richness and the presence of certain influential species (sampling effect) drive the stability and functionality of ecosystems as well as primary production and biomass of consumers. However, little is known about these floristic effects on richness and community composition of soil biota in forest habitats owing to methodological constraints. We developed a DNA metabarcoding approach to identify the major eukaryote groups directly from soil with roughly species-level resolution. Using this method, we examined the effects of tree diversity and individual tree species on soil microbial biomass and taxonomic richness of soil biota in two experimental study systems in Finland and Estonia and accounted for edaphic variables and spatial autocorrelation. Our analyses revealed that the effects of tree diversity and individual species on soil biota are largely context dependent. Multiple regression and structural equation modelling suggested that biomass, soil pH, nutrients and tree species directly affect richness of different taxonomic groups. The community composition of most soil organisms was strongly correlated due to similar response to environmental predictors rather than causal relationships. On a local scale, soil resources and tree species have stronger effect on diversity of soil biota than tree species richness per se.

[Recent advance in solidification/stabilization technology for the remediation of heavy metals-contaminated soil].

PubMed

Hao, Han-zhou; Chen, Tong-bin; Jin, Meng-gui; Lei, Mei; Liu, Cheng-wu; Zu, Wen-pu; Huang, Li-mi

2011-03-01

Remediation of heavy metals-contaminated soil is still a difficulty and a hotspot of international research projects. At present, the technologies commonly adopted for the remediation of contaminated sites mainly include excavation, solidification/stabilization (S/S), soil washing, soil vapor extraction (SVE), thermal treatment, and bioremediation. Based on the S/S technical guidelines of Unite State Environmental Protection Agency (EPA) and United Kingdom Environment Agency (EA) and the domestic and foreign patents, this paper introduced the concepts of S/S and its development status at home and abroad, and discussed its future development directions. Solidification refers to a process that binds contaminated media with a reagent, changing the media's physical properties via increasing its compressive strength, decreasing its permeability, and encapsulating the contaminants to form a solid material. Stabilization refers to the process that involves a chemical reaction which reduces the leachability of a waste, chemically immobilizes the waste and reduces its solubility, making the waste become less harmful or less mobile. S/S technology includes cement solidification, lime pozzolanic solidification, plastic materials stabilization, vitrification, and regent-based stabilization. Stabilization (or immobilization) treatment processes convert contaminants to less mobile forms through chemical or thermal interactions. In stabilization technology, the aim of adding agents is to change the soil physical and chemical properties through pH control technology, redox potential technology, precipitation techniques, adsorption technology, and ion-exchange technology that change the existing forms of heavy metals in soil, and thus, reduce the heavy metals bioavailability and mobility. This review also discussed the S/S evaluation methods, highlighted the need to enhance S/S technology in the molecular bonding, soil polymers, and formulation of China's S/S technical guidelines.

Achievements and opportunities from ESF Research Networking Programme: Natural molecular structures as drivers and tracers of terrestrial C fluxes, and COST Action 639: Greenhouse gas budget of soils under changing climate and land use

NASA Astrophysics Data System (ADS)

Boeckx, P.; Rasse, D.; Jandl, R.

2009-04-01

One of the activities of the European Science Foundation (ESF, www.esf.org) is developing European scale Research Networking Programmes (RNPs). RNPs lay the foundation for nationally funded research groups to address major scientific and research infrastructure issues, in order to advance the frontiers of existing science. MOLTER (www.esf.org/molter or www.molter.no) is such an RNP. MOLTER stands for "Natural molecular structures as drivers and tracers of terrestrial C fluxes" aims at stimulating the use of isotopic and organic chemistry to study carbon stabilization and biogeochemistry in terrestrial ecosystems and soils in particular. The understanding of the formation, stabilization and decomposition of complex organic compounds in the environment is currently being revolutionized by advanced techniques in identification, quantification, and origin tracing of functional groups and individual molecules. MOLTER focuses on five major research themes: - Molecular composition and turnover time of soil organic matter; - Plant molecular structures as drivers of C stabilisation in soils; - Fire transformations of plant and soil molecular structures - Molecular markers in soils; - Dissolved organic molecules in soils: origin, functionality and transport. These research themes are covered via the following activities: - Organisation of international conferences; - Organisation of specific topical workshops; - Organisation of summer schools for PhD students; - Short- and long-term exchange grants for scientists. MOLTER is supported by research funding or performing agencies from Austria, Belgium, France, Germany, the Netherlands, Norway, Romania, Spain, Sweden, Switzerland and the United Kingdom. The ESF is also the implementing agency of COST (European Cooperation in Science and Technology, www.cost.esf.org), one of the longest-running European instruments supporting cooperation among scientists and researchers across Europe. COST Action 639 "Greenhouse gas budget of soils under changing climate and land use" (BurnOut) (www.cost.esf.org/domains_actions/essem/Actions/changing_climate or bfw.ac.at/rz/bfwcms.web?dok=5906) BurnOut aims at improving the management of greenhouse gas emissions from European soils under different regimes of ecosystem disturbances and land-use change. This will allow the identification of soil and site conditions (hot spots) that are vulnerable to greenhouse gas emissions. The specific objectives are: - Identification of hot spots of greenhouse gas emissions from soils; - Identification of soil and site conditions that are vulnerable to GHG emissions; - Development of an advanced greenhouse gas reporting concept across different of land forms, land use and land use changes; - Communication of policy relevant GHG reporting concepts; Burnout covers the following activities: - Organisation of specific topical workshops; - Short-term scientific visits for scientists. Participating countries in BurnOut are: Austria, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, Finland, Germany, Greece, Hungary, Ireland, Israel, Italy, Lithuania, Netherlands, Norway, Portugal, Romania, Slovak Republic, Slovenia, Spain, Spain, Sweden, Switzerland, Turkey, United Kingdom, Russian Federation, and Bosnia Herzegovina. During this oral presentation, possible lines of cooperation, opportunities and recent achievements will be exemplified and the audience will be invited to contribute their views on these initiatives.

Integrating plant litter quality, soil organic matter stabilization, and the carbon saturation concept

USDA-ARS?s Scientific Manuscript database

Recent research suggests labile plant litters promote the stabilization of soil organic matter (SOM) in physico-chemically protected fractions with relatively slow turnover. However, the effect of litter quality on SOM stabilization is inconsistent. Labile, ‘high quality’ litters characterized by hi...

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...

[Stabilization Treatment of Pb and Zn in Contaminated Soils and Mechanism Studies].

PubMed

Xie, Wei-qiang; Li, Xiao-mingi; Chen, Can; Chen, Xun-feng; Zhong, Yu; Zhong, Zhen-yu; Wan, Yong; Wang, Yan

2015-12-01

In the present work, the combined application of potassium dihydrogen phosphate, quick lime and potassium chloride was used to immobilize the Pb and Zn in contaminated soils. The efficiency of the process was evaluated through leaching tests and Tessier sequential extraction procedure. The mechanism of stabilization was analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) to reveal the mechanism of stabilization. The results showed that the stabilizing efficiency of Pb contaminated soils was above 80% and the leaching concentrations of Pb, Zn were far below the threshold when the ratio of exogenous P and soil (mol · mol⁻¹) was 2:1-4: 1, the dosing ratio of CaO was 0.1%-0.5% ( mass fraction) and the dosage of potassium chloride was 0.02-0. 04 mol. Meanwhile, Pb and Zn in soil were transformed from the exchangeable fraction into residual fraction, which implied that the migration of Pb, Zn in soil could be confined by the stabilization treatment. XRD and SEM analysis revealed that Ca-P-Pb precipitation, lead orthophosphate [PbHP0₄, Pb₃ (PO₄)₂], pyromorphite (Pb-PO₄-Cl/OH) and mixed heavy metal deposits (Fe-PO₄- Ca-Pb-Zn-OH) could be formed after solidification/stabilization in which Pb and Zn could be wrapped up to form a solidified composition and to prevent leaching.

Stabilization of the As-contaminated soil from the metal mining areas in Korea.

PubMed

Ko, Myoung-Soo; Kim, Ju-Yong; Bang, Sunbeak; Lee, Jin-Soo; Ko, Ju-In; Kim, Kyoung-Woong

2012-01-01

The stabilization efficiencies of arsenic (As) in contaminated soil were evaluated using various additives such as limestone, steel mill slag, granular ferric hydroxide (GFH), and mine sludge collected from an acid mine drainage treatment system. The soil samples were collected from the Chungyang area, where abandoned Au-Ag mines are located. Toxicity characteristic leaching procedure, synthetic precipitation leaching procedure, sequential extraction analysis, aqua regia digestion, cation exchange capacity, loss on ignition, and particle size distribution were conducted to assess the physical and chemical characteristics of highly arsenic-contaminated soils. The total concentrations of arsenic in the Chungyang area soil ranged up to 145 mg/kg. After the stabilization tests, the removal percentages of dissolved As(III) and As(V) were found to differ from the additives employed. Approximately 80 and 40% of the As(V) and As(III), respectively, were removed with the use of steel mill slag. The addition of limestone had a lesser effect on the removal of arsenic from solution. However, more than 99% of arsenic was removed from solution within 24 h when using GFH and mine sludge, with similar results observed when the contaminated soils were stabilized using GFH and mine sludge. These results suggested that GFH and mine sludge may play a significant role on the arsenic stabilization. Moreover, this result showed that mine sludge can be used as a suitable additive for the stabilization of arsenic.

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.

Using three-dimensional plant root architecture in models of shallow-slope stability.

PubMed

Danjon, Frédéric; Barker, David H; Drexhage, Michael; Stokes, Alexia

2008-05-01

The contribution of vegetation to shallow-slope stability is of major importance in landslide-prone regions. However, existing slope stability models use only limited plant root architectural parameters. This study aims to provide a chain of tools useful for determining the contribution of tree roots to soil reinforcement. Three-dimensional digitizing in situ was used to obtain accurate root system architecture data for mature Quercus alba in two forest stands. These data were used as input to tools developed, which analyse the spatial position of roots, topology and geometry. The contribution of roots to soil reinforcement was determined by calculating additional soil cohesion using the limit equilibrium model, and the factor of safety (FOS) using an existing slope stability model, Slip4Ex. Existing models may incorrectly estimate the additional soil cohesion provided by roots, as the spatial position of roots crossing the potential slip surface is usually not taken into account. However, most soil reinforcement by roots occurs close to the tree stem and is negligible at a distance >1.0 m from the tree, and therefore global values of FOS for a slope do not take into account local slippage along the slope. Within a forest stand on a landslide-prone slope, soil fixation by roots can be minimal between uniform rows of trees, leading to local soil slippage. Therefore, staggered rows of trees would improve overall slope stability, as trees would arrest the downward movement of soil. The chain of tools consisting of both software (free for non-commercial use) and functions available from the first author will enable a more accurate description and use of root architectural parameters in standard slope stability analyses.

Using Three-dimensional Plant Root Architecture in Models of Shallow-slope Stability

PubMed Central

Danjon, Frédéric; Barker, David H.; Drexhage, Michael; Stokes, Alexia

2008-01-01

Background The contribution of vegetation to shallow-slope stability is of major importance in landslide-prone regions. However, existing slope stability models use only limited plant root architectural parameters. This study aims to provide a chain of tools useful for determining the contribution of tree roots to soil reinforcement. Methods Three-dimensional digitizing in situ was used to obtain accurate root system architecture data for mature Quercus alba in two forest stands. These data were used as input to tools developed, which analyse the spatial position of roots, topology and geometry. The contribution of roots to soil reinforcement was determined by calculating additional soil cohesion using the limit equilibrium model, and the factor of safety (FOS) using an existing slope stability model, Slip4Ex. Key Results Existing models may incorrectly estimate the additional soil cohesion provided by roots, as the spatial position of roots crossing the potential slip surface is usually not taken into account. However, most soil reinforcement by roots occurs close to the tree stem and is negligible at a distance >1·0 m from the tree, and therefore global values of FOS for a slope do not take into account local slippage along the slope. Conclusions Within a forest stand on a landslide-prone slope, soil fixation by roots can be minimal between uniform rows of trees, leading to local soil slippage. Therefore, staggered rows of trees would improve overall slope stability, as trees would arrest the downward movement of soil. The chain of tools consisting of both software (free for non-commercial use) and functions available from the first author will enable a more accurate description and use of root architectural parameters in standard slope stability analyses. PMID:17766845

Effects of plastic mulches and high tunnel raspberry production systems on soil physicochemical quality indicators

NASA Astrophysics Data System (ADS)

Domagała-Świątkiewicz, Iwona; Siwek, Piotr

2018-01-01

In horticulture, degradable materials are desirable alternatives to plastic films. Our aim was to study the impact of soil plastic mulching on the soil properties in the high tunnel and open field production systems of raspberry. The raised beds were mulched with a polypropylene non-woven and two degradable mulches: polypropylene with a photodegradant and non-woven polylactide. The results indicated that the system of raspberry production, as well as the type of mulching had significant impact on soil organic carbon stock, moisture content and water stable aggregate amount. Soils taken from the open field system had a lower bulk density and water stability aggregation index, but higher organic carbon and capillary water content as compared to soils collected from high tunnel conditions. In comparison with the open field system, soil salinity was also found to be higher in high tunnel, as well as with higher P, Mg, Ca, S, Na and B content. Furthermore, mulch covered soils had more organic carbon amount than the bare soils. Soil mulching also enhanced the water capacity expressed as a volume of capillary water content. In addition, mulching improved the soil structure in relation to the bare soil, in particular, in open field conditions. The impact of the compared mulches on soil quality indicators was similar.

Clay stabilization by using gypsum and paddy husk ash with reference to UCT and CBR value

NASA Astrophysics Data System (ADS)

Roesyanto; Iskandar, R.; Hastuty, I. P.; Dianty, W. O.

2018-02-01

Clays that have low shear strength need to be stabilized in order to meet the technical requirements to serve as a subgrade material. One of the usual soil stabilization methods is by adding chemicals such as Portland cement, lime, and bitumen. The clay stabilization research was done by adding gypsum and paddy husk ash. The research goals were to find out the value of engineering properties of clay due to the addition of 2% gypsum and 2% - 15% paddy husk ash. The soil was classified as Clay - Low Plasticity (CL) based on USCS and was classified as A-7-6 (10) based on AASHTO classification system. The UCT value of original soil was 1.41 kg/cm2. While the CBR soaked and unsoaked values of original soil were 4.41% and 6.23% respectively. The research results showed the addition of paddy husk ash decreased the value of unconfined compressive strength as well as CBR. The stabilized soil by 2% gypsum and 0% paddy husk ash gave maximum UCT value of 1.67 kg/cm2, while the maximum value of CBR were found 6.71% for CBR soaked and 8.00% for CBR unsoaked. The addition of paddy husk ash did not alter the soil classification according to AASHTO or USCS, even degrade the engineering properties of original soil.

Using foamed asphalt as a stabilizing agent in full depth reclamation of Route 8 in Belgrade.

DOT National Transportation Integrated Search

2002-02-01

Maine has a variety of soil types throughout the state. Most of these soil types degrade rapidly and have : poor stability. To eliminate the cost of supplying quality road base material from a distant source and : increase the stability of existing s...

Soil recycling paves the way for treating brownfields

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

Gladdys, R.

A soil recycling and stabilization process allows once-contaminated soil to be incorporated into paving materials. Contaminated soils is more widespread than often realized, with one of the more common sources being petroleum products such as fuel oil and gasoline. Until recently, the conventional solution was to have the material excavated, separated from remining soil and trucked to a hazardous waste landfill. This article describes an alternative approach under the following topics: move the solution, not the problem; on site recycling; heavy metals stabilization; economics.

Clay Stabilization Using the Ash of Mount Sinabung in Terms of the Value of California Bearing Ratio (CBR)

NASA Astrophysics Data System (ADS)

Hastuty, I. P.; Roesyanto, R.; Napitupulu, S. M. A.

2018-02-01

Most areas in Indonesia consist of clay soils with high plasticity so that to meet technical requirements the soil needs improvement, which is known as soil stabilization.There are three ways of soil stabilization process, i.e. mechanical, physical and chemical. In this study, chemical stabilization was performed, that was by adding stabilizing agents to the soil. The stabilizing agent used was the ash of Mount Sinabung. Since 2010 until now, Sinabung Mountain is still experiencing eruption that produces a lot of volcanic ash and it inconveniences the environment. So, it is expected that this research will be able to optimize the utilization of Sinabung ash. The purpose of this study was to investigate the effect of the addition of Mount Sinabung ash to CBR (California Bearing Ratio) value, to determine the effect of the curing time of one day and fourteen days mixture on the CBR value, and to find the mixed content with effective curing time to produce the largest CBR value. Based on this study, the soil type CL (Clay - Low Plasticity) was obtained, based on the classification of USCS (Unified Soil Classification System) and categorized as A-6 (6) based on the classification of AASHTO (American Association of State Highway and Transportation officials) with the most effective mixed stabilizer material which was the variation of 10% Mount Sinabung ash with fourteen days of curing time. The CBR value resulted from the mixture of 10% Sinabung ash that was cured within fourteen days was 8.95%. By the increase of the content of the Sinabung ash, the CBR value always improved to the level of 10%, Sinabung ash then decreased and became constant at the mixture of higher volcanic ash mixture but remained above the CBR value of the original soil.

Modeling of Heavy Metal Transformation in Soil Ecosystem

NASA Astrophysics Data System (ADS)

Kalinichenko, Kira; Nikovskaya, Galina N.

2017-04-01

The intensification of industrial activity leads to an increase in heavy metals pollution of soils. In our opinion, sludge from biological treatment of municipal waste water, stabilized under aerobic-anaerobic conditions (commonly known as biosolid), may be considered as concentrate of natural soil. In their chemical, physical and chemical and biological properties these systems are similar gel-like nanocomposites. These contain microorganisms, humic substances, clay, clusters of nanoparticles of heavy metal compounds, and so on involved into heteropolysaccharides matrix. It is known that microorganisms play an important role in the transformation of different nature substances in soil and its health maintenance. The regularities of transformation of heavy metal compounds in soil ecosystem were studied at the model of biosolid. At biosolid swelling its structure changing (gel-sol transition, weakening of coagulation contacts between metal containing nanoparticles, microbial cells and metabolites, loosening and even destroying of the nanocomposite structure) can occur [1, 2]. The promotion of the sludge heterotrophic microbial activities leads to solubilization of heavy metal compounds in the system. The microbiological process can be realized in alcaligeneous or acidogeneous regimes in dependence on the type of carbon source and followed by the synthesis of metabolites with the properties of flocculants and heavy metals extragents [3]. In this case the heavy metals solubilization (bioleaching) in the form of nanoparticles of hydroxycarbonate complexes or water soluble complexes with oxycarbonic acids is observed. Under the action of biosolid microorganisms the heavy metals-oxycarbonic acids complexes can be transformed (catabolised) into nano-sizing heavy metals- hydroxycarbonates complexes. These ecologically friendly complexes and microbial heteropolysaccharides are able to interact with soil colloids, stay in the top soil profile, and improve soil structure due to the formation of water-stable aggregates. The alkaligeneous microbiological process in natural ecosystems by co-metabolism of appropriate carbon source is more advantages for environment. Thus the possibility of solubilization of heavy metal compounds in the soil due to stimulating its biological activities of native microorganisms is proved. The studies on the interactions in the system of sludge solid has allowed to develop the "green" biotechnological process of heavy metals solubilization in contaminated soils and sludges. 1. Kalinichenko KV, Nikovskaya GN, and Ulberg ZR (2012) Bioextraction of heavy metals from colloidal sludge systems. Colloid Journ. 74(5) : 553-557. 2. Kalinichenko KV, Nikovskaya GN, and Ulberg ZR (2013) Changes in the surface properties and stability of biocolloids of a sludge system upon extraction of heavy metals. Colloid Journ. 75(3) : 274-278. 3. Nikovskaya GN, Kalinichenko KV (2013) Bioleaching of heavy metals from sludge after biological treatment of municipal effluent. Journ. of Water Chem. and Techn. 35(2) : 80-85.

Rice (Oryza sativa L) plantation affects the stability of biochar in paddy soil.

PubMed

Wu, Mengxiong; Feng, Qibo; Sun, Xue; Wang, Hailong; Gielen, Gerty; Wu, Weixiang

2015-05-05

Conversion of rice straw into biochar for soil amendment appears to be a promising method to increase long-term carbon sequestration and reduce greenhouse gas (GHG) emissions. The stability of biochar in paddy soil, which is the major determining factor of carbon sequestration effect, depends mainly on soil properties and plant functions. However, the influence of plants on biochar stability in paddy soil remains unclear. In this study, bulk and surface characteristics of the biochars incubated without rice plants were compared with those incubated with rice plants using a suite of analytical techniques. Results showed that although rice plants had no significant influence on the bulk characteristics and decomposition rates of the biochar, the surface oxidation of biochar particles was enhanced by rice plants. Using (13)C labeling we observed that rice plants could significantly increase carbon incorporation from biochar into soil microbial biomass. About 0.047% of the carbon in biochar was incorporated into the rice plants during the whole rice growing cycle. These results inferred that root exudates and transportation of biochar particles into rice plants might decrease the stability of biochar in paddy soil. Impact of plants should be considered when predicting carbon sequestration potential of biochar in soil systems.

Biological soil crusts exhibit a dynamic response to seasonal rain and release from grazing with implications for soil stability

USGS Publications Warehouse

Jimenez, Aguilar A.; Huber-Sannwald, E.; Belnap, J.; Smart, D.R.; Arredondo, Moreno J.T.

2009-01-01

In Northern Mexico, long-term grazing has substantially degraded semiarid landscapes. In semiarid systems, ecological and hydrological processes are strongly coupled by patchy plant distribution and biological soil crust (BSC) cover in plant-free interspaces. In this study, we asked: 1) how responsive are BSC cover/composition to a drying/wetting cycle and two-year grazing removal, and 2) what are the implications for soil erosion? We characterized BSC morphotypes and their influence on soil stability under grazed/non-grazed conditions during a dry and wet season. Light- and dark-colored cyanobacteria were dominant at the plant tussock and community level. Cover changes in these two groups differed after a rainy season and in response to grazing removal. Lichens with continuous thalli were more vulnerable to grazing than those with semi-continuous/discontinuous thalli after the dry season. Microsites around tussocks facilitated BSC colonization compared to interspaces. Lichen and cyanobacteria morphotypes differentially enhanced resistance to soil erosion; consequently, surface soil stability depends on the spatial distribution of BSC morphotypes, suggesting soil stability may be as dynamic as changes in the type of BSC cover. Longer-term spatially detailed studies are necessary to elicit spatiotemporal dynamics of BSC communities and their functional role in biotically and abiotically variable environments. ?? 2009 Elsevier Ltd.

Rice (Oryza sativa L) plantation affects the stability of biochar in paddy soil

PubMed Central

Wu, Mengxiong; Feng, Qibo; Sun, Xue; Wang, Hailong; Gielen, Gerty; Wu, Weixiang

2015-01-01

Conversion of rice straw into biochar for soil amendment appears to be a promising method to increase long-term carbon sequestration and reduce greenhouse gas (GHG) emissions. The stability of biochar in paddy soil, which is the major determining factor of carbon sequestration effect, depends mainly on soil properties and plant functions. However, the influence of plants on biochar stability in paddy soil remains unclear. In this study, bulk and surface characteristics of the biochars incubated without rice plants were compared with those incubated with rice plants using a suite of analytical techniques. Results showed that although rice plants had no significant influence on the bulk characteristics and decomposition rates of the biochar, the surface oxidation of biochar particles was enhanced by rice plants. Using 13C labeling we observed that rice plants could significantly increase carbon incorporation from biochar into soil microbial biomass. About 0.047% of the carbon in biochar was incorporated into the rice plants during the whole rice growing cycle. These results inferred that root exudates and transportation of biochar particles into rice plants might decrease the stability of biochar in paddy soil. Impact of plants should be considered when predicting carbon sequestration potential of biochar in soil systems. PMID:25944542

Bio-transformation and stabilization of arsenic (As) in contaminated soil using arsenic oxidizing bacteria and FeCl3 amendment.

PubMed

Karn, Santosh Kumar; Pan, Xiangliang; Jenkinson, Ian R

2017-05-01

A combination of biological and chemical methods was applied in the present study to evaluate the removal of arsenic (As) from contaminated soil. The treatment involved As-oxidizing microbes aimed of transforming the more toxic As (III) to less toxic As (V) in the soil. FeCl 3 was added at three different concentrations (1, 2, and 3%) to stabilize the As (V). Leaching of the treated soil was investigated by making a soil column and passing tap water through it to determine solubility. Experimental results indicated that the bacterial activity had a pronounced positive effect on the transformation of As, and decreased the soluble exchangeable fraction from 50 to 0.7 mg/kg as compared to control and from 50 to 44 mg/kg after 7 days of treatment. FeCl 3 also played an indispensable role in the adsorption/stabilization of As in the soil; 1 and 2% FeCl 3 strongly influenced the adsorption of As (V). The soil leachate contained negligible amount of As and trace metals, which indicates that combining an efficient microbe with a chemical treatment is very effective route for the removal and stabilization of As from contaminated soil in the environment.

Warming alters the energetic structure and function but not resilience of soil food webs

PubMed Central

Schwarz, Benjamin; Barnes, Andrew D.; Thakur, Madhav P.; Brose, Ulrich; Ciobanu, Marcel; Reich, Peter B.; Rich, Roy L.; Rosenbaum, Benjamin; Stefanski, Artur; Eisenhauer, Nico

2017-01-01

Climate warming is predicted to alter the structure, stability, and functioning of food webs1–5. Yet, despite the importance of soil food webs for energy and nutrient turnover in terrestrial ecosystems, warming effects on these food webs—particularly in combination with other global change drivers—are largely unknown. Here, we present results from two complementary field experiments testing the interactive effects of warming with forest canopy disturbance and drought on energy fluxes in boreal-temperate ecotonal forest soil food webs. The first experiment applied a simultaneous above- and belowground warming treatment (ambient, +1.7°C, +3.4°C) to closed canopy and recently clear-cut forest, simulating common forest disturbance6. The second experiment crossed warming with a summer drought treatment (-40% rainfall) in the clear-cut habitats. We show that warming reduces energy fluxes to microbes, while forest canopy disturbance and drought facilitates warming-induced increases in energy flux to higher trophic levels and exacerbates reductions in energy flux to microbes, respectively. Contrary to expectations, we find no change in whole-network resilience to perturbations, but significant losses of ecosystem functioning. Warming thus interacts with forest disturbance and drought, shaping the energetic structure of soil food webs and threatening the provisioning of multiple ecosystem functions in boreal-temperate ecotonal forests. PMID:29218059

Warming alters energetic structure and function but not resilience of soil food webs

NASA Astrophysics Data System (ADS)

Schwarz, Benjamin; Barnes, Andrew D.; Thakur, Madhav P.; Brose, Ulrich; Ciobanu, Marcel; Reich, Peter B.; Rich, Roy L.; Rosenbaum, Benjamin; Stefanski, Artur; Eisenhauer, Nico

2017-12-01

Climate warming is predicted to alter the structure, stability, and functioning of food webs1-5. Yet, despite the importance of soil food webs for energy and nutrient turnover in terrestrial ecosystems, the effects of warming on these food webs—particularly in combination with other global change drivers—are largely unknown. Here, we present results from two complementary field experiments that test the interactive effects of warming with forest canopy disturbance and drought on energy flux in boreal-temperate ecotonal forest soil food webs. The first experiment applied a simultaneous above- and belowground warming treatment (ambient, +1.7 °C, +3.4 °C) to closed-canopy and recently clear-cut forest, simulating common forest disturbance6. The second experiment crossed warming with a summer drought treatment (-40% rainfall) in the clear-cut habitats. We show that warming reduces energy flux to microbes, while forest canopy disturbance and drought facilitates warming-induced increases in energy flux to higher trophic levels and exacerbates the reduction in energy flux to microbes, respectively. Contrary to expectations, we find no change in whole-network resilience to perturbations, but significant losses in ecosystem functioning. Warming thus interacts with forest disturbance and drought, shaping the energetic structure of soil food webs and threatening the provisioning of multiple ecosystem functions in boreal-temperate ecotonal forests.

Environmental Controls of Soil Organic Carbon in Soils Across Amazonia

NASA Astrophysics Data System (ADS)

Quesada, Carlos Alberto; Paz, Claudia; Phillips, Oliver; Nonato Araujo Filho, Raimundo; Lloyd, Jon

2015-04-01

Amazonian forests store and cycle a significant amount of carbon on its soils and vegetation. Yet, Amazonian forests are now subject to strong environmental pressure from both land use and climate change. Some of the more dramatic model projections for the future of the Amazon predict a major change in precipitation followed by savanization of most currently forested areas, resulting in major carbon losses to the atmosphere. However, how soil carbon stocks will respond to climatic and land use changes depend largely on how soil carbon is stabilized. Amazonian soils are highly diverse, being very variable in their weathering levels and chemical and physical properties, and thus it is important to consider how the different soils of the Basin stabilize and store soil organic carbon (SOC). The wide variation in soil weathering levels present in Amazonia, suggests that soil groups with contrasting pedogenetic development should differ in their predominant mechanism of SOC stabilization. In this study we investigated the edaphic, mineralogical and climatic controls of SOC concentration in 147 pristine forest soils across nine different countries in Amazonia, encompassing 14 different WRB soil groups. Soil samples were collected in 1 ha permanent plots used for forest dynamics studies as part of the RAINFOR project. Only 0-30 cm deep averages are reported here. Soil samples were analyzed for carbon and nitrogen and for their chemical (exchangeable bases, phosphorus, pH) and physical properties, (particle size, bulk density) and mineralogy through standard selective dissolution techniques (Fe and Al oxides) and by semi-quantitative X-Ray diffraction. In Addition, selected soils from each soil group had SOC fractionated by physical and chemical techniques. Our results indicate that different stabilization mechanisms are responsible for SOC stabilization in Amazonian soils with contrasting pedogenetic level. Ferralsols and Acrisols were found to have uniform mineralogy (kaolinitic) and thus the clay plus silt fraction was the best correlate for SOC but with crystalline iron oxides (dithionite-citrate minus ammonium oxalate - oxalic acid extractable iron) being also correlated to SOC in these soils (R2 = 0.74). Most of SOC in these soils was found on the clay+silt fraction and in stable, clay rich aggregates. However, SOC of high activity clays and other less weathered soils such as Alisols, Cambisols and Plinthosols showed no correlation with particle size or iron oxides, being mostly stabilized by aluminium complexes. We found SOC of these soils to be better explained by a three way interaction among soil pH, carbon quality and dithionite-citrate extractable Al (R2 = 0.85). Consistent with this observation, SOC in the less weathered soils was mostly found in the colloidal fraction (75%). SOC of Podzols and Arenosols on the other hand had only a small but significant influence from their clay plus silt fraction (R2 = 0.31), with particulate organic matter accounting for most of its SOC.

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.

Molecular and microscopic insights into the persistence of soil organic matter in a red pine rhizosphere

USDA-ARS?s Scientific Manuscript database

Microbially-derived carbon inputs to soils play an important role in stabilization of soil organic matter (SOM), but detailed knowledge of basic mechanisms of carbon (C) cycling, such as stabilization of organic C compounds originating from rhizodeposition, is lacking. This study aimed to investigat...

Summary Reviews of Soil Stabilization Processes. Report 7. Electrical Stabilization of Fine-Grained Soils

DTIC Science & Technology

1961-10-01

Observations . . . . . . . .................. 3 Double Layer Theory ................. .... 4 The Electroosmotic Phenomenon in Soils . . . . ... 6 Helmholtz...lL PART III: EFFECTS OF ELECTROOSMOSIS . ............. .. 133 Electroosmotic Dewatering ........ ................ ... 13 Electroosmotic ... electroosmotic flow based on the theories of Helmholtz-Smoluchowski and Schmid are compared. It is apparent that the applicability of the theoretical concepts

How ISCO Can Interfere in Soil Pore Distribution and Solute Transport

NASA Astrophysics Data System (ADS)

Favero, M.; Freitas, J. G.; Furquim, S. A. C.; Thomson, N. R.; Cooper, M.

2016-12-01

Recently in situ chemical oxidation (ISCO) has been a remedy of choice for sites contaminated with organic compounds. However, the impact of the chemical oxidant on soil properties and, therefore, on solute transport and remediation efficiency still lacks understanding. This research effort sought to evaluate the changes in soil physical properties and solute transport behavior in a typical tropical soil (Oxisol) resulting from exposure to persulfate. The Oxisol used had a microaggregate structure, resulting in a relatively high hydraulic conductivity despite the high clay content (67%). One-dimensional laboratory experiments were performed using a saturated undisturbed column. The injection of an ideal tracer (bromide), a reactive tracer (phenol) and persulfate (12 ± 1 gL-1 for 30 d) were performed consecutively. The tracer tests were repeated following persulfate injection. Transport parameters (longitudinal dispersivity: αL and retardation factor: R) and the effective porosity (ne) were obtained by fitting the breakthrough curves with an analytical solution for one-dimensional transport. Micromorphological analyses of porosity were conducted on impregnated soil blocks from control and oxidized systems. The bromide and phenol tracer test data yielded αL of 2.431 ± 0.002 cm, ne of 41.99 ± 1.52 %, R of 1.10, and a first-order decay rate coefficient of 6.5x10-5 min-1 prior to persulfate exposure. The effluent persulfate concentration stabilized at C/Co of 0.8 after 4 d of injection and the breakthrough was delayed relative to bromide. Concurrent with the breakthrough of persulfate, the pH decreased and a progressive release of Al (III) over the first 4 d with subsequent stabilization were observed. Following persulfate exposures the hydraulic conductivity increased about one-order of magnitude. Micromorphological analysis showed that persulfate produced alterations in poroids types, with an increase of complex packing voids. It was verified that persulfate promotes the dissolution of soil minerals, and likely affects the microaggregates structure of the Oxisol, resulting in formation of preferential paths and changing the flux patterns within the soil column.

[Characteristics of soil nematode community along an age sequence of sandy desert soil cultivation in a marginal oasis of middle reaches of Heihe River].

PubMed

Wang, Xue-Feng; Su, Yong-Zhong; Yang, Rong

2010-08-01

This paper studied the characteristics of soil nematode community following the conversion of native sandy desert soil to irrigated farmland in a marginal oasis of the middle reaches of Heihe River basin, aimed to approach the bioindicating function of soil nematodes in soil evolution process. A total of 27921 soil nematode individuals were captured, belonging to 25 families and 34 genera. The total number of nematodes increased gradually with increasing age of cultivation. At all sampling sites, bacterivores and plant parasites were the dominant trophic groups, and made up the main parts of nematode community in oasis farmland. Through the analysis of the evenness index (J) and dominance index (lambda) of nematode community, the ecosystems were found to be fragile for the farmlands having cultivated for 0, 10, and > 50 years. The maturity index MI2-5 and MMI decreased with increasing cultivation age, suggesting that the practice of agricultural use enhanced the disturbance on farmland. The soil properties changed significantly after 10 years of cultivation, which was at a significant change stage for the structure stability of soil ecosystems. The characteristics of soil nematode community could be used as the bioindicator of soil evolution following the conversion of native desert soil to irrigated farmland.

Why biochar application did not improve the soil water retention of a sandy soil: An investigation into the underlying mechanisms.

NASA Astrophysics Data System (ADS)

Jeffery, Simon; Meinders, Marcel B. J.; Stoof, Cathelijne; Bezemer, T. Martijn; vande Voorde, Tess F. J.; Mommer, Liesje; Willem van Groenigen, Jan

2015-04-01

Biochar application to soil is currently being widely touted as a means to improve soil quality and to enhance the provision of numerous ecosystem services, including water storage, in soils. However, evidence for hydrological effects in the primary literature remain inconclusive with contradictory effects reported. The mechanisms behind such contradictory results are not yet elucidated. As such we aimed to investigate the effects of biochar on soil water retention and infiltration, as well as the underlying mechanisms. To do so we set up two field experiments with biochar produced from herbaceous feedstock through slow pyrolysis at two temperatures (400°C and 600°C). In the first experiment both biochars were applied at a rate of 10 t ha-1 to separate plots in a sandy soil in a North European grassland. In a separate experiment, the biochar produced at 400°C was applied to a different set of plots in the same grassland at rates equivalent to 1, 5, 20 and 50 t ha-1. Soils from these experiments were analysed for soil water retention and infiltration rate as well as aggregate stability and other soil physical parameters. The pore structure of the biochar was fully characterised using X-ray computed micro-tomography (XRT) and hydrophobicity determined using contact angle measurements. There were no significant effects of biochar application on soil water retention, field saturated conductivity or aggregate stability in either experiment. XRT analysis of the biochars confirmed that the biochars were highly porous, with 48% and 57% porosity for the 400°C and 600°C biochars, respectively. More than 99% of internal pores of the biochar particles were connected to the surface, suggesting a potential role for biochars in improving soil water retention. However, the biochars were highly hydrophobic as demonstrated by the high contact angles when water was applied. We suggest that this hydrophobicity greatly diminished water infiltration into the biochar particles, prohibiting an effect on soil water retention. Our results indicate that, in addition to characterizing pore space, biochars should be analysed for hydrophobicity when assessing their capacity for improving soil physical properties.

The long-term effects on aggregate stability (AS) from a forest fire of varying intensity in a Mediterranean environment (1994-2012).

NASA Astrophysics Data System (ADS)

Velasco, Antonio; Alcañiz, Meritxell; Úbeda, Xavier; Pereira, Paulo; Mataix-Solera, Jorge

2013-04-01

Forest fires can affect many soil properties and this fact is deeply connected with fire severity, intensity, soil type and many others factors. Aggregate stability (AS) indicates the soil structure resilience in response to external mechanical forces. AS is one of the factors that strongly affect on soil erodibility and infiltration. This property can be used as an indicator of the state of the soil structure and physical stability. The aim of this study is to analyze the soil AS of a determined area that suffered a wildfire in 1994 and compare them with a control area with the same characteristics. The study area is located in the Cadiretes Massif, in the northernmost zone of the Catalan Coastal Ranges, northeast Spain, at an altitude of around 190 - 250 m.a.m.s.l. The Cadiretes Massif is predominantly granite, although soils developed over Paleozoic metamorphic rocks such as schist and slates can also be found. In some areas metamorphic features underlie this relief. The massif is covered by dense Mediterranean vegetation, e.g. Quercus suber, Arbutus unedo, Erica arborea, and in some places Pinus pinaster plantations are found. This area receives about 700 - 800 mm of annual rainfall, with a fairly marked seasonal variability. The maximum is registered in autumn. Summer temperatures often surpass 25°C, while in winter temperatures are generally mild. The predominant soil type in Cadiretes is classified as a Lithic Xerept, with a 15 cm deep sandy-loam A horizon. In the control forest area, this horizon is protected by a 3 cm deep O horizon of moder humus. Three areas with different burnt intensity were identified in 1994 and they are the same plots that were chosen to sample in 2012. The 4 plots (Low intensity, Medium Intensity, High Intensity and Control) had the same orientation (S) and slope (5%). The TDI (Ten Drop Impact) test, that simulates rainfall impact on aggregates, was used to measure AS in the laboratory. Twenty samples were collected per plot. Ten aggregates for each plot, of 4 - 4.8 mm were selected and subjected to the impact of 10 drops from a burette fixed at a height of 1 m. the aggregates were placed on a 2.8 mm sieve to allow the disaggregated sample to flow away. The drops of distilled water weighed 0.1 ± 0.001 g and had a diameter of 5.8 mm. The statistical comparison between the four treatments (high, medium and low intensity and control area) in 2012 samples shows that the disintegration percentage is higher in the high intensity area (13.5%). Medium and low intensity areas showed less percentage of aggregate disintegration: 10.4 and 11.1 respectively but still higher than the control area's one (5.45%). This analysis has demonstrated that after 18 years there are still significant AS differences between the three areas with different burnt intensity and the control area. Keywords: forest fire, aggregate stability, TDI test, Mediterranean area

Minerals vs. Microbes: Biogeochemical Controls on Carbon Storage in Humid Tropical Forest Soils

NASA Astrophysics Data System (ADS)

Hall, S. J.; Silver, W. L.

2012-12-01

Humid tropical forest soils contain a substantial portion (~500 Pg) of the terrestrial carbon (C) pool, yet their response to climate change remains unclear due to mechanistic uncertainty in the biogeochemical controls on soil C storage in these ecosystems. Poorly-crystalline minerals have long been known to stabilize soil C, but few studies have explored their relative importance in comparison with other likely controls such as rhizosphere processes, oxygen deficiency (anaerobiosis), and C quality. We examined relationships among soil C and a suite of biogeochemical variables measured in 162 samples from surface soils (ultisols and oxisols) collected over scales of landforms to landscapes (m - km) in the Luquillo Experimental Forest, Puerto Rico. We measured iron (Fe), aluminum (Al), and manganese (Mn) oxides in 0.5M hydrochloric acid (HCl), sodium citrate/ascorbic acid (CA), and citrate/dithionite (CD) extractions, along with clay content, root biomass, C quality (C/N ratios), and anaerobiosis using HCl-extractable reduced iron (Fe(II)) concentrations as a proxy. We used mixed-effects models to compare the relative importance of the above variables (normalized by mean and standard deviation) as predictors of soil C, with random effects to account for spatial structure. Poorly-crystalline Al oxide concentrations (CA extraction), soil C/N ratio, and Fe(II) concentrations each had highly significant (p < 0.0001) positive relationships with soil C concentrations that conveyed equivalent explanatory power, assessed by comparing standardized regression coefficients. The optimal mixed model explained 82 % of the variation of the residual sum of squares of soil C concentrations, which varied between 2 - 20 % C among samples. Fine root biomass had a weak but significantly positive association with soil C concentrations (p < 0.05), while crystalline Fe oxide concentrations (CD extraction) displayed a negative correlation (p < 0.01), and clay contents had no significant relationship. The latter results are surprising given the documented role of Fe oxides and clay minerals in C stabilization, yet may indicate the importance of C supply via roots in controlling C concentrations in humid tropical ecosystems. Samples associated with high concentrations of crystalline Fe and high clay contents may represent soils from deeper in the soil profile exposed by landslides, characterized by poorly-developed aggregate structure and fewer C inputs since disturbance. Our optimal mixed model suggested an equivalent importance of soil mineralogy, anaerobiosis, and C quality as correlates of soil C concentrations across tropical forest ecosystems varying in temperature, precipitation, and community composition. Whereas soil mineralogy may be relatively static over timescales of years to decades, O2 availability and the chemical composition of soil C inputs and can potentially vary more rapidly. Our model suggests that changes in temperature and precipitation regimes that alter O2 availability and/or increase the lability of C inputs may lead to decreased soil C storage in humid tropical forest soils.

Rhizophores in Rhizophora mangle L: an alternative interpretation of so-called ''aerial roots''.

PubMed

Menezes, Nanuza L de

2006-06-01

Rhizophora mangle L., one of the most common mangrove species, has an aerial structure system that gives it stability in permanently swampy soils. In fact, these structures, known as "aerial roots" or "stilt roots", have proven to be peculiar branches with positive geotropism, which form a large number of roots when in contact with swampy soils. These organs have a sympodial branching system, wide pith, slightly thickened cortex, collateral vascular bundles, polyarch stele and endarch protoxylem, as in the stem, and a periderm produced by a phellogen at the apex similar to a root cap. They also have the same type of trichosclereid that occurs in the stem, with negative geotropism, unlike true Rhizophora roots, which do not form trichosclereids at all. On the other hand, these branches do not form leaves and in this respect they are similar to roots. These peculiar branches are rhizophores or special root-bearing branches, analogous to those found in Lepidodendrales and other Carboniferous tree ferns that grew in swampy soils.

Stabilization of Pb and Cd contaminated soils and soil quality improvements using waste oyster shells.

PubMed

Ok, Yong Sik; Lim, Jung Eun; Moon, Deok Hyun

2011-02-01

Large amounts of oyster shells are produced as a by-product of shellfish farming in coastal regions without beneficial use options. Accordingly, this study was conducted to evaluate the potential for the use of waste oyster shells (WOS) containing a high amount of CaCO₃ to improve soil quality and to stabilize heavy metals in soil. To accomplish this, an incubation experiment was conducted to evaluate the ability of the addition of 1-5 wt% WOS to stabilize the Pb (total 1,246 mg/kg) and Cd (total 17 mg/kg) in a contaminated soil. The effectiveness of the WOS treatments was evaluated using various single extraction techniques. Soil amended with WOS was cured for 30 days complied with the Korean Standard Test method (0.1 M·HCl extraction). The Pb and Cd concentrations were less than the Korean warning and countermeasure standards following treatment with 5 wt% WOS. Moreover, the concentrations of Cd were greatly reduced in response to WOS treatment following extraction using 0.01 M·CaCl₂, which is strongly associated with phytoavailability. Furthermore, the soil pH and exchangeable Ca increased significantly in response to WOS treatment. Taken together, the results of this study indicated that WOS amendments improved soil quality and stabilized Pb and Cd in contaminated soil. However, extraction with 0.43 M·CH₃ COOH revealed that remobilization of heavy metals can occur when the soil reaches an acidic condition.

Use of cement-fly ash-based stabilization techniques for the treatment of waste containing aromatic contaminants

NASA Astrophysics Data System (ADS)

Banaszkiewicz, Kamil; Marcinkowski, Tadeusz

2017-11-01

Research on evaluation of evaporation rate of volatile organic compounds from soil beds during processing is presented. For the experiment, soil samples were prepared with the same amounts of benzene and stabilized using a mixture of CEMI 42.5R cement and fly ash from pit-coal combustion. Solidification of soils contaminated with BTEX hydrocarbons using hydraulic binders involves a risk of releasing vapours of these compounds during homogenization of waste with stabilizing mixture introduced and its dilution with water. The primary purposes of the research were: analysis of benzene volume emitted from soil during stabilization/solidification process and characterization of factors that may negatively affect the quality of measurements/the course of stabilization process. Analysis of benzene emission intensity during the process was based on concentration (C6H6) values, recorded with flame-ionization detector above the surface of reacting mixture. At the same time, gaseous contaminants emitted during waste stabilization were passed through pipes filled with activated carbon (SCK, Anasorb CSC). Benzene vapours adsorbed on activated carbon were subjected to analysis using gas chromatograph Varian 450-GC. Evaporation characteristics of benzene during processing contaminated soils revealed the stages creating the highest danger to workers' health, as well as a need for actions connected with modification of technological line.

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.

Using foamed asphalt as a stabilizing agent in full depth reclamation of Route 8 in Belgrade : final report.

DOT National Transportation Integrated Search

2009-03-01

Maine has a variety of soil types throughout the state. A majority of these soil types degrade rapidly and : have poor stability. To eliminate the cost of supplying quality road base material from a distant source and : increase the stability of exis...

Poro-mechanical coupling influences on potential for rainfall-induced shallow landslides in unsaturated soils

NASA Astrophysics Data System (ADS)

Wu, L. Z.; Selvadurai, A. P. S.; Zhang, L. M.; Huang, R. Q.; Huang, Jinsong

2016-12-01

Rainfall-induced landslides are a common occurrence in terrain with steep topography and soils that have degradable strength. Rainfall infiltration into a partially saturated slope of infinite extent can lead to either a decrease or complete elimination of soil suction, compromising the slopes' stability. In this research the rainfall infiltration coupled with deformation of a partially saturated soil slope during rainfall infiltration is analyzed. The limit equilibrium conditions and the shear strength relationship of a partially saturated soil are employed to develop an analytical solution for calculating the stability of an infinite partially saturated slope due to rainfall infiltration. The analytical solutions are able to consider the influence of the coupled effects on the stability of the slope. The factors that affect the safety of a partially saturated slope of infinite extent are discussed. The results indicate that the poro-mechanical coupling of water infiltration and deformation has an important effect on the stability of the infinite unsaturated slope.

Does mycorrhizal inoculation benefit plant survival, plant development and small-scale soil fixation? Results from a perennial eco-engineering field experiment in the Swiss Alps.

NASA Astrophysics Data System (ADS)

Bast, Alexander; Grimm, Maria; Graf, Frank; Baumhauer, Roland; Gärtner, Holger

2015-04-01

In mountain environments superficial slope failures on coarse grained, vegetation-free slopes are common processes and entail a certain risk for humans and socio-economic structures. Eco-engineering measures can be applied to mitigate slope instabilities. In this regard, limited plant survival and growth can be supported by mycorrhizal inoculation, which was successfully tested in laboratory studies. However, related studies on a field scale are lacking. Furthermore, mycorrhizae are known to enhance soil aggregation, which is linked to soil physics such as shear strength, and hence it is a useful indicator for near-surface soil/slope stability. The overall objective of our contribution was to test whether mycorrhizal inoculation can be used to promote eco-engineering measures in steep alpine environments based on a five-year field experiment. We hypothesized that mycorrhizal inoculation (i) enhances soil aggregation, (ii) stimulate plant survival and fine root development, (iii) effects plant performance, (iv) the stimulated root development in turn influences aggregate stability, and (v) that climatic variations play a major role in fine-root development. We established mycorrhizal and non-mycorrhizal treated eco-engineered research plots (hedge layers mainly consisting of Alnus spp. and Salix spp.) on a field experimental scale. The experimental site is in the eastern Swiss Alps at an erosion-prone slope where many environmental conditions can be seen as homogeneous. Soil aggregation, fine root development and plant survival was quantified at the end of four growing seasons (2010, '11, '12, '14). Additionally, growth properties of Alnus spp. and Salix spp. were measured and their biomass estimated. Meteorological conditions, soil temperature and soil water content were recorded. (i) The introduced eco-engineering measures enhanced aggregate stability significantly. In contrast to published greenhouse and laboratory studies, mycorrhizal inoculation delayed soil aggregate stabilization relative to the non-inoculated site but resulted in a significantly higher aggregate stability compared to the control and the non-inoculated site at the end of the third growing season. (ii) Plant survival was significantly improved by the inoculation. Fine-root development was stimulated but not immediately. At the end of the third growing season, root length density tended to be higher and mean root diameter was significantly increased at the mycorrhizal treated site. (iii) Analyses on plant performance of Alnus and Salix demonstrated that the inoculated saplings achieved significantly higher survival rates. There was no treatment effect on plant growth properties except in 2010, where plant height and main stem diameter of Alnus was increased at the mycorrhizal treated site. The estimated total biomass of Alnus and Salix was higher at the mycorrhizal treated site. (iv) There was a positive correlation between root length density and aggregate stability, whereas roots < 0.5 mm were most influential on aggregate stability. (v) Interannual climatic variations seem to have a crucial influence on root development and, hence, on slope stability. There is a temporal offset of two growing seasons between inoculation effects tested in greenhouse/laboratory and the presented field experiment. However, the application of a commercial mycorrhizal inoculum in eco-engineering measures is a beneficial promoter to mitigate slope instability and surface erosion but needs to be tested at other sites. The contribution is mainly based on Bast (2014) and was funded by the Wolfermann Nägeli Stiftung Zürich and the Swiss Federal Office for Environment (BAFU No.: 09.0027.PJ/I211-3446). Bast, A. (2014): Mycorrhizal inoculation as a promoter for sustainable eco-engineering measures in steep alpine environments? Results of a three-year field experiment in the Arieschbach catchment, Fideris, eastern Swiss Alps. PhD Thesis. University of Berne: 149pp.

Heavy-machinery traffic impacts methane emissions as well as methanogen abundance and community structure in oxic forest soils.

PubMed

Frey, Beat; Niklaus, Pascal A; Kremer, Johann; Lüscher, Peter; Zimmermann, Stephan

2011-09-01

Temperate forest soils are usually efficient sinks for the greenhouse gas methane, at least in the absence of significant amounts of methanogens. We demonstrate here that trafficking with heavy harvesting machines caused a large reduction in CH(4) consumption and even turned well-aerated forest soils into net methane sources. In addition to studying methane fluxes, we investigated the responses of methanogens after trafficking in two different forest sites. Trafficking generated wheel tracks with different impact (low, moderate, severe, and unaffected). We found that machine passes decreased the soils' macropore space and lowered hydraulic conductivities in wheel tracks. Severely compacted soils yielded high methanogenic abundance, as demonstrated by quantitative PCR analyses of methyl coenzyme M reductase (mcrA) genes, whereas these sequences were undetectable in unaffected soils. Even after a year after traffic compression, methanogen abundance in compacted soils did not decline, indicating a stability of methanogens here over time. Compacted wheel tracks exhibited a relatively constant community structure, since we found several persisting mcrA sequence types continuously present at all sampling times. Phylogenetic analysis revealed a rather large methanogen diversity in the compacted soil, and most mcrA gene sequences were mostly similar to known sequences from wetlands. The majority of mcrA gene sequences belonged either to the order Methanosarcinales or Methanomicrobiales, whereas both sites were dominated by members of the families Methanomicrobiaceae Fencluster, with similar sequences obtained from peatland environments. The results show that compacting wet forest soils by heavy machinery causes increases in methane production and release.

Plant species richness sustains higher trophic levels of soil nematode communities after consecutive environmental perturbations.

PubMed

Cesarz, Simone; Ciobanu, Marcel; Wright, Alexandra J; Ebeling, Anne; Vogel, Anja; Weisser, Wolfgang W; Eisenhauer, Nico

2017-07-01

The magnitude and frequency of extreme weather events are predicted to increase in the future due to ongoing climate change. In particular, floods and droughts resulting from climate change are thought to alter the ecosystem functions and stability. However, knowledge of the effects of these weather events on soil fauna is scarce, although they are key towards functioning of terrestrial ecosystems. Plant species richness has been shown to affect the stability of ecosystem functions and food webs. Here, we used the occurrence of a natural flood in a biodiversity grassland experiment that was followed by a simulated summer drought experiment, to investigate the interactive effects of plant species richness, a natural flood, and a subsequent summer drought on nematode communities. Three and five months after the natural flooding, effects of flooding severity were still detectable in the belowground system. We found that flooding severity decreased soil nematode food-web structure (loss of K-strategists) and the abundance of plant feeding nematodes. However, high plant species richness maintained higher diversity and abundance of higher trophic levels compared to monocultures throughout the flood. The subsequent summer drought seemed to be of lower importance but reversed negative flooding effects in some cases. This probably occurred because the studied grassland system is well adapted to drought, or because drought conditions alleviated the negative impact of long-term soil waterlogging. Using soil nematodes as indicator taxa, this study suggests that high plant species richness can maintain soil food web complexity after consecutive environmental perturbations.

Incorporation of bitumen and calcium silicate in cement and lime stabilized soil blocks

NASA Astrophysics Data System (ADS)

Kwan, W. H.; Cheah, C. B.; Ramli, M.; Al-Sakkaf, Y. K.

2017-04-01

Providing affordable housing is the most critical problem in many of the developing countries. Using earth materials in building construction is one of the feasible methods to address this issue and it can be a way towards sustainable construction as well. However, the published information on the stabilized soil blocks is limited. Therefore, the present study is conducted to examine the characterization of the soils and engineering properties of the stabilized soil blocks. Four types of stabilizer were used in the study, namely; cement, slaked lime, bitumen emulsion and calcium silicate. Cement and slaked lime were added at different percentages in the range of 5% to 15%, with interval of 2.5%. The percentage was determined based on weight of soil. Meanwhile, bitumen emulsion and calcium silicate were incorporated at various percentages together with 10% of cement. Dosage of bitumen emulsion is in the range of 2% to 10% at interval of 2% while calcium silicate was incorporated at 0.50%, 0.75%, 1.00%, 1.25%, 1.50% and 2.00%. Results show that cement is the most viable stabilizer for the soil block among all stabilizers in this study. The bulk density, optimum moisture content and compressive strengths were increased with the increasing cement content. The most suitable cement content was 10% added at moisture content of 12%. Lime, bitumen and calcium contents were recommended at 5.0%, 6.0% and 1.25%, respectively.

Disentangling controls on mineral-stabilized soil organic matter using a slurry incubation

NASA Astrophysics Data System (ADS)

Lavallee, J. M.; Cotrufo, M. F.; Paul, E. A.; Conant, R. T.

2014-12-01

Mineral-stabilized organic matter (OM) is the largest and oldest pool of soil carbon and nitrogen. Mineral stabilization limits OM availability to soil microbes, preventing its decomposition and prolonging its turnover. Thus, understanding controls on the decomposition of mineral-stabilized OM is key to understanding soil carbon and nitrogen dynamics. The very slow turnover of mineral-stabilized OM makes it challenging to study in a typical incubation, and as a result, many potential controls (temperature, OM chemistry, and mineralogy) on its turnover remain unclear. We aimed to better understand controls on decomposition of mineral-stabilized OM by employing a slurry incubation technique, which speeds up microbial processing of OM by maximizing OM accessibility to microbes. In a slurry incubation, we expect that any OM that is not stabilized on mineral surfaces will be available for decomposition and will be converted to CO2. Using this technique, we studied the interactive effects of incubation temperature, plant material type (aboveground vs. belowground), and soil fraction (silt vs. clay) on CO2 efflux and OM stabilization. We separated silt-sized and clay-sized fractions from an agricultural soil, added aboveground or belowground plant material to each, and incubated them at 15°C, 25°C and 35°C. The added plant material was isotopically labeled (13C and 15N), which allowed us to trace it through the system and distinguish between the responses of the new (derived from the plant material) and old (derived from what was already present in the silt and clay) OM to warming. We measured CO2 efflux and 13CO2 efflux throughout the incubation. We performed one short-term harvest at day 6 and one final harvest at day 60. Initial results show higher cumulative CO2 efflux at warmer temperatures regardless of plant material type or soil fraction. A larger fraction of that CO2 came from OM that was initially present in the silt and clay, rather than from the plant material that we added, which suggests faster turnover of that "old" OM at warmer temperatures. We will present CO2 efflux data in addition to total [C] and [N] and the isotopic ratios of 13C and 15N in the silt and clay at each harvest to explain how the interactions between warming, plant material type and soil fraction affect turnover of mineral stabilized OM.

Reductive immobilization of chromate in water and soil using stabilized iron nanoparticles.

PubMed

Xu, Yinhui; Zhao, Dongye

2007-05-01

Laboratory batch and column experiments were conducted to investigate the feasibility of using a new class of stabilized zero-valent iron (ZVI) nanoparticles for in situ reductive immobilization of Cr(VI) in water and in a sandy loam soil. Batch kinetic tests indicated that 0.08g/L of the ZVI nanoparticles were able to rapidly reduce 34mg/L of Cr(VI) in water at an initial pseudo first-order rate constant of 0.08h(-1). The extent of Cr(VI) reduction was increased from 24% to 90% as the ZVI dosage was increased from 0.04 to 0.12g/L. The leachability of Cr preloaded in a Cr-loaded sandy soil was reduced by nearly 50% when the soil was amended with 0.08g/L of the ZVI nanoparticles in batch tests at a soil-to-solution ratio of 1g: 10mL. Column experiments indicated that the stabilized ZVI nanoparticles are highly deliverable in the soil column. When the soil column was treated with 5.7 bed volumes of 0.06g/L of the nanoparticles at pH 5.60, only 4.9% of the total Cr was eluted compared to 12% for untreated soil under otherwise identical conditions. The ZVI treatment reduced the TCLP leachability of Cr in the soil by 90%, and the California WET (Waste Extraction Test) leachability by 76%. The stabilized ZVI nanoparticles may serve as a highly soil-dispersible and effective agent for in situ reductive immobilization of chromium in soils, groundwater, or industrial wastes.

Modeling soil processes - are we lost in diversity?

NASA Astrophysics Data System (ADS)

Vogel, Hans-Joerg; Schlüter, Steffen

2015-04-01

Soils are among the most complex environmental systems. Soil functions - e.g. production of biomass, habitat for organisms, reactor for and storage of organic matter, filter for ground water - emerge from a multitude of processes interacting at different scales. It still remains a challenge to model and predict these functions including their stability and resilience towards external perturbations. As an inherent property of complex systems it is prohibitive to unravel all the relevant process in all detail to derive soil functions and their dynamics from first principles. Hence, when modeling soil processes and their interactions one is close to be lost in the overwhelming diversity and spatial heterogeneity of soil properties. In this contribution we suggest to look for characteristic similarities within the hyperdimensional state space of soil properties. The underlying hypothesis is that this state space is not evenly and/or randomly populated but that processes of self organization produce attractors of physical, chemical and biological properties which can be identified. (The formation of characteristic soil horizons is an obvious example). To render such a concept operational a suitable and limited set of indicators is required. Ideally, such indicators are i) related to soil functions, ii) are measurable and iii) are integral measures of the relevant physical, chemical and biological soil properties. This would allow for identifying suitable attractors. We will discuss possible indicators and will focus on soil structure as an especially promising candidate. It governs the availability of water and gas, it effects the spatial distribution of organic matter and, moreover, it forms the habitat of soil organisms and it is formed by soil biota. Quantification of soil structural properties became possible only recently with the development of more powerful tools for non-invasive imaging. Future research need to demonstrate in how far these tools can be used to identify functional soil types (i.e. attractors) allowing for modeling soil processes at an integral level. We provide an example from the 100-years fertilization experiment in Bad-Lauchstädt.

Effect of hydraulic hysteresis on the stability of infinite slopes under steady infiltration

USGS Publications Warehouse

Chen, Pan; Mirus, Benjamin B.; Lu, Ning; Godt, Jonathan W.

2017-01-01

Hydraulic hysteresis, including capillary soil water retention (SWR), air entrapment SWR, and hydraulic conductivity, is a common phenomenon in unsaturated soils. However, the influence of hydraulic hysteresis on suction stress, and subsequently slope stability, is generally ignored. This paper examines the influence of each of these three types of hysteresis on slope stability using an infinite slope stability analysis under steady infiltration conditions. First, hypothetical slopes for representative silty and sandy soils are examined. Then a monitored hillslope in the San Francisco Bay Area, California is assessed, using observed rainfall conditions and measured hydraulic and geotechnical properties of the colluvial soil. Results show that profiles of suction stress and the corresponding factor of safety are generally strongly affected by hydraulic hysteresis. Results suggest that each of the three types of hydraulic hysteresis may play a major role in the occurrence of slope failure, indicating that ignoring hydraulic hysteresis will likely lead to underestimates of failure potential and hence to inaccurate slope stability analysis.

Structural adaptation of cold-active RTX lipase from Pseudomonas sp. strain AMS8 revealed via homology and molecular dynamics simulation approaches.

PubMed

Mohamad Ali, Mohd Shukuri; Mohd Fuzi, Siti Farhanie; Ganasen, Menega; Abdul Rahman, Raja Noor Zaliha Raja; Basri, Mahiran; Salleh, Abu Bakar

2013-01-01

The psychrophilic enzyme is an interesting subject to study due to its special ability to adapt to extreme temperatures, unlike typical enzymes. Utilizing computer-aided software, the predicted structure and function of the enzyme lipase AMS8 (LipAMS8) (isolated from the psychrophilic Pseudomonas sp., obtained from the Antarctic soil) are studied. The enzyme shows significant sequence similarities with lipases from Pseudomonas sp. MIS38 and Serratia marcescens. These similarities aid in the prediction of the 3D molecular structure of the enzyme. In this study, 12 ns MD simulation is performed at different temperatures for structural flexibility and stability analysis. The results show that the enzyme is most stable at 0°C and 5°C. In terms of stability and flexibility, the catalytic domain (N-terminus) maintained its stability more than the noncatalytic domain (C-terminus), but the non-catalytic domain showed higher flexibility than the catalytic domain. The analysis of the structure and function of LipAMS8 provides new insights into the structural adaptation of this protein at low temperatures. The information obtained could be a useful tool for low temperature industrial applications and molecular engineering purposes, in the near future.

Genetic diversity and structure of an endangered desert shrub and the implications for conservation

Treesearch

Zhihao Su; Bryce A. Richardson; Li Zhuo; Xiaolong Jiang; Wenjun Li; Xiaoshan Kang

2017-01-01

Population genetic information can provide valuable insight for the conservation and management of threatened and endangered plant species. Tamarix taklamakanensis is an endangered shrub endemic to arid basins of northwestern China. This species serves to stabilize soils in this region, but has seen substantial loss in its abundance due to depletion of ground water....

Evaluation of different amendments to stabilize antimony in mining polluted soils.

PubMed

Álvarez-Ayuso, E; Otones, V; Murciego, A; García-Sánchez, A

2013-02-01

Soil pollution with antimony is of increasing environmental concern worldwide. Measures for its control and to attenuate the risks posed to the ecosystem are required. In this study the application of several iron and aluminium oxides and oxyhydroxides as soil amendments was evaluated in order to assess their feasibility to stabilize Sb in mining polluted soils. Mine soils with different pollution levels were amended with either goethite, ferrihydrite or amorphous Al oxide at various ratios (0-10%). The effectiveness of such treatments was assessed by both batch and column leaching tests. The use of ferrihydrite or amorphous Al oxide proved to be highly effective to stabilize Sb. Immobilization levels of 100% were found when doses of 5% ferrihydrite or 10% amorphous Al oxide were applied, regardless of the soil Sb load. Column leaching studies also showed a high Sb leaching reduction (>75%) when soils were amended with 1% ferrihydrite or 5% amorphous Al oxide. Moreover, such treatments proved to simultaneously immobilize As and Pb in a great extent when soils were also polluted with such toxic elements. Copyright © 2012 Elsevier Ltd. All rights reserved.

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.

Chemical stabilization of subgrade soil for the strategic expeditionary landing field

NASA Astrophysics Data System (ADS)

Conaway, M. H.

1983-06-01

The Strategic Expeditionary Landing Field (SELF) is a military expeditionary-type airfield with an aluminum matted surface that is designed for sustained tactical and cargo airlift operations in an amphibious objective area. Because of the operational traffic parameters such as loads of the various types of aircraft, tire pressures and volume of traffic, a base layer must be constructed over subgrade soil support conditions which may be only marginal. The base layer could be constructed with conventional soil construction techniques (compaction) and yield the required strength. It would be difficult, however, to maintain this strength for the required one-year service life under many climatic conditions due to the degrading effects of water on the support capacity of many soils. Chemical soil stabilization with lime, portland cement and asphalt stabilizing agents could be used to treat the soil. These additives, when properly mixed with certain types of soils, initiate reactions which will increase soil support strength and enhance durability (resistance to the degrading effects of water). Technically, this procedure is quite viable but logistically, it may not be feasible.

Microbial community controls on decomposition and soil carbon storage

NASA Astrophysics Data System (ADS)

Frey, S. D.

2016-12-01

Soil is one of the most diverse habitats on Earth and one of the least characterized in terms of the identification and ecological roles of soil organisms. Soils also contain the largest repository of organic C in the terrestrial biosphere and the activities of heterotrophic soil organisms are responsible for one of the largest annual fluxes of CO2 to the atmosphere. A fundamental controversy in ecosystem ecology is the degree to which identification of microbial taxa informs our ability to understand and model ecosystem-scale processes, such as soil carbon storage and fluxes. We have evidence that microbial identity does matter, particularly in a global change context where soil microorganisms experience selective pressures to adapt to changing environments. In particular, our work at the Harvard Forest Long-term Ecological Research (LTER) site demonstrates that the microbial community is fundamentally altered by global change stressors (climate warming, nitrogen deposition, biotic invasion) and that microbial taxa exposed to long-term environmental change exhibit an altered capacity to decompose organic matter. This talk will discuss the relative importance of changes in microbial community structure versus microbial physiology for soil organic matter degradation and stabilization.

Multiscale responses of soil stability and invasive plants to removal of non-native grazers from an arid conservation reserve

USGS Publications Warehouse

Beever, E.A.; Huso, M.; Pyke, D.A.

2006-01-01

Disturbances and ecosystem recovery from disturbance both involve numerous processes that operate on multiple spatial and temporal scales. Few studies have investigated how gradients of disturbance intensity and ecosystem responses are distributed across multiple spatial resolutions and also how this relationship changes through time during recovery. We investigated how cover of non-native species and soil-aggregate stability (a measure of vulnerability to erosion by water) in surface and subsurface soils varied spatially during grazing by burros and cattle and whether patterns in these variables changed after grazer removal from Mojave National Preserve, California, USA. We compared distance from water and number of ungulate defecations - metrics of longer-term and recent grazing intensity, respectively, - as predictors of our response variables. We used information-theoretic analyses to compare hierarchical linear models that accounted for important covariates and allowed for interannual variation in the disturbance-response relationship at local and landscape scales. Soil stability was greater under perennial vegetation than in bare interspaces, and surface soil stability decreased with increasing numbers of ungulate defecations. Stability of surface samples was more affected by time since removal of grazers than was stability of subsurface samples, and subsurface soil stability in bare spaces was not related to grazing intensity, time since removal, or any of our other predictors. In the high rainfall year (2003) after cattle had been removed for 1-2 years, cover of all non-native plants averaged nine times higher than in the low-rainfall year (2002). Given the heterogeneity in distribution of large-herbivore impacts that we observed at several resolutions, hierarchical analyses provided a more complete understanding of the spatial and temporal complexities of disturbance and recovery processes in arid ecosystems. ?? 2006 Blackwell Publishing Ltd.

Multi-scale responses of soil stability and invasive plants to removal of non-native grazers from an arid conservation reserve

USGS Publications Warehouse

Beever, Erik A.; Huso, Manuela M. P.; Pyke, David A.

2006-01-01

Disturbances and ecosystem recovery from disturbance both involve numerous processes that operate on multiple spatial and temporal scales. Few studies have investigated how gradients of disturbance intensity and ecosystem responses are distributed across multiple spatial resolutions and also how this relationship changes through time during recovery. We investigated how cover of non-native species and soil-aggregate stability (a measure of vulnerability to erosion by water) in surface and subsurface soils varied spatially during grazing by burros and cattle and whether patterns in these variables changed after grazer removal from Mojave National Preserve, California, USA. We compared distance from water and number of ungulate defecations — metrics of longer-term and recent grazing intensity, respectively, — as predictors of our response variables. We used information-theoretic analyses to compare hierarchical linear models that accounted for important covariates and allowed for interannual variation in the disturbance–response relationship at local and landscape scales. Soil stability was greater under perennial vegetation than in bare interspaces, and surface soil stability decreased with increasing numbers of ungulate defecations. Stability of surface samples was more affected by time since removal of grazers than was stability of subsurface samples, and subsurface soil stability in bare spaces was not related to grazing intensity, time since removal, or any of our other predictors. In the high rainfall year (2003) after cattle had been removed for 1–2 years, cover of all non-native plants averaged nine times higher than in the low-rainfall year (2002). Given the heterogeneity in distribution of large-herbivore impacts that we observed at several resolutions, hierarchical analyses provided a more complete understanding of the spatial and temporal complexities of disturbance and recovery processes in arid ecosystems.

Using foamed asphalt as a stabilizing agent in full depth reclamation of Route 8 in Belgrade : interim report - first year, December 2003.

DOT National Transportation Integrated Search

2003-12-01

Maine has a variety of soil types throughout the state. Most of these soil types degrade rapidly and have : poor stability. To eliminate the cost of supplying quality road base material from a distant source and : increase the stability of existing s...

Using foamed asphalt as a stabilizing agent in full depth reclamation of Route 8 in Belgrade : interim report - third and fourth year, October 2006.

DOT National Transportation Integrated Search

2006-10-01

Maine has a variety of soil types throughout the state. A majority of these soil types degrade rapidly and : have poor stability. To eliminate the cost of supplying quality road base material from a distant source and : increase the stability of exis...

Response of soil microbial communities to red mud-based stabilizer remediation of cadmium-contaminated farmland.

PubMed

Li, Hui; Liu, Lemian; Luo, Lin; Liu, Yan; Wei, Jianhong; Zhang, Jiachao; Yang, Yuan; Chen, Anwei; Mao, Qiming; Zhou, Yaoyu

2018-04-01

In this work, a field test was conducted to investigate the effects of heavy metal stabilizer addition on brown rice and microbial variables in a cadmium (Cd)-contaminated farmland from April to October in 2016. Compared with the control, red mud-based stabilizer (RMDL) effectively reduced the concentration of Cd in brown rice (with the removal rate of 48.14% in early rice, 20.24 and 47.62% in late rice). The results showed that adding 0.3 kg m -2 RDML in early rice soil or soil for both early and late rice increased the microbial biomass carbon (MBC), the number of culturable heterotrophic bacteria and fungi, and the catalase activity in soil at different stages of paddy rice growth. Furthermore, there was no notable difference in the diversity of the bacterial species, community composition, and relative abundance at phylum (or class) or operational taxonomic unit (OTU) levels between the control and treatment (RMDL addition) groups. In a word, RMDL could be highly recommended as an effective remediation stabilizer for Cd-contaminated farmland, since its continuous application in paddy soil cultivating two seasons rice soil could effectively decrease the Cd content in brown rice and had no negative impact on soil microorganisms.

Large-scale Patterns of 14C Age of Bulk Organic Carbon and Various Molecular Components in Grassland Soils

NASA Astrophysics Data System (ADS)

Jia, J.; Liu, Z.; Cao, Z.; Chen, L.; He, J. S.; Haghipour, N.; Wacker, L.; Eglinton, T. I.; Feng, X.

2017-12-01

Unraveling the fate of organic carbon (OC) in soils is essential to understanding the impact of global changes on the global carbon cycle. Previous studies have shown that while various soil OC components have different decomposability, chemically labile OC can have old 14C ages. However, few studies have compared the 14C age of various soil OC components on a large scale, which may provide important information on the link between the age or turnover of soil OC components to their sources, molecular structures as well as environmental variables. In this project, a suite of soil profiles were sampled along a large-scale transect of temperate and alpine grasslands across the Tibetan and Mongolian Plateaus in China with contrasting climatic, vegetation and soil properties. Bulk OC and source-specific compounds (including fatty acids (FAs), diacids (DAs) and lignin phenols) were radiocarbon-dated to investigate the age and turnover dynamics of different OC pools and the mechanisms controlling their stability. Our results show that lignin phenols displayed a large 14C variability. Short-chain (C16, 18) FAs sourced from vascular plants as well as microorganisms were younger than plant-derived long-chain FAs and DAs, indicating that short-chain FAs were easier to be decomposed or newly synthesized. In the temperate grasslands, long-chain DAs were younger than FAs, while the opposite trend was observed in the alpine grasslands. Preliminary correlation analysis suggests that the age of short-chain FAs were mainly influenced by clay contents and climate, while reactive minerals, clay or silt particles were important factors in the stabilization of long-chain FAs, DAs and lignin phenols. Overall, our study provided a unique 14 C dataset of soil OC components in grasslands, which will provide important constraints on soil carbon turnover in future investigations.

Changes in Carbon Chemistry and Stability Along Deep Tropical Soil Profiles at the Luquillo Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Stone, M.; Hockaday, W. C.; Plante, A. F.

2014-12-01

Tropical forests are the largest terrestrial carbon (C) sink, and tropical forest soils contribute disproportionately to the poorly-characterized deep soil C pool. The goal of this study was to evaluate how carbon chemistry and stability change with depth in tropical forest soils formed on two contrasting parent materials. We used soils from pits excavated to 140 cm depth that were stratified across two soil types (Oxisols and Inceptisols) at the Luquillo Critical Zone Observatory in northeast Puerto Rico. We used 13C nuclear magnetic resonance (NMR) spectroscopy to characterize soil C chemistry and differential scanning calorimetry (DSC) coupled with evolved gas analysis (CO2-EGA) to evaluate the thermal stability of soil C during ramped combustion. Thirty-four samples with an initial C concentration ≥1% were chosen from discrete depth intervals (0, 30, 60, 90 & 140 cm) for 13C NMR analysis, while DSC was performed on 122 samples that included the NMR sample set and additional samples at 20, 50, 80 and 110 cm depth. Preliminary 13C NMR results indicate higher alkyl : O-alkyl ratios and an enrichment of aliphatic and proteinaceous C with depth, compared with greater aromatic and carbohydrate signals in surface soils. The energy density of soil C (J mg-1 C) also declined significantly with depth. In Oxisols, most CO2 evolution from combustion occurred around 300ºC, while most CO2 evolution occurred at higher temperatures (400-500ºC) in Inceptisols. Our findings suggest soil C is derived primarily of plant biomolecules in surface soils and becomes increasingly microbial with depth. Soil matrix-mediated differences in C transport and preservation may result in differences in C chemistry between the two soil types and a more thermally labile C pool in the Oxisols. We suggest that energy-poor substrates, combined with potentially stronger organo-mineral interactions in subsoils, may explain the long-term stability of deep C in highly weathered tropical soils.

Linking the soil moisture distribution pattern to dynamic processes along slope transects in the Loess Plateau, China.

PubMed

Wang, Shuai; Fu, Bojie; Gao, Guangyao; Zhou, Ji; Jiao, Lei; Liu, Jianbo

2015-12-01

Soil moisture pulses are a prerequisite for other land surface pulses at various spatiotemporal scales in arid and semi-arid areas. The temporal dynamics and profile variability of soil moisture in relation to land cover combinations were studied along five slopes transect on the Loess Plateau during the rainy season of 2011. Within the 3 months of the growing season coupled with the rainy season, all of the soil moisture was replenished in the area, proving that a type stability exists between different land cover soil moisture levels. Land cover combinations disturbed the trend determined by topography and increased soil moisture variability in space and time. The stability of soil moisture resulting from the dynamic processes could produce stable patterns on the slopes. The relationships between the mean soil moisture and vertical standard deviation (SD) and coefficient of variation (CV) were more complex, largely due to the fact that different land cover types had distinctive vertical patterns of soil moisture. The spatial SD of each layer had a positive correlation and the spatial CV exhibited a negative correlation with the increase in mean soil moisture. The soil moisture stability implies that sampling comparisons in this area can be conducted at different times to accurately compare different land use types.

[Study on composite stabilization of arsenic (As) contaminated soil].

PubMed

Wang, Hao; Pan, Li-xiang; Zhang, Xiang-yu; Li, Meng; Song, Bao-hua

2013-09-01

Since the contaminated soil may contain various kinds of heavy metals, use of single chemical reagent leads to poor remediation and high cost. In this study, soil containing As, Zn, Cd was sampled, and different reagents were selected to carry out the rapid stabilization of contaminated soil. The TCLP (toxicity characteristic leaching procedure) was used to evaluate the leachate toxicity of heavy metals and the results indicated that calcium-containing, sulphur-containing and iron-containing reagents had good performance in reducing the metal mobility. The stabilization efficiency of the six reagents tested ranked in the order of CaO > Na2S > organic sulfur > Chitosan > FeSO4 > (C2H5)2NCS2Na. Two types of reagents (six reagents) were combined based on the target properties of different reagents and the stabilization efficiency was evaluated and analyzed. The results indicated that the composite reagents had higher stabilization efficiency: the efficiency of 3% FeSO4 + 5% CaO was 81.7%, 97.2% and 68.2% for As, Cd and Zn, respectively, and the efficiency of 3% CaO + 5% organic sulfur was 76.6%, 95.7% and 93.8% for these three metals, respectively. Speciation analysis was carried out in this study and the results suggested that it was the change of metals from the exchangeable state to the reduction (for inorganic reagent) or oxidation state (for organic reagent) that caused the soil stabilization and the degree of change determined the stabilization efficiency.

Key Process Uncertainties in Soil Carbon Dynamics: Comparing Multiple Model Structures and Observational Meta-analysis

NASA Astrophysics Data System (ADS)

Sulman, B. N.; Moore, J.; Averill, C.; Abramoff, R. Z.; Bradford, M.; Classen, A. T.; Hartman, M. D.; Kivlin, S. N.; Luo, Y.; Mayes, M. A.; Morrison, E. W.; Riley, W. J.; Salazar, A.; Schimel, J.; Sridhar, B.; Tang, J.; Wang, G.; Wieder, W. R.

2016-12-01

Soil carbon (C) dynamics are crucial to understanding and predicting C cycle responses to global change and soil C modeling is a key tool for understanding these dynamics. While first order model structures have historically dominated this area, a recent proliferation of alternative model structures representing different assumptions about microbial activity and mineral protection is providing new opportunities to explore process uncertainties related to soil C dynamics. We conducted idealized simulations of soil C responses to warming and litter addition using models from five research groups that incorporated different sets of assumptions about processes governing soil C decomposition and stabilization. We conducted a meta-analysis of published warming and C addition experiments for comparison with simulations. Assumptions related to mineral protection and microbial dynamics drove strong differences among models. In response to C additions, some models predicted long-term C accumulation while others predicted transient increases that were counteracted by accelerating decomposition. In experimental manipulations, doubling litter addition did not change soil C stocks in studies spanning as long as two decades. This result agreed with simulations from models with strong microbial growth responses and limited mineral sorption capacity. In observations, warming initially drove soil C loss via increased CO2 production, but in some studies soil C rebounded and increased over decadal time scales. In contrast, all models predicted sustained C losses under warming. The disagreement with experimental results could be explained by physiological or community-level acclimation, or by warming-related changes in plant growth. In addition to the role of microbial activity, assumptions related to mineral sorption and protected C played a key role in driving long-term model responses. In general, simulations were similar in their initial responses to perturbations but diverged over decadal time scales. This suggests that more long-term soil experiments may be necessary to resolve important process uncertainties related to soil C storage. We also suggest future experiments examine how microbial activity responds to warming under a range of soil clay contents and in concert with changes in litter inputs.

The effects of soil suction on shallow slope stability.

DOT National Transportation Integrated Search

2013-07-01

This study investigates the slope failures associated with clayey soils so engineers can better : understand the problem and better predict shallow slope stability, and implement preventive : measures if necessary. This research also examines the mec...

Stabilization of soft clay subgrades in Virginia : phase I laboratory study.

DOT National Transportation Integrated Search

2005-01-01

Many pavement subgrades in Virginia consist of wet, highly plastic clay or other troublesome soils. Such soils can be treated with traditional lime and cement stabilization methods. Alternatives, including lignosulfonates and polymers, are available,...

Soil-Geosynthetic Interaction Test to Develop Specifications for Geosynthetic-Stabilized Roadways

DOT National Transportation Integrated Search

2018-05-01

soil-geosynthetic composite (KSGC) for a wide range of geosynthetics. The tests were conducted after establishment of test configurations that were found suitable for specification of geosynthetic-stabilized base roadways. Field performance of experi...

Structural quality of on Oxisol in recovery for 18 years

NASA Astrophysics Data System (ADS)

dos Santos Batista Bonini, C.; Alves, M. C.; Marchini, D. C.; Garcia de Arruda, O.; Nilce Souto Filho, S.

2012-04-01

Incorrect use of soil and large buildings construction in rural areas are causing changes to it, making them less productive and thus increasing the degraded areas. Techniques aimed at ecological restoration of degraded soils have been investigated. In this sense we investigated the positive changes in the structural quality of a soil that was beheaded in human intervention techniques for recovery for 18 years, having been used green manures, gypsum and pasture. The studied area is located in Mato Grosso do Sul, Brazil. The experimental design was a completely randomized with seven treatments and four replications. The treatments were: control (tilled soil without culture); Stizolobium aterrium; Cajanus cajan; lime+S. aterrimum; lime+C. cajan; lime+gypsum+S. aterrimum; lime+gypsum+C. cajan. In 1994, all treatments with C. cajan were replaced by Canavalia ensiformis and in 1999, Brachiaria decumbens was implanted in all treatments. Data from vegetated treatments were compared with the control bare soil and native vegetation (savannah). We evaluated the distribution and aggregate stability in water, soil samples were collected in 2010 in the depths: 0.00-0.10; 0.10-0.20 and 0,20-0.40 m. The results were analyzed by analysis of variance, following Scott-Knott test (5%) of probability to compare averages. Evaluating the results is noted that in the depth of 0.00-0.10 m, the control bare soil and savannah soil had lower and higher DMP, respectively. All recovery treatments were DMP greater than found for the bare soil control. Treatments: S. aterrimum, lime + gypsum + C. cajan and lime + gypsum + S. aterrimum and the savannah control were similar in the depth of 0.00-0.10 m. All of the recovery treatment in the depth from 0.00-0.10 m with values is close to the native vegetation of the savannah. Depths of 0.10-0.20 and 0.20-0.40 m results obtained for DMP treatments in recovery are similar to the bare soil, except for treatments with S. aterrimum and lime + gypsum + S. aterrimum that had values were similar to the savannah control. This behavior shows that the recovery of soil treatments were eficient only the superficial layer soil and other depths in the structure is still in recovery. It is concluded that the recovery treatment have positively influenced the structure quality in the 0.00-0.10 m depth : the recovery treatment with S. aterrimum and lime + gypsum + S. aterrimum were the most promising in the recovery structural quality.

Main factors controlling microbial community structure, growth and activity after reclamation of a tailing pond with aided phytostabilization

NASA Astrophysics Data System (ADS)

Zornoza, Raúl; Acosta, José A.; Martínez-Martínez, Silvia; Faz, Ángel; Bååth, Erland

2015-04-01

Reclamation on bare tailing ponds has the potential to represent soil genesis in Technosols favoring the understanding of the changes of microbial communities and function. In this study we used phytostabilization aided with calcium carbonate and pig slurry/manure to reclaim an acidic bare tailing pond with the aim of investigating the effect of amending and different species on microbial community structure and function. We sampled after two years of amending and planting: unamended tailing soil (UTS), non-rhizospheric amended tailing soil (ATS), rhizospheric soil from four species, and non-rhizospheric native forest soil (NS), which acted as reference. The application of amendments increased pH up to neutrality, organic carbon (Corg), C/N and aggregate stability, while decreased salinity and heavy metals availability. No effect of rhizosphere was observed on physicochemical properties, metals immobilization and microbial community structure and function. To account for confounding effects due to soil organic matter, microbial properties were expressed per Corg. The high increments in pH and Corg have been the main factors driving changes in microbial community structure and function. Bacterial biomass was higher in UTS, without significant differences among the rest of soils. Fungal biomass followed the trend UTS < ATS = rhizospheric soils < NS. Bacterial growth increased and fungal growth decreased with increasing pH, despite the high availability of metals at low pH. Enzyme activities were lower in UTS, being β-glucosidase and β-glucosaminidase activities highly correlated with bacterial growth. Microbial activities were not correlated with the exchangeable fraction of heavy metals, indicating that microbial function is not strongly affected by these metals, likely due to the efficiency of the reclamation procedure to reduce metals toxicity. Changes in microbial community composition were largely explained by changes in pH, heavy metals availability and Corg, with increments in fungal and actinobacterial proportions with soil amending. Acknowledgements R. Zornoza acknowledges the financial support to Fundación Séneca-Agencia de Ciencia y Tecnología de la Región de Murcia (Spain).

The influence of using quicklime and volcanic ash as stabilizing materials in clay viewed from CBR value

NASA Astrophysics Data System (ADS)

Hastuty, Ika Puji; Sofyan, Tri Alby; Roesyanto

2017-11-01

The condition of the soil in Indonesia in varied, viewed from its bearing capacity. The soil is one of the materials which plays a very important role in a construction or foundation so that it is very necessary to have soil with its adequate technical properties. In reality, often founding inadequate soil properties such as in its compressibility, permeability, and plasticity. The objective of the research was to find out the physical properties, technical properties, CBR value, and stabilization of clay by adding quicklime and volcanic ash as stabilizing materials. The mixing combination is 2%, 4% quicklime, and 2%-24% volcanic ash. The value of Water Content for original soil was 34.33% and Specific Gravity original soil was 2.65. The result of the research showed that the stabilizing materials from quicklime and volcanic ash could improve the physical and mechanical properties of clay. The value of Atterberg Limits decreased from 29.88% to 11.33% in the variation of 4% Q+24% VA, while the most maximal value of CBR was found in the variation of 4% Q+8% VA at 9.01%.

Surface-water quality, Twin Ponies watershed, Pottawattamie and Mills counties, Iowa

USGS Publications Warehouse

Detroy, Mark G.

1981-01-01

It is probable that the variations between constituent concentrations in samples collected during runoff and those collected during low flow will be similar after grade-stabilization structures have been constructed on streams and after land-treatment measures have been implemented in the watershed as proposed by the U.S. Soil Conservation Service. Grade-stabilization structures should reduce gully and channel erosion in the watershed by dissipating the erosive energy of streamflow during significant runoff. Land-treatment measures to be implemented in conjunction with the project would help reduce sediment yield to stream channels. With the impoundments~ a decrease in velocity of the in-flowing water should produce a decrease of both the suspended~sediment concentrations and the chemical and biological constituents associated with the suspended sediMent in the impounded water.

Organic matter dynamics in Technosols created with metalliferous mine residues, biochar and marble waste

NASA Astrophysics Data System (ADS)

Moreno-Barriga, Fabián; Acosta, José A.; Ángeles Muñoz, M.; Faz, Ángel; Zornoza, Raúl

2017-04-01

Creation of Technosols by use of different materials can be a sustainable strategy to reclaim mine tailings spread on the environment. A proper selection of materials is critical to efficiently contribute to soil creation, with development of soil structure, organic matter stabilization and stimulation of microbial growth. For this purpose, a short-term incubation experiment was designed with biochars derived from different feedstocks, added to tailings alone or in combination with marble waste (MaW). We aimed to assess the effects of the different materials on the evolution of C and N contents and pools, greenhouse gas (GHG) emissions, aggregate stability, and microbial biomass and activity. Results showed that carbonates provided by MaW increased pH around the target value of 8, with significant decrease in salinity by precipitation of soluble salts. Organic C and total N remained stable during the incubation, with high recalcitrant indices. Labile and soluble C and N pools were low in Technosols, with no differences with unamended tailings at the end of incubation. All biochars increased aggregate stability with regard to control by 40%, with no effect of addition of MaW. Biochars significantly increased microbial biomass C during the first 7 days of incubation; however, from this date, there were no significant differences with unamended tailings. The β-glucosidase activity was below detection limit in all samples, while arylesterase activity increased in biochar-amended samples favored by increases in pH. CO2 emissions were not significantly affected by any amendment, while N2O emissions increased with the addition of biochars with lower recalcitrance. CH4 emissions decreased in all Technosols receiving biochar. Thus, the combined use of biochar and MaW contributed to soil C sequestration and improved soil structure. However, labile sources of organic compounds would be needed to stimulate microbial populations in the Technosols. Acknowledgements This work was supported by Fundación Séneca (Agency of Science and Technology of the Region of Murcia, Spain) [grant number 18920/JLI/13].

Persistence of soil organic matter in eroding versus depositional landform positions

USGS Publications Warehouse

Berhe, Asmeret Asefaw; Harden, Jennifer W.; Torn, Margaret S.; Kleber, Markus; Burton, Sarah D.; Harte, John

2012-01-01

Soil organic matter (SOM) processes in dynamic landscapes are strongly influenced by soil erosion and sedimentation. We determined the contribution of physical isolation of organic matter (OM) inside aggregates, chemical interaction of OM with soil minerals, and molecular structure of SOM in controlling storage and persistence of SOM in different types of eroding and depositional landform positions. By combining density fractionation with elemental and spectroscopic analyses, we showed that SOM in depositional settings is less transformed and better preserved than SOM in eroding landform positions. However, which environmental factors exert primary control on storage and persistence of SOM depended on the nature of the landform position considered. In an annual grassland watershed, protection of SOM by physical isolation inside aggregates and chemical association of organic matter (complexation) with soil minerals, as assessed by correlation with radiocarbon concentration, were more effective in the poorly drained, lowest-lying depositional landform positions, compared to well-drained landform positions in the upper parts of the watershed. Results of this study demonstrated that processes of soil erosion and deposition are important mechanisms of long-term OM stabilization.

Application of Electrokinetic Stabilisation (EKS) Method for Soft Soil: A Review

NASA Astrophysics Data System (ADS)

Azhar, ATS; Azim, MAM; Syakeera, NN; Jefferson, IF; Rogers, CDF

2017-08-01

Soil properties such as low shear strength, excessive compression, collapsing behavior, high swell potential are some of the undesirable properties of soils in geotechnical engineering and those properties would cause severe distress to the structures. To solve these, an innovative stabilization of Electrokinetic (EKS) has been introduced. Electrokinetic is an applicable technique to transport charged particles and fluid in an electric potential. The EKS demonstrates changes in soil pH due to electrolysis reactions, water flow between the electrodes and migration of ions towards the cathode. This treatment has proven its efficiency in consolidating organic, peat and clayey silt as well as less expensive than other methods. Otherwise, this method also gives advantage by not disturbing site. The primary objective of this review is to discuss the application of electrokinetic and to investigate the current knowledge of electrokinetic in geotechnical application through a literature search and review, including consideration of certain aspects related to the soft soil application that may be relevant to the future study and at the same time addressing some key issues and their implications on soil behaviors.

Stabilization of carbon in composts and biochars in relation to carbon sequestration and soil fertility.

PubMed

Bolan, N S; Kunhikrishnan, A; Choppala, G K; Thangarajan, R; Chung, J W

2012-05-01

There have been increasing interests in the conversion of organic residues into biochars in order to reduce the rate of decomposition, thereby enhancing carbon (C) sequestration in soils. However energy is required to initiate the pyrolysis process during biochar production which can also lead to the release of greenhouse gasses. Alternative methods can be used to stabilize C in composts and other organic residues without impacting their quality. The objectives of this study include: (i) to compare the rate of decomposition among various organic amendments and (ii) to examine the effect of clay materials on the stabilization of C in organic amendments. The decomposition of a number of organic amendments (composts and biochars) was examined by monitoring the release of carbon-dioxide using respiration experiments. The results indicated that the rate of decomposition as measured by half life (t(1/2)) varied between the organic amendments and was higher in sandy soil than in clay soil. The half life value ranged from 139 days in the sandy soil and 187 days in the clay soil for poultry manure compost to 9989 days for green waste biochar. Addition of clay materials to compost decreased the rate of decomposition, thereby increasing the stabilization of C. The half life value for poultry manure compost increased from 139 days to 620, 806 and 474 days with the addition of goethite, gibbsite and allophane, respectively. The increase in the stabilization of C with the addition of clay materials may be attributed to the immobilization of C, thereby preventing it from microbial decomposition. Stabilization of C in compost using clay materials did not impact negatively the value of composts in improving soil quality as measured by potentially mineralizable nitrogen and microbial biomass carbon in soil. Copyright © 2012 Elsevier B.V. All rights reserved.

The diversity of methoxyphenols released by pyrolysis-gas chromatography as predictor of soil carbon storage.

PubMed

Jiménez-González, Marco A; Álvarez, Ana M; Carral, Pilar; González-Vila, Francisco J; Almendros, Gonzalo

2017-07-28

The variable extent to which environmental factors are involved in soil carbon storage is currently a subject of controversy. In fact, justifying why some soils accumulate more organic matter than others is not trivial. Some abiotic factors such as organo-mineral associations have classically been invoked as the main drivers for soil C stabilization. However, in this research indirect evidences based on correlations between soil C storage and compositional descriptors of the soil organic matter are presented. It is assumed that the intrinsic structure of soil organic matter should have a bearing in the soil carbon storage. This is examined here by focusing on the methoxyphenols released by direct pyrolysis from a wide variety of topsoil samples from continental Mediterranean ecosystems from Spain with different properties and carbon content. Methoxyphenols are typical signature compounds presumptively informing on the occurrence and degree of alteration of lignin in soils. The methoxyphenol assemblages (12 major guaiacyl- and syringyl-type compounds) were analyzed by pyrolysis-gas chromatography-mass spectrometry. The Shannon-Wiener diversity index was chosen to describe the complexity of this phenolic signature. A series of exploratory statistical analyses (simple regression, partial least squares regression, multidimensional scaling) were applied to analyze the relationships existing between chemical and spectroscopic characteristics and the carbon content in the soils. These treatments coincided in pointing out that significant correlations exist between the progressive molecular diversity of the methoxyphenol assemblages and the concentration of organic carbon stored in the corresponding soils. This potential of the diversity in the phenolic signature as a surrogate index of the carbon storage in soils is tentatively interpreted as the accumulation of plant macromolecules altered into microbially reworked structures not readily recognized by soil enzymes. From a quantitative viewpoint, the partial least squares regression models exclusively based on total abundances of the 12 major methoxyphenols were especially successful in forecasting soil carbon storage. Copyright © 2017 Elsevier B.V. All rights reserved.

Integrating plant-microbe interactions to understand soil C stabilization with the MIcrobial-MIneral Carbon Stabilization model (MIMICS)

NASA Astrophysics Data System (ADS)

Grandy, Stuart; Wieder, Will; Kallenbach, Cynthia; Tiemann, Lisa

2014-05-01

If soil organic matter is predominantly microbial biomass, plant inputs that build biomass should also increase SOM. This seems obvious, but the implications fundamentally change how we think about the relationships between plants, microbes and SOM. Plant residues that build microbial biomass are typically characterized by low C/N ratios and high lignin contents. However, plants with high lignin contents and high C/N ratios are believed to increase SOM, an entrenched idea that still strongly motivates agricultural soil management practices. Here we use a combination of meta-analysis with a new microbial-explicit soil biogeochemistry model to explore the relationships between plant litter chemistry, microbial communities, and SOM stabilization in different soil types. We use the MIcrobial-MIneral Carbon Stabilization (MIMICS) model, newly built upon the Community Land Model (CLM) platform, to enhance our understanding of biology in earth system processes. The turnover of litter and SOM in MIMICS are governed by the activity of r- and k-selected microbial groups and temperature sensitive Michaelis-Menten kinetics. Plant and microbial residues are stabilized short-term by chemical recalcitrance or long-term by physical protection. Fast-turnover litter inputs increase SOM by >10% depending on temperature in clay soils, and it's only in sandy soils devoid of physical protection mechanisms that recalcitrant inputs build SOM. These results challenge centuries of lay knowledge as well as conventional ideas of SOM formation, but are they realistic? To test this, we conducted a meta-analysis of the relationships between the chemistry of plant liter inputs and SOM concentrations. We find globally that the highest SOM concentrations are associated with plant inputs containing low C/N ratios. These results are confirmed by individual tracer studies pointing to greater stabilization of low C/N ratio inputs, particularly in clay soils. Our model and meta-analysis results suggest that current ideas about plant-microbe-SOM relationships are unraveling. If so, our reconsideration of the mechanisms stabilizing SOM will also challenge long-held views about how to optimize plant community management to increase SOM.

Soil organic matter stabilization in grazing highland soils from the Andean Plateau

NASA Astrophysics Data System (ADS)

Muñoz, M. A.; Faz, A.; Zornoza, R.

2012-04-01

Grasslands comprise approximately 40% of the earth's land area and play a critical role in the global carbon cycle. Apolobamba is a grazing highland located in the Andean Plateau where sustainable vicuna (Vicugna vicugna) management programme is carried out. Understanding the soil properties and the organic matter dynamics is fundamental to determine the grazing impacts in the carbon reservoirs. However, the labile and recalcitrant fractions of C have not been widely studied under field conditions, especially in high grasslands. The objectives of this survey were to: (i) achieve a soil characterization through general physico-chemical properties and (ii) study soil organic matter stabilization through recalcitrant and labile carbon budgets in Apolobamba. Regarding the lastly vicuna censuses carried out in the studied area, eight representative zones with different vicuna densities were selected and soil samples were collected. Other characteristics were also considered to select the study zones: (1) alpaca densities, (2) vegetation communities (3) plant cover and (4) landscape and geo-morphological description. Recalcitrant and water soluble organic carbon were determined as well as recalcitrant index. General soil characterization showed strongly acid and no saline soils with high cation exchange capacity and sandy-loam and loam textures. Total nitrogen contents indicated no limitation for the native vegetation growth. In general, no relationships were found among general soil properties, vicuna and alpaca densities; however, zones with highest alpaca density could be prone to soil erosion based on the available P distribution and the texture results. Additionally, a negative alpaca grazing influence in the soil organic carbon stocks was observed. On the other hand, high soil recalcitrant carbon contents (3.7 ± 0.3 kg m-2) and recalcitrance index (0.8 ± 0.1) were found. Likewise, labile C exhibited similar values to those obtained from researchers conducted in grasslands. These observations could be positive aspects in the preservation or stabilization of the soil mineral particles and the long term carbon sequestration. We suggest that the soil C stabilization mechanisms in mountain grassland may be affected by the lower temperatures and acid soil pH. In conclusion, Apolobamba could have a significant reservoir of stabilized soil organic matter. However, there is an urgent need to establish soil protection strategies against the alpaca overexploitation in order to protect the organic matter stocks and to continue with the vicuna sustainable management in the Andean Plateau. Keywords: carbon reservoirs, highland soils, recalcitrant carbon, vicuna

Soil development along a glacial chronosequence (Pré de Bar glacier, NW Italy)

NASA Astrophysics Data System (ADS)

Letey, Stéphanie; Freppaz, Michele; Filippa, Gianluca; Stanchi, Silvia; Cerli, Chiara; Pogliotti, Paolo; Zanini, Ermanno

2010-05-01

After the maximum expansion phase of the Little Ice Age, soils located in proglacial areas in the Italian Alps evolved over a time span of about 190 years. In the future, as a consequence of climate change, additional areas will become ice-free and therefore subject to pedogenesis. In such conditions, ice retreat time and topography are expected to play a major role among soil formation factors. Due to extreme environmental characteristics, soil evolution will be rather slow, and heavily influenced by severe soil loss phenomena (e.g. water erosion due to extreme rainfall event and snowmelt, avalanche erosion). We investigated the soil formation along a glacial chronosequence of an Alpine glacier foreland. The Pré de Bar glacier is located in North West Italy (Aosta Valley Region), in the Mont Blanc massif, between 3750 and 2150 m a.s.l. and it covers an area of 340 ha. The glacier was chosen because of the availability of old photographs documenting the glacier retreat phases starting from 1820. At the present time, the cumulative retreat length of the Pré de Bar glacier has reached 1600 m. Along this length, sampling sites were established at 6 successional stages from 6 to 189 years since deglaciation, from 2100 to 1880 m a.s.l.. Soil profiles were opened and sampled according to diagnostic horizons, then they were characterized by means of standard chemical and physical methods. Moreover, as recently deglaciated soils, characterized by incipient pedogenesis, may be particularly vulnerable from the physical point of view, the Atterberg Limits (LL, Liquid Limit; and PL, Plastic Limit) and the WAS (Water Aggregate Stability) index were determined, as indicators of soil physical quality. Soil samples were also subjected to organic matter density fractionation to assess the role of organic C in structure development. All the analyzed soils were classified as Lythic Cryorthents (higher elevation) or Typic Cryorthents (lower elevation) (USDA - Soil Taxonomy), with depth ranging between 25 and 40 cm, regularly increasing with years since deglaciation. A similar trend was observed for the organic C content. A true organo-mineral horizon (A) was first identified approximately 65 years after deglaciation. We observed a general increase of soil physical quality along the chronosequence. Recently deglaciated soils displayed higher vulnerability to aggregate and consistence losses, i.e. lower LL and scarce or no plasticity, while the profiles at lower altitudes, on the oldest surfaces, displayed better properties, i.e. more developed structure and consistence, even for relatively young soils. Therefore in this area the stabilization of the material after the deglaciation resulted relatively fast, with a reduction of its vulnerability to mass and erosive processes, through soil development. This research is carried out as part of "PERMANET - Permafrost Long-Term Monitoring Network", a EU co-funded Interreg Project under the Alpine Space Programme 2007-2013.

Deep Soil Carbon in the Critical Zone: Amount and Nature of Carbon in Weathered Bedrock, and its Implication for Soil Carbon Inventory

NASA Astrophysics Data System (ADS)

Moreland, K. C.; Tian, Z.; Berhe, A. A.; O'Geen, A. T.

2017-12-01

Globally, soils store more carbon (C) than the vegetation and the atmosphere combined. Up to 60-80% of the C stored in soils is found in below 30cm soil depth, but there is little data on C storage in weathered bedrock or saprolite. Deep soil organic matter (SOM) can be a mixture of new and old SOM; that is rendered relatively stable due to burial, aggregation, its disconnection from decomposers, and chemical association that organic matter forms with soil minerals. The limited data available on deep SOM dynamics suggests that stock, distribution, and composition of deep SOM are strongly correlated to climate. The overall objective of this research is to investigate how climate regulates OM storage, composition, stability, and stabilization mechanisms. Expecting that the amount of OM stored in deep soil and the stability are a function of soil thickness and availability of weathering products (i.e. reactive minerals), the stock and stability of deep SOM is expected to follow a similar relationship with climate, as does the intensity of weathering. This research is conducted in the NSF funded Southern Sierra Critical Zone Observatories that is located along a climosequence, the western slopes of the Sierra Naevada Mountains of California. Here we will present results derived from characterization of soils and weathered bedrock using elemental and stable isotope elemental analysis, and Fourier Transformed Infrared Spectroscopy to determine OM concentration and functional group level composition of bulk SOM. Our findings show that adding in subsoil and weathered bedrock C stocks increases estimates of soil C stock by 1/3rd to 2/3rd.

Annual Removal of Aboveground Plant Biomass Alters Soil Microbial Responses to Warming

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

Xue, Kai; Yuan, Mengting M.; Xie, Jianping

Clipping (i.e., harvesting aboveground plant biomass) is common in agriculture and for bioenergy production. However, microbial responses to clipping in the context of climate warming are poorly understood. We investigated the interactive effects of grassland warming and clipping on soil properties and plant and microbial communities, in particular, on microbial functional genes. Clipping alone did not change the plant biomass production, but warming and clipping combined increased the C4 peak biomass by 47% and belowground net primary production by 110%. Clipping alone and in combination with warming decreased the soil carbon input from litter by 81% and 75%, respectively. Withmore » less carbon input, the abundances of genes involved in degrading relatively recalcitrant carbon increased by 38% to 137% in response to either clipping or the combined treatment, which could weaken long-term soil carbon stability and trigger positive feedback with respect to warming. Clipping alone also increased the abundance of genes for nitrogen fixation, mineralization, and denitrification by 32% to 39%. Such potentially stimulated nitrogen fixation could help compensate for the 20% decline in soil ammonium levels caused by clipping alone and could contribute to unchanged plant biomass levels. Moreover, clipping tended to interact antagonistically with warming, especially with respect to effects on nitrogen cycling genes, demonstrating that single-factor studies cannot predict multifactorial changes. These results revealed that clipping alone or in combination with warming altered soil and plant properties as well as the abundance and structure of soil microbial functional genes. Aboveground biomass removal for biofuel production needs to be reconsidered, as the long-term soil carbon stability may be weakened. IMPORTANCE Global change involves simultaneous alterations, including those caused by climate warming and land management practices (e.g., clipping). Data on the interactive effects of warming and clipping on ecosystems remain elusive, particularly in microbial ecology. This study found that clipping alters microbial responses to warming and demonstrated the effects of antagonistic interactions between clipping and warming on microbial functional genes. Clipping alone or combined with warming enriched genes degrading relatively recalcitrant carbon, likely reflecting the decreased quantity of soil carbon input from litter, which could weaken long-term soil C stability and trigger positive warming feedback. These results have important implications in assessing and predicting the consequences of global climate change and indicate that the removal of aboveground biomass for biofuel production may need to be reconsidered.« less

Annual Removal of Aboveground Plant Biomass Alters Soil Microbial Responses to Warming

DOE PAGES

Xue, Kai; Yuan, Mengting M.; Xie, Jianping; ...

2016-09-27

Clipping (i.e., harvesting aboveground plant biomass) is common in agriculture and for bioenergy production. However, microbial responses to clipping in the context of climate warming are poorly understood. We investigated the interactive effects of grassland warming and clipping on soil properties and plant and microbial communities, in particular, on microbial functional genes. Clipping alone did not change the plant biomass production, but warming and clipping combined increased the C4 peak biomass by 47% and belowground net primary production by 110%. Clipping alone and in combination with warming decreased the soil carbon input from litter by 81% and 75%, respectively. Withmore » less carbon input, the abundances of genes involved in degrading relatively recalcitrant carbon increased by 38% to 137% in response to either clipping or the combined treatment, which could weaken long-term soil carbon stability and trigger positive feedback with respect to warming. Clipping alone also increased the abundance of genes for nitrogen fixation, mineralization, and denitrification by 32% to 39%. Such potentially stimulated nitrogen fixation could help compensate for the 20% decline in soil ammonium levels caused by clipping alone and could contribute to unchanged plant biomass levels. Moreover, clipping tended to interact antagonistically with warming, especially with respect to effects on nitrogen cycling genes, demonstrating that single-factor studies cannot predict multifactorial changes. These results revealed that clipping alone or in combination with warming altered soil and plant properties as well as the abundance and structure of soil microbial functional genes. Aboveground biomass removal for biofuel production needs to be reconsidered, as the long-term soil carbon stability may be weakened. IMPORTANCE Global change involves simultaneous alterations, including those caused by climate warming and land management practices (e.g., clipping). Data on the interactive effects of warming and clipping on ecosystems remain elusive, particularly in microbial ecology. This study found that clipping alters microbial responses to warming and demonstrated the effects of antagonistic interactions between clipping and warming on microbial functional genes. Clipping alone or combined with warming enriched genes degrading relatively recalcitrant carbon, likely reflecting the decreased quantity of soil carbon input from litter, which could weaken long-term soil C stability and trigger positive warming feedback. These results have important implications in assessing and predicting the consequences of global climate change and indicate that the removal of aboveground biomass for biofuel production may need to be reconsidered.« less

Modelling and interpreting biologically crusted dryland soil sub-surface structure using automated micropenetrometry

NASA Astrophysics Data System (ADS)

Hoon, Stephen R.; Felde, Vincent J. M. N. L.; Drahorad, Sylvie L.; Felix-Henningsen, Peter

2015-04-01

Soil penetrometers are used routinely to determine the shear strength of soils and deformable sediments both at the surface and throughout a depth profile in disciplines as diverse as soil science, agriculture, geoengineering and alpine avalanche-safety (e.g. Grunwald et al. 2001, Van Herwijnen et al. 2009). Generically, penetrometers comprise two principal components: An advancing probe, and a transducer; the latter to measure the pressure or force required to cause the probe to penetrate or advance through the soil or sediment. The force transducer employed to determine the pressure can range, for example, from a simple mechanical spring gauge to an automatically data-logged electronic transducer. Automated computer control of the penetrometer step size and probe advance rate enables precise measurements to be made down to a resolution of 10's of microns, (e.g. the automated electronic micropenetrometer (EMP) described by Drahorad 2012). Here we discuss the determination, modelling and interpretation of biologically crusted dryland soil sub-surface structures using automated micropenetrometry. We outline a model enabling the interpretation of depth dependent penetration resistance (PR) profiles and their spatial differentials using the model equations, σ {}(z) ={}σ c0{}+Σ 1n[σ n{}(z){}+anz + bnz2] and dσ /dz = Σ 1n[dσ n(z) /dz{} {}+{}Frn(z)] where σ c0 and σ n are the plastic deformation stresses for the surface and nth soil structure (e.g. soil crust, layer, horizon or void) respectively, and Frn(z)dz is the frictional work done per unit volume by sliding the penetrometer rod an incremental distance, dz, through the nth layer. Both σ n(z) and Frn(z) are related to soil structure. They determine the form of σ {}(z){} measured by the EMP transducer. The model enables pores (regions of zero deformation stress) to be distinguished from changes in layer structure or probe friction. We have applied this method to both artificial calibration soils in the laboratory, and in-situ field studies. In particular, we discuss the nature and detection of surface and buried (fossil) subsurface Biological Soil Crusts (BSCs), voids, macroscopic particles and compositional layers. The strength of surface BSCs and the occurrence of buried BSCs and layers has been detected at sub millimetre scales to depths of 40mm. Our measurements and field observations of PR show the importance of morphological layering to overall BSC functions (Felde et al. 2015). We also discuss the effect of penetrometer shaft and probe-tip profiles upon the theoretical and experimental curves, EMP resolution and reproducibility, demonstrating how the model enables voids, buried biological soil crusts, exotic particles, soil horizons and layers to be distinguished one from another. This represents a potentially important contribution to advancing understanding of the relationship between BSCs and dryland soil structure. References: Drahorad SL, Felix-Henningsen P. (2012) An electronic micropenetrometer (EMP) for field measurements of biological soil crust stability, J. Plant Nutr. Soil Sci., 175, 519-520 Felde V.J.M.N.L., Drahorad S.L., Felix-Henningsen P., Hoon S.R. (2015) Ongoing oversanding induces biological soil crust layering - a new approach for BSC structure elucidation determined from high resolution penetration resistance data (submitted) Grunwald, S., Rooney D.J., McSweeney K., Lowery B. (2001) Development of pedotransfer functions for a profile cone penetrometer, Geoderma, 100, 25-47 Van Herwijnen A., Bellaire S., Schweizer J. (2009) Comparison of micro-structural snowpack parameters derived from penetration resistance measurements with fracture character observations from compression tests, Cold Regions Sci. {& Technol.}, 59, 193-201

Soil carbon sequestration potential of permanent pasture and continuous cropping soils in New Zealand.

PubMed

McNally, Sam R; Beare, Mike H; Curtin, Denis; Meenken, Esther D; Kelliher, Francis M; Calvelo Pereira, Roberto; Shen, Qinhua; Baldock, Jeff

2017-11-01

Understanding soil organic carbon (SOC) sequestration is important to develop strategies to increase the SOC stock and, thereby, offset some of the increases in atmospheric carbon dioxide. Although the capacity of soils to store SOC in a stable form is commonly attributed to the fine (clay + fine silt) fraction, the properties of the fine fraction that determine the SOC stabilization capacity are poorly known. The aim of this study was to develop an improved model to estimate the SOC stabilization capacity of Allophanic (Andisols) and non-Allophanic topsoils (0-15 cm) and, as a case study, to apply the model to predict the sequestration potential of pastoral soils across New Zealand. A quantile (90th) regression model, based on the specific surface area and extractable aluminium (pyrophosphate) content of soils, provided the best prediction of the upper limit of fine fraction carbon (FFC) (i.e. the stabilization capacity), but with different coefficients for Allophanic and non-Allophanic soils. The carbon (C) saturation deficit was estimated as the difference between the stabilization capacity of individual soils and their current C concentration. For long-term pastures, the mean saturation deficit of Allophanic soils (20.3 mg C g -1 ) was greater than that of non-Allophanic soils (16.3 mg C g -1 ). The saturation deficit of cropped soils was 1.14-1.89 times that of pasture soils. The sequestration potential of pasture soils ranged from 10 t C ha -1 (Ultic soils) to 42 t C ha -1 (Melanic soils). Although meeting the estimated national soil C sequestration potential (124 Mt C) is unrealistic, improved management practices targeted to those soils with the greatest sequestration potential could contribute significantly to off-setting New Zealand's greenhouse gas emissions. As the first national-scale estimate of SOC sequestration potential that encompasses both Allophanic and non-Allophanic soils, this serves as an informative case study for the international community. © 2017 John Wiley & Sons Ltd.

Identification and stabilization methods for problematic silt soils : technical summary.

DOT National Transportation Integrated Search

2002-05-01

The objective of this research are to (1) identify the soil properties and characteristics that contribute to a pumping condition, (2) evaluate the effectiveness of selected chemical stabilization techniques, and (3) provide a recommendation for alte...

Biofuel co-product uses for pavement geo-materials stabilization : tech transfer summary, April 2010.

DOT National Transportation Integrated Search

2010-04-01

Objectives : Evaluate the ability of biofuel co-product (BCP) to function as an effective soil stabilizing agent. : Investigate the effect of BCP on the engineering properties of soil-BCP mixtures for Iowa conditions.

The Microbial Efficiency-Matrix Stabilization (MEMS) framework integrates plant litter decomposition with soil organic matter stabilization: do labile plant inputs form stable soil organic matter?

PubMed

Cotrufo, M Francesca; Wallenstein, Matthew D; Boot, Claudia M; Denef, Karolien; Paul, Eldor

2013-04-01

The decomposition and transformation of above- and below-ground plant detritus (litter) is the main process by which soil organic matter (SOM) is formed. Yet, research on litter decay and SOM formation has been largely uncoupled, failing to provide an effective nexus between these two fundamental processes for carbon (C) and nitrogen (N) cycling and storage. We present the current understanding of the importance of microbial substrate use efficiency and C and N allocation in controlling the proportion of plant-derived C and N that is incorporated into SOM, and of soil matrix interactions in controlling SOM stabilization. We synthesize this understanding into the Microbial Efficiency-Matrix Stabilization (MEMS) framework. This framework leads to the hypothesis that labile plant constituents are the dominant source of microbial products, relative to input rates, because they are utilized more efficiently by microbes. These microbial products of decomposition would thus become the main precursors of stable SOM by promoting aggregation and through strong chemical bonding to the mineral soil matrix. © 2012 Blackwell Publishing Ltd.

Biological degradation of gas-filled composite materials on the base of polyethylene

NASA Astrophysics Data System (ADS)

Grigoreva, E. A.; Kolesnikova, N. N.; Popov, A. A.; Olkhov, A. A.

2017-12-01

Gas-filled composite materials based on polyethylene were obtained. It was assumed that introduction of porosity in polyethylene will improve the biodegradability of synthetic materials. The morphological and structural changes were estimated, physical and mechanical properties, stability in water and soil of these materials were determined. It is stated that filling the polymer matrix with pores increases the ability to degrade in nature.

Evaluating the potential of three Fe- and Mn-(nano)oxides for the stabilization of Cd, Cu and Pb in contaminated soils.

PubMed

Michálková, Zuzana; Komárek, Michael; Šillerová, Hana; Della Puppa, Loïc; Joussein, Emmanuel; Bordas, François; Vaněk, Aleš; Vaněk, Ondřej; Ettler, Vojtěch

2014-12-15

The potential of three Fe- and Mn-(nano)oxides for stabilizing Cd, Cu and Pb in contaminated soils was investigated using batch and column experiments, adsorption tests and tests of soil microbial activity. A novel synthetic amorphous Mn oxide (AMO), which was recently proposed as a stabilizing amendment, proved to be the most efficient in decreasing the mobility of the studied metals compared to nano-maghemite and nano-magnetite. Its application resulted in significant decreases of exchangeable metal fractions (92%, 92% and 93% decreases of Cd, Cu and Pb concentrations, respectively). The adsorption capacity of the AMO was an order of magnitude higher than those recorded for the other amendments. It was also the most efficient treatment for reducing Cu concentrations in the soil solution. No negative effects on soil microorganisms were recorded. On the other hand, the AMO was able to dissolve soil organic matter to some extent. Copyright © 2014 Elsevier Ltd. All rights reserved.

Subsurface Characterization using Geophysical Seismic Refraction Survey for Slope Stabilization Design with Soil Nailing

NASA Astrophysics Data System (ADS)

Ashraf Mohamad Ismail, Mohd; Ng, Soon Min; Hazreek Zainal Abidin, Mohd; Madun, Aziman

2018-04-01

The application of geophysical seismic refraction for slope stabilization design using soil nailing method was demonstrated in this study. The potential weak layer of the study area is first identify prior to determining the appropriate length and location of the soil nail. A total of 7 seismic refraction survey lines were conducted at the study area with standard procedures. The refraction data were then analyzed by using the Pickwin and Plotrefa computer software package to obtain the seismic velocity profiles distribution. These results were correlated with the complementary borehole data to interpret the subsurface profile of the study area. It has been identified that layer 1 to 3 is the potential weak zone susceptible to slope failure. Hence, soil nails should be installed to transfer the tensile load from the less stable layer 3 to the more stable layer 4. The soil-nail interaction will provide a reinforcing action to the soil mass thereby increasing the stability of the slope.

Stability numerical analysis of soil cave in karst area to drawdown of underground water level

NASA Astrophysics Data System (ADS)

Mo, Yizheng; Xiao, Rencheng; Deng, Zongwei

2018-05-01

With the underground water level falling, the reliable estimates of the stability and deformation characteristics of soil caves in karst region area are required for analysis used for engineering design. Aimed at this goal, combined with practical engineering and field geotechnical test, detail analysis on vertical maximum displacement of top, vertical maximum displacement of surface, maximum principal stress and maximum shear stress were conducted by finite element software, with an emphasis on two varying factors: the size and the depth of soil cave. The calculations on the soil cave show that, its stability of soil cave is affected by both the size and depth, and only when extending a certain limit, the collapse occurred along with the falling of underground water; Additionally, its maximum shear stress is in arch toes, and its deformation curve trend of maximum displacement is similar to the maximum shear stress, which further verified that the collapse of soil cave was mainly due to shear-failure.

Soil Microbial Community Structure across a Thermal Gradient following a Geothermal Heating Event

PubMed Central

Norris, Tracy B.; Wraith, Jon M.; Castenholz, Richard W.; McDermott, Timothy R.

2002-01-01

In this study microbial species diversity was assessed across a landscape in Yellowstone National Park, where an abrupt increase in soil temperature had occurred due to recent geothermal activity. Soil temperatures were measured, and samples were taken across a temperature gradient (35 to 65°C at a 15-cm depth) that spanned geothermally disturbed and unimpacted soils; thermally perturbed soils were visually apparent by the occurrence of dead or dying lodgepole pine trees. Changes in soil microbial diversity across the temperature gradient were qualitatively assessed based on 16S rRNA sequence variation as detected by denaturing gradient gel electrophoresis (DGGE) using both ribosomal DNA (rDNA) and rRNA as PCR templates and primers specific for the Bacteria or Archaea domain. The impact of the major heating disturbance was apparent in that DGGE profiles from heated soils appeared less complex than those from the unaffected soils. Phylogenetic analysis of a bacterial 16S rDNA PCR clone library from a recently heated soil showed that a majority of the clones belonged to the Acidobacterium (51%) and Planctomyces (18%) divisions. Agar plate counts of soil suspensions cultured on dilute yeast extract and R2A agar media incubated at 25 or 50°C revealed that thermophile populations were two to three orders of magnitude greater in the recently heated soil. A soil microcosm laboratory experiment simulated the geothermal heating event. As determined by both RNA- and DNA-based PCR coupled with DGGE, changes in community structure (marked change in the DGGE profile) of soils incubated at 50°C occurred within 1 week and appeared to stabilize after 3 weeks. The results of our molecular and culture data suggest that thermophiles or thermotolerant species are randomly distributed in this area within Yellowstone National Park and that localized thermal activity selects for them. PMID:12450855

Soil microbial community structure across a thermal gradient following a geothermal heating event.

PubMed

Norris, Tracy B; Wraith, Jon M; Castenholz, Richard W; McDermott, Timothy R

2002-12-01

In this study microbial species diversity was assessed across a landscape in Yellowstone National Park, where an abrupt increase in soil temperature had occurred due to recent geothermal activity. Soil temperatures were measured, and samples were taken across a temperature gradient (35 to 65 degrees C at a 15-cm depth) that spanned geothermally disturbed and unimpacted soils; thermally perturbed soils were visually apparent by the occurrence of dead or dying lodgepole pine trees. Changes in soil microbial diversity across the temperature gradient were qualitatively assessed based on 16S rRNA sequence variation as detected by denaturing gradient gel electrophoresis (DGGE) using both ribosomal DNA (rDNA) and rRNA as PCR templates and primers specific for the Bacteria or Archaea domain. The impact of the major heating disturbance was apparent in that DGGE profiles from heated soils appeared less complex than those from the unaffected soils. Phylogenetic analysis of a bacterial 16S rDNA PCR clone library from a recently heated soil showed that a majority of the clones belonged to the Acidobacterium (51%) and Planctomyces (18%) divisions. Agar plate counts of soil suspensions cultured on dilute yeast extract and R2A agar media incubated at 25 or 50 degrees C revealed that thermophile populations were two to three orders of magnitude greater in the recently heated soil. A soil microcosm laboratory experiment simulated the geothermal heating event. As determined by both RNA- and DNA-based PCR coupled with DGGE, changes in community structure (marked change in the DGGE profile) of soils incubated at 50 degrees C occurred within 1 week and appeared to stabilize after 3 weeks. The results of our molecular and culture data suggest that thermophiles or thermotolerant species are randomly distributed in this area within Yellowstone National Park and that localized thermal activity selects for them.

Linking soil bacterial biodiversity and soil carbon stability.

PubMed

Mau, Rebecca L; Liu, Cindy M; Aziz, Maliha; Schwartz, Egbert; Dijkstra, Paul; Marks, Jane C; Price, Lance B; Keim, Paul; Hungate, Bruce A

2015-06-01

Native soil carbon (C) can be lost in response to fresh C inputs, a phenomenon observed for decades yet still not understood. Using dual-stable isotope probing, we show that changes in the diversity and composition of two functional bacterial groups occur with this 'priming' effect. A single-substrate pulse suppressed native soil C loss and reduced bacterial diversity, whereas repeated substrate pulses stimulated native soil C loss and increased diversity. Increased diversity after repeated C amendments contrasts with resource competition theory, and may be explained by increased predation as evidenced by a decrease in bacterial 16S rRNA gene copies. Our results suggest that biodiversity and composition of the soil microbial community change in concert with its functioning, with consequences for native soil C stability.

Nuclear Magnetic Resonance Relaxation and Imaging Studies on Water Flow in Soil Cores

NASA Astrophysics Data System (ADS)

Pohlmeier, Andreas; Haber-Pohlmeier, Sabina; Stapf, Siegfried

2010-05-01

Magnetic resonance imaging (MRI) is applied to the study of flow processes in a model and a natural soils core. Since flow velocities in soils are mostly too slow to be monitored directly by MRI flow velocity imaging, Gd-DTPA was used as contrast agent for the first time for flow processes in soils. Apart from its chemical stability the main advantage is the anionic net charge in neutral aqueous solution. Here we can show that this property hinders the adsorption at soil mineral surfaces and therefore retardation. Gd-DTPA turns out to be a very convenient conservative tracer for the investigation of flow processes in model and natural soil cores. With respect to the flow processes in the coaxial model soil column and the natural soil column we found total different flow patterns: In the first case tracer plume moves quite homogeneously only in the inner highly conductive core. No penetration into the outer fine material takes place. In contrast, the natural soil core shows a flow pattern which is characterized by preferential paths avoiding dense regions and preferring loose structures. In the case of the simpler model column also the local flow velocities are calculated by the application of a peak tracking algorithm.

Tundra fire disturbance homogonizes belowground food web structure, function and dynamics

NASA Astrophysics Data System (ADS)

Moore, J. C.; Pressler, Y.; Koltz, A.; Asmus, A.; Simpson, R.

2016-12-01

Tundra fires on Alaska's North Slope are on the rise due to increased lightning strikes since 2000. On July 16, 2007 lightning ignited the Anaktuvuk River fire, burning a 40-by-10 mile swath of tundra about 24 miles north of Toolik Field Station. The fire burned 401 square miles, was visible from space, and released more than 2.3 million tons of carbon into the atmosphere. A large amount of the organic layer of the soil was burned, changing the over all composition of the site and exposing deeper soil horizons. Due to fundamental transitions in soil characteristics and vegetation we hypothesized that the belowground food web community would be affected both in terms of biomass and location within the soil profile. Microbial biomass was reduced with burn severity. In the lower organic horizon there was a significant reduction in fungal biomass but we did not observe this effect in the upper organic soil. We did not observe a significant effect of burn severity on individual group biomass within higher trophic levels. Canonical Discriminant Analysis using the biomass estimates of the functional groups in the food webs found that the webs are becoming increasingly homogenized in the severely burned site compared to the moderately burned and unburned sites. The unburned soils differed significantly from soil at both burn sites; the greatest effects on food web structure were at the lower organic depth, whereas. We modeled the effects of the fire on soil organic matter processing rates and energy flow through the three food webs. The model estimated a decrease in C and N mineralization with fire severity, due in large part to the loss of organic material. While the organic horizon at the unburned site had 12 times greater C and N mineralization than the mineral soils, we observed little to no difference in C and N mineralization between the organic and mineral soil horizons in the moderately and severely burned sites. Our results show that the fire significantly altered the trophic structure of the soil food web, with loss of trophic complexity with increasing fire severity, which correlated strongly with C and N processing and food web stability.

Water and solute transport in agricultural soils predicted by volumetric clay and silt contents

NASA Astrophysics Data System (ADS)

Karup, Dan; Moldrup, Per; Paradelo, Marcos; Katuwal, Sheela; Norgaard, Trine; Greve, Mogens H.; de Jonge, Lis W.

2016-09-01

Solute transport through the soil matrix is non-uniform and greatly affected by soil texture, soil structure, and macropore networks. Attempts have been made in previous studies to use infiltration experiments to identify the degree of preferential flow, but these attempts have often been based on small datasets or data collected from literature with differing initial and boundary conditions. This study examined the relationship between tracer breakthrough characteristics, soil hydraulic properties, and basic soil properties. From six agricultural fields in Denmark, 193 intact surface soil columns 20 cm in height and 20 cm in diameter were collected. The soils exhibited a wide range in texture, with clay and organic carbon (OC) contents ranging from 0.03 to 0.41 and 0.01 to 0.08 kg kg- 1, respectively. All experiments were carried out under the same initial and boundary conditions using tritium as a conservative tracer. The breakthrough characteristics ranged from being near normally distributed to gradually skewed to the right along with an increase in the content of the mineral fines (particles ≤ 50 μm). The results showed that the mineral fines content was strongly correlated to functional soil structure and the derived tracer breakthrough curves (BTCs), whereas the OC content appeared less important for the shape of the BTC. Organic carbon was believed to support the stability of the soil structure rather than the actual formation of macropores causing preferential flow. The arrival times of 5% and up to 50% of the tracer mass were found to be strongly correlated with volumetric fines content. Predicted tracer concentration breakthrough points as a function of time up to 50% of applied tracer mass could be well fitted to an analytical solution to the classical advection-dispersion equation. Both cumulative tracer mass and concentration as a function of time were well predicted from the simple inputs of bulk density, clay and silt contents, and applied tracer mass. The new concept seems promising as a platform towards more accurate proxy functions for dissolved contaminant transport in intact soil.

Plant stimulation of soil microbial community succession: how sequential expression mediates soil carbon stabilization and turnover

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

Firestone, Mary

2015-03-31

It is now understood that most plant C is utilized or transformed by soil microorganisms en route to stabilization. Hence the composition of microbial communities that mediate decomposition and transformation of root C is critical, as are the metabolic capabilities of these communities. The change in composition and function of the C-transforming microbial communities over time in effect defines the biological component of soil C stabilization. Our research was designed to test 2 general hypotheses; the first two hypotheses are discussed first; H1: Root-exudate interactions with soil microbial populations results in the expression of enzymatic capacities for macromolecular, complex carbonmore » decomposition; and H2: Microbial communities surrounding roots undergo taxonomic succession linked to functional gene activities as roots grow, mature, and decompose in soil. Over the term of the project we made significant progress in 1) quantifying the temporal pattern of root interactions with the soil decomposing community and 2) characterizing the role of root exudates in mediating these interactions.« less

Enhancing the engineering properties of expansive soil using bagasse ash

NASA Astrophysics Data System (ADS)

Silmi Surjandari, Niken; Djarwanti, Noegroho; Umri Ukoi, Nafisah

2017-11-01

This paper deals with stabilization of expansive soil on a laboratory experimental basis. The aim of the research was to evaluate the enhancement of the engineering properties of expansive soil using bagasse ash. The soil is treated with bagasse ash by weight (0, 5, 10, 15, and 20%) based on dry mass. The performance of bagasse ash stabilized soil was evaluated using physical and strength performance tests, namely the plasticity index, standard Proctor compaction, and percentage swelling. An X-ray diffraction (XRD) test was conducted to evaluate the clay mineral, whereas an X-ray fluorescence (XRF) was to the chemical composition of bagasse ash. From the results, it was observed that the basic tests carried out proved some soil properties after the addition of bagasse ash. Furthermore, the plasticity index decreased from 53.18 to 47.70%. The maximum dry density of the specimen increased from 1.13 to 1.24 gr/cm3. The percentage swelling decreased from 5.48 to 3.29%. The outcomes of these tests demonstrate that stabilization of expansive soils using bagasse ash can improve the strength.

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.

Dynamics of a microbial community associated with manure hot spots as revealed by phospholipid fatty acid analyses.

PubMed Central

Frostegård, A; Petersen, S O; Bååth, E; Nielsen, T H

1997-01-01

Microbial community dynamics associated with manure hot spots were studied by using a model system consisting of a gel-stabilized mixture of soil and manure, placed between layers of soil, during a 3-week incubation period. The microbial biomass, measured as the total amount of phospholipid fatty acids (PLFA), had doubled within a 2-mm distance from the soil-manure interface after 3 days. Principal-component analyses demonstrated that this increase was accompanied by reproducible changes in the composition of PLFA, indicating changes in the microbial community structure. The effect of the manure was strongest in the 2-mm-thick soil layer closest to the interface, in which the PLFA composition was statistically significantly different (P < 0.05) from that of the unaffected soil layers throughout the incubation period. An effect was also observed in the soil layer 2 to 4 mm from the interface. The changes in microbial biomass and community structure were mainly attributed to the diffusion of dissolved organic carbon from the manure. During the initial period of microbial growth, PLFA, which were already more abundant in the manure than in the soil, increased in the manure core and in the 2-mm soil layer closest to the interface. After day 3, the PLFA composition of these layers gradually became more similar to that of the soil. The dynamics of individual PLFA suggested that both taxonomic and physiological changes occurred during growth. Examples of the latter were decreases in the ratios of 16:1 omega 7t to 16:1 omega 7c and of cyclopropyl fatty acids to their respective precursors, indicating a more active bacterial community. An inverse relationship between bacterial PLFA and the eucaryotic 20:4 PLFA (arachidonic acid) suggested that grazing was important. PMID:9172342

Evaluation of seismic testing for quality assurance of lime-stabilized soil.

DOT National Transportation Integrated Search

2013-08-01

This study sought to determine the technical feasibility of using seismic techniques to measure the : laboratory and field seismic modulus of lime-stabilized soils (LSS), and to compare/correlate test results : from bench-top (free-free resonance) se...

LOW COST SOLIDIFICATION/STABILIZATION TREATMENT FOR SOILS CONTAMINATED WITH DIOXIN, PCP AND CREOSOTE

EPA Science Inventory

The USEPA's NRMRL conducted successful treatability tests of innovative solidification/stabilization (S/S) formulations to treat soils contaminated with dioxins, pentachlorophenol (PCP), and creosote from four wood preserving sites. Formulations developed during these studies wer...

Rapid stabilization of thawing soils For enhanced vehicle mobility: a field demonstration project

DOT National Transportation Integrated Search

1999-02-01

Thawing soil presents a formidable challenge for vehicle operations cross-country and on unsurfaced roads. To mitigate the problem, a variety of stabilization techniques were evaluated for their suitability for rapid employment to enhance military ve...

Engineering properties of stabilized subgrade soils for implementation of the AASHTO 2002 pavement design guide.

DOT National Transportation Integrated Search

2009-06-01

A comprehensive laboratory study was undertaken to determine engineering properties of cementitiously stabilized common subgrade soils in Oklahoma for the design of roadway pavements in accordance with the AASHTO 2002 Mechanistic-Empirical Pavement D...

Case history : use of Tenax and Tensar geogrids for base course stabilization : technical assistance report.

DOT National Transportation Integrated Search

1999-01-01

Geogrids can be used successfully for subgrade stabilization under permanent pavements. To be successful, proper designs incorporating existing soil conditions and anticipated loading need to be performed. subgrade soil strength should be determined ...

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.

Validation of the solidifying soil process using laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Lin, Zhao-Xiang; Liu, Lin-Mei; Liu, Lu-Wen

2016-09-01

Although an Ionic Soil Stabilizer (ISS) has been widely used in landslide control, it is desirable to effectively monitor the stabilization process. With the application of laser-induced breakdown spectroscopy (LIBS), the ion contents of K, Ca, Na, Mg, Al, and Si in the permeable fluid are detected after the solidified soil samples have been permeated. The processes of the Ca ion exchange are analyzed at pressures of 2 and 3 atm, and it was determined that the cation exchanged faster as the pressure increased. The Ca ion exchanges were monitored for different stabilizer mixtures, and it was found that a ratio of 1:200 of ISS to soil is most effective. The investigated plasticity and liquidity indexes also showed that the 1:200 ratio delivers the best performance. The research work indicates that it is possible to evaluate the engineering performances of soil solidified by ISS in real time and online by LIBS.

Efficient Meshfree Large Deformation Simulation of Rainfall Induced Soil Slope Failure

NASA Astrophysics Data System (ADS)

Wang, Dongdong; Li, Ling

2010-05-01

An efficient Lagrangian Galerkin meshfree framework is presented for large deformation simulation of rainfall-induced soil slope failure. Detailed coupled soil-rainfall seepage equations are given for the proposed formulation. This nonlinear meshfree formulation is featured by the Lagrangian stabilized conforming nodal integration method where the low cost nature of nodal integration approach is kept and at the same time the numerical stability is maintained. The initiation and evolution of progressive failure in the soil slope is modeled by the coupled constitutive equations of isotropic damage and Drucker-Prager pressure-dependent plasticity. The gradient smoothing in the stabilized conforming integration also serves as a non-local regularization of material instability and consequently the present method is capable of effectively capture the shear band failure. The efficacy of the present method is demonstrated by simulating the rainfall-induced failure of two typical soil slopes.

Temperature Responses of Soil Organic Matter Components With Varying Recalcitrance

NASA Astrophysics Data System (ADS)

Simpson, M. J.; Feng, X.

2007-12-01

The response of soil organic matter (SOM) to global warming remains unclear partly due to the chemical heterogeneity of SOM composition. In this study, the decomposition of SOM from two grassland soils was investigated in a one-year laboratory incubation at six different temperatures. SOM was separated into solvent- extractable compounds, suberin- and cutin-derived compounds, and lignin monomers by solvent extraction, base hydrolysis, and CuO oxidation, respectively. These SOM components had distinct chemical structures and recalcitrance, and their decomposition was fitted by a two-pool exponential decay model. The stability of SOM components was assessed using geochemical parameters and kinetic parameters derived from model fitting. Lignin monomers exhibited much lower decay rates than solvent-extractable compounds and a relatively low percentage of lignin monomers partitioned into the labile SOM pool, which confirmed the generally accepted recalcitrance of lignin compounds. Suberin- and cutin-derived compounds had a poor fitting for the exponential decay model, and their recalcitrance was shown by the geochemical degradation parameter which stabilized during the incubation. The aliphatic components of suberin degraded faster than cutin-derived compounds, suggesting that cutin-derived compounds in the soil may be at a higher stage of degradation than suberin- derived compounds. The temperature sensitivity of decomposition, expressed as Q10, was derived from the relationship between temperature and SOM decay rates. SOM components exhibited varying temperature responses and the decomposition of the recalcitrant lignin monomers had much higher Q10 values than soil respiration or the solvent-extractable compounds decomposition. Our study shows that the decomposition of recalcitrant SOM is highly sensitive to temperature, more so than bulk soil mineralization. This observation suggests a potential acceleration in the degradation of the recalcitrant SOM pool with global warming.

Microbial carbon pump and its significance for carbon sequestration in soils

NASA Astrophysics Data System (ADS)

Liang, Chao

2017-04-01

Studies of the decomposition, transformation and stabilization of soil organic carbon have dramatically increased in recent years due to growing interest in studying the global carbon cycle as it pertains to climate change. While it is readily accepted that the magnitude of the organic carbon reservoir in soils depends upon microbial involvement because soil carbon dynamics are ultimately the consequence of microbial growth and activity, it remains largely unknown how these microbe-mediated processes lead to soil carbon stabilization. Here, two pathways, ex vivo modification and in vivo turnover, were defined to jointly explain soil carbon dynamics driven by microbial catabolism and/or anabolism. Accordingly, a conceptual framework consisting of the raised concept of the soil "microbial carbon pump" (MCP) was demonstrated to describe how microbes act as an active player in soil carbon storage. The hypothesis is that the long-term microbial assimilation process may facilitate the formation of a set of organic compounds that are stabilized (whether via protection by physical interactions or a reduction in activation energy due to chemical composition), ultimately leading to the sequestration of microbial-derived carbon in soils. The need for increased efforts was proposed to seek to inspire new studies that utilize the soil MCP as a conceptual guideline for improving mechanistic understandings of the contributions of soil carbon dynamics to the responses of the terrestrial carbon cycle under global change.

Shear Strength of Stabilized Kaolin Soil Using Liquid Polymer

NASA Astrophysics Data System (ADS)

Azhar, A. T. S.; Fazlina, M. I. S.; Nizam, Z. M.; Fairus, Y. M.; Hakimi, M. N. A.; Riduan, Y.; Faizal, P.

2017-08-01

The purpose of this research is to investigate the suitability of polymer in soil stabilization by examining its strength to withstand compressive strength. Throughout this research study, manufactured polymer was used as a chemical liquid soil stabilizer. The liquid polymer was diluted using a proposed dilution factor of 1 : 3 (1 part polymer: 3 parts distilled water) to preserve the workability of the polymer in kaolin mixture. A mold with a diameter of 50 mm and a height of 100 mm was prepared. Kaolin soil was mixed with different percentages of polymer from 10%, 15%, 20%, 25%, 30% and 35% of the mass of the kaolin clay sample. Kaolin mixtures were tested after a curing period of 3 days, 7 days, 14 days and 28 days respectively. The physical properties were determined by conducting a moisture content test and Atterberg limit test which comprise of liquid limit, plastic limit and shrinkage limit. Meanwhile, the mechanical properties of the soil shear strength were identified through an unconfined compressive strength (UCS) test. Stabilized kaolin soil showed the highest compressive strength value when it was mixed with 35% of polymer compared to other percentages that marked an increment in strength which are 45.72% (3 days), 67.57% (7 days), 81.73% (14 days) and 77.84% (28 days). Hence, the most effective percentage of liquid polymer which should be used to increase the strength of kaolin soil is 35%.

Assessment of soil stabilization by chemical extraction and bioaccumulation using earthworm, Eisenia fetida

NASA Astrophysics Data System (ADS)

Lee, Byung-Tae; Abd Aziz, Azilah; Han, Heop Jo; Kim, Kyoung-Woong

2014-05-01

Soil stabilization does not remove heavy metals from contaminated soil, but lowers their exposures to ecosystem. Thus, it should be evaluated by measuring the fractions of heavy metals which are mobile and/or bioavailable in soils. The study compared several chemical extractions which intended to quantify the mobile or bioaccessible fractions with uptake and bioaccumulation by earthworm, Eisenia fetida. Soil samples were taken from the abandoned mine area contaminated with As, Cd, Cu, Pb and/or Zn. To stabilize heavy metals, the soils were amended with limestone and steel slag at 5% and 2% (w/w), respectively. All chemical extractions and earthworm tests were applied to both the contaminated and the stabilized soils with triplicates. The chemical extractions consisted of six single extractions which were 0.01M CaCl2 (unbufferred), EDTA or DTPA (chelating), TCLP (acidic), Mehlich 3 (mixture), and aqua regia (peudo-total). Sequential extractions were also applied to fractionate heavy metals in soils. In earthworm tests, worms were exposed to the soils for uptake of heavy metals. After 28 days of exposure to soils, worms were transferred to clean soils for elimination. During the tests, three worms were randomly collected at proper sampling events. Worms were rinsed with DI water and placed on moist filter paper for 48 h for depuration. Filter paper was renewed at 24 h to prevent coprophagy. The worms were killed with liquid nitrogen, dried in the oven, and digested with aqua regia for ICP-MS analysis. In addition to the bioaccumulation, several toxicity endpoints were observed such as burrowing time, mortality, cocoon production, and body weight changes. Toxicokinetics was applied to determine the uptake and elimination heavy metals by the earthworms. Bioaccumulation factor (BAF) was estimated using total metal concentrations and body burdens. Pearson correlation and simple linear regression were applied to evaluate the relationship between metal fractions by single extractions or sequential extractions with bioaccumulations. Finally, we discussed the advantages or disadvantages of simple chemical extractions which are commonly used to estimate the efficacy of stabilization.

Soil C dynamics under intensive oil palm plantations in poor tropical soils

NASA Astrophysics Data System (ADS)

Guillaume, Thomas; Ruegg, Johanna; Quezada, Juan Carlos; Buttler, Alexandre

2017-04-01

Oil palm cultivation mainly takes place on heavily-weathered tropical soils where nutrients are limiting factors for plant growth and microbial activity. Intensive fertilization and changes of C input by oil palms strongly affects soil C and nutrient dynamics, challenging long-term soil fertility. Oil palm plantations management offers unique opportunities to study soil C and nutrients interactions in field conditions because 1) they can be considered as long-term litter manipulation experiments since all aboveground C inputs are concentrated in frond pile areas and 2) mineral fertilizers are only applied in specific areas, i.e. weeded circle around the tree and interrows, but not in harvest paths. Here, we determined impacts of mineral fertilizer and organic matter input on soil organic carbon dynamics and microbial activity in mature oil palm plantation established on savanna grasslands. Rates of savanna-derived soil organic carbon (SOC) decomposition and oil palm-derived SOC net stabilization were determined using changes in isotopic signature of in C input following a shift from C4 (savanna) to C3 (oil palm) vegetation. Application of mineral fertilizer alone did not affect savanna-derived SOC decomposition or oil palm-derived SOC stabilization rates, but fertilization associated with higher C input lead to an increase of oil palm-derived SOC stabilization rates, with about 50% of topsoil SOC derived from oil palm after 9 years. High carbon and nutrients inputs did not increase microbial biomass but microorganisms were more active per unit of biomass and SOC. In conclusion, soil organic matter decomposition was limited by C rather than nutrients in the studied heavily-weathered soils. Fresh C and nutrient inputs did not lead to priming of old savanna-derived SOC but increased turnover and stabilization of new oil palm-derived SOC.

Chemical characterization of iron-mediated soil organic matter stabilization in tropical subsoils

NASA Astrophysics Data System (ADS)

Coward, E.; Plante, A. F.; Thompson, A.

2015-12-01

Tropical forest soils contribute disproportionately to the poorly-characterized and persistent deep soil carbon (C) pool. Highly-weathered and often extending one to two meters deep, these soils also contain an abundance of semicrystalline, Fe- and Al-containing short-range-order (SRO) minerals, metastable derivatives of framework silicate and ferromagnesian parent materials. SRO minerals are capable of soil organic matter (SOM) stabilization through sorption or co-precipitation, a faculty enhanced by their high specific surface area (SSA). As such, SRO-mediated organomineral associations may prove a critical, yet matrix-selective, driver of SOM stabilization capacity in tropical soils, particularly at depth. Surface (0-20 cm) and subsoil (50-80 cm) samples were taken from 20 quantitative soil pits dug in the Luquillo Critical Zone Observatory, located in northeast Puerto Rico. Soils were stratified across granodiorite and volcaniclastic parent materials, spanning primary mineral contents of 5 to 40%. Selective dissolution procedures were used to isolate distinct forms of Fe-C interactions: (1) sodium pyrophosphate to isolate organo-mineral complexes, (2) hydroxylamine and (3) oxalate to isolate SRO phases, and (4) inorganic dithionite to isolate crystalline Fe oxides. Extracts were analysed for dissolved organic C (DOC) and Fe and Al concentrations to estimate SOM associated with each mineral phase. Soils were also subjected to SSA analysis, 57Fe-Mössbauer spectroscopy and X-ray diffraction before and after extraction to determine the contribution of extracted mineral phases to SOM stabilization capacity. Preliminary results indicate a dominance of secondary (hydr)oxides and kaolin minerals in surface soils, strongly driven by parent material. With depth, however, we observe a marked shift towards SRO mineral phases across both parent materials, suggesting that SRO-mediated organomineral associations are significant contributors to observed C storage in tropical subsoils.

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.

Impact of vegetation on stability of slopes subjected to rainfall - numerical aspect

NASA Astrophysics Data System (ADS)

Switala, Barbara Maria; Tamagnini, Roberto; Sudan Acharya, Madhu; Wu, Wei

2015-04-01

Recent years brought a significant development of soil bioengineering methods, considered as an ecological and economically effective measure for slope stabilization. This work aims to show the advantages of the soil bioengineering solutions for a slope subjected to a heavy rainfall, with the help of a numerical model, which integrates most of the significant plant and slope features. There are basically two different ways in which vegetation can affect stability of a slope: root reinforcement (mechanical impact) and root water uptake (evapotranspiration). In the numerical model, the first factor is modelled using the Cam-Clay model extended for unsaturated conditions by Tamagnini (2004). The original formulation of a constitutive model is modified by introducing an additional constitutive parameter, which causes an expansion of the yield surface as a consequence of an increase in root mass in a representative soil element. The second factor is the root water uptake, which is defined as a volumetric sink term in the continuity equation of groundwater flow. Water removal from the soil mass causes an increase in suction in the vicinity of the root zone, which leads to an increase in the soil cohesion and provides additional strength to the soil-root composite. The developed numerical model takes into account the above mentioned effects of plants and thus considers the multi-phase nature of the soil-plant-water relationship. Using the developed method, stability of some vegetated and non-vegetated slopes subjected to rainfall are investigated. The performance of each slope is evaluated by the time at which slope failure occurs. Different slope geometries and soil mechanical and hydrological properties are considered. Comparison of the results obtained from the analyses of vegetated and non-vegetated slopes leads to the conclusion, that the use of soil bioengineering methods for slope stabilization can be effective and can significantly delay the occurrence of a rainfall induced landslide. On the contrary, vegetation removal can have serious consequences, especially on steep and forested slopes.

Organomineral Complexation at the Nanoscale: Iron Speciation and Soil Carbon Stabilization

NASA Astrophysics Data System (ADS)

Coward, E.; Thompson, A.; Plante, A. F.

2016-12-01

Much of the uncertainty in the biogeochemical behavior of soil carbon (C) in tropical ecosystems derives from an incomplete understanding of soil C stabilization processes. The 2:1 phyllosilicate clays often associated with temperate organomineral complexation are largely absent in tropical soils due to extensive weathering. In contrast, these soils contain an abundance of Fe- and Al-containing short-range-order (SRO) mineral phases capable of C stabilization through sorption or co-precipitation, largely enabled by high specific surface area (SSA). SRO-mediated organomineral associations may thus prove a critical, yet matrix-selective, driver of the long-term C stabilization capacity observed in tropical soils. Characterizing the interactions between inherently heterogeneous organic matter and amorphous mineralogy presses the limits of current analytical techniques. This work pairs inorganic selective dissolution with high-resolution assessment of Fe speciation to determine the contribution of extracted mineral phases to the mineral matrix, and to C stabilization capacity. Surface (0-20 cm) samples were taken from 20 quantitative soil pits within the Luquillo Critical Zone Observatory in northeast Puerto Rico stratified across granodioritic and volcaniclastic parent materials. 57Fe-Mössbauer spectroscopy (MBS) and x-ray diffraction (XRD) before and after Fe-SOM extraction were used to assess changes in the mineralogical matrix associated with SOM dissolution, while N2-BET sorption was used to determine the contributions of the extractable phases to SSA. Results indicate (1) selective extraction of soil C produces significant shifts in Fe phase distribution, (2) SRO minerals contribute substantially to SSA, and (3) SRO minerals appear protected by more crystalline phases via physical mechanisms, rather than dissolution-dependent chemical bonds. This nanoscale characterization of Fe-C complexes thus provides evidence for both anticipated mineral-organic and unexpected mineral-mineral associations, which may dynamically impact the temporal fate of tropical soil C.

Investigation of Biological Soil Crusts Metabolic Webs Using Exometabolomic Analysis

NASA Astrophysics Data System (ADS)

Northen, T.; Karaoz, U.; Jenkins, S.; Lau, R.; Bowen, B.; Cadillo-Quiroz, H.; Garcia-Pichel, F.; Brodie, E.; Richard, B.

2014-12-01

Desert biological soil crusts are simple cyanobacteria-dominated surface soil microbial communities found in areas with infrequent wetting, often extreme temperatures, low coverage of vascular plants and constitute the world's largest biofilm. They exist for extended periods in a desiccated dormant state, yet rapidly re-boot metabolism within minutes of wetting. These soil microbial communities are highly dependent on filamentous cyanobacteria such as Microcoleus vaginatusto stabilize the soil and to act as primary producers for the community through the release carbon sources to feed a diversity of heterotrophs. Exometabolomic analysis was performed using liquid chromatography coupled to tandem mass spectrometry on biological soil crust pore water and spent media of key soil bacterial isolates. Comparison of spent vs. fresh media was used to determine uptake or release of metabolites by specific microbes. To link pore water experiments with isolate studies, metabolite extracts of authentic soil were used as supplements for isolate exometabolomic profiling. Our soil metabolomics methods detected hundreds of metabolites from soils including may novel compounds. Only a small set of which being targeted by all isolates. Beyond these few metabolites, the individual bacteria examined showed specialization towards specific metabolites. Surprisingly, many of the most abundant oligosaccharides and other metabolites were ignored by these isolates. The observed specialization of biological soil crust bacteria may play a significant role in determining community structure.

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.

Bringing life to soil physical processes

NASA Astrophysics Data System (ADS)

Hallett, P. D.

2013-12-01

When Oklahoma's native prairie grass roots were replaced by corn, the greatest environmental (and social) disaster ever to hit America ensued. The soils lost structure, physical binding by roots was annihilated and when drought came the Great Dust Bowl commenced. This form of environmental disaster has repeated over history and although not always apparent, similar processes drive the degradation of seemingly productive farmland and forests. But just as negative impacts on biology are deleterious to soil physical properties, positive impacts could reverse these trends. In finding solutions to soil sustainability and food security, we should be able to exploit biological processes to improve soil physical properties. This talk will focus on a quantitative understanding of how biology changes soil physical behaviour. Like the Great Dust Bowl, it starts with reinforcement mechanisms by plant roots. We found that binding of soil by cereal (barley) roots within 5 weeks of planting can more than double soil shear strength, with greater plant density causing greater reinforcement. With time, however, the relative impact of root reinforcement diminishes due to root turnover and aging of the seedbed. From mechanical tests of individual roots, reasonable predictions of reinforcement by tree roots are possible with fibre bundle models. With herbaceous plants like cereals, however, the same parameters (root strength, stiffness, size and distribution) result in a poor prediction. We found that root type, root age and abiotic factors such as compaction and waterlogging affect mechanical behaviour, further complicating the understanding and prediction of root reinforcement. For soil physical stability, the interface between root and soil is an extremely important zone in terms of resistance of roots to pull-out and rhizosphere formation. Compounds analogous to root exudates have been found with rheological tests to initially decrease the shear stress where wet soils flow, but after decomposition of these exudates by microbes the shear stress increases. This suggests an initial dispersion, followed by aggregation of the soil, which explains the structural arrangement of soil particles in the rhizosphere observed by microscopy. Dispersion of soil minerals in the root zone is important to release bound nutrients from mineral surfaces. Using fracture mechanics we measured large impacts of biological exudates on the toughness and interparticle bond energy of soils. Now novel tests are being developed to quantify interparticle bonding by biological exudates on single and multiple particle contacts, including mechanical test specimens that can be inoculated with specific bacteria or fungi. This will allow for clay mineralogy, water potential and solution chemistry impacts on interparticle bonding to be quantified directly. Wettability experiments with the same samples measure hydrological properties such as contact angle. Basic information from these tests will help explain biological processes that drive soil structure formation and stabilisation, providing data for models of soil structure dynamics.

Retrospective assessment of dryland soil stability in relation to grazing and climate change.

PubMed

Washington-Allen, Robert A; West, Neil E; Ramsey, R Douglas; Phillips, Debra H; Shugart, Herman H

2010-01-01

Accelerated soil erosion is an aspect of dryland degradation that is affected by repeated intense drought events and land management activities such as commercial livestock grazing. A soil stability index (SSI) that detects the erosion status and susceptibility of a landscape at the pixel level, i.e., stable, erosional, or depositional pixels, was derived from the spectral properties of an archived time series (from 1972 to 1997) of Landsat satellite data of a commercial ranch in northeastern Utah. The SSI was retrospectively validated with contemporary field measures of soil organic matter and erosion status that was surveyed by US federal land management agencies. Catastrophe theory provided the conceptual framework for retrospective assessment of the impact of commercial grazing and soil water availability on the SSI. The overall SSI trend was from an eroding landscape in the early drier 1970s towards stable conditions in the wetter mid-1980s and late 1990s. The landscape catastrophically shifted towards an extreme eroding state that was coincident with the "The Great North American Drought of 1988". Periods of landscape stability and trajectories toward stability were coincident with extremely wet El Niño events. Commercial grazing had less correlation with soil stability than drought conditions. However, the landscape became more susceptible to erosion events under multiple droughts and grazing. Land managers now have nearly a year warning of El Niño and La Niña events and can adjust their management decisions according to predicted landscape erosion conditions.

Soil stabilization linked to plant diversity and environmental context in coastal wetlands.

PubMed

Ford, Hilary; Garbutt, Angus; Ladd, Cai; Malarkey, Jonathan; Skov, Martin W

2016-03-01

Plants play a pivotal role in soil stabilization, with above-ground vegetation and roots combining to physically protect soil against erosion. It is possible that diverse plant communities boost root biomass, with knock-on positive effects for soil stability, but these relationships are yet to be disentangled. We hypothesize that soil erosion rates fall with increased plant species richness, and test explicitly how closely root biomass is associated with plant diversity. We tested this hypothesis in salt marsh grasslands, dynamic ecosystems with a key role in flood protection. Using step-wise regression, the influences of biotic (e.g. plant diversity) and abiotic variables on root biomass and soil stability were determined for salt marshes with two contrasting soil types: erosion-resistant clay (Essex, southeast UK) and erosion-prone sand (Morecambe Bay, northwest UK). A total of 132 (30-cm depth) cores of natural marsh were extracted and exposed to lateral erosion by water in a re-circulating flume. Soil erosion rates fell with increased plant species richness ( R 2  = 0.55), when richness was modelled as a single explanatory variable, but was more important in erosion-prone ( R 2  = 0.44) than erosion-resistant ( R 2  = 0.18) regions. As plant species richness increased from two to nine species·m -2 , the coefficient of variation in soil erosion rate decreased significantly ( R 2  = 0.92). Plant species richness was a significant predictor of root biomass ( R 2  = 0.22). Step-wise regression showed that five key variables accounted for 80% of variation in soil erosion rate across regions. Clay-silt fraction and soil carbon stock were linked to lower rates, contributing 24% and 31%, respectively, to variation in erosion rate. In regional analysis, abiotic factors declined in importance, with root biomass explaining 25% of variation. Plant diversity explained 12% of variation in the erosion-prone sandy region. Our study indicates that soil stabilization and root biomass are positively associated with plant diversity. Diversity effects are more pronounced in biogeographical contexts where soils are erosion-prone (sandy, low organic content), suggesting that the pervasive influence of biodiversity on environmental processes also applies to the ecosystem service of erosion protection.

Efficacy of road bond and condor as soil stabilizers : final report.

DOT National Transportation Integrated Search

2013-08-01

The Oklahoma Department of Transportation (ODOT) uses lime-based stabilizers including quick lime, hydrated lime, Class C fly ash (CFA) and cement kiln dust (CKD) to increase bearing capacity of fine-grained subgrade soils within the state of Oklahom...

Soil stabilization with recycled materials improves subgrade performance : research spotlight.

DOT National Transportation Integrated Search

2016-02-29

The use of recycled materials for subgrade stabilization can provide the support needed for construction vehicle loading and more typical long-term traffic loading. This is a particular need in Michigan due to the prevalence of weak subgrade soils. U...

How do soil physical conditions for crop growth vary over time under established contrasting tillage regimes?

NASA Astrophysics Data System (ADS)

Hallett, Paul; Stobart, Ron; Valentine, Tracy; George, Timothy; Morris, Nathan; Newton, Adrian; McKenzie, Blair

2014-05-01

When plant breeders develop modern cereal varieties for the sustainable intensification of agriculture, insufficient thought is given to the impact of tillage on soil physical conditions for crop production. In earlier work, we demonstrated that barley varieties that perform best in ploughed soil (the approach traditionally used for breeding trials) were not the same as those performing best under shallow non-inversion or zero-tillage. We also found that the Quantitative Trait Loci (QTL) associated with improved phosphorus uptake, and hence useful for marker assisted breeding, were not robust between different tillage regimes. The impact of the soil environment had greater impact than the genetics in GxE interactions. It is obvious that soil tillage should be considered when breeding the next generation of crops. Tillage may also have important impacts on carbon storage, but we found that despite greater soil carbon at shallow depths under non-inversion tillage, the carbon stored throughout the soil profile was not affected by tillage. Studies on soil tillage impacts to crop productivity and soil quality are often performed in one season, on single sites that have had insufficient time to develop. Our current research explores multiple sites, on different soils, with temporal measurements of soil physical conditions under contrasting tillage regimes. We use the oldest established contemporary tillage experiments in the United Kingdom, with all sites sharing ploughed and shallow (7cm) non-inversion tillage treatments. In eastern Scotland (Mid Pilmore), the site also has zero tillage and deep ploughing (40 cm) treatments, and was established 11 years ago. In east England there are two sites, both also having a deep non-inversion tillage treatment, and they were established 6 (New Farm Systems) and 8 (STAR) years ago. We measure a range of crop and soil properties at sowing, one month after sowing and post-harvest, including rapid lab based assays that allow high-throughput. Samples are taken over the rooting zone in the topsoil, plough pan and subsoil. The first year's dataset from this comprehensive project will be presented. Early data identified plough pans under shallow non-inversion tillage that will limit root growth at all sites. Aggregate stabilities vary as expected, with plough soils at shallow depth being less stable than non-inversion tillage, but greater stability in plough soils at greater depth due to incorporated organic matter. Very rapidly following cultivation, the seedbeds coalesce, resulting in a more challenging physical environment for crop growth. We are exploring the mechanisms in soil structure temporal dynamics in greater detail, including the resilience of seedbeds to structural degradation through natural weathering and the action of plants. These profound differences in soil conditions will impact the root ideotype of crops for these different conditions. This has implications for the way in which breeding and genotype selection is performed in the future. Ultimately, we aim to identify crop varieties suited to local soil conditions and management, possibly with root traits that boost yields and soil physical quality.

Changes in vegetation and biological soil crust communities on sand dunes stabilizing after a century of grazing on San Miguel Island, Channel Island National Park, California

USGS Publications Warehouse

Zellman, Kristine L.

2014-01-01

San Miguel Island is the westernmost of the California Channel Islands and one of the windiest areas on the west coast of North America. The majority of the island is covered by coastal sand dunes, which were stripped of vegetation and subsequently mobilized due to droughts and sheep ranching during the late 19th century and early 20th century. Since the removal of grazing animals, vegetation and biological soil crusts have once again stabilized many of the island's dunes. In this study, historical aerial photographs and field surveys were used to develop a chronosequence of the pattern of change in vegetation communities and biological soil crust levels of development (LOD) along a gradient of dune stabilization. Historical aerial photographs from 1929, 1954, 1977, and 2009 were georeferenced and used to delineate changes in vegetation canopy cover and active (unvegetated) dune extent among 5 historical periods (pre-1929, 1929–1954, 1954–1977, 1977–2009, and 2009–2011). During fieldwork, vegetation and biological soil crust communities were mapped along transects distributed throughout San Miguel Island's central dune field on land forms that had stabilized during the 5 time periods of interest. Analyses in a geographic information system (GIS) quantified the pattern of changes that vegetation and biological soil crust communities have exhibited on the San Miguel Island dunes over the past 80 years. Results revealed that a continuing increase in total vegetation cover and a complex pattern of change in vegetation communities have taken place on the San Miguel Island dunes since the removal of grazing animals. The highly specialized native vascular vegetation (sea rocket, dunedelion, beach-bur, and locoweed) are the pioneer stabilizers of the dunes. This pioneer community is replaced in later stages by communities that are dominated by native shrubs (coastal goldenbush, silver lupine, coyote-brush, and giant coreopsis), with apparently overlapping or cyclical succession pathways. Many of the dunes that have been stabilized the longest (since before 1929) are dominated by exotic grasses. Stands of biological soil crusts (cyanobacteria) are found only on dunes where vascular vegetation is already present. Biological soil crusts are not found on dunes exhibiting a closed vascular plant canopy, which may indicate that the role of soil crusts in dune stabilization on the island is transitory. Particle-size analyses of soil samples from the study area reveal that higher biological soil crust LOD is positively correlated with increasing fine grain content. The findings indicate that changes in vegetation communities may be the most rapid at earlier and later stages of dune stabilization and that regular monitoring of dunes may help to identify the interactions between vegetation and soil crusts, as well as the potential transitions between native and exotic plant communities.

[Effect of pine plantations on soil arthropods in a high Andean forest].

PubMed

León-Gamboa, Alba Lucía; Ramos, Carolina; García, Mary Ruth

2010-09-01

One of the most common problems in the Colombian mountains has been the replacement of native vegetation by pine plantations. Soil arthropods are a fundamental component of forest ecosystem, since they participate in the organic matter fragmentation, previous to decomposition. This role is more valuable in high altitude environments, where low temperatures limit the dynamics of biological processes, where the effects of pine plantations on soil arthropods are still not well-known. In a remnant of high-andean forest (Neusa - Colombia) and a pine plantation of about 50 years-old, it was evaluated the composition, richness and abundance of arthropods at surface (S), organic horizon (O) and mineral horizon (A) of soil, to establish the differences associated to the soil use transformation. It was used "Pitfall" sampling to register the movement of the epigeous fauna, and extraction by funnel Berlese for determining the fauna density from O and A horizons. The Shannon and Simpson indexes estimated the diversity at different places and horizons, and the trophic structure of the community was evaluated. Overall, there were collected 38 306 individuals from forest and 17 386 individuals from pine plantation, mainly distributed in Collembola (42.4%), Acari (27%), Diptera (17.6%) and Coleoptera (4.6%). The most important differences were given in the surface, where the mobilization in forest (86 individuals/day) almost triplicates the one in pine plantation (33 individuals/day). The differences in composition were given in Collembola, Araneae, Hemiptera, Homoptera and Hymenoptera. The dynamics of richness and abundance along the year had significant high values in the native forest than in the pine plantation. The general trophic structure was dominated by saprophagous (75%), followed by predators (14%) and phytophagous (9%), but in two layers of the pine plantation soil (S and O) this structural pattern was not given. Based on the results, it was concluded that pine plantations affect the diversity, composition, community dynamic and trophic structure of soil arthropods. Also, some estimators of soil stability give signals that these effects are reducing the ecosystem function in the region.

Mechanisms for Reduction of Natural Waters Technogenic Pollution by Metals due to Complexions with Humus Substances (Zoning: Western Siberia and the European Territory of Russia)

NASA Astrophysics Data System (ADS)

Dinu, M. I.

2017-11-01

The article described the complexation of metal ions with humus substances in natural waters (small lakes). Humus substances as the major biochemical components of natural water have a significant impact on the forms and migration of metals and the toxicity of natural objects. This article presents the results of large-scale chemical experiments: the study of the structural features (zonal aspects) of humus substances extracted from soil and water natural climatic zones (more than 300 objects) in Russia (European Russia and West Siberia); the influence of structural features on the physic-chemical parameters of humus acids and, in particular, on their complexing ability. The functional specifics of humus matter extracted from soils is estimated using spectrometric techniques. The conditional stability constants for Fe(III), Cu(II), Pb(II), Cd(II), Zn(II), Ni(II), Co(II), Mn(II), Cr(III), Ca(II), Mg(II), Sr(II), and Al(III) are experimentally determined with the electrochemical, spectroscopic analysis methods. The activities of metals are classified according to their affinity to humus compounds in soils and water. The determined conditional stability constants of the complexes are tested by model experiments, and it is demonstrated that Fe and Al ions have higher conditional stability constants than the ions of alkali earth metals, Pb, Cu, and Zn. Furthermore, the influence of aluminium ions and iron on the complexation of copper and lead as well as the influence of lead and copper on complexation of cobalt and nickel have been identified. The metal forms in a large number of lakes are calculated basing on the experiments’ results. The main chemical mechanisms of the distribution of metals by forms in the water of the lakes in European Russia and West Siberia are described.

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.

Remediation aspect of microbial changes of plant rhizosphere in mercury contaminated soil.

PubMed

Sas-Nowosielska, Aleksandra; Galimska-Stypa, Regina; Kucharski, Rafał; Zielonka, Urszula; Małkowski, Eugeniusz; Gray, Laymon

2008-02-01

Phytoremediation, an approach that uses plants to remediate contaminated soil through degradation, stabilization or accumulation, may provide an efficient solution to some mercury contamination problems. This paper presents growth chamber experiments that tested the ability of plant species to stabilize mercury in soil. Several indigenous herbaceous species and Salix viminalis were grown in soil collected from a mercury-contaminated site in southern Poland. The uptake and distribution of mercury by these plants were investigated, and the growth and vitality of the plants through a part of one vegetative cycle were assessed. The highest concentrations of mercury were found at the roots, but translocation to the aerial part also occurred. Most of the plant species tested displayed good growth on mercury contaminated soil and sustained a rich microbial population in the rhizosphere. The microbial populations of root-free soil and rhizosphere soil from all species were also examined. An inverse correlation between the number of sulfur amino acid decomposing bacteria and root mercury content was observed. These results indicate the potential for using some species of plants to treat mercury contaminated soil through stabilization rather than extraction. The present investigation proposes a practical cost-effective temporary solution for phytostabilization of soil with moderate mercury contamination as well as the basis for plant selection.

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

Improved chemometric methodologies for the assessment of soil carbon sequestration mechanisms

NASA Astrophysics Data System (ADS)

Jiménez-González, Marco A.; Almendros, Gonzalo; Álvarez, Ana M.; González-Vila, Francisco J.

2016-04-01

The factors involved soil C sequestration, which is reflected in the highly variable content of organic matter in the soils, are not yet well defined. Therefore, their identification is crucial for understanding Earth's biogeochemical cycle and global change. The main objective of this work is to contribute to a better qualitative and quantitative assessment of the mechanisms of organic C sequestration in the soil, using omic approaches not requiring the detailed knowledge of the structure of the material under study. With this purpose, we have carried out a series of chemometric approaches on a set of widely differing soils (35 representative ecosystems). In an exploratory phase, we used multivariate statistical models (e.g., multidimensional scaling, discriminant analysis with automatic backward variable selection…) to analyze arrays of more than 200 independent soil variables (physicochemical, spectroscopic, pyrolytic...) in order to select those factors (descriptors or proxies) that explain most of the total system variance (content and stability of the different C forms). These models showed that the factors determining the stabilization of organic material are greatly dependent on the soil type. In some cases, the molecular structure of organic matter seemed strongly correlated with their resilience, while in other soil types the organo-mineral interactions played a significant bearing on the accumulation of selectively preserved C forms. In any case, it was clear that the factors driving the resilience of organic matter are manifold and not exclusive. Consequently, in a second stage, prediction models of the soil C content and their biodegradability (laboratory incubation experiments) were carried out by massive data processing by partial least squares (PLS) regression of data from Py-GC-MS and Py-MS. In some models, PLS was applied to a matrix of 150 independent variables corresponding to major pyrolysis compounds (peak areas) from the 35 samples of whole soils. The variable importance in the projection (VIP) histogram obtained from this treatment (total C and total mineralization coefficients as dependent variables) illustrated the contribution of the individual compounds to the total inertia of the models (e.g., carbohydrate-derived compounds, methoxyphenols, or specific alkylbenzenes were relevant in explaining the total quality and the biodegradation rates of the organic matter). Further simplified models consisting of direct PLS analysis of the debugged ion matrix calculated by averaging all ions (45 - 250 amu) in the whole chromatographic area in the 5-60 min range (here referred to as 'rebuilt MS spectra' or 'Py-MS spectra' when obtained connecting directly the pyrolyser to the MS detector through suitable interfaces) were carried out. The above three approaches coincided in pointing out that C sequestration behave as an emergent soil property depending on the complexity of its progressive molecular levels. Most of the total variance is explained by specific assemblages of variables, strongly depending on the soil types. On the other hand, chemical biodiversity (e.g., Shannon indices or coefficients from multivariate data models) behaved as a common background in the prediction models including very different soil types. In fact, assessment of chemodiversity of the pyrolytic compound assemblages (or the Py-MS ion data) would represent a valid clue for the assessment of the extent to which the original biomass has been diagenetically reworked into chaotic structures with non-repeatable units, providing a useful proxy to forecast at least a portion of the total variance in the soil organic matter biodegradability.

Rapid Soil Stabilization of Soft Clay Soils for Contingency Airfields

DTIC Science & Technology

2006-12-01

quicklime or calcium carbide, could possibly crosslink the polymers of sodium or potassium polyacrylic acid together to form a harder material. Very...LiquiBlock 40K and 41K are both potassium salts of crosslinked polyacrylic acids/polyacrylamide copolymers in granular form that also gel in the presence...communication, 2006), soil could possibly be stabilized with calcium and super absorbent polymers, such as sodium or potassium polyacrylic acids. This

Beyond clay - using selective extractions to improve predictions of soil carbon content

NASA Astrophysics Data System (ADS)

Rasmussen, C.; Berhe, A. A.; Blankinship, J. C.; Crow, S. E.; Druhan, J. L.; Heckman, K. A.; Keiluweit, M.; Lawrence, C. R.; Marin-Spiotta, E.; Plante, A. F.; Schaedel, C.; Schimel, J.; Sierra, C. A.; Thompson, A.; Wagai, R.; Wieder, W. R.

2016-12-01

A central component of modern soil carbon (C) models is the use of clay content to scale the relative partitioning of decomposing plant material to respiration and mineral stabilized soil C. However, numerous pedon to plot scale studies indicate that other soil mineral parameters, such as Fe- or Al-oxyhydroxide content and specific surface area, may be more effective than clay alone for predicting soil C content and stabilization. Here we directly address the following question: Are there soil physicochemical parameters that represent mineral C association and soil C content that can replace or be used in conjunction with clay content as scalars in soil C models. We explored the relationship of soil C content to a number of soil physicochemical and physiographic parameters using the National Cooperative Soil Survey database that contains horizon level data for > 62,000 pedons spanning global ecoregions and geographic areas. The data indicated significant variation in the degree of correlation among soil C, clay and Fe-/Al-oxyhydroxides with increasing moisture variability. Specifically, dry, water-limited systems (PET/MAP > 1) presented strong positive correlations between clay and soil C, that decreased significantly to little or no correlation in wet, energy-limited systems (PET/MAP < 1). In contrast, the correlation of soil C to oxalate extractable Al+Fe increased significantly with increasing moisture availability. This pattern was particularly well expressed for subsurface B horizons. Multivariate analyses indicated similar patterns, with clear climate and ecosystem level variation in the degree of correlation among soil C and soil physicochemical properties. The results indicate a need to modify current soil C models to incorporate additional C partitioning parameters that better account for climate and ecoregion variability in C stabilization mechanisms.

Unlocking the Physiochemical Controls on Organic Carbon Dynamics from the Soil Pore- to Core-Scale

NASA Astrophysics Data System (ADS)

Smith, A. P.; Tfaily, M. M.; Bond-Lamberty, B. P.; Todd-Brown, K. E.; Bailey, V. L.

2015-12-01

The physical organization of soil includes pore networks of varying size and connectivity. These networks control microbial access to soil organic carbon (C) by spatially separating microorganisms and C by both distance and size exclusion. The extent to which this spatially isolated C is vulnerable to microbial transformation under hydrologically dynamic conditions is unknown, and limits our ability to predict the source and sink capacity of soils. We investigated the effects of shifting hydrologic connectivity and soil structure on greenhouse gas C emissions from surface soils collected from the Disney Wilderness Preserve (Florida, USA). We subjected intact soil cores and re-packed homogenized soil cores to simulated groundwater rise or precipitation, monitoring their CO2 and CH4 emissions over 24 hours. Soil pore water was then extracted from each core using different suctions to sample water retained by pore throats of different sizes and then characterized by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Greater respiration rates were observed from homogenized cores compared to intact cores, and from soils wet from below, in which the wetting front is driven by capillary forces, filling fine pores first. This suggests that C located in fine pores may turn over via diffusion processes that lead to the colocation of this C with other resources and microorganisms. Both the complexity and concentration of soluble-C increased with decreasing pore size domains. Pore water extracted from homogenized cores had greater C concentrations than from intact cores, with the greatest concentrations in pore waters sampled from very fine pores, highlighting the importance of soil structure in physically protecting C. These results suggest that the spatial separation of decomposers from C is a key mechanism stabilizing C in these soils. Further research is ongoing to accurately represent this protection mechanism, and the conditions under which it breaks down, in new and improved Earth system models.

Rangeland health attributes and indicators for qualitative assessment

USGS Publications Warehouse

Pyke, David A.; Herrick, J.E.; Pellant, Mike

2002-01-01

Panels of experts from the Society for Range Management and the National Research Council proposed that status of rangeland ecosystems could be ascertained by evaluating an ecological site's potential to conserve soil resources and by a series of indicators for ecosystem processes and site stability. Using these recommendations as a starting point, we developed a rapid, qualitative method for assessing a moment-in-time status of rangelands. Evaluators rate 17 indicators to assess 3 ecosystem attributes (soil and site stability, hydrologic function, and biotic integrity) for a given location. Indicators include rills, water flow patterns, pedestals and terracettes, bare ground, gullies, wind scour and depositional areas, litter movement, soil resistance to erosion, soil surface loss or degradation, plant composition relative to infiltration, soil compaction, plant functional/structural groups, plant mortality, litter amount, annual production, invasive plants, and reproductive capability. In this paper, we detail the development and evolution of the technique and introduce a modified ecological reference worksheet that documents the expected presence and amount of each indicator on the ecological site. In addition, we review the intended applications for this technique and clarify the differences between assessment and monitoring that lead us to recommend this technique be used for moment-in-time assessments and not be used for temporal monitoring of rangeland status. Lastly, we propose a mechanism for adapting and modifying this technique to reflect improvements in understanding of ecosystem processes. We support the need for quantitative measures for monitoring rangeland health and propose some measures that we believe may address some of the 17 indicators.

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.

Peat soils stabilization using Effective Microorganisms (EM)

NASA Astrophysics Data System (ADS)

Yusof, N. Z.; Samsuddin, N. S.; Hanif, M. F.; Syed Osman, S. B.

2018-04-01

Peat soil is known as geotechnical problematic soil since it is the softest soil having highly organic and moisture content which led to high compressibility, low shear strength and long-term settlement. The aim of this study was to obtain the stabilized peat soils using the Effective Microorganisms (EM). The volume of EM added and mixed with peat soils varied with 2%, 4%, 6%, 8% and 10% and then were cured for 7, 14 and 21 days. The experiment was done for uncontrolled and controlled moisture content. Prior conducting the main experiments, the physical properties such as moisture content, liquid limit, specific gravity, and plastic limit etc. were measure for raw peat samples. The Unconfined Compressive Strength (UCS) test was performed followed by regression analysis to check the effect of EM on the soil strength. Obtained results have shown that the mix design for controlled moisture contents showed the promising improvement in their compressive strength. The peat soil samples with 10% of EM shows the highest increment in UCS value and the percentage of increments are in the range of 44% to 65% after curing for 21 days. The regression analysis of the EM with the soil compressive strength showed that in controlled moisture conditions, EM significantly improved the soil stability as the value of R2 ranged between 0.97 – 0.78. The results have indicated that the addition of EM in peat soils provides significant improving in the strength of the soil as well as the other engineering properties.

Surface disturbances: their role in accelerating desertification

USGS Publications Warehouse

Belnap, Jayne

1995-01-01

Maintaining soil stability and normal water and nutrient cycles in desert systems is critical to avoiding desertification. These particular ecosystem processes are threatened by trampling of livestock and people, and by off-road vehicle use. Soil compaction and disruption of cryptobiotic soil surfaces (composed of cyanobacteria, lichens, and mosses) can result in decreased water availability to vascular plants through decreased water infiltration and increased albedo with possible decreased precipitation. Surface disturbance may also cause accelerated soil loss through wind and water erosion and decreased diversity and abundance of soil biota. In addition, nutrient cycles can be altered through lowered nitrogen and carbon inputs and slowed decomposition of soil organic matter, resulting in lower nutrient levels in associated vascular plants. Some cold desert systems may be especially susceptible to these disruptions due to the paucity of surface-rooting vascular plants for soil stabilization, fewer nitrogen-fixing higher plants, and lower soil temperatures, which slow nutrient cycles. Desert soils may recover slowly from surface disturbances, resulting in increased vulnerability to desertification. Recovery from compaction and decreased soil stability is estimated to take several hundred years. Re-establishment rates for soil bacterial and fungal populations are not known. The nitrogen fixation capability of soil requires at least 50 years to recover. Recovery of crusts can be hampered by large amounts of moving sediment, and re-establishment can be extremely difficult in some areas. Given the sensitivity of these resources and slow recovery times, desertification threatens million of hectares of semiarid lands in the United States.

Clay:organic-carbon and organic carbon as determinants of the soil physical properties: reassessment of the Complexed Organic Carbon concept

NASA Astrophysics Data System (ADS)

Matter, Adrien; Johannes, Alice; Boivin, Pascal

2016-04-01

Soil Organic Carbon (SOC) is well known to largely determine the soil physical properties and fertility. Total porosity, structural porosity, aeration, structural stability among others are reported to increase linearly with increasing SOC in most studies. Is there an optimal SOC content as target in soil management, or is there no limit in physical fertility improvement with SOC? Dexter et al. (2008) investigated the relation between clay:SOC ratio and the physical properties of soils from different databases. They observed that the R2 of the relation between SOC and the physical properties were maximized when considering the SOC fraction limited to a clay:SOC ratio of 10. They concluded that this fraction of the SOC was complexed, and that the additional SOC was not influencing the physical properties as strongly as the complexed one. In this study, we reassessed this approach, on a database of 180 undisturbed soil samples collected from cambiluvisols of the Swiss Plateau, on an area of 2400 km2, and from different soil uses. The physical properties were obtained with Shrinkage Analysis, which involved the parameters used in Dexter et al., 2008. We used the same method, but detected biases in the statistical approach, which was, therefore, adapted. We showed that the relation between the bulk density and SOC was changing with the score of visual evaluation of the structure (VESS) (Ball et al., 2007). Therefore, we also worked only on the "good" structures according to VESS. All shrinkage parameters were linearly correlated to SOC regardless of the clay:SOC ratio, with R2 ranging from 0.45 to 0.8. Contrarily to Dexter et al. (2008), we did not observed an optimum in the R2 of the relation when considering a SOC fraction based on the clay:SOC ratio. R2 was increasing until a Clay:SOC of about 7, where it reached, and kept, its maximum value. The land use factor was not significant. The major difference with the former study is that we worked on the same soil group, on a large range of texture, with less sandy soils and accounting for structural state. Our results show that, on this soil group, any SOC increase almost linearly increases the physical properties and, therefore, the physical fertility and the ecological functions of the soil, regardless of the clay:SOC ratio. When considering the whole SOC instead of a fraction, we show that the 10 clay:SOC ratio, however corresponds to a good structure according to VESS and optimal physical values. Therefore, we think reaching a clay:SOC ratio of 10 must be considered as an objective for farmers and advisers. Ball, B.C., T. Batey, and L.J. Munkholm. 2007. Field assessment of soil structural quality - a development of the Peerlkamp test. Soil Use Manag. 23(4): 329-337. Dexter, A.R., G. Richard, D. Arrouays, E.A. Czyz, C. Jolivet, and O. Duval. 2008. Complexed organic matter controls soil physical properties. Geoderma 144(3-4): 620-627.

Techniques for the stabilization and assessment of treated copper-, chromium-, and arsenic-contaminated soil.

PubMed

Maurice, Christian; Lidelöw, Sofia; Gustavsson, Björn; Lättström, Anders; Ragnvaldsson, Daniel; Leffler, Per; Lövgren, Lars; Tesfalidet, Solomon; Kumpiene, Jurate

2007-09-01

Remediation mainly based on excavation and burial of the contaminated soil is impractical with regard to the large numbers of sites identified as being in need of remediation. Therefore, alternative methods are needed for brownfield remediation. This study was conducted to assess a chemical stabilization procedure of CCA-contaminated soil using iron (Fe)-containing blaster sand (BS) or oxygen-scarfing granulate (OSG). The stabilization technique was assessed with regard to the feasibility of mixing ameliorants at an industrial scale and the efficiency of the stabilization under different redox conditions. The stability was investigated under natural conditions in 1-m3 lysimeters in a field experiment, and the effect of redox conditions was assessed in a laboratory experiment (10 L). The treatments with high additions of ameliorant (8% and 17%) were more successful in both the laboratory and field experiments, even though there was enough Fe on a stochiometric basis even at the lowest addition rates (0.1% and 1%). The particle size of the Fe and the mixing influenced the stabilization efficiency. The development of anaerobic conditions, simulated by water saturation, increases the fraction of arsenic (AsIII) and, consequently, As mobility. The use of high concentrations of OSG under aerobic conditions increased the concentrations of nickel (Ni) and copper (Cu) in the pore water. However, under anaerobic conditions, it decreased the As leaching compared with the untreated soil, and Ni and Cu leaching was not critical. The final destination of the treated soil should govern the amendment choice, that is, an OSG concentration of approximately 10% may be suitable if the soil is to be landfilled under anaerobic conditions. Alternatively, the soil mixed with 1% BS could be kept under aerobic conditions in a landfill cover or in situ at a brownfield site. In addition, the treatment with BS appeared to produce better effects in the long term than treatment with OSG.

Fall conservation deep tillage stabilizes maize residues into soil organic matter

USDA-ARS?s Scientific Manuscript database

Efforts for increasing soil organic matter (SOM) content under agricultural systems have primarily focused on management practices that reduce exposure of SOM to decomposition via minimum tillage. We assess an alternative approach, termed ‘fall conservation deep tillage’ (FCDT), to SOM stabilization...

Effects of combined lime and fly ash stabilization on the elastic moduli of montmorillonitic soils : final report.

DOT National Transportation Integrated Search

1988-04-01

A laboratory study using bentonite to simulate the montmorillonite component of soils common to Louisiana was undertaken to evaluate the effects of combined lime and fly ash additions on stabilization reactions. Samples containing bentonite (75 weigh...