Soil Clay Particles Research Articles

Mechanistic insight into the effects of interaction between biochar and soil with different properties on phenanthrene sorption

Soil composition varies considerably in nature, so it is vital to investigate the mechanism of the effect of various soil parameters on biochar sorption capacity. In this study, two biochars (W4 and W7) were derived from wheat straw at temperatures of 400 and 700 °C and were incubated with three different soils. Changes in biochar surface features by aging in the soils and the consequent impact on phenanthrene sorption were examined. The results showed that the effect of adding biochar on phenanthrene sorption capacity (Koc) varied by soil. When biochar was freshly mixed with soil, the Koc value in soil with higher clay content was more dramatically altered by biochar, which is due to clay particles adhering to the biochar surface. Moreover, the Koc value was significantly decreased by the addition of W4 but increased by the addition of W7 in general. After aging, most of the Koc value decreased. The greatest decrease in Koc value was observed in biochar and soil composed with the highest clay content for W4 (24–63%), as well as soil composed with the highest organic matter content for W7 (46–64%). This is because the surface polarity and micropores of biochar dropped the most rapidly in these mixes, resulting in a significant decrease in hydrophobic and pore-filling properties. The results revealed that the impact of biochar-soil interactions on phenanthrene sorption is related to not only biochar properties but also soil clay particles, soil organic matter content and pH. The findings of the study can be utilized to assess the efficacy of biochar application in soil remediation for various features.

Polybrominated diphenyl ethers and their alternatives in soil cores from a typical flame-retardant production park: Vertical distribution and potential influencing factors

With the prohibition on the production and use of polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE) and organophosphate flame retardants (OPFRs) have emerged as their alternatives. However, the vertical transport and associated influencing factors of these chemicals into soil are not clearly understood. To clarify the vertical distribution of the pollutants and related influencing factors, surface soil and soil core samples were collected at a depth in the range of 0.10–5.00 m in a typical 20-year-old flame-retardant production park and surrounding area. PBDEs and DBDPE show a clear point source distribution around the production park with their central concentrations up to 2.88 × 104 and 8.46 × 104 ng/g, respectively. OPFRs are mainly found in residential areas. The production conversion of PBDEs to DBDPE has obvious environmental characteristics. The vertical distribution revealed that most of the pollutants have penetrated into the soil 5.00 m or even deeper. The median concentrations of deca-BDE and DBDPE reached 50.9 and 9.85 × 103 ng/g, respectively, even at a depth of 5.00 m. Soil organic matter plays a crucial role in determining the vertical distribution, while soil clay particles have a greater impact on the high molecular weight and/or highly brominated compounds.

The potential of NAA and ICP-MS for determining soil dispersibility in relation to landslide incidents

Dispersive soils pose significant challenges due to their inherent tendency to rapidly respond to the presence of water, resulting in erosion and heightened susceptibility to landslides. The inclusion of sodium (Na) onto the surface of soil clay particles results in the attenuation of the electrochemical interactions between the dispersed soil, leading to the repulsion and subsequent migration of the clay particles away from one another. This study employed Neutron Activation Analysis (NAA) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to assess the Sodium Adsorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP) as indicators of soil dispersibility. The results indicate that soils containing montmorillonite clay mineral exhibit greater values of SAR > 11 and ESP > 20 in comparison to soils containing other clay minerals i.e. kaolinite, illite, and vermiculite. The calculated SAR and ESP values obtained from both analyses demonstrate a notable agreement, indicating a positive correlation. In conclusion, it is apparent that both NAA and ICP-MS method has the capability to be applied for the purpose of predicting soil dispersibility in landslide-prone regions of Malaysia.

Multifractal characteristics of soil particle size distribution of abandoned homestead reclamation under different forest management modes

In this study, fast-growing poplar reclaimed from abandoned homestead in Xixian New District, Xi’an City, Shaanxi Province, was used as the research object to explore the multi-fractal characteristics of soil particle size distribution under different management modes of abandoned land (control), irrigation, fertilizer irrigation and mixed fertilizer irrigation. The results showed that the mean values of soil clay, silt and sand in abandoned land were 14.58%, 81.21% and 4.22% respectively, 14.08%, 79.92% and 5.99% under irrigation, 15.17%, 81.19% and 3.64% under fertilizer irrigation, and 16.75%, 80.20% and 3.05% in mixed fertilizer treatment. From 40 cm, with increasing soil depth, soil clay particles increase under irrigation, fertilizer irrigation, and mixed fertilizer irrigation modes. The single fractal dimension of soil particle size distribution (D) in each treatment ranges from 2.721 to 2.808. At 60–100 cm, D shows fertilizer irrigation > mixed fertilizer irrigation > irrigation > abandoned land, indicating that fertilization and irrigation can increase the fine-grained matter of deep soil particles and reduce soil roughness. Compared with abandoned land, under irrigation, fertilizer irrigation and mixed fertilizer modes the capacity dimension (D0), entropy dimension (D1), correlation dimension(D2), shape characteristics of the multifractal spectrum (Δf) and overall inhomogeneity of the soil particle size distribution (D0–D10) indicate an uneven distribution of soil particle size; fractal structure characteristics of soil (D−10–D0) indicate a simplified soil structure, and degree of dispersion of soil particle size distribution (D1/D0) indicates that soil particle size is distributed in dense areas. Pearson correlation analysis showed that D was significantly correlated with clay, sand, D0–D10, soil organic matter (SOM) and soil available phosphorus (SAP) (P < 0.05). Stepwise regression analysis showed that clay was the main controlling factor of D and D0–D10 changes. The research results can provide some potential indicators for the quality evaluation of abandoned homestead reclamation.

Evidence for immune activation in pathogenesis of the HLA class II associated disease, podoconiosis

Available evidences suggest that podoconiosis is triggered by long term exposure of bare feet to volcanic red clay soil particles. Previous genome-wide studies in Ethiopia showed association between the HLA class II region and disease susceptibility. However, functional relationships between the soil trigger, immunogenetic risk factors and the immunological basis of the disease are uncharted. Therefore, we aimed to characterise the immune profile and gene expression of podoconiosis patients relative to endemic healthy controls. Peripheral blood immunophenotyping of T cells indicated podoconiosis patients had significantly higher CD4 and CD8 T cell surface HLA-DR expression compared to healthy controls while CD62L expression was significantly lower. The levels of the activation markers CD40 and CD86 were significantly higher on monocytes and dendritic cell subsets in patients compared to the controls. RNA sequencing gene expression data indicated higher transcript levels for activation, scavenger receptors, and apoptosis markers while levels were lower for histones, T cell receptors, variable, and constant immunoglobulin chain in podoconiosis patients compared to healthy controls. Our finding provides evidence that podoconiosis is associated with high levels of immune activation and inflammation with over-expression of genes within the pro-inflammatory axis. This offers further support to a working hypothesis of podoconiosis as soil particle-driven, HLA-associated disease of immunopathogenic aetiology.

Changes in crack width on the surface of heavy soils during drought, determined by precise measurement and calculation

Abstract In heavy soils, changes in humidity incur soil volume changes. In the horizontal plane, these are manifested by cracks formation and in the vertical plane by the movement of the soil surface. Cracks have a significant impact on hydrodynamics of the soil profile. The work is based on the hypothesis that soil volume changes depend on both the content of clay particles in soil and soil volumetric moisture. The aim of the work is to measure and analyze the changes in the width of the cracks and their reaction to the changes in volumetric soil moisture. One of the objectives of the work was to design a simple tool for accurate measurement and calculation of the crack width on the soil surface. For the study of crack width, a soil profile in an area on the East Slovakia Lowland was selected. The profile was examined under conditions of extreme drought, at the turn of July and August 2022. Crack width varied between 1.0 cm and 3.3 cm. The calculation procedure was evaluated as satisfactory for estimating the change in crack width on the soil surface.

Using the Soil Texture Triangle to Evaluate the Effect of Soil Texture on Water Flow: A Review

Abstract: Water flow through soil is a critical process that affects many aspects of soil health and environmental sustainability. Soil texture, which is the relative proportion of sand, silt, and clay particles in soil, plays a significant role in regulating water flow through soils. The soil texture triangle is a widely used tool for classifying soil texture based on the proportions of sand, silt, and clay particles. This review paper aims to evaluate the effect of soil texture on water flow through soils using the soil texture triangle. The paper presents an overview of the soil texture triangle and its applications in soil texture classification, followed by a discussion of the relationship between soil texture and water flow. The paper reviews existing literature on the impact of soil texture on water flow and summarizes the key findings. The review highlights the importance of soil texture in regulating water flow through soils and discusses the implications for soil management and environmental sustainability. The paper concludes by identifying areas for future research to improve our understanding of the relationship between soil texture and water flow.

Studying the Effect of Agriculturally Exploited Soils on the Transformation of Mica Minerals using Infrared Spectroscopy (IR)

Five soil sites were selected in the Middle Euphrates region, represented by the governorates (Diwaniyah, Najaf, Babel, and Muthanna), for soils of different agricultural exploitation (rice, vegetables, wheat, and palm trees), in addition to an unexploited agricultural soil. The soils were distinguished by having the same topography and climatic conditions and similar texture in order to study the weathering of mica minerals by using the infrared technique. The appearance of the absorption spectrum at the frequency of 3550 cm-1, with medium broadening in the unexploited agriculture soil (Muthanna), indicated a gradual transformation of mica towards di-octahedra minerals, and reflected the increasing substitution of Al+3 in tetrahedral sheet in these soils. The results of the examination of clay particles in soils exploited for cultivation of rice (Diwaniyah) showed that the absorption spectrum at the wavelength of 1642 cm-1 represents the absorption of zeolite water, while the presence of absorption spectra at the frequencies of 796, 1036, 3418, and 3616 cm-1 indicated the presence of mica minerals in all rice soils, also the presence of the broad absorption spectrum band at the frequency of 3418 cm-1, which was accompanied by the presence of the spectrum band at the frequency of 1036 cm-1.

Depth-dependent drivers of soil microbial necromass carbon across Tibetan alpine grasslands.

Microbial necromass carbon (C) has been considered an important contributor to persistent soil C pool. However, there still lacks large-scale systematic observations on microbial necromass C in different soil layers, particularly for alpine ecosystems. Besides, it is still unclear whether the relative importance of biotic and abiotic variables such as plant C input and mineral properties in regulating microbial necromass C would change with soil depth. Based on the combination of large-scale sampling along a ~2200km transect across Tibetan alpine grasslands and biomarker analysis, together with a global data synthesis across grassland ecosystems, we observed a relatively low proportion of microbial-derived C in Tibetan alpine grasslands compared to global grasslands (topsoil: 45.4% vs. 58.1%; subsoil: 41.7% vs. 53.7%). We also found that major determinants of microbial necromass C depended on soil depth. In topsoil, both plant C input and mineral protection exerted dominant effects on microbial necromass C. However, in subsoil, the physico-chemical protection provided by soil clay particles, iron-aluminum oxides, and exchangeable calcium dominantly facilitated the preservation of microbial necromass C. The differential drivers over microbial necromass C between soil depths should be considered in Earth system models for accurately forecasting soil C dynamics and its potential feedback to global warming.

Study on soil compaction and its causative factors at apple orchards in the Weibei Dry Highland of China

AbstractThe aim of this study was to investigate the extent and causes of soil compaction of the apple orchards in the Weibei Dry Highland. Nine ‘Red Fuji’ apple orchards with number of planting years in the ranges of &lt;10‐year, 10–20‐year and &gt;20‐year were included. Soil bulk density, porosity, penetration resistance, organic matter (SOM), clay, water and soil aggregate size distribution were determined. The results showed that the subsoil (20–30 cm) of apple orchards was compacted. The bulk density and packing density (PD) of subsoil increased sharply by an average of 17.9% and 18.0%, respectively, relative to topsoil (0–10 cm), and the porosity decreased by 17.0%. The depths of the soil layer with penetration resistance exceeding 1,000 kPa became shallower with increased planting years. Compared with &lt;10‐year apple orchards, the bulk density, PD and soil penetration resistance in 10–20‐year and &gt;20‐year apple orchards were increased, respectively, by 5.3%, 5.3% and 29.3%, but the porosity decreased by an average of 8.2%. Compared with topsoil, the water‐stable aggregates of &gt;0.25 mm and the mean weight diameter of wet sieve aggregates (MWDW) of compacted soil were 57.6% and 25.4% lower, respectively. Soil clay content increased with soil depth from 0 to 60 cm, but the SOM showed an opposite trend. Additionally, there was a dry soil layer at a depth of 20–40 cm. Thus, the factors affecting the soil compaction process were determined to be inferior agglomeration ability of soil, internal soil desiccation, and the downward migration of soil clay particles.

Influence of Soil Particle Size on the Temperature Field and Energy Consumption of Injected Steam Soil Disinfection

Soil steam disinfection (SSD) technology is an effective means of eliminating soil borne diseases. Among the soil cultivation conditions of facility agriculture in the Yangtze River Delta region of China, the clay soil particles (SPs) are fine, the soil pores are small, and the texture is relatively viscous. When injection disinfection technology is applied in the clay soil, the diffusion of steam is hindered and the heating efficiency is substantially affected. To increase the heating efficiency of SSD, we first discretized the continuum model of Philip and De Vries into circular particle porous media of different sizes and random distribution. Then with Computational Fluid Dynamics (CFD) numerical simulation technology, a single-injection steam disinfection model for different SP size conditions was constructed. Furthermore, the diffusion pattern of the macro-porous vapor flow and matrix flow and the corresponding temperature field were simulated and analyzed. Finally, a single-pipe injection steam disinfection verification test was performed for different SP sizes. The test results show that for the clay soil in the Yangtze River Delta region of China, the test temperature filed results are consistent with the simulation results when the heat flow reaches H = 20 cm in the vertical direction, the simulation and test result of the heat flow in the maximum horizontal diffusion distance are L = 13 cm and 12 cm, respectively. At the same disinfection time, the simulated soil temperature change trend is consistent with the test results, and the test temperature is lower than the simulated temperature. The difference between the theoretical temperature and the experimental temperature may be attributed to the heat loss in the experimental device. Further, it is necessary to optimize the CFD simulation process and add the disintegration and deformation processes of soil particle size with the change of water content. Furthermore, the soil pores increase as the SP size increases and that a large amount of steam vertically diffuses along the macropores and accumulates on the soil surface, causing ineffective heat loss. Moreover, soil temperature distribution changes from oval (horizontal short radius/vertical long radius = 0.65) to irregular shape. As the SP size decreases, the soil pore flow path becomes fine; the steam primarily diffuses uniformly around the soil in the form of a matrix flow; the diffusion distance in the horizontal direction gradually increases; and the temperature distribution gradually becomes even, which is consistent with the soil temperature field simulation results. Similar to the energy consumption analysis, the maximum energy consumption for SP sizes&gt;27mm and &lt;2mm was 486and 477kJ, respectively. Therefore, proper pore growth was conducive to the diffusion of steam, but excessive pores cause steam to overflow, which increased energy consumption of the system. Considering that the test was carried out in an ideal soil environment, the rotary tiller must be increased for fine rotary tillage in an actual disinfection operation. Although large particles may appear during the rotary tillage process, an appropriate number of large particles contributes to the formation of a large pore flow, under the common effect of matrix flow, it will simultaneously promote greater steam diffusion and heating efficiency. The above theoretical research has practical guiding significance for improving the design and disinfection effect of soil steam sterilizers in the future.

Bio-remediation of desiccation cracking in clayey soils through microbially induced calcite precipitation (MICP)

Desiccation cracking is a common natural phenomenon in clayey soils, considerably degrading their mechanical and hydraulic properties. Typical remediation methods are associated with high labor costs, high maintenance costs, or the usage of environment-unfriendly chemicals. Microbially induced calcite precipitation (MICP) has emerged as a green and sustainable soil improvement technique. The application of MICP in clayey soils remains poorly investigated due to the presence of microscopic pores among clay soil particles that restrain the free passage of bacteria. In this study, we carry out cyclic wetting-drying tests to characterize the effect of MICP on the desiccation cracking behaviors of clayey soils. We prepare four groups of soil samples sprayed with deionized water, bacteria solution, cementation solution, and both bacteria and cementation solutions, respectively. Soil desiccation cracking behaviors captured by a high-resolution camera are quantified using image processing. We resort to optical microscopy and scanning electron microscopy for microstructural characterizations. Experimental results reveal the effects of fluid type and treatment cycle number on the crack evolution and volumetric deformation of soils. Comparatively, the MICP treatment involving both bacteria and cementation solutions work most effectively in lowering the soil cracking potential. Geometrical parameters featuring the crack pattern such as surface crack ratio, average crack width, total crack length, crack width distribution range and the most probable value of crack width decrease significantly with the increasing treatments. This study is expected to improve the fundamental understanding of desiccation cracking mechanisms in the MICP-treated soils and provide insights into the potential application of MICP for cracking remediation in clayey soils.

Retention and release of nutrients from polyhalite to soil

AbstractRecent discoveries of polyhalite (K2SO4.MgSO4.2CaSO4.2H2O) in the UK provide an alternative to conventional fertilizer sources. This work investigated the interaction of polyhalite, commercially known as POLY4, with soil using leaching columns. Different physical forms of polyhalite (powder, crushed rock and granules) were compared to potassium chloride (KCl) for the movement of potassium, calcium, magnesium and sulphur (as sulphate) through the soil profile using 19.7 L of water, equivalent to 4,500 mm rainfall. The nutrients from polyhalite were found to be available at 30 cm depth, with calcium showing signs of interacting with the soil clay particles to release cationic nutrients. Polyhalite granules showed the greatest release of sulphate, magnesium and calcium as a proportion of the additional nutrient with 127%, 71% and 102%, respectively leached. For potassium, all forms of polyhalite had greater release than KCl (powder = 58%; granules = 86%; crushed rock = 57% and KCl 16%). Nutrients from polyhalite and those mobilized from soil interactions are present in soil solution indicating availability for plant growth.

The Effect of Diffusion on the Sedimentation Rate of Soil Microparticles

The submitted paper presents the results of the experiment aimed at quantifying the effect of diffusion on the sedimentation rate of soil microparticles of different fractions. The goal of the experiment was to specify the determination of the texture composition of soils. The textural composition of the soil gives basic information about its hydrophysical properties. Standard methods for determination of granulometric soil composition are based on sedimentation methods. Measuring errors occur in the measurement of the soil microparticle rate, which are usually made of clay particles. Their source is the effect of diffusion. In the settling process with the gradual formation of the colloidal dispersion system, the deposition rate decreases. The rate of sedimentation of the dispersion particles approaches the rate of the mean diffusion feed in the opposite direction. Gradually, the state of dynamic sedimentation equilibrium occurs. The dispersion ratio was in dispersed system formed by clay soil particles from the Senne site. The dispersed medium was distilled water. Grain analyzes were performed by a laser diffraction method on a Mastersizer 2000 from MALVERN Instruments. The soil microparticles’ rates were measured on the basis of the time and the path of particles with diameter d (90). The output of the experiment is the diffusion coefficient, diffusion average feed and sedimentation rate for soil particles of different sizes. The results of the work show that with size of sedimented soil particles, the effect of diffusion increased. On this basis, it is possible to verify the lower limit of the results of grain size analyzes based on the sedimentation method. The results of the work show that the reduction of the size of the settled soil particles increases the effect of diffusion. On this basis, it is possible to quantify the lower limit of the results of grain size analyzes based on the sedimentation method and the particle size at which dynamic sedimentation equilibrium occurs.

Effect of optimum compaction moisture content formulations on the strength and durability of sustainable stabilised materials

The achievement of Optimum Compaction Moisture Content (OCMC) of clay soil plays an important role in compaction as well as the durability and strength of compacted soil. This is due to its effect on the structure and orientation of the clay soil particles. Most researchers on stabilised systems involving soils and/or industrial waste by-product additives for applications in roads and buildings are faced with the problem of how to approach the establishment of OCMC, when the complex mixtures involved. This paper reports on the laboratory investigation of theoretical methods of two different approaches to establish the OCMC in the stabilisation of clay soil involving multi-binary binder in cementitious binder system. Furthermore, this research also explores the use of an industrial by-product, Pulverized Fuel Ash (PFA) as partial target material and ground granulated blastfurnace slag (GGBS), with a view to reducing the reliance on the traditional cementitious binders, such as lime and/or Portland Cement (PC), in stabilising Lower Oxford Clay (LOC) soil combining with PFA at 50:50 ratio. LOC + PFA was stabilised both in conventional manner using Lime and PC as control and using sustainable binders incorporating GGBS. The results show that there was no one particular approach to the establishment of the optimal compaction moisture content for best strength development and durability. The best approach being dependent on the period of curing, stabiliser content and whether GGBS was blended with Lime or with PC. Of the various stabilisers studied, the highest strength magnitudes were however recorded with LOC-PFA stabilised using the blended binders incorporating GGBS. For all 7, 28 and 56 days of curing periods, the PC-based stabilisers were observed to be less sensitive to the different approaches to compaction moisture content, relative to the lime-based systems.

Runoff of the herbicides triclopyr and glufosinate ammonium from oil palm plantation soil

This study focused on the residue detection of the herbicides triclopyr and glufosinate ammonium in the runoff losses from the Tasik Chini oil palm plantation area and the Tasik Chini Lake under natural rainfall conditions in the Malaysian tropical environment. Triclopyr and glufosinate ammonium are post-emergence herbicides. Both herbicides were foliar-sprayed on 0.5ha of oil palm plantation plots, which were individualized by an uneven slope of 10-15%. Samples were collected at 1, 3, 7, 15, 30, 45, 60, 90, and 120days after treatment. The concentrations of both herbicides quickly diminished from those in the analyzed sample by the time of collection. The highest residue levels found in the field surface leachate were 0.031 (single dosage, triclopyr), 0.041 (single dosage, glufosinate ammonium), 0.017 (double dosage, triclopyr), and 0.037μg/kg (double dosage, glufosinate ammonium). The chromatographic peaks were observed at "0" day treatment (2h after herbicide application). From the applied active ingredients, the triclopyr and glufosinate losses were 0.025 and 0.055%, respectively. The experimental results showed that both herbicides are less potent than other herbicides in polluting water systems because of their short persistence and strong adsorption onto soil clay particles.

Сравнительная оценка методов определения педогенного органического углерода в углесодержащих почвах

The research considered determination of carbon reserves of soil organic substances in coal-bearing soils as an important problem of the study of technogenic landscape soils of coal deposits. Basing on the ability of soils of technogenic landscapes to perform the functions of natural undisturbed soils, the total fund of soil organic substance in such soils is said to be formed not only by humic compounds, but also by oxidized carbonaceous particles. Therefore, only developing the methods for differentiating soil organic substance performing the function of humus, and non-transformed lithogenic organic substance can solve the problem of evaluating the state of coal-bearing soils. The aim of the work is a comparative evaluation of the possibility of using traditional approaches and two those which we propose to determine the content of pedogenic organic carbon in soils of coal deposit dumps. Embryosems formed on the surface of coal and brown coal deposit dumps in Kemerovo oblast (N 53 o 39'; E 86 o 53') and Krasnoyarsk Krai (N 55 o 58'; E 90 o 23') were objects of the research. Methodically, along with traditional methods based on the content of total and organic carbon determination, we use approaches that rely on functional characteristics of soil organic substance. The first approach is based on the ability of soil organic substances to deposit nitrogen in soils. This approach involves calculation of carbon content of pedogenic organic substances using the parameters of soil nitrogen reserves and its ratio with carbon (C / N) in zonal undisturbed soils. The second approach is based on the ability of soil organic substance to form organic and mineral complexes with clay particles. At the same time, the content of pedogenic carbon is determined by the value of lithogenic potential of humus accumulation (LPHA), which depends on the number of clay particles in soils. Our research has shown that for carbon-containing soils, methods based on determination of total and organic carbon give incorrect results and cannot be used in complex ecological studies of techogenic soils and landscapes. Approbation of the proposed approaches has shown that, the definition of LPHA makes it possible to obtain reliable results for embryozems formed on a dense, stony substrate of coal deposits (See Table 2), since the accumulation of clay particles in such soils is the result of biochemical weathering and their amount is proportional to the reserves of organic substance. For embriozems formed on a loose substrate of brown coal deposit dumps, the results obtained with the help of C / N ratio and nitrogen content in the investigated soils are the most representative (See Table 2). Thus, we can conclude that, even in this approximation, the proposed approaches allow carrying out large-scale studies on evaluating the ecological state and resource potential of coal-bearing soils of technogenic landscapes. The article contains 2 Tables, 39 References.

Nickel speciation in several serpentine (ultramafic) topsoils via bulk synchrotron-based techniques

Serpentine soils have elevated concentrations of trace metals including nickel, cobalt, and chromium compared to non-serpentine soils. Identifying the nickel bearing minerals allows for prediction of potential mobility of nickel. Synchrotron-based techniques can identify the solid-phase chemical forms of nickel with minimal sample treatment. Element concentrations are known to vary among soil particle sizes in serpentine soils. Sonication is a useful method to physically disperse sand, silt and clay particles in soils. Synchrotron-based techniques and sonication were employed to identify nickel species in discrete particle size fractions in several serpentine (ultramafic) topsoils to better understand solid-phase nickel geochemistry. Nickel commonly resided in primary serpentine parent material such as layered-phyllosilicate and chain-inosilicate minerals and was associated with iron oxides. In the clay fractions, nickel was associated with iron oxides and primary serpentine minerals, such as lizardite. Linear combination fitting (LCF) was used to characterize nickel species. Total metal concentration did not correlate with nickel speciation and is not an indicator of the major nickel species in the soil. Differences in soil texture were related to different nickel speciation for several particle size fractionated samples. A discussion on LCF illustrates the importance of choosing standards based not only on statistical methods such as Target Transformation but also on sample mineralogy and particle size. Results from the F-test (Hamilton test), which is an underutilized tool in the literature for LCF in soils, highlight its usefulness to determine the appropriate number of standards to for LCF. EXAFS shell fitting illustrates that destructive interference commonly found for light and heavy elements in layered double hydroxides and in phyllosilicates also can occur in inosilicate minerals, causing similar structural features and leading to false positive results in LCF.

Soil Surface Wetting Pattern under Trickle Source in Arid Lands : Badia Regions

Arid regions are characterized by fragile soils that differ in behavior according to their physical and chemical compositions. In this study, the wetted soil surface area was measured for four different soil types to assess the impact of the individual soil particles (silt, sand and clay separates) on soil surface wetting area, under different application rates using point source trickle irrigation. Three flow rates were tested 4, 8 and 12 liters per hour (Lph) on four different soil types (silt loam, loam, sandy loam58sand and sandy loam77sand). Soil surface wetted area increases as emitter flow rate increases. The results showed that increasing emitter flow rate from 4 to 8 and to 12 Lph, increased soil surface wetted area by about 60 and 160%, respectively. Soil surface wetted areas in loam soil and silt loam soils were 1.5 and 2.8 times that in sandy loam soils, respectively. Soil surface wetted area increases rapidly with time initially, but then increases at a decreasing rate, until the application rate became in equilibrium with soil infiltration rate. The surface wetted area had good correlation with the percentages of silt, sand and clay soil particles, with regression correlation ranging from 0.90 to 0.97. The trends were increased wetting with clay and silt and decreased wetting with sand. The expected losses on the form of evaporation in arid soils suffering from surface crust, therefore, would increase in soils dominated by silt or clay when compared with sand, indicating that cropping pattern in arid environments should be carefully selected in areas with scarce water resources.

Multiscale effects on biological soil crusts cover and spatial distribution in the Monte Desert

Biological soil crusts (BSC) play diverse roles in arid and semi-arid ecosystems such as increasing soil fertility and reducing soil loss due to aeolian and hydric erosion, but they are very sensitive to disturbances. These attributes point to the relevance of BSC for soil conservation and restoration. In order to use BSC for restoration of degraded soils, we need to understand the ecological drivers of BSC. In this study, we analyzed the effect of environmental factors on BSC cover at different spatial scales in the central Monte Desert (Argentina), including landform, slope, aspect, vascular plants, and disturbance intensity. We evaluated the effects of different factors with linear mixed effect models, comparing the adjustment of models of different complexity, which included different number of factors. First, at the landscape scale, we analyzed BSC cover in two geomorphological units with different soils, topography, and vegetation. BSC cover was higher in the old riverbed, which has a higher proportion of fine clay soil particles, than in the aeolian plain. Disturbance effects were apparent in the old riverbed, showing increasing BSC cover at higher distances from settlements, and BSC located both, under and outside plant canopies. At the mesoscale, we found no differences of BSC cover in dune flanks and inter-dune valleys of the aeolian plain. Finally, at the microscale, BSC patches of higher surface cover were found in association with vascular plants (Larrea divaricata, Bulnesia retama, Lycium sp.), on mounds, and in microsites of southern exposure and high slopes. Our findings suggest that BSC develop preferentially associated with vascular plants, which generate mounds and sloped microsites with southern exposure, where lower irradiances reduce desiccation in these extremely dry environments.