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In order to explore the effects of two plants on the spatial distribution and nutrient distribution of crusts in different directions and distances after 30 years of aerial seeding, as well as the relationship between crust thickness and nutrient content, this paper takes the aerial seeding afforestation area in the northeastern margin of Tengger Desert as the research area, and the crusts under the plants of Hedysarum scoparium and Calligonum mongolicum as the research objects. The distribution of crust thickness and nutrients was analyzed, and the relationship between them was constructed. The thickness of the crust of H. scoparium and C. mongolicum was the largest in the southeast direction and the smallest in the northwest direction. With increasing distance from the plant, it shows a significant decreasing trend. The crust thickness of H. scoparium was higher than that of C. mongolicum. The nutrient indexes in the southeast direction of the crust of H. scoparium and C. mongolicum were significantly higher than those in the northwest direction; With the increase of the distance from the root of the plant, the nutrient content showed a significant decreasing trend. The contents of organic matter and available nitrogen in the crust of C. mongolicum were higher than those of H. scoparium, and the contents of available potassium and available phosphorus were lower than those of H. scoparium. The trend of nutrient enrichment rate of the crusts of the two plants was consistent with the trend of nutrient distribution. There was a significant positive correlation between the crust thickness and nutrients in the four directions under C. mongolicum. There was a significant positive correlation between the crust thickness and nutrients in the southwest direction under H. scoparium. The changes of available nitrogen, available phosphorus, available potassium and organic matter content in the crust under H. scoparium can explain 52.5% of the change of its thickness. The changes of available nitrogen, available phosphorus, available potassium and organic matter content in the crust under C. mongolicum can explain 78.5% of the change of its thickness. After 30 years of aerial seeding in Tengger Desert, the thickness and nutrients of the crust in the southeast direction of H. scoparium and C. mongolicum were significantly higher than those in the northwest direction and showed a decreasing trend with the increase of distance from the root of the plant. There was a positive correlation between crust nutrient and thickness. [ABSTRACT FROM AUTHOR]

Collapsing erosion is a unique phenomenon commonly observed on the granite residue hillslopes in the tropical and subtropical regions of southern China, characterized by its abrupt occurrence and significant erosion volumes. However, the impacts of soil crust conditions on the erosion of colluvial deposits with granite residual soils have only been studied to a limited extent. To address this issue, this study investigates the impacts of three soil crust conditions (i.e., without crust, 10-minute crust, and 20-minute crust) on gully morphology, rainfall infiltration, and runoff and sediment yield during slope erosion of colluvial deposits with granite residues (classified as Acrisols) in Yudu County, Ganzhou City, Jiangxi Province, China, using simulated rainfall tests and photographic methods. The results showed that as the strength of the soil crust increased, the capacity of moisture infiltration and the width and depth of the gully as well as the sediment concentration and yield ratio decreased; at the same time, the runoff ratio increased. The sediment yield in the without-crust test was found to be 1.24 and 1.43 times higher than that observed in the 10-minute crust and 20-minute crust tests, respectively. These results indicate that soil crusts can effectively prevent slope erosion and moisture infiltration, while providing valuable insights for the management of soil erosion in natural environments. [ABSTRACT FROM AUTHOR]

Soil crust is of high concern in soybean cultivation due to its adverse impact on seedling emergence. Despite the necessity of soybean varieties with stable seedling emergence against soil surface crust, genotypic variation of this trait has not been well understood because there have been no general protocols widely applicable to a set of accessions. The major constraint in conducting such experiments is the difficulty in reproducing soil crust with uniform hardness for each set of experiments. In this study, a simple method that can evaluate the seedling emergence under the conditions of uniform hardness of soil crust using gypsum mixed soil was developed and tested for 82 soybean accessions. Among the tested accessions, five genotypes with high seedling emergence under soil crust conditions were identified.

Aims: The surface crust formed by the drop impact of rainfall and/or irrigation is a prevalent characteristic in many Mediterranean soils. However, the temporal variation of soil hydraulic properties induced by surface crust during the high-frequency irrigation has rarely been investigated. Methods: Beerkan infiltration tests in conjunction with the BEST method were used to investigate the effects of surface crusting on the spatio-temporal variation of saturated soil hydraulic conductivity (Ks, mm s−1), sorptivity (S, mm s−0.5), mean pore size (r, mm), number of effective pores per unit area (N, m−2) in Agramunt, NE Spain. Results: In response to autumn tillage, intensive tillage (IT) increased Ks and S due to higher r and N, but both declined after 60 days. Reduced tillage (RT), maintained comparable Ks and S values, despite having a lower N value. After the spring tillage, both IT and RT developed crusted layers, resulting in decreased Ks, S and N. Long-term no-tillage (NT) showed an increasing trend of Ks and S over time, except for the last sampling. Spatial variation (i.e., between the rows, B-row vs. within the row of crops, W-row) of Ks and S was found, and non-crusted soils (W-row) had consistently higher Ks and S than crusted soils (B-row). Conclusions: Conservation tillage i.e., RT and NT improve the surface soil structure and reduce the risk of crust development. Surface cover by crops may help to prevent crust formation within the row of crops, improving soil hydraulic conductivity. [ABSTRACT FROM AUTHOR]

Seepage control is critically essential for dams, slopes, and the stability of many engineering structures, developing over many years using different methods. This study presents a novel approach for seepage control using the photopolymerization technique to form an impermeable crust at the soil surface. Effects of exposure duration (5, 10, 15, and 30 min) and light intensities (140, 550, 710, and 1000 W/m2) on the seepage control effectiveness of four different sand soils were investigated by using the photopolymerization technique. The three-point bending, permeability and acid rain simulation tests were performed to illustrate the effect of photopolymerization on the seepage control of sand soils. Furthermore, the influence of photopolymerization on the microstructure of soils was examined with the aid of SEM analysis. The results indicated that the photopolymerization technique could improve the crust strength, acid rain durability, and permeability of sand soils. The crusts at the surface layer of soils were formed after the photopolymer was applied to the sand surface and then exposed to UV light. These crusts of different soils have bending strengths and thicknesses in the range of 34.57 and 68.07 MPa, 2.13 and 6.18 mm, respectively. The increase in exposure duration and light intensity, resulted in the gradual increment of soil crust thickness. On the other hand, the increase in light intensities have more effective on the crust thickness. The formed soil crust has been provided an impermeable surface that prevents the weight loose from the surface of the soil under acid rain conditions. The SEM analysis indicated that the photopolymerized gels were homogeneously distributed between the grains in all samples, although the grain distribution of soils were different. Since the photopolymerization method has a short treatment duration and is easier to apply on the sand surface, the occurrence of the crust at the soil surface by this technique may open a new and improvable path for seepage control. The obtained results showed that the photopolymerization method is promising for repairing, restoring, and strengthening the construction materials in different engineering areas, as well as seepage control. [ABSTRACT FROM AUTHOR]

Soil is one of the most important parts of an ecosystem. If soil particles are conserved in a basin, it will be possible for the ecosystem to survive. In this study, clay, silt and sand particles were selected as soil conservation compounds and strength and wind erosion tests were performed to assess the crust strength of these compounds. Moreover, due to the lack of clear relationships between these parameters, this research aims to identify the correlations among them. These particles were coded at specific intervals in terms of application rate and then used as inputs in Design Expert software. After 48 h, a penetrometer test was performed on crust layers. The results showed that based on significant correlations between the simulation and laboratory data, the best models are the 2FI mathematical model (strength test) and quadratic (wind erosion). The simulation results indicate that the values of R2 and Adj-R2 were 0.8994 and 0.9311 respectively, and the signal-to-noise ratio was 21.254. The interaction effect of the treatments showed that application of clay in the studied compounds increased penetration strength of the layer. Also, with the increase in clay content, wind erosion first increased and then decreased, and this trend is directly related to the characteristics of clay. Further, the accuracy of the wind erosion simulation results was R2 = 0.9561. According to the optimization results, the maximum soil resistance occurred with 15 g each of clay, silt, and sand. However, it remained constant when sand content increased. This study suggests that application of each compound creates a very different behavior in the formation of soil crust that can be used in many projects on a local and global scale.

Arid and semiarid ecosystems around the world are often prone to both soil salinization and accelerated soil erosion by wind. Soil salinization, the accumulation of salts in the shallow portions of the soil profile, is known for its ability to decreases soil fertility and inhibit plant growth. However, the effect of salts on soil erodibility by wind and the associated dust emissions in the early stages of soil salinization (low salinity conditions) remains poorly understood. Here we use wind tunnel tests to detect the effects of soil salinity on the threshold velocity for wind erosion and dust production in dry soils with different textures treated with salt‐enriched water at different concentrations. We find that the threshold velocity for wind erosion increases with soil salinity. We explain this finding as the result of salt‐induced (physical) aggregation and soil crust formation, and the increasing strength of surface soil crust with increasing soil salinity, depending on soil texture. Even though saline soils showed resistance to wind erosion in the absence of abraders, the salt crusts were readily ruptured by saltating sand grains resulting in comparable or sometimes even higher particulate matter emissions compared to non‐saline soils. Interestingly, the salinity of the emitted dust is found to be significantly higher (5–10 times more) than that of the parent soil, suggesting that soil salts are preferentially emitted, and airborne dust is enriched of salts. Plain Language Summary: In this study we investigated how the use of slightly saline irrigation water may affect soil susceptibility to wind erosion and the dust emission potential of dry soils, and how these processes are affected by the amount of clay in the soil. Results indicated that, even though salinity decreased the susceptibility of soils to wind erosion due to aggregation and crust formation, abrasion by sand particles resulted in the breakdown of saline crusts, leading to emissions comparable or sometimes even higher to those of non‐saline soils. The higher salt concentration found in the dust than in the dust‐emitting soil suggests that the airborne transport of salts may have important implications for contaminant transport and salinization of downwind areas. Key Points: Threshold velocities for wind erosion increase with increasing soil salinity because salts induce the formation of a soil crustCrust formation and aggregation can delay dust emission from soil surfaces even under low salinity conditionsSalts are preferentially emitted and amplified in airborne dust [ABSTRACT FROM AUTHOR]

Copyright of Misr Journal of Agricultural Engineering is the property of Egyptian National Agricultural Library (ENAL) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Biological soil crust can effectively prevent wind erosion of sand and soil, which is of great significance to ecological restoration in desert areas. There have been few studies that have screened different planting patterns by analyzing biological crust properties. In this study, high-throughput sequencing was used to analyze the bacterial 16S rRNA community structure of biologically crusted soil in sandy bare land (CK), planting corn soil crust (CB), planting potato soil crust (TB) and planting alfalfa soil crust (AB), and nutrient profiles of each soil type were also analyzed. The results showed that soil nutrient content was significantly increased by the biological layer, and the organic matter, available phosphorus, and available potassium contents were significantly increased. In terms of bacterial communities, the TB treatment had more endemic genera (100). The top 10 phyla in terms of relative abundance accounted for around 95% of the total community, with Actinobacteria being the highest. The community structure of CB and AB was similar, and the diversity and richness indices of CB were significantly increased compared to those of CK. The available phosphorus and total nitrogen were found to be the main factors affecting bacterial community structure. The dominant role of Actinobacteria was mainly determined by pH. Overall, the results show that corn planting could be most helpful in the early restoration period of sandy land. [ABSTRACT FROM AUTHOR]

【Objective】 Crust is a thin soil layer formed on soil surface when water on the soil surface recedes; continuing soil drying after that could result in cracks to develop. Crusts and cracks could significantly affect water infiltration and soil water evaporation, and the purpose of this paper is to experimentally study how crusts form and cracks subsequently develop following a rainfall on a slope. 【Method】 The experiment was conducted on a slope watered by artificial rainfall. After the rainfall stopped, we measured physical properties of the crusts, imaged the initiation and development of cracks in them at different locations on the slop. These images were processed using MATLAB to quantify their morphological characteristics as well as their relationship with soil water content. 【Result】 Based on where the crusts were formed, they can be classified into structural crusts, depositional crusts and transitional crusts, with different physical properties. The depositional crusts have the highest volumetric weight and clay content. In contrast, the structural crusts have the greatest sand particle content. The morphology of cracks developed in the crusts at different locations in the gully differed from each other significantly. For crusts where the cracks developed, their impacts on crack area ratio (RC), length density of the cracks (LC), and the average width of the crack (Wi) were ranked in the order of depositional crusts

The quantity and quality of soil organic matter (SOM) depending on many edaphic and environmental factors may change in response to agriculture-related practices. The SOM humification process can be supported by the application of mineral fertilizers, but in the production vineyards, such information is lacking. NPK fertilizer alters the soil quality, and therefore, the aim of this study was to: (1) assess the extent and dynamics of different NPK (control—no fertilization; 1st NPK; and 3rd NPK levels) rates to the soil with grass sward cover in a productive vineyard on changes in SOM, humic substances (HS), and soil structure, and (2) identify relationships between SOM, HS, and soil structure. Results showed that the share of humic acids in soil organic carbon decreased only in NPK1 compared to control and NPK3 treatments. The color quotient of humic substance values in NPK1 and NPK3 increased by 4 and 5%, respectively, compared to control. Over a period of 14 years, the content of soil organic carbon increased by 0.71, 0.69, and 0.53 g kg−1 year−1 in the control, NPK1, and NPK3, respectively. The content of HS increased linearly with slight differences due to NPK application. The vulnerability of the soil structure decreased due to fertilization—more at the higher NPK level. The rate of formed soil crust was decreasing in the following order: control > NPK1 > NPK3. In the control treatment, the relations between SOM, HS, and soil structure were most abundant and with the greatest significance, while with the increasing level of NPK, these relations lost their significance. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) are important for restoring vegetation and improving soil fertility in arid or semiarid desertified land. However, studies on the contribution of BSC microbes to phosphorus (P) transformation remains limited. The microbial diversity involved in P transformation and its dynamic along BSC development should be examined to further understand the microbial regulatory mechanism of the P-cycling process. This paper investigates the soil properties, P fractions, and potential of P transformation across a chronosequence (0-, 8-, 20-, and 35-year) of the BSC under Caragana microphylla plantation on the moving sand dunes in Horqin Grassland, China. An abundance of phoD and gcd genes was detected, and the diversities and structures of phoD - and gcd -haboring microbial communities were illustrated via high-throughput sequencing. Soil nutrient content, activity of alkaline phosphomonoesterase, potential of organic P (OP) mineralization, and the abundance of phoD and gcd genes all linearly increased along with BSC age. The microbial quantity and species diversity of the phoD community were greater than those of gcd. BSC development increased the availability of inorganic P (IP) fractions, and both NaHCO3-Pi and NaOH-Pi were positively correlated with the abundance of the two genes and the activity of alkaline phosphomonoesterase. The phyla of Actinobacteria, Planctomycetes, and Proteobacteria and the family of Streptomycetaceae were the most dominant taxa in the phoD community, Proteobacteria was the dominant phylum in the gcd community in BSC soils, and Rhizobium and Planctomyces were the most dominant genera. The dominant taxa quantitatively responded to soil property improvement, but the basic compositions and dominant taxa did not change along with BSC development. The structures of phoD and gcd communities were linked to soil properties, and pH available K, and total K tend to be the direct determining factors. [ABSTRACT FROM AUTHOR]

Physical soil crusts will form on most soils during and after rainfall, which has important impacts on hydrological and erosion processes by affecting soil pore structure. However, the soil pore characteristics of physical crusts of two typical erodible soils (quaternary red clay [QRC] and granite red soil [GRS]) in southern China are still unclear due to the limitations of objective and accurate quantitative methods. We scanned physical crusted (structural crust [SC] and depositional crust [DC]) soil samples from the QRC and GRS at various slopes using X‐ray computed tomography, and extracted and analysed soil pore characteristics using two‐ and three‐dimensional indexes. The averages of the two‐dimensional pore indexes, that is, pore number, porosity, circularity, and equivalent diameter across the four soil sample types were 116–205, 4.83%–8.31%, 0.83–0.87, and 0.19–0.28 mm, respectively, indicating the characteristics of a large number of small pores with nearly circular shape. The mean values of pore number and circularity were significantly smaller for the structural crust samples than the depositional crust samples, and the porosity and equivalent diameter were significantly larger for the structural crust samples than the depositional crust samples. The three‐dimensional pore indexes also differed among the four soil sample types, where the mean fractal dimension and surface area values for QRC were 2.62 and 1959.77 mm2, respectively, which were significantly larger than those for GRS (2.52 and 1457.97 mm2). The pore number and circularity decreased, the equivalent diameter increased, and the surface area and connectivity density increased initially and then decreased with the slope, mainly due to differences in the run‐off and sediment process, and crust formation process on slopes with different gradients. The results provide a scientific basis for the objective quantification of physical soil crusts to facilitate further studies on physical crusts affect run‐off and sediment processes. Highlights: CT method was first used to quantify pore structure of crusted soil samples in southern China.The crusted soil pores had a feature of a large number of small pores with nearly circular shape.The two‐ and three‐dimensional soil pore indexes were differed among the four soil sample types.The slope had a negligible influence on soil pore structure. [ABSTRACT FROM AUTHOR]

Objective: The plant canopy, plant roots, and biological soil crusts play important roles in soil detachment by overland flow. This study aims to quantify and analyze the effects of the plant canopy, plant roots, and soil crust on soil detachment via in situ experiments. Materials and methods: Two typical dominant species, Bothriochloa ischaemum (Linn.) Keng (an herb) and Sophora davidii (Franch.) Skeel (a shrub) on the Loess Plateau, China, were selected. Four treatments were denoted T0 (bare land), T1 (canopy + root + crust), T2 (root + crust), and T3 (root) and subjected to flow scouring with a discharge of 5 L min−1 on a 20° slope. Results and discussion: The soil detachment rate (SDr) in all treatments decreased sharply in the first 3 min due to changes in the internal force of the soil particles. As the effects of the canopy, roots, and soil crust were subsequently superimposed, the SDr decreased by 87.42–93.42% compared with that of the bare land. The plant canopy, roots, and soil crust contributed 8.57–9.54%, 92.36–95.27%, and −1.90 to −3.84% of the soil detachment reduction (SDR), respectively. Additionally, the naturally restored herb roots decreased soil detachment by flowing water more significantly than shrub roots in the study area. Conclusions: The effects of canopy, roots, and soil crust on SDr in grassland were similar to those in shrubland. Roots played a crucial role in strengthening soil resistance to detachment. Although shrubland had a greater effect on soil detachment reduction than grassland, herbs are strongly recommended for reducing soil erodibility due to the greater erosion-reducing potential of roots and their drought resistance on the Loess Plateau. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) are important for restoring vegetation and improving soil fertility in arid or semiarid desertified land. However, studies on the contribution of BSC microbes to phosphorus (P) transformation remains limited. The microbial diversity involved in P transformation and its dynamic along BSC development should be examined to further understand the microbial regulatory mechanism of the P-cycling process. This paper investigates the soil properties, P fractions, and potential of P transformation across a chronosequence (0-, 8-, 20-, and 35-year) of the BSC under Caragana microphylla plantation on the moving sand dunes in Horqin Grassland, China. An abundance of phoD and gcd genes was detected, and the diversities and structures of phoD- and gcd-haboring microbial communities were illustrated via high-throughput sequencing. Soil nutrient content, activity of alkaline phosphomonoesterase, potential of organic P (OP) mineralization, and the abundance of phoD and gcd genes all linearly increased along with BSC age. The microbial quantity and species diversity of the phoD community were greater than those of gcd. BSC development increased the availability of inorganic P (IP) fractions, and both NaHCO3-Pi and NaOH-Pi were positively correlated with the abundance of the two genes and the activity of alkaline phosphomonoesterase. The phyla of Actinobacteria, Planctomycetes, and Proteobacteria and the family of Streptomycetaceae were the most dominant taxa in the phoD community, Proteobacteria was the dominant phylum in the gcd community in BSC soils, and Rhizobium and Planctomyces were the most dominant genera. The dominant taxa quantitatively responded to soil property improvement, but the basic compositions and dominant taxa did not change along with BSC development. The structures of phoD and gcd communities were linked to soil properties, and pH available K, and total K tend to be the direct determining factors.

Photosynthetic microorganisms are widely distributed in the soil and play an important role in plant-free soil crusts. However, the distribution and environmental drivers of phototrophic microbial communities in physical soil crusts, where the abundance of cyanobacteria is low, are scarcely understood. Here, we performed high-throughput sequencing of pufM and 18S rRNA genes in soil crusts at different elevations on the Tibetan Plateau and used the data combined with environmental variables to analyze the diversity and structure of phototrophic microbial communities. We found that the dominant taxa of aerobic anoxygenic phototrophic bacteria (AAPB) and eukaryotic phototrophic microorganisms (EPM) were shown to shift with elevation. The phototrophic microbial diversity showed a single-peak pattern, with the lowest diversity of AAPB and highest diversity of EPM at middle elevations. Moreover, the elevation and soil property determined the phototrophic microbial community. Soil salts, especially Cl−, were the most important for AAPB. Likewise, soil nutrients, especially carbon, were the most important for EPM. The relationship between high-abundance taxa and environmental variables showed that Rhizobiales was significantly negatively correlated with salt ions and positively correlated with chlorophyll. Rhodobacterales showed the strongest and significant positive associations with Cl−. Chlorophyceae and Bacillariophyceae were positively correlated with CO32−. These results indicated that salinity and soil nutrients affected the diversity and structure of microbial communities. This study contributes to our understanding of the diversity, composition, and structure of photosynthetic microorganisms in physical soil crusts and helps in developing new approaches for controlling desertification and salinization and improving the desert ecological environment. [ABSTRACT FROM AUTHOR]

The aim of this study was to analyze the transformation specifics of the surface layer in the arable horizons of chernozem, gray forest and soddy-podzolic soils under the impact of atmospheric precipitation. The research was carried out using soil samples collected at the key sites and the model experiment results. The soil surface condition, its color, micromorphological features and microtomographic structure, as well as the chemical composition of soil were analyzed. Atmospheric precipitation has been found to change the properties of the surface layer in the arable soil horizon. Changes in the mineralogy are pronounced in the redistribution of minerals between granulometric fractions. The longer the soil surface remains open to alternating precipitation and drying, the more pronounced is the formation of surface wash-out (eluvial) and wash-in (illuvial) microlayers differing in the content of fine dispersed organomineral substances and their structural arrangement. The initial state of humus and the soil texture predetermine peculiar features of microhorizons formed on the surface. In the upper part, a silty or sandy layer is formed with the minimal amount of microaggregates and fine matter; whereas below, the size and number of aggregates increase markedly. The revealed regularities must be taken into account upon remote sensing and mapping soil properties. To assess the humus content in the arable horizon, areal or satellite images of newly plowed and burrowed fields are required. The mineral composition, in turn, is detectable better using the images of transformed arable soil surface. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Irrigation & Drainage is the property of Journal of Irrigation & Drainage Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Arctic soils are an important reservoir of soil organic carbon (SOC) and their role in determining arctic ecosystem functioning in global carbon budgets requires closer attention. We investigated the coupling of soil properties and SOC stabilization mechanisms in high Arctic terrestrial habitats differing in vegetation cover and organic matter input. We focused on soil physical and chemical properties in glacier foreland, soil crust, dry tundra, wet tundra, and bird cliff meadow habitats on Svalbard (Norway). Concurrently, we performed physical fractionation to determine the amount of SOC stabilized by mineral associations or occlusion in macro and microaggregates. Initial stages of soil development (glacier foreland and soil crust habitats) exhibited characteristically high bulk density and pH, and low moisture and nutrient contents, whereas more developed soils (dry and wet tundra habitats) showed opposite trends. Contrastingly, bird cliff meadow showed low bulk density, intermediate moisture, and very high nutrient content. The amount of SOC stabilized by mineral associations and occlusion in aggregates generally increased with vegetation cover; hence, the more developed habitats supported higher contents of stabilized SOC. However, SOC was stabilized in aggregates even in initial stages of soil development. SOC content in most fractions correlated positively with contents of dissolved organic carbon and nitrogen, suggesting that both dissolved organic carbon and nitrogen might have provided some degree of SOC stabilization through increased formation of aggregates and suppression of microbial mineralization of soil organic matter, respectively. Our findings underscore the notion that models of SOC sequestration in the Arctic should account not only for total SOC content, but also SOC stabilization mechanisms, as represented by SOC content in respective soil fractions. Key Points: Soils of initial habitats exhibited high bulk density and pH, and low moisture and nutrient contents as opposed to soils of developed habitatsContent of soil organic carbon (SOC) stabilized by occlusion in aggregates or by adsorption on mineral particles generally increased with vegetation cover, hence more developed habitats provide a large degree of SOC stabilizationSOC content in most of the fractions positively correlated with dissolved organic C as well as dissolved N content [ABSTRACT FROM AUTHOR]

Surface crusts are often hardened with the platy surface of soil layers, particularly widely distributed in arid and semi-arid areas. There are also some important influences on the soil and water conservation, as well as the ecological environment, due mainly to the special pore structure and hydraulic characteristics. In this study, three-dimensional images of real soil crust samples were acquired to characterize pore morphology and structure distribution, combining X-ray tomography with pore-scale simulation. The water infiltration process was then simulated in soil samples, thereby to quantitatively analyze the relationship between pore structure and hydraulic characteristics. Three soil samples were collected with the surface crust (the porosity of 0.196, 0.144, and 0.093) using X-ray tomography. Furthermore, a systematic investigation was made on the variation of pore structure along the depth direction of crust soil samples. Specifically, each soil sample was then sliced into 9 layers from the upper surface with each layer of 100 voxels depth. The permeability of each soil layer was then calculated using the lattice Boltzmann method. Subsequently, the correlation analysis was conducted between structural characteristic parameters and permeability. A fractal dimension model was also proposed to calculate the permeability using soil porosity and complexity. The pore structure analysis showed that the porosity and pore connectivity of the surface and bottom layer were smaller than those of the intermediate soil layer in the three soil samples. The maximum pore connectivities of soil layers were 99.21%, 94.64%, and 57.35% in the three soil samples located in the middle of the soil, respectively. The minimum were 45.99%, 27.30%, and 11.74%, respectively, located at both ends of the soil sample. The pore structure of topsoil was different from that of the adjacent soil layer, where the variation coefficient was E>5%. The average pore diameter of each soil layer decreased, with the increase of depth, from 0.43, 0.37, and 0.50 mm to 0.15, 0.14, and 0.14 mm, respectively. More importantly, the soil layer with higher porosity presented better pore connectivity and lower pore complexity, where the correlation coefficient was 0.972. The permeability calculation showed that the surface layer of soil samples behaved low local permeability of 7.472, 0.006, and 6.960 μm2 in the three samples, respectively, indicating there was a blocking effect of crust on soil seepage. Better permeability was achieved in the soil layer with higher porosity, better pore connectivity, and lower pore complexity. As such, a new permeability prediction model was finally proposed, where the specific surface area in the Kozeny-Carman equation was replaced by pore complexity. A higher prediction accuracy was obtained in the improved model, where the determination coefficient R2 increased from 0.964 to 0.982, while the root mean square error (RMSE) decreased from 25.1 to 18.3, compared with the simplified one. This finding can offer strong support to water resources management and ecological environment protection in arid and semi-arid areas. [ABSTRACT FROM AUTHOR]

The cover management factor (C‐factor) has become one of the most sensitive and complex parameters in the revised universal soil loss equation (RUSLE) because of its sensitivity to anthropogenic activities. However, due to the regionally limited scope of conventional models, direct applications of the C‐factor prediction have been hindered in China. Alternative C‐factor estimation approaches often consider vegetation coverage alone. This can decrease the accuracy of the estimation to an extent. In this study, several cropping systems were established to investigate the coupling effect of surface changes under different management practices and crop cover in preventing soil loss at the plot scale. Five experimental (CP, cropped; SSR, roughened; SC, crusted; CP‐SSR, cropped‐roughened; CP‐SC, cropped‐crusted) plots were set, compared to bare plot (BP). The impact of cropping systems on soil loss was estimated by SLR (soil loss ratio), according to the universal soil loss equation (USLE). The SLR estimation models were provided via identifying the related sub‐factors, subsequently, combined with the distribution curve of rainfall erosivity to allow the novel C‐factor estimation. The results showed that compared with SLRCP, the decrease in SLRCP − SSR varied from 12% to 43% with a mean of 25.50%; and the decrease in SLRCP − SC varied from 24% to 51% with a mean of 34.75%. Crop coverage, plant height, root weight density, < 0.5 mm root length density (both at 0–5 cm depth), initial roughness, and initial crust thickness were significantly correlated with SLR. For cropped plot, SLRCP − estimated can achieve more accurate simulation result than conventional models obtained from literature findings, with RMSE (root mean square error) coefficient of 0.17. For a comprehensive understanding of the C‐factor, multiple crops should be considered, and more experiments in the experimental group to better verify SLRCP − SSR − estimated and SLRCP − SC − estimated are recommended. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil crusts from difference Lake Urmia playa surfaces are investigated. • Clay flats and clay flats-salt crusts have the most stable crusts. • Clay, Organics, silt and NaCl are the key factors in the crust stability. • Large size geologic carbonates as aragonite and dolomite reduce crust stability. • Sand sheets have the least stable crusts due to high sand and geologic carbonates. The recession of lake shores, including the ones of Lake Urmia (LU), and later exposure of the lake bed sediments to wind erosion as a consequence of climate change and drought, is a devastating phenomenon worldwide. In the absence of stable surface crusts, these areas can be the source of airborne dust causing health and environmental issues. The present study aims at investigating the crust formation and development on Lake Urmia playa (LUP) surfaces through physicochemical and morphological studies and to determine the major factors affecting crust stability. To achieve the above goals, 50 soil crust samples from playa surfaces of the western LU playa were collected. The soil crust thickness and compressive strength were determined by a digital micro penetrometer. By means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), the main morphological and chemical factors responsible for the crust development and evolution in LUP were identified. Results showed that crust samples from clay flats (CFs) and clay flats-salt crusts (CF-SC) possessed the most stable crusts with a thickness of 2.2 and 1.9 cm and maximum compressive strength of 6709 and 7399 kPa, respectively, while sand sheets (Sa-sheets) showed weak and locally restricted crust development. Evaluation of correlation coefficients (CC) between soil crust physicochemical properties and crust stability parameters revealed that clay, silt, and organic matter enhance the crust stability and decrease the erodible fraction by increasing the crust thickness, while salt content quantified as Na+ concentration and electrical conductivity increase the firmness of the crusts. Interestingly, total carbonates quantified as calcium carbonate equivalent (CCE) correlated negatively with crust stability although pedogenic calcite is known as cementing agent in soils. XRD together with FTIR spectroscopy revealed that calcite is indeed the predominant mineral form in most soils with the exception of Sa-sheets with the highest share of carbonates, in which aragonite prevailed over calcite. While carbonates of pedogenic origin act as cementing agent, geologic carbonates present as coarse aragonite particles decrease soil stability. Therefore, samples with the highest total carbonate content exhibited the weakest crust, which explains the negative correlation between soil crust and CCE. SEM coupled with Energy Dispersive X-ray (EDX) and elemental mapping revealed that NaCl is the major cementing agent of the soil particles in crusts developed on LU playa surfaces. Its coexistence with phyllosilicates has increased the crust stability and resilience against wind erosion in CF and CF-SC samples while in the Sa-sheet samples, the absence of clay-size minerals (silt and clay) along with the prevalence of geologic carbonates (dolomite and aragonite) and lower NaCl content, limited crust formation and stability. This study emphasizes the importance of the intrinsic soil physicochemical properties together with the secondary (pedogenic) carbonate formation and more importantly the presence of NaCl, as the best determining factors controlling crust formation over LU playa surfaces. [ABSTRACT FROM AUTHOR]

The quantity and quality of soil organic matter (SOM) depending on many edaphic and environmental factors may change in response to agriculture-related practices. The SOM humification process can be supported by the application of mineral fertilizers, but in the production vineyards, such information is lacking. NPK fertilizer alters the soil quality, and therefore, the aim of this study was to: (1) assess the extent and dynamics of different NPK (control—no fertilization; 1st NPK; and 3rd NPK levels) rates to the soil with grass sward cover in a productive vineyard on changes in SOM, humic substances (HS), and soil structure, and (2) identify relationships between SOM, HS, and soil structure. Results showed that the share of humic acids in soil organic carbon decreased only in NPK1 compared to control and NPK3 treatments. The color quotient of humic substance values in NPK1 and NPK3 increased by 4 and 5%, respectively, compared to control. Over a period of 14 years, the content of soil organic carbon increased by 0.71, 0.69, and 0.53 g kg−1 year−1 in the control, NPK1, and NPK3, respectively. The content of HS increased linearly with slight differences due to NPK application. The vulnerability of the soil structure decreased due to fertilization—more at the higher NPK level. The rate of formed soil crust was decreasing in the following order: control > NPK1 > NPK3. In the control treatment, the relations between SOM, HS, and soil structure were most abundant and with the greatest significance, while with the increasing level of NPK, these relations lost their significance.

Biocrusts are critical components of drylands where they regulate a wide range of ecosystem functions, however, their response to the world‐wide phenomenon of shrub encroachment and to livestock grazing, the most extensive land use in drylands, is not well studied. Grazing by livestock and increases in shrub cover could influence biocrust communities directly via trampling or shading, or indirectly, by altering biotic interactions amongst biocrust taxa. The extent of these changes in biocrust cover, diversity and composition are poorly known.We used linear models and structural equation modelling to examine the direct effects of grazing and shrubs on biocrust community composition and the indirect effects mediated by changes in species interactions.Biocrust richness and cover increased with increasing shrub cover at the site level. This pattern occurred despite the negative response we found (lower cover and richness) under shrub patches versus open areas, which was consistent irrespective of the grazing level. Functional diversity and evenness were similar between shrubs and open at low grazing intensity, but at high grazing functional diversity was greater in the open. Competition between biocrust species was an important driver of their community assembly irrespective of shrub cover, grazing intensity or patch type. Structural equation models showed that the effects of grazing and shrub cover on functional evenness, functional diversity and richness were controlled by biotic interactions within the shrub microsites. In the open, however, these effects were either direct or mediated by changes in cover.Biocrust cover, species richness and functional diversity increase with shrub cover at the site scale, despite the negative effects at the microsite level. We demonstrate here that drivers of community assembly differ markedly at small spatial scales. Though biocrust communities were directly driven by environmental filtering in the open, biotic interactions played a fundamental role in their assembly when growing beneath shrubs. A free plain language summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Abstract Under homogeneous habitat conditions, fairy circles are extremely ordered grassland gaps that are densely packed and that function as an extra source of water for the surrounding matrix vegetation. While the origin of fairy circles is still disputed, most of the research has so far focused on such typical habitat conditions where the fairy circles are almost round and have a grid-like hexagonal pattern. However, Namibian fairy circles also occur under atypical habitat conditions where topographical heterogeneity or extreme aridity are forcing the circles to change their shapes and patterns. In this pilot study, we are describing some striking and new examples how shapes and patterns of fairy circles may change under such atypical environmental conditions. We emphasize the need to study fairy circles in disturbed catchment areas, mega circles in drainage lines, as well as soil-water budgets of irregularly spaced fairy circles in very arid locations. Furthermore, there is need to understand the formation of the very large mega circles and desertification fronts in flat habitat. Finally, we also discuss the potential role of abiotic drivers such as soil-crust formation in the vegetation matrix or aeolian erosion and subsequent de-rooting of grasses in forming unusual fairy circle shapes, sizes and patterns. Graphical abstract Image 1 Highlights • Fairy circles in Namibia have not yet been studied in heterogeneous environments. • In such atypical habitats they may change their patterns, density, size, and shape. • Understanding the abiotic drivers of these pattern changes is a research challenge. [ABSTRACT FROM AUTHOR]

Predicting the distribution of biocrust species, mosses, lichens and liverworts associated with surface soils is difficult, but climatic legacies (changes in climate over the last 20 k years) can improve our prediction of the distribution of biocrust species. To provide empirical support for this hypothesis, we used a combination of network analyses and structural equation modelling to identify the role of climatic legacies in predicting the distribution of ecological clusters formed by species of mosses, lichens and liverworts using data from 282 large sites distributed across 0.6 million km2 of eastern Australia. Two ecological clusters contained 87% of the 120 moss, lichen and liverwort species. Both clusters contained lichen, moss and liverwort species, but were dominated by different families. Sites where the air temperature increased the most over 20k years (positive temperature legacies) were associated with reductions in the relative abundance of species from the lichen (Peltulaceae and Teloschistaceae) and moss (Bryaceae) families (Cluster A species), greater groundstorey plant cover and lower soil pH. Sites where precipitation has increased over the past 20k years (positive precipitation legacy) were associated with increases in the relative abundance of lichen (Cladoniaceae, Lecideaceae and Thelotremataceae) and moss (Pottiaceae) families (Cluster B species) and lower levels of soil pH. Sites where temperatures have increased the most in the past 20k years suppressed the negative effects of plant cover on Cluster B by reducing plant cover. Increased intensity of grazing suppressed the negative effect of soil pH and the positive effect of soil carbon, on the relative abundance of Cluster B taxa. Finally, increasing temperature and precipitation legacies reduced the negative effect of soil pH on Cluster B. Understanding of the importance of climatic legacies improves our ability to predict how biocrust assemblies might respond to ongoing global environmental change associated with increasing land use intensification, increasing temperature and reduced rainfall. A knowledge of climatic legacies can improve our understanding of how species might change under altered climates and land uses. Ecological clusters of biological soil crust taxa responded differently to climatic legacies. Rainfall and temperature legacies influenced the current distribution of major ecological clusters of biocrust species. [ABSTRACT FROM AUTHOR]