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Soil rill erodibility (Kr) and critical shear stress (τc) are important parameters in some physical soil erosion models. In the present study, the temporal variations in Kr and τc by overland flow were investigated using undisturbed topsoil samples collected from three cropped plots (ryegrass, lucerne, and corn) and a fallow plot. In this study, the potential factors leading to these changes were examined from March to September 2022 in western Sichuan Province, China. The results revealed significant seasonal variations in Kr, τc, soil bulk density (SD), soil cohesion (SC), and soil water-stable aggregate (WSA). The Kr values were significantly lower, whereas τc values were slightly higher for cropped plots when compared to that for the fallow plot. The mean Kr values for cropped plots were 4.51~17.26 times lower than that for the fallow plot. In contrast, the mean τc values for the cropped plots were 1.03~1.08 times higher than that for the fallow plots. The results also indicated a negative correlation of Kr with SD, SC, WSA, soil organic matter content (SOC), and root weight density (RWD), while a positive correlation of τc with SD, SC, WSA, and RWD. Furthermore, an exponential decrease in Kr was observed with an increase in SD, SC, WSA, SOC, and RWD. An increase in SD, SC, WSA, and RWD of the experimental plots led to a further increase in τc.

Soil organic matter (SOM) content is an effective indicator of desertification; thus, monitoring its spatial‒temporal changes on a large scale is important for combating desertification. However, mapping SOM content in desertified land is challenging owing to the heterogeneous landscape, relatively low SOM content and vegetation coverage. Here, we modeled the SOM content in topsoil (0–20 cm) of desertified land in northern China by employing a high spatial resolution dataset and machine learning methods, with an emphasis on quarterly green and non-photosynthetic vegetation information, based on the Google Earth Engine (GEE). The results show: 1) the machine learning model performed better than the traditional multiple linear regression model (MLR) for SOM content estimation, and the Random Forest (RF) model was more accurate than the Support Vector Machine (SVM) model; 2) the quarterly information regarding green vegetation and non-photosynthetic were identified as key covariates for estimating the SOM content in desertified land, and an obvious improvement could be observed after simultaneously combining the Dead Fuel Index (DFI) and Normalized Difference Vegetation Index (NDVI) of the four quarters (R2 increased by 0.06, the root mean square error decreased by 0.05, the ratio of prediction deviation increased by 0.2, and the ratio of performance to interquartile distance increased by 0.5). In particular, the effects of the DFI in Q1 (the first quarter) and Q2 (the second quarter) on estimating low SOM content (

Soil and water conservation (SWC) measures such as stone bunds and trenches integrated with fodder species (ISWC) have been implemented to tackle soil erosion in Ethiopian highlands. However, effects of ISWC measures on soil aggregate stability (SAS) and soil organic carbon stocks (SOCS) have been less studied. Fifteen disturbed composite and 15 undisturbed soil samples were collected from cropland sites treated with ISWC measures, SWC structures alone and no SWC measures (NSWC). Results revealed that mean values of stability index (SI) and stability quotient (SQ) are: 15 and 712 for sites with ISWC measures, 8 and 268 for sites with SWC structures alone and 6 and 187 for sites with NSWC measures. The SOCS (t ha-1) and SOM contents are: 12.7 and 1.7% for sites with ISWC, 8.0 and 1.2% for SWC alone and 6.3 and 0.7% for NSWC. SI, SQ SOCS and SOM content are significantly higher (p0.05) in SI, SQ and SOCS, between sites with SWC alone and NSWC. This study strongly suggests that, application of ISWC measures has considerable potential to enhance SAS, SOCS and SOM content.

Grassland degradation is a worldwide problem that often leads to substantial loss of soil organic matter (SOM). To estimate the potential for carbon (C) accumulation in degraded grassland soils, we first need to understand how SOM content influences the transformation of plant C and its stabilization within the soil matrix. We conducted a greenhouse experiment using C3 soils with six levels of SOM content; we planted the C4 grass Cleistogenes squarrosa or added its litter to the soils to investigate how SOM content regulates the storage of new soil C derived from litter and roots, the decomposition of extant soil C, and the formation of soil aggregates. We found that with the increase in SOM content, microbial biomass carbon (MBC) and the mineralization of litter C increased. Both the litter addition and planted treatments increased the amount of new C inputs to soil. However, the mineralization of extant soil C was significantly accelerated by the presence of living roots but was not affected by litter addition. Accordingly, the soil C content was significantly higher in the litter addition treatments but was not affected by the planted treatments by the end of the experiment. The soil macroaggregate fraction increased with SOM content and was positively related to MBC. Our experiment suggests that as SOM content increases, plant growth and soil microbial activity increase, which allows microbes to process more plant-derived C and promote new soil C formation. Although long-term field experiments are needed to test the robustness of our findings, our greenhouse experiment suggests that the interactions between SOM content and plant C inputs should be considered when evaluating soil C turnover in degraded grasslands. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) content is one of the most important indicators of the sustainability of soil. To maintain sustainable soil utilization and management in fragile Hani terraced field, it is meaningful to investigate the effects of topography and land use type on SOM content. Descriptive statistics and geostatistics were used to analyze the data and the kriging method was applied to map the spatial patterns of SOM content. The results showed that the mean SOM content was 32.76 g/kg, with a variation coefficient of 40%. The SOM content was affected by elevation and land use type. As the increase of elevation, the SOM content in Hani terraced field also increased obviously. The SOM content in tea garden, which is almost at high elevation, was the highest in all six land use types, and the SOM content decreased in a following sequence: tea garden > paddy field > corn field > banana garden > cassava field > sugarcane field. In addition, at the same elevation, the paddy field had the highest SOM content compared with other land use types. All these results demonstrate that paddy field is the most efficient and suitable land use type for SOM conservation at high, middle or low elevations in the fragile Hani terraced field. In order to protect soil quality and maintain the sustainable agricultural development, it is necessary to maintain or even to enlarge the area of paddy field in Yuanyang county, Yunnan Province, China.

O parâmetro S representa o valor da inclinação da curva de retenção de água no seu ponto de inflexão. Um aumento nos valores de S indica uma ampla distribuição de tamanho de poros, condizente com condições estruturais que estabelecem um adequado funcionamento físico do solo. Neste trabalho, testou-se a sensibilidade do parâmetro S, proposto na literatura, em relação a algumas propriedades físicas de solos do Sul do Brasil. O parâmetro S não se relacionou com o teor de argila total, nem com o teor de argila dispersa dos sete solos utilizados neste trabalho. Para o grupamento dos solos argilosos e muito argilosos, o parâmetro S apresentou decréscimo exponencial com o aumento da densidade do solo e um crescimento exponencial com o aumento da matéria orgânica do solo. Nesses solos, a água disponível às plantas aumentou de forma linear (ADP= 3,19*S) passando pela origem e a pressão de pré-consolidação reduziu exponencialmente com o aumento do valor de S. Conclui-se que o parâmetro S apresentou sensibilidade para determinar a qualidade física dos solos de textura argilosa e muito argilosa.The S index corresponds to the slope of the soil water retention curve at its inflection point. A high S value indicates the presence of structural pores, which are essential for a good soil physical condition. The objective of this study was to evaluate the sensitivity of the index of soil physical quality (S), as proposed in the literature for some physical properties of soils from Southern Brazil. In the seven soils used here, no relationship was found between clay and water dispersible clay content with soil physical quality index S. However, in soils with high clay content, the S index decreases with an increase in soil bulk density and increases with an increase in soil organic matter content. For a given texture class, plant available water increased linearly (PAW= 3.19*S) to the origin and the preconsolidation pressure decreased exponentially with the increasing S index. The S index is sensitive to be used as an index of soil physical quality for soils with a high clay content.

Soil bulk density was investigated as a function of soil contents of clay and organic matter in arable agricultural soils at a range of locations. The contents of clay and organic matter were used in an algorithmic procedure to calculate the amounts of clay-organic complex in the soils. Values of soil bulk density as a function of soil organic matter content were used to estimate the amount of pore space occupied by unit amount of complex. These estimations show that the effective density of the clay-organic matter complex is very low with a mean value of 0.17 ± 0.04 g ml-1 in arable soils. This value is much smaller than the soil bulk density and smaller than any of the other components of the soil considered separately (with the exception of the gas content). This low value suggests that the clay-soil complex has an extremely porous and open structure. When the complex is considered as a separate phase in soil, it can account for the observed reduction of bulk density with increasing content of organic matter. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) content is one of the most important indicators of the sustainability of soil. To maintain sustainable soil utilization and management in fragile Hani terraced field, it is meaningful to investigate the effects of topography and land use type on SOM content. Descriptive statistics and geostatistics were used to analyze the data and the kriging method was applied to map the spatial patterns of SOM content. The results showed that the mean SOM content was 32.76 g/kg, with a variation coefficient of 40%. The SOM content was affected by elevation and land use type. As the increase of elevation, the SOM content in Hani terraced field also increased obviously. The SOM content in tea garden, which is almost at high elevation, was the highest in all six land use types, and the SOM content decreased in a following sequence: tea garden > paddy field > corn field > banana garden > cassava field > sugarcane field. In addition, at the same elevation, the paddy field had the highest SOM content compared with other land use types. All these results demonstrate that paddy field is the most efficient and suitable land use type for SOM conservation at high, middle or low elevations in the fragile Hani terraced field. In order to protect soil quality and maintain the sustainable agricultural development, it is necessary to maintain or even to enlarge the area of paddy field in Yuanyang county, Yunnan Province, China. [ABSTRACT FROM AUTHOR]

Soil property maps at continental and national scales provide important input for research on biogeochemical and hydrological cycles. This paper develops a methodology for producing soil property maps at a continental or national scale based on soil samples from continental or national soil surveys (especially geochemical baseline surveys) with a 2–70 km grid, soil maps, and Digital Elevation Model data. The proposed method consists of four major steps: 1) determining the overall trend of soil property distribution using the linkage method; 2) estimating the variation inside each polygon through an extended Inverse Distance Weighted interpolation based on both the environmental similarity and spatial autocorrelation with stratification; 3) integrating variations in the soil property with its overall trend; 4) re-estimating soil properties in transition zones by using a weighted average of soil properties estimated from soil samples from different neighboring soils to produce a continuous soil property map across soil boundaries. A case study using Soil Organic Matter content as an example was conducted in Jilin Province (190,000 km2) in China based on soil samples from a 8–32 km grid from the China Soil Pollution Survey, the 1:1 million soil map of China and Shutter Radar Topographic Mission Digital Elevation Model data. Independent validation indicated that the proposed method decreased the mean error, the mean absolute error and the root mean square error by 10–30% compared with two commonly used soil mapping methods, the linkage method and Inverse Distance Weighted interpolation. The SOM map produced by the proposed method improved defects in the maps produced through Inverse Distance Weighted interpolation and the linkage method such as "bull's eye" patterns, abrupt change across soil boundaries and the ignored variation inside polygons on the maps. The proposed approach generates more accurate soil property maps at a continental or national scale based on grid soil samples from continental or national soil surveys than those produced through commonly used methods. • We develop a methodology to produce soil property maps based on sparse grid samples. • The method integrates an extended IDW interpolation and the linkage method. • The method improves estimation in soil transition zones. • It is more accurate and has fewer defects than maps produced via common methods. [ABSTRACT FROM AUTHOR]