Soil degradation is an essential environmental problem that threatens agricultural productivity and sustainability in the typical black soil region in northeast China. Assessing the degradation status and risks of sloping cropland is necessary to restore and reconstruct degraded soil. This study aimed to map soil degradation status based on a newly developed soil degradation index (SDI) and assess the uncertainty associated with degradation risk mapping using Ordinary Kriging and Sequential Gaussian simulation (SGS). The results showed that SDI ranged from 0.013 to 0.864, with a mean value of 0.445. The realization with 200 times by SGS was the best, with an increasing pattern of SDI from north to south in the study area. Mildly degraded and moderately degraded sloping cropland accounted for 35.3% and 52.4% of the total area of sloping cropland, respectively. High-risk areas were mainly distributed in the Greater Xingan Mountains and Changbai Mountains to the Songnen Plain. Proactive measures are necessary to control and mitigate further degradation by developing soil management and weakening the interaction between slope gradient and ridge-slope angle. The developed risk assessment maps provide baseline information for regional sustainable development.

Clearing the status of sloping cropland degradation in typical black soil region is the basis for restoring and reconstructing degraded black soil. To date, the spatial distribution pattern of degree of soil degradation is lacking. In this paper, we predicted the spatial distribution of degree of soil degradation based on the soil degradation index (SDI). We compared the accuracy of Ordinary Kriging (OK) and Sequential Gaussian Simulation (SGS) with different simulation times. SGS was also used to evaluate the degradation risk of sloping cropland in typical black soil region of Northeast China. The results showed that: SDI ranged from 0.013 to 0.864, with a mean value of 0.445. The realization with 200 times by SGS was the best, with an increasing pattern of SDI from north to south in the study area. Mildly degraded soil, moderate degraded soil, severe degraded soil, and extremely severe degraded soil accounted for 35.3%, 52.4%, 12.1%, and 0.2% of total sloping cropland, respectively. The potential degradation risk and high-risk areas were about 53.4% and 23.1% of the total sloping cropland, respectively. The result of risk assessment could serve for making decisions by relevant departments.

Soil microorganisms are the main driving force in soil ecological and biogeochemical processes, such as carbon mineralization, humus formation, and nutrient cycles. Soil erosion may dramatically alter microbial properties. However, it is still unclear how soil microbial characteristics affected by soil erosion. In hilly areas, soil erosion is highly attributed to topographic characteristics such as slope position and slope gradient. Herein, we compared the soil microbial characteristics between different slope gradients and positions in the farmland in the typical black soil area of Northeast China. The relative abundances of major microbial phyla are illustrated. Proteobacteria, Acidobacteria, Gemmatimonadetes, Planctomycetes, and Actinobacteria accounted for 83% of the total bacterial sequences, and Ascomycota, Basidiomycota, and chytridiomycosis accounted for 78% of total fungal sequences in the studied area. Microbial alpha-diversity (Bacteria and Fungi) was similar among the slope gradients or slope positions. The bacterial and fungal community composition was only affected by slope gradient, which was significantly lower in the highest slope gradient level than in others. This study suggests that slope gradient but not slope gradient affecting microbial community composition in the cropland of black soil region.