Characteristics of cultivated layer soil shear strength for sloping farmland in response to soil erosion in the Three Gorges Reservoir Area, China

Soil shear strength (SS) is an important parameter for evaluating soil erosion sensitivity and precision tillage activity. This study is ascertains how the cultivated layer SS of sloping farmland varies with soil erosion and management measures. The typical purple soil sloping farmland in the Three Gorges Reservoir Area of China was selected, and in situ tests of five erosion degrees were performed on sloping farmland using the shovel erosion simulation test method. No fertilizer (CK) was established as the control measure, and two types of restorative management measures, chemical fertilizer (F) and biochar + chemical fertilizer (BF), were established to measure SS and other soil physicochemical properties for each treatment. The results showed that cultivated layer SS had a significant response to interactions between soil erosion and management measures (P < 0.01) and was more sensitive to soil management measures than erosion. According to single-factor analysis, surface soil SS was lower than bottom soil SS; with erosion intensification, surface soil was lost, bottom soil with high SS was retained, and the SS of residual soil, following surface erosion, was 13.99% higher than that of noneroded soil. Concurrently, BF can significantly reduced topsoil SS and was 8.44% and 5.79% lower than CK and F, respectively. After correlation analysis, seven physicochemical factors significantly related to SS were retained; stepwise linear regression determined that soil bulk density and water content were the key factors affecting cultivated layer SS. Our study also showed that coarse ossification and sterility of purple soil sloping farmland could indicate the occurrence of soil erosion in the Three Gorges Reservoir Area, and biochar could restore the soil quality of erosive cultivated land to a certain extent.