Response of Soil Organic Carbon Content in Different Slope Positions to Fertilization Management in Purple Soil Sloping Fields

The purple soil sloping field is the main cultivated land type in the Three Gorges area, and the soil fertility directly determines crop yield. In order to explore the effects of different fertilization treatments on the soil organic carbon content at different slope positions, field experiments were carried out at the Three Gorges Reservoir Test Station of Chengdu Institute of Mountain and Disasters, Chinese Academy of Sciences. A total of five treatments were set up:no fertilization(CK), conventional fertilization(T1), optimum fertilization(T2), biochar combined with 85% of T2(T3), and straw combined with 85% of T2(T4), to study the differences in soil aggregate composition, soil total organic carbon, soluble organic carbon, and microbial carbon content at different slope positions under different fertilization treatments. The results showed that:①Fertilization increased the content of soil mass and improved the organic carbon content of soil, especially with T3 and T4 treatments. ②The sequence of distribution of soil organic carbon content with CK, T1, and T2 treatments in different slope positions was downslope position>middle slope position>upslope position, while the soil organic carbon content of T3 and T4 treatments was the highest at the middle slope position. ③With the decrease of slope, the soluble organic carbon content of CK, T1, T2, and T3 treated soil showed an increasing trend; the carbon content of CK, T1, T2, and T4 treated soil microorganisms increased; while the distribution of T3 treated soil microbial carbon on the slope was highest at the middle slope followed by the lower slope. In general, both biochar and straw treatments can significantly increase soil carbon content and delay the migration of soil carbon on slopes, which provides guidance for improving the soil quality and reducing water pollution of purple soil dry slopes in the Three Gorges reservoir area.