Effects of Biochar on Soil Organic Carbon of Eroded Cultivated Layer of Slope Farmland in Purple Hilly Area

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Soil organic carbon (SOC) is the largest carbon pool in the terrestrial ecosystem. It is not only the core index of cultivated land soil quality evaluation but also an important part of the global carbon cycle. In order to understand the response characteristics of SOC in the cultivated layer to the interaction of soil erosion and management measures, the eroded cultivated layer of typical purple soil slope farmland in the Three Gorges Reservoir area was the research object. The in-situ tests of five erosion degrees on sloping farmland were established using the shovel erosion simulation test method; taking no fertilizer (CK) as a control measure, two types of restorative management measures were set up, namely chemical fertilizer (F) and biochar+chemical fertilizer (BF), to clarify the differences in SOC content under different erosion degrees and management measures and to analyze the variation characteristics and interannual variation trend of SOC along the cultivated-layer profile. The results showed that:① BF significantly increased the soil organic carbon content in the cultivated layer of purple soil slope farmland; the SOC of BF was 90.25% and 23.84% higher than that of CK and F on average, respectively. Soil erosion significantly reduced the content of SOC (12.25%-27.74%) under CK measures, but there was no significant difference in the profile distribution of SOC under different erosion degrees. ② The SOC content in the surface layer (0-10 cm) of slope farmland was the highest, and the two measures had the most obvious effect on improving the SOC contents, which were 120.59% and 66.90%, respectively. ③ After three consecutive years of experiments, the SOC content in the cultivated-layer of slope farmland changed significantly. Under CK, the average annual loss of SOC was 12.52%, whereas under BF, the average annual increase in SOC content was 9.31%. ④ The correlation between SOC and soil physical and chemical properties was different in the various soil layers; the deeper the soil layer was, the weaker the correlation was. Therefore, biochar combined with chemical fertilizer (BF) was an important management measure to improve the erosive cultivated layer and enhance soil fertility for slope farmland in the purple hilly area. The results of this study can provide basic parameters for the rational regulation of cultivated layers and the improvement of soil fertility.