Redistribution of SOC driven by erosion and deposition in cultivated black soils of Northeast China

Soil erosion causes the thinning of topsoil and redistribution of soil organic carbon (SOC) in Northeast China, thereby affecting the carbon cycling process. Understanding how soil erosion and deposition redistribute SOC on cultivated slopes is essential for comprehending the impact of soil erosion on carbon cycling. In this study, we collected samples of ¹³⁷Cs and soil profiles on a cultivated slope with 1300 m slope length. This was combined with runoff plots observation data to analyze the patterns of erosion and deposition on long-gentle slopes and their effects on the redistribution of SOC. The results showed that the soil erosion rate on the slope under up and down ridge tillage was 16.9 t·ha⁻¹·yr⁻¹, with an average value at the top of the slope being 1.4 times that of the middle. The bottom of the slope was primarily characterized by deposition, and the period length of soil erosion and deposition changes on the slope was 245.7 m. The average SOC on the whole slope was 66.8 g·kg⁻¹, with the tilled layer (0–20 cm) having the highest organic carbon content, accounting for 58.2 % of the total organic carbon content. The average soil organic carbon content in the deposition zone was 49.0 g·kg⁻¹, which was 1.3 times that of the erosion zone. Topography was the main factor influencing soil erosion rates in the black soil region. The relationship between slope gradient (θ) and soil erosion rate (SL, mm·yr⁻¹) was expressed as: SL = 0.962∙θ. The process of soil erosion led to the redistribution of SOC, and there was a significant negative correlation between the soil erosion rate and the SOC content in the tilled layer. This is because clay particles were the main carriers of soil organic carbon and were most sensitive to soil erosion rate.