Short-term emissions effect of rainfall erosion on soil CO2 in red soil sloped farmland in southern China

Climate change alters rainfall patterns, increasing soil erosion and carbon emissions from agricultural fields, threatening agricultural ecosystems and soil carbon cycling. However, rainfall-induced erosion′s impact on soil CO₂ emissions in sloped farmlands remains unclear. This study used experimental plots to simulate four tillage practices: plastic mulching (PM), cross-slope ridge tillage (RT), downslope ridge tillage (DT), and conventional flat-tillage (CT). Controlled indoor rainfall simulations were conducted to investigate the effects of rainfall erosion on soil CO₂ emissions from red soil sloping farmland under these tillage practices. Results showed that surface runoff was the primary runoff form for PM and DT during rainfall, while interflow was the dominant runoff form in RT. The effectiveness of the four tillage practices in controlling organic carbon (OC) loss was RT>PM>CT>DT. Surface runoff was the main pathway of OC loss, accounting for 58 % of the total. After rainfall, soil temperature decreased, while soil moisture initially sharply increased before its later decline. Soil CO₂ emission fluxes during the growing season ranged from 60.53 to 818.90 mg·m⁻²·h⁻¹ . Compared to PM, emissions from RT, DT, and CT were reduced by 22.1 %, 1.8 %, and 15.2 %, respectively. Rainfall erosion significantly induced a "Birch effect", increasing soil CO₂ emissions by 19.42 %-259.72 %, returning to pre-rainfall levels within three days. Increasing rainfall intensity amplified this stimulating effect. Structural equation modeling (SEM) revealed that total OC loss is a key factor affecting soil CO₂ emissions, reducing soil temperature and humidity sensitivity. Comprehensive analysis indicates RT effectively prevents OC loss and reduces soil CO₂ emissions, suggesting its potential for red soil sloping farmland. RT′s demonstrated effectiveness warrants its prioritization in managing red soil sloped farmland.