Effects of long-term cultivation on soil aggregate stability and transport processes in karst sloping cropland of Southwest China

Sloping cropland faces accelerated soil erosion and rocky desertification due to long-term cultivation and rainfall, becoming a major ecological issue in Southwest China's karst region. This study focuses on soil from karst sloping croplands ( Calcaric Cambisol ) under continuous cultivation for 2, 8, 13, 18, 25, and 30 years. We used wet sieving, the Le Bissonnais (LB) methods, and concentrated flow scouring experiments, to evaluated the distribution, stability, and erosion resistance of soil aggregates, and assess the impacts of cultivation duration on soil physicochemical properties, aggregate breakdown, and detachment-transport mechanisms. Results demonstrated that continuous cultivation reduced soil organic carbon (SOC) from 37.33 to 17.02 g·kg -1 , cation exchange capacity (CEC) decreased by 39.04%, clay content dropped from 44.89% to 35.53%, while sand content increased from 19.37% to 28.90%, leading to marked deterioration of soil structure and erosion resistance. Both wet sieving and LB analyses revealed a decrease in >2 mm aggregates (down by 41.10%), while the 0.25–0.1 mm and <0.1 mm fractions increased and mean weight diameter (MWD) decreased by 50.70%. The soil erodibility (K-Factor) increased by 5.20%, and the relative sensitivity index (RSI) increased by 22.04. Under concentrated flow, the content of >5 mm aggregates declined by up to 58.38%, while MWD decreased by up to 2.04 mm. Correlation and machine learning analyses revealed that aggregate stability was most influenced by SOC, pH, CEC, and clay content. This study provides new insights into soil detachment mechanisms in karst sloping croplands and offers scientific support for sustainable management.