Temporal variation in soil erodibility indicators of sloping croplands with different straw-incorporation rates

Soil and crop characteristics are susceptible to straw-incorporation and can change considerably over time. These changes are likely to lead to variations in the soil structure, aggregate stability, and shear strength, thereby altering the soil erodibility. Currently, the temporal variation in the soil erodibility of sloping croplands affected by straw-incorporation rate (SIR) is unknown. The objectives of this study were to evaluate the temporal variation in soil erodibility using a comprehensive soil erodibility index (CSEI) with different SIRs, and to identify the dominant influencing factors in a small agricultural watershed in a semi-humid region. The CSEI was quantified using soil organic matter (SOM), K factor, structural stability index (SSI), slaking rate (SR), mean weight diameter (MWD), mean number of drop impacts (MND), soil cohesion (Coh), soil penetration resistance (PR), and saturated hydraulic conductivity (Ks). The results demonstrated that nine soil erodibility indicators exhibited different changes over time during each growing season. Over time, SOM, SSI, Coh, and PR increased, whereas Ks decreased. No distinct variation was observed in the K factor. The MND and MWD generally increased and then decreased over time, whereas the SR showed the opposite trend. Soil erodibility indicators were strongly affected by the SIR. MND, MWD, Ks, Coh, SSI, and SOM were positively correlated with SIR, whereas the K factor, PR, and SR were negatively correlated. CSEI under different SIR showed significant differences in fluctuations with temporal variation (p < 0.05). Compared to the control treatment, the mean CSEI was reduced by 21 %, 36 %, 40 %, 53 %, 66 %, and 56 % for straw-incorporation rates of 1.125, 2.25, 4.5, 6.75, 9, and 13.5 t hm⁻², respectively. The main factors influencing temporal variation in the CSEI were aboveground biomass, root mass density, straw residual mass density (SRD), and straw decomposition amount (SD). The effects of SRD and SD on CSEI were the greatest at 60 d after straw incorporation. Thus, straw-incorporation can effectively reduce soil erosion. For semi-humid regions with high soil organic matter content, the optimal SIR was 9.0 t hm⁻².