Seasonal dynamics of soil erodibility regulated by straw decomposition and associated improvements in soil structure and root growth in degraded croplands

Soil erosion resulting from intensive agricultural practices has accelerated widespread topsoil deterioration and nutrient loss on sloping croplands, posing a significant threat to global food security. Straw incorporation is a management practice that can alter soil erodibility and mitigate land degradation, yet its seasonal effects and underlying mechanisms across different degradation levels in sloping croplands remain poorly understood. In this study, we examined the seasonal dynamics of soil erodibility and its controlling mechanisms in the black soil region of Northeast China. The results demonstrated that soil erodibility of degraded croplands varied significantly throughout the growing season. Compared with the treatment without straw incorporation, straw incorporation reduced soil erodibility by 22.9%-41.7%, 17.3%-23.0%, 10.2%-18.1%, and 2.6%-11.1% in ND, LD, MD, and SD croplands, respectively, with its effectiveness declining progressively as degradation intensified. Redundancy analysis identified bulk density, capillary porosity, soil water holding capacity, field capacity, humic acid, and root mass density as the primary factors controlling the temporal variation of soil erodibility. Structural equation modeling further indicated that straw decomposition reduced soil erodibility by improving soil biochemical properties, aggregation, pore structure, and root growth. These findings suggest that the reduction in soil erodibility through straw incorporation is mainly mediated by changes in the soil-crop system and its interactions. Moreover, reduced soil erodibility plays a crucial role in limiting sediment-associated losses of nitrogen, phosphorus, and potassium and increasing crop yield, yet these benefits are constrained by reduced straw decomposition under severe degradation. Therefore, supplementary measures such as organic fertilizer application and microbial inoculation may help accelerate straw decomposition and enhance the effectiveness of straw incorporation in controlling erosion and maintaining land productivity, particularly in severely degraded croplands. Overall, these results provide a viable strategy for mitigating soil erosion and sustaining soil health in degraded croplands of intensively managed agricultural regions.