Response of Soil Detachment Capacity to Land Use Change Mediated by Ecological Engineering in Southwest China

After two decades of afforestation implementation in purple soil areas, land use has transformed, subsequently altering the erosional environment. The inherent complexity and uncertainty associated with soil properties and plant root characteristics within root–soil systems across different land uses hinder a deep understanding of soil detachment capacity (D_c) changes and their driving factors. Therefore, this study systematically investigated the interrelationships between root traits and soil properties to quantifying land use effects on D_c in purple soil areas and identify key influencing factors. Soil samples from croplands, orchards and woodlands were subjected to scouring experiments in a 4 × 0.35 m hydraulic flume under six shear stresses (ranging from 3.79 to 16.24 Pa). The results showed significant variations in mean D_c across land uses with croplands exhibiting the highest erosion susceptibility (2.64 kg m⁻² s⁻¹), followed by orchards (1.39 kg m⁻² s⁻¹) and woodlands demonstrating the lowest detachment rates (0.06 kg m⁻² s⁻¹). The observed D_c variability was attributed to differential interactions between hydraulic conditions, soil properties and plant root traits across land uses. Among hydraulic parameters, the stream power (w) emerged as the most effective predictor for D_c estimation. Path analysis indicated that soil organic matter (SOM) and root mass density (RMD) were the primary determinants influencing D_c variations. A predictive model was subsequently established incorporating w, SOM and RMD as independent variables, demonstrating high accuracy (R² = 0.92, NSE = 0.91). These provide valuable insights into soil detachment mechanisms under different land uses and offer theoretical support for optimising conservation strategies in the ‘Grain for Green’ program.