Mechanism and modeling of different plant root effects on soil detachment rate

Plant roots significantly affect soil erosion, although the mechanism of how roots affect the soil detachment rate (SDR) by overland flow on the Loess Plateau is not fully understood. This study was conducted to investigate the mechanism of how roots affect SDR using natural undisturbed soil samples taken from five sampling plots with the dominant species of Agropyron cristatum, Caragana korshinskii, Medicago sativa, Caragana korshinskii, and Robinia pseudoacacia. Bare land was used as the control plot. The samples were subjected to flow scouring through hydraulic flume experiments under six different shear stresses. The results showed that the roots could significantly reduce the SDR by > 83.48% compared with the bare soil. The herbs with fibrous roots (A. cristatum) had a strong root-reducing effect on the SDR. Due to the weaker root-reducing effect of herbs with taproots, the comprehensive reducing effect of herb roots was lower than that of shrubs (C. korshinskii). Because of the higher soil organic matter, the tree roots (R. pseudoacacia) still had a higher reduction effect on the SDR even with a smaller root content, and its SDR was between that of herbs and shrubs. The SDR could be divided into 3 zones based on root mass density (RMD): zone I (SDR is sensitive to root action), zone II (the effect of soil properties on SDR is prominent), and zone III (SDR is relatively stable). The critical conditions between different zones and the main controlling factors affecting the SDR in different zones were analyzed. The prediction accuracy of the SDR model could be improved by constructing the model using the zoning method (NSE > 0.95). A prediction model of SDR suitable for root-soil complexes of different plant species was developed (NSE = 0.90).