Influence of the vegetation restoration age on the soil detachment of root-soil composites on the Loess Plateau of China

Vegetation restoration processes significantly affect near-surface characteristics, thus affecting soil detachment. Existing research has primarily focused on analysing soil detachment via root morphological parameters and soil physical and chemical properties. However, few studies have focused on analysing the variation in soil detachment with restoration age from a mechanical parameter perspective. Natural, undisturbed soil samples were collected from five grasslands restored for 1-22 years and from one bare plot (0 years of restoration, employed as the control). The collected samples were subjected to flow scouring in hydraulic flume experiments under six stream powers. The relationship between the soil detachment rate (SDR) and the mechanical parameters of the root-soil composites, namely root cohesion and soil shear strength (tau 200), were quantified to reveal the mechanical mechanism underlying soil detachment during vegetation restoration. The results indicated that the SDR decreased, whereas root cohesion increased with increasing vegetation restoration age. The dominant factors influencing the SDR changed from hydrodynamics at the early restoration stage to the mechanical properties of the root-soil composites at the late stage. An SDR model with a high prediction accuracy (Nash-Sutcliffe efficiency = 0.96 and R2 = 0.96) was developed based on mechanical parameters, and the fitting effect was greater than that of the SDR prediction model developed based on root morphological parameters and soil physical and chemical properties. This study aimed to analyse the SDR variation mechanism from the perspective of mechanics and could provide reference for the study of the erosion reduction effect of roots.