Effect of roots on the soil detachment process in grassland and shrubland

Plant roots play an important role in reducing soil detachment and increasing soil erosion resistance. Current studies have mainly focused on the quantification of the soil detachment rate (SDR). However, few studies have been conducted to explore the variation in the SDR and root effects during the soil detachment process. In this study, undisturbed soil samples were collected from four shrublands (with the main species Caragana korshinskii, C. korshinskii mixed with Agropyron cristatum, C. korshinskii mixed with Bothriochloa ischaemum, and C. korshinskii mixed with Artemisia gmelinii) and three grasslands (with the main species B. ischaemum, B. ischaemum mixed with A. cristatum, and B. ischaemum mixed with A. gmelinii) on the Loess Plateau, China. The samples were subjected to flow scouring through hydraulic flume experiments under six different shear stresses. The duration of this experiment was 6 min, and the SDR of each minute was estimated. The results showed that the SDR of shrubland was higher than that of grassland in each detachment process. The dominant factors affecting SDR gradually changed from the root-soil composite properties to the hydrodynamic parameters in this process. The effect of roots on the SDR was stronger than that of soil properties in the root-soil composite. In the early detachment stage, the 0-2 mm fine roots had the strongest effect on the SDR, while it was affected by the combined effect of fine roots and coarse roots in the later stage. When the fibrous roots were mixed with the tap roots, the fibrous roots had a significant negative effect on the SDR and mainly affected the early detachment stage. However, the tap roots had a weak effect in all stages. With the detachment process, the soil erosion resistance first increased and then stabilized, and the variations were mainly concentrated from 0 to 3 min. The roots mainly affected the SDR and soil erosion resistance by influencing rill erodibility parameters.