Impacts of near soil surface factors on soil detachment process in benggang alluvial fans

Soil detachment processes are greatly impacted by vegetation recovery. However, the understanding of these relationships on bengggang alluvial fans in southeast China is limited. In this research, the impacts of near soil surface factors (litter stems, biological crusts, and roots) on soil detachment is quantitated by overland flow with two introduced grass species (Paspalum mandiocanum and Pennisetum giganteum) in the alluvial fans. Flow scouring was performed on soil samples obtained from two grasslands under nine forms of shear stress ranging from 2.70 to 10.51 Pa. Paspalum mandiocanum and Pennisetum giganteum significantly reduced the soil detachment capacity of alluvial fans by 94% and 98%, respectively. The roots of the two kinds of grass were most effective in reducing soil detachment (48% and 63%), the situation of > 80% was caused by root binding; besides, the contribution of biological crusts (37% and 20%) was higher than that of litter-stems (9% and 15%). Compared with bare land, roots and biological crusts under Paspalum mandiocanum and Pennisetum giganteum decreased rill erodibility by 43% and 40%, 60% and 20%, respectively; meanwhile, they increased the critical shear stress by 0.92- to 3.02-fold, 1.15- to 3.34-fold, respectively. Roots of the two plants increased soil resistance more than the biological crusts mainly by root binding. Overall, Pennisetum giganteum (a deep roots plant) showed a slightly better performance in controlling soil detachment than Paspalum mandiocanum (a shallow roots plant); among them, the roles of roots and litter-stems of Pennisetum giganteum were greater than those of Paspalum mandiocanum while the role of biological crusts of Paspalum mandiocanum was greater than that of Pennisetum giganteum. These findings highlight the significance of litter-stems, biological crusts and roots in controlling soil erosion and are helpful for selecting suitable grasses for vegetation recovery in alluvial fans of benggang.