Fine root densities of grasses and perennial sugarcane significantly reduce stream channel erosion in southern China

Stream Channel (SC) erosion results in immense soil and nutrient losses and eutrophication of downstream lakes and rivers. Among other factors, the lack of vegetation cover within SCs and on adjacent soils can accelerate soil and nutrient losses. The combined impact of perennial sugarcane plantation and grass cover on increasing SC erosion losses have not been previously studied. Current study determined SC erosion and associated nutrient losses and clarified the effect of grass roots within SCs and the ratooned sugarcane grown on adjacent lands in Nala watershed in southern subtropics of China. Six SCs in two sub-watersheds (SW1 and SW2) surveyed after revegetation during 2019 were compared with initial survey conducted in 2017 and 2018. The SC erosion was significantly (P < 0.05) reduced by 84.2% (5.19 ± 2.16 Mg ha-1) in entire watershed in 2019 compared to 2018 (43.9 ± 15.2 Mg ha-1). It notably decreased by 99.23% and 96.50% in SC-1-3 at SW1 and SC2-3 at SW2, respectively. Total N and P losses decreased by 84.9% and 82.5%, respectively, in entire watershed. The decreases in SC erosion and nutrient losses are attributed to increasing vegetative cover (R2 = 0.7543, P < 0.001), and grass root densities of <1 mm (R2 = 0.7543, P < 0.001), 1-2 mm (R2 = 0.7051, P < 0.001) and >2 mm (R2 = 0.5746, P < 0.001). Principal component regression analysis confirmed that root densities of SC grasses, perennial sugarcane, and organic matter had positive impacts on controlling SC erosion and consequent nutrient losses.