Determining the optimal vegetation coverage for controlling soil erosion in Cynodon dactylon grassland in North China

Soil erosion has been a widely studied hydrological issue, and the further deterioration of soil and water environments caused by soil erosion has attracted extensive attention from global scholars. At present, there are relatively few studies on preventing and controlling soil erosion to avoid the introduction of pollutants from surface runoff in grasslands during rainfall events. To identify the optimal vegetation coverage of Cynodon dactylon grassland for controlling soil erosion during rainfall events, bare land (0%) was used as the control in this experiment. Simulated rainfall experiments were carried out with three levels of coverage (30%, 60% and 90%) under four slope conditions (0°, 5°, 10° and 20°) and four rainfall intensities (20 mm/h, 30 mm/h, 60 mm/h and 90 mm/h). The results suggested that the capacity of Cynodon dactylon grassland to reduce the runoff coefficient and sediment yield decreased with increasing rainfall intensity and slope but increased with increasing vegetation coverage. The results of the structural equation model revealed close relationships between vegetation coverage and the reduction rate of the runoff coefficient and the reduction rate of the sediment yield. The results of the response surface methodology suggested that the vegetation coverage of Cynodon dactylon grassland should be higher than 86% to ensure that the reduction rate of the runoff and sediment of grassland is greater than 60%, and it is advisable that the planting slope of grassland not exceed 10°. The results of this study serve as a guide for the recovery and restoration of grasslands to control soil erosion and prevent the production as well as further spreading of pollutants in China. This study highlights the need to consider the prevention and control of soil erosion as a source of pollutants.