Effects of Litter Mulch Type and Coverage Amount on Slope Runoff and Sediment Yield in Simulated Rainfall

Soil erosion poses a significant threat to slope stability and ecological functionality. The litter layer, with its complex physical structure, enhances surface roughness, mitigates direct rainfall impact, and improves rainwater interception and soil retention. A litter of three typical slope-protection plant species from Wuhan, Hubei Province, China (Cynodon dactylon, Indigofera amblyantha, and Cinnamomum camphora) was selected for this experiment. This study quantified the effects of litter mulch at four coverage levels (0, 500, 800, and 1000 g/m2 based on dry mass) on slope runoff and sediment yield under simulated rainfall conditions at an intensity of 60 mm/h for a duration of one hour. The results indicated that (1) all litter types and coverage amounts effectively delayed the initiation of slope runoff, though their efficiencies in runoff and sediment reduction varied significantly. (2) Compared with the bare slope, the sediment yield in the plots covered with litter from Cynodon dactylon, Cinnamomum camphora, and Indigofera amblyantha decreased by 96.5%, 67.5%, and 9.4%, respectively, at a coverage of 800 g/m2. Runoff yield decreased by 56.9% and 29.7% in the plots covered with Cynodon dactylon and Cinnamomum camphora litter, whereas Indigofera amblyantha litter cover instead increased runoff yield by 31.6%. (3) Furthermore, increasing litter coverage from 500 to 1000 g/m2 progressively reduced runoff by 29% to 84% and sediment yield by 27.3% to 93.6% compared to the bare slope. These findings demonstrate the importance of litter cover in reducing runoff and soil erosion, offering quantitative support for optimizing vegetation-based slope management.