The contribution rate of stem‐leaf and root of alfalfa (Medicago sativa L.) to sediment and runoff reduction

Abstract Seasonal changes in ground canopy and root density induced by the growth of alfalfa ( Medicago sativa L.) may strongly influence the variation in runoff and sediment across alfalfa growth stages. In this study, eight alfalfa plots with and without ground canopy and two bare soil plots (CK) were used to investigate the effect of alfalfa growth on the regulation of runoff and sediment during one growing season (seedling stage, S1; budding stage, S2; flowering stage, S3; podding stage, S4). The experiments involved four slope gradients of 8.6%, 17.6%, 26.8%, and 36.4% and one rainfall intensity of 90 mm h −1 . The time to runoff initiation (TR), runoff volume (RV), and sediment yield (SY) were recorded, and runoff reduction benefits (RRBs) and sediment reduction benefits (SRBs) were calculated. The results have shown that TR was delayed with the growth of alfalfa and advanced with an increasing slope gradient. From S1 to S4, compared with CK, alfalfa grassland reduced the runoff by 10.36% to 85.80% and the sediment by 15.34% to 94.48%. The root systems of alfalfa reduced the runoff by 1.29% to 34.86% and the sediment by 0.87% to 49.97%. RV and SY decreased exponentially with aboveground biomass and root density during the growing season. The SRBs were greater than the RRBs, and the contribution of stem leaves for SRBs and RRBs was higher than that for roots under the same growing seasons and slope gradient. This study deepens our understanding of herbaceous plants in regulating runoff and sediment at different growth stages and clarifies the contribution of vegetation components to soil and water loss control.