Effects of Soil and Water Conservation Measures on Runoff and Sediment Yield in Red Soil Slope Farmland under Natural Rainfall

This paper analyzes the relationship between runoff, soil erosion, sediment particles, and natural rainfall characteristics on sloping farmland in the red soil region of southern China. The surface runoff and soil loss data were measured on runoff plots during 66 natural rainfall events from 2015 to 2018 in Jiangxi Province. The results show that the maximum 30-min rainfall intensity (I-30) is positively related to the runoff depth, soil erosion modulus, and sediment mean weight diameter (MWD). With the increase in I-30 during rainfall, the coarse sand content increases, and the fine sand content decreases. The average annual runoff of slope tillage, hedgerows with slope tillage, straw mulching with conventional tillage, and contour tillage decreased by 32.56%, 65.87%, 83.99%, and 87.30%, respectively, compared with that of bare land. Soil and water conservation measures can significantly reduce slope runoff. The flow-reduction effect of contour tillage and straw mulching with conventional tillage increases as I-30 increases, and the flow-reduction effect of hedgerows with slope tillage first increases and then decreases as I-30 increases. The coefficients of variation and standard deviations of the flow-reduction effects of different soil and water conservation measures decrease with increasing I-30. The average annual soil erosion moduli of slope tillage, hedgerows with slope tillage, contour tillage, and straw mulching with conventional tillage decreased by 59.33%, 91.29%, 97.17%, and 98.45%, respectively, compared with that of bare land. Soil and water conservation measures can significantly reduce the sediment yield on slopes. The flow-reduction effects of hedgerows with slope tillage, contour tillage, and straw mulching with conventional tillage all increase with I-30, and their coefficients of variation and standard deviations decrease with I-30. The average single rainfall erosion sediment MWD of decreased by 5.91%, 8.33%, 9.69%, and 13.32%, respectively, compared with that of bare land. Straw mulching with conventional tillage can significantly reduce the MWD of erosion sediment, effectively reduce the content of coarse sand, and increase the content of fine sand. Straw mulching with conventional tillage is a very good soil and water conservation measure for sloping farmland. It not only has the best effect on reducing flow and sediment, but also can effectively intercept coarse sand and reduce the MWD of erosion sediment.