Slope planting patterns are superior to ditch grassing in reducing ditch erosion load to rivers: Evidenced from a five-year study in an intensive sugarcane growth watershed

Abstract

Large-scale sugarcane cultivation accelerates downstream ditch erosion and causes significant soil C, N, and P losses, resulting in water pollution. The sugarcane planting pattern, i.e. the area ratio of newly planted sugarcane and perennial sugarcane, significantly affects slope soil erosion and nutrient loss. However, the influence of slope planting pattern change on downstream ditch soil erosion and pollution into the river remains unclear. We designed four experimental treatments: bare ditch-high area ratio of newly planted sugarcane (BD-H), 1-year ditch grassing-low area ratio of newly planted sugarcane (GD1-L), 2-year ditch grassing-middle area ratio of newly planted sugarcane (GD2-M), and 3-year ditch grassing-middle area ratio of newly planted sugarcane (GD3-M). Using a combination of a five-year field observation and compound-specific stable isotope (CSSI) tracing techniques, we determined the relative role of grass planting in the ditch and slope planting pattern on ditch erosion and associated nutrient loss in an intensive sugarcane cultivation watershed. The results showed that the effect of the area ratio of newly planted sugarcane on the upstream slope was significantly greater than that of grass planting on the downstream ditch erosion and river pollution. Newly planted sugarcane ratios on the upstream slope were significantly and positively correlated with the runoff in the downstream ditch (p < 0.01). The vegetation coverage, root density, and soil organic matter significantly increased with grass planting years of ditches (p < 0.01). The area ration newly planted sugarcane accounted for 57% of the variation of ditch erosion parameters (N, P, and SOC loss) (p < 0.01), and grass planting (soil organic matter, vegetation coverage, and root density) accounted for 27% of the variation of ditch erosion parameters (p < 0.05). In large-scale sugarcane-growing areas in tropical and subtropical regions, to prevent and control ditch erosion and pollution into the river, attention should be paid to vegetation restoration in the downstream ditch and the rational allocation of planting patterns in the upstream slope catchment area.