Reducing nitrogen and phosphorus losses from arable slope land with contour hedgerows and perennial alfalfa mulching in Three Gorges Area, China

The loss of nitrogen and phosphorus from arable slope land threatens the aquatic environment in the Three Gorges Area, China, and the protection of these slopes will play an important role in regional agricultural development. During the last 10 years, a long-term comparison of ecological methods to reduce losses of nitrogen and phosphorus has been carried out with five treatments: perennial alfalfa soil mulching (G1), ryegrass and grain amaranth (soybean) rotation (G2), peanut rotation with wheat and intercropping with contour Toona sinensis hedgerows (G3), peanut rotation with wheat and intercropping with contour alfalfa hedgerows (G4) and a wheat–peanut rotation with conventional management practices (G5). Rainfall (P), runoff, rainfall intensities (I10, I20, I30, I60), sediment yield, and nitrogen and phosphorus losses from slope plots were analyzed for each rainfall event. The results showed that compared with wheat–peanut rotation and conventional management, perennial soil mulching, wheat–peanut rotation with alfalfa contour hedgerows and wheat–peanut rotation with toon contour hedgerows could effectively reduce runoff, sediment yield and losses of nitrogen and phosphorus from arable slope land. The reductions of sediment yield and losses of nitrogen and phosphorus increased with the increase of rainfall intensities and rainfall integrated indexes (PI10, PI20, PI30, PI60). In 9 years, average runoff was each reduced by 42%, 34% and 26% respectively, and sediment yields were each reduced by 87%, 86% and 84% respectively. In 8 years, average nitrogen loss was each reduced by 71%, 50% and 42% respectively; and phosphorus losses of those were each reduced by 84%, 68% and 64% respectively.