Nitrogen (N) runoff loss from paddy fields contributes significantly to non-point source pollution. Straw return to soil may affect N runoff loss by changing soil biochemistry. In situ N runoff monitoring combined with an analysis of soil biochemical indicators was implemented to explore the effect of straw return lasting for five or six years on N runoff loss and its potential mechanism in five rice rotation systems. The results showed that straw return reduced total N (TN) runoff losses by 2.29%− 26.10% through physical and biochemical pathways, and the reduction in inorganic N (IN) was the largest (53.56%–82.42%) through biochemistry. This was mainly achieved by the increase in soil C:N due to straw return, thereby increasing the immobilization of microbial N and reducing the soil IN. At the same time, the abundance of functional genes (AOA, AOB, nxrA) participating in the nitrification process was also conducive to the decrease in TN runoff concentration. More importantly, the reduction in IN and functional genes of the nitrification process did not affect N uptake by rice, and the increase in the atmospheric N fixation gene (nifH) was also beneficial to N supplementation in soil. However, the positive effects of straw return under the five rice rotation systems were different, and the TN loss reduction in double-cropping rice was the lowest. With the lower soil C:N in the single-cropping and paddy-upland systems, the increase in soil C:N after straw was more effective, and had greater potential to reduce TN runoff loss. This study provides a new perspective on N cycling in soil biochemistry by straw return, so as to select optimal measures to protect the water environment in different rice rotation systems.

稻田中的氮 (N) 径流流失是造成非点源污染的重要原因。秸秆还田可能通过改变土壤生物化学影响氮径流损失。【摘要】：采用原位氮径流监测结合土壤生化指标分析,探究五六年秸秆还田对五个水稻轮作系统氮径流损失的影响及其潜在机制。结果表明，秸秆还田通过物理生化途径减少总氮（TN）径流损失2.29%~26.10%，其中无机氮（IN）通过生化途径减少量最大（53.56%~82.42%）。这主要是由于秸秆还田增加了土壤 C:N，从而增加了微生物 N 的固定化，降低了土壤 IN。同时，丰富的功能基因（AOA、nxrA )参与硝化过程也有利于TN径流浓度的降低。更重要的是，硝化过程中 IN 和功能基因的减少并不影响水稻对 N 的吸收，而大气固氮基因（nifH) 也有利于土壤中的 N 补充。但五种水稻轮作制度下秸秆还田的正效应不同，双季稻TN损失减少量最低。在单作和水旱两熟制土壤C:N较低的情况下，秸秆还田后增加土壤C:N更为有效，减少TN径流流失的潜力更大。本研究为秸秆还田土壤生物化学中的氮循环提供了新的视角，从而在不同的水稻轮作系统中选择保护水环境的最佳措施。