Emissions of nitrous oxide (N 2O) from agricultural soils contribute to global warming and stratospheric ozone depletion. Applications of fertilizer nitrogen (N) increase N 2O emission, but also increase agricultural production. Here, we report on the responses of crop yield, N 2O emission and yield-scaled N 2O emission (N 2O emission per unit N uptake by grain and aboveground biomass) to different N fertilizer rates in a winter wheat-summer corn double-cropping system in the North China Plain. Soil N 2O emission measurements were carried out for two years in a long-term field experiment, under semi-arid conditions with four flood irrigations events per year. Our results indicated that N 2O emissions were linear functions and yield-scaled N 2O emissions were cubic functions of N fertilizer application rate. Yield-scaled N 2O emissions were lowest at application rates of 136 kg N ha -1 yr -1. Using a quadratic-plateau model, it was found that maximal crop yields were achieved at an application rate of 317 kg N ha -1 yr -1, which is 20% less than current practice. This level is suggested to be a compromise between achieving food security and mitigation N 2O emissions.
