An optimal regional nitrogen application threshold for wheat in the North China Plain considering yield and environmental effects

North China Plain is the bread basket for Chinese. However, the over-use of N fertilizer has resulted serious environmental pollution and even threat the food security owing to the soil degradation in North China Plain. It is essential to develop a suit of optimal regional nitrogen application threshold. In this study, we attempted to build the threshold by using dataset of literature review and field experiments. Results showed that the optimal N fertilizer rate should be around 185 kg N ha−1 for the wheat cultivation with achieved yield at 7000 kg ha−1. Both literatures reviewed and field experiments agreed well on this threshold. The wheat yield under this optimal N fertilizer rate was about 2% lower than the theory maximum achievable yield (7203 kg ha−1) in this region; however, the N rate could be reduced by 25% compared to the N rate under the maximum yield. This threshold entailed decreases of 25.25%, 20.17%, 27.89% and 38.80% in nitrogen application rates, residual inorganic soil nitrogen (0-100 cm), nitrate leaching and ammonia volatilization, respectively, on the regional scale. In addition, reducing theory maximum achievable yield by 2% was not statistically significant and would not result in additional risks because fluctuations in wheat yields over time (−57.07% to 34.73%) and space (−23.78% to 33.07%) were higher than 2% in this area.