Optimizing the nitrogen application rate for maize and wheat based on yield and environment on the Northern China Plain

Highlights: • Optimal N rates under some yield, economic and NUE target constraints were quantified. • N rate based on N uptake was largest, followed by crop yield and economic income. • N rates were reduced by 20–30% when environmental costs were considered. • For maize, the optimal ecological N rate was 43 kg N ha^{− 1} less than that when NB = 0. • The optimal N rates were 179 kg ha^{− 1} for maize and 202 kg ha^{− 1} for wheat. Optimizing the nitrogen (N) application rate can increase crop yield while reducing the environmental risks. However, the optimal N rates vary substantially when different targets such as maximum yield or maximum economic benefit are considered. Taking the wheat-maize rotation cropping system on the North China Plain as a case study, we quantified the variation of N application rates when targeting constraints on yield, economic performance, N uptake and N utilization, by conducting field experiments between 2011 and 2013. Results showed that the optimal N application rate was highest when targeting N uptake (240 kg ha^{− 1} for maize, and 326 kg ha^{− 1} for wheat), followed by crop yield (208 kg ha^{− 1} for maize, and 277 kg ha^{− 1} for wheat) and economic income (191 kg ha^{− 1} for maize, and 253 kg ha^{− 1} for wheat). If environmental costs were considered, the optimal N application rates were further reduced by 20–30% compared to those when targeting maximum economic income. However, the optimal N rate, with environmental cost included, may result in soil nutrient mining under maize, and an extra input of 43 kg N ha^{− 1} was needed to make the soil N balanced and maintain soil fertility in the long term. To obtain a win-win situation for both yield and environment, the optimal N rate should be controlled at 179 kg ha^{− 1} for maize, which could achieve above 99.5% of maximum yield and have a favorable N balance, and at 202 kg ha^{− 1} for wheat to achieve 97.4% of maximum yield, which was about 20 kg N ha^{− 1} higher than that when N surplus was nil. Although these optimal N rates vary on spatial and temporal scales, they are still effective for the North China Plain where 32% of China's total maize and 45% of China's total wheat are produced. More experiments are still needed to determine the optimal N application rates in other regions. Use of these different optimal N rates would contribute to improving the sustainability of agricultural development in China.