Determining the optimal nitrogen rate for summer maize in China by integrating agronomic, economic, and environmental aspects
The concept of high yield with a goal of minimum environmental cost has become widely accepted. However, the trade-offs and complex linkages among agronomic, economic, and environmental factors are not yet well understood. In this study, reactive nitrogen (N r) losses were estimated using an empirical model, and an economic indicator and an evaluation model were used to account for the environmental costs of N fertilizer production and use. The minimum N rate to achieve the maximum yield benefit (agronomically optimal N rate), maximum economic benefit (economically optimal N rate: economic benefit was defined as yield benefit minus N fertilizer cost), and maximum net benefit (ecologically optimal N rate: net benefit was defined as yield benefit minus N fertilizer and environmental costs) were estimated based on 91 on-farm experiment sites with five N levels for summer maize production on the North China Plain. Across all experimental sites, the agronomically, economically, and ecologically optimal N rates (N agr, N eco, and N ecl, respectively) averaged 289, 237, and 171 kg N ha −1, respectively. N ecl management increased net benefit by 53% with a 46% decrease in total environmental costs, and a 51% decrease in N r loss intensity from N fertilizer use (47, 65, and 38% for N 2O emission, N leaching, and NH 3 volatilization, respectively) and maintained grain yield, compared with N agr management. Compared with N eco management, N ecl increased net benefit by 12%, with a 31% decrease in total environmental costs and a 33% decrease in N r loss intensity from N fertilizer use, and maintained economic benefit and grain yield. No differences in N ecl were observed between soil types or years, but significant variation among counties was revealed. N ecl increased with the increase in N-derived yield with an R2 of 0.83. In conclusion, N ecl was primarily affected by N-derived yield and could enhance profitability as well as reduce N r losses associated with the maize grain yield.