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 N2O emission, N leaching, and NH3 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 R-2 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.