Optimizing the N Rate for Maize Forage to Balance Profits and N Ecological Stress

Abstract

The N application used for the production of forage affects environment stress. The N application rate used for the production of the whole maize (Zea mays L.) plant (WMP) affects the produced feed and environment. We carried out a 2-year field experiment aiming to measure how N application rates affect WMP forage production, and estimated the impact on the environment. Five N application treatments (0, 100, 200, 300 and 400 kg N ha−1) were included in our study. The results showed that N application improved forage yield, achieving a higher economic and ecological profit. After reaching a certain optimal rate, however, increasing the N rate further no longer increased the yield and quality of WMP forage, but instead greatly increased estimated N losses, thereby reducing ecological profits. The comprehensive benefit of the optimal N rate was ordered: the optimal N rate that maximized agronomic profit > that maximized economic profit > that maximized ecological benefit. The optimal N rate maximizing ecological profit was lower by 21% and 37% than that maximizing economic profit and forage yield, respectively. N application rates with the highest ecological profit (USD 2478 ha−1 in 2017 and USD 2448 ha−1 in 2018) were 248 and 245 kg N ha−1, respectively, in 2017 and 2018. The optimized N rate that maximized ecological profit maintained the economic profit while reducing N fertilizer input and associated N losses; it also carried a lower economic and ecological cost due to estimated N losses. Ecological criteria, which combine economic profit and economic losses due to their environmental impact, are more efficient than agronomic or economic criteria when used to provide guidance for WMP forage production. Therefore, in WMP forage production, optimizing N application rate by ecological criteria could maintain a high forage yield and economic profit, but greatly reduce input costs and ecological stress, maximizing ecological profit.