Optimizing nitrogen fertilization for forage maize production to maximize profit and minimize environmental costs in a rainfed region in China

ABSTRACT Appropriate nitrogen (N) fertilizer application can improve crop yield, increase N-use efficiency and reduce environmental pollution. A two-year field experiment was performed to explore the influences of N fertilizer rates on dry matter yield, crop N removal, N-use efficiency and apparent N budget. Five N application rates, i.e. 0, 70, 140, 210 and 280 kg N ha−1 (referred to as N0, N70, N140, N210 and N280) were tested. The application of fertilizer N markedly increased the dry matter yield of forage maize, which was highest for N210 with a two-year average of 22.6 t ha−1. The N210 treatment increased crop N removal by 34.9% on average compared with N0. As the N rate increased, soil nitrate-N accumulation increased exponentially, apparent N loss increased linearly and agronomic efficiency clearly decreased. The apparent N loss and soil nitrate-N accumulation decreased by 19.4% and 19.0%, respectively, and partial-factor productivity increased by 24.5% under the N rate that maximizes profit (195.1 kg ha−1) in comparison with those under the N rate that maximizes yield (244.4 kg ha−1). The N rate (195.1 kg ha−1) is recommended to maximize profit and minimize environmental costs in forage maize production in the semi-arid region in China.