Determining the Critical Nitrogen Application Rate for Maximizing Yield While Minimizing NO3−-N Leaching and N2O Emissions in Maize Growing on Purple Soil

Optimization of nitrogen (N) fertilizer application is essential to achieve higher crop yields at lower environmental costs. This study investigated the impacts of N application rates (0, 180, and 360 kg N ha−1) on maize productivity, N use efficiency (NUE), NO3−-N leaching, cumulative N2O emissions, and N surplus in maize growing in the purple soil of Southwest China through a 2-year field study. The critical N rate balancing yield optimization with reduced NO3−-N leaching and N2O emissions was identified. The results showed that grain yield initially increased linearly and then stabilized with increasing N rates, while NUE significantly decreased. NO3−-N leaching, N2O emissions, and N surplus exhibited quadratic increase. Regression analysis indicated that 158–163 kg N ha−1 achieved optimal yield while maintaining acceptable NO3−-N leaching and N2O emissions compared to 360 kg N ha−1. This range also enhanced NUE and minimized soil N residue.