Effects of Different Nitrogen Substitution Practices on Nitrogen Utilization, Surplus, and Footprint in the Sweet Maize Cropping System in South China

Long-term excessive application of nitrogen fertilizers in sweet maize farmland in South China has led to low nitrogen absorption and high emissions of reactive nitrogen (RN). In this study, four kinds of organic materials, including maize straw, cow manure, biochar, and biogas residue, were applied to sweet maize farmland for three consecutive cropping seasons to substitute 20% of synthetic nitrogen fertilizer. We compared the effects of different nitrogen substitution practices on nitrogen use efficiency (NUE), nitrogen surplus (NSP), and nitrogen footprint (NF) in farmland, with conventional fertilization as the control (CK). Results demonstrated that nitrogen substitution practices increased crop nitrogen uptake by 18.80–52.37%, NUE by 16.00–43.03%, and nitrogen partial factor productivity (PFPN) by 46.18–74.31%, while reducing nitrogen surplus and loss by 7.84–21.84% and 12.08–42.88%, respectively. From a life cycle assessment perspective, nitrogen footprint per unit area (NFA) and per unit yield (NFY) decreased by 13.64–32.24% and 34.26–47.64%, respectively. The results demonstrated that partial substitution with organic fertilizers improved nitrogen utilization as well as reduced nitrogen surplus, loss and, footprint in the sweet maize cropping system in South China. Biochar substitution achieved the most significant improvements. This study provides a research basis for nitrogen management in the sweet maize cultivation system in South China and valuable information for achieving sustainable agricultural development in typical subtropical areas in East Asia.