Integrative fertilizer nitrogen management mitigates nitrogen leaching and gray water footprint in a subtropical vegetable rotation system

Nitrogen (N) leaching is a major pathway of N loss in subtropical crop production systems, contributing to groundwater pollution and thus posing serious threats to human health. However, the characteristics of annual N leaching in subtropical open-field vegetable systems and the effectiveness of integrative N fertilization management practices in reducing N leaching remain poorly understood. In this study, two plot-based field experiments were conducted with open-field Chinese cabbage–pepper rotation system in subtropical Southwest China to quantify annual N leaching and evaluate the effectiveness of integrated N fertilization management practices. Experiment 1 compared five N fertilizer application rates using conventional urea, while Experiment 2 compared different N sources including conventional urea, organic fertilizer, nitrification inhibitor-based fertilizer, and controlled-release urea which were all applied at the optimized N rate. Results showed that the annual N leaching under farmers’ N practice (FNP) was 251 kg N ha^-1, with contributions of 55, 31, and 14% from the pepper season, Chinese cabbage season, and fallow period, respectively. Total N leaching increased exponentially with N rate. The seasonal N leaching factor was 32% for pepper and 17% for Chinese cabbage in the FNP treatment, respectively. Compared to FNP, optimizing N rate based on crop requirement and soil supply significantly reduced N leaching by 68% and gray water footprint by 66–75%, while improving N use efficiency (NUE) from 35 to 54%. In Experiment 2, mixing organic and inorganic fertilizers, applying nitrification inhibitor, and using controlled-release urea further reduced annual N leaching by 27, 54, and 25%, respectively, compared to conventional urea. These practices also improved crop yields by 2–11% and NUE by 10–13%, and lowered gray water footprint by 28–58%. In summary, integrative N stewardship practices, particularly use of nitrification inhibitors under optimized N rates, effectively reduced N leaching while achieving high NUE and vegetable yields, providing a promising strategy for sustainable subtropical vegetable production.