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.

The food system is a complex mega system consisting of all elements and activities related to the production, processing, distribution, preparation and consumption of food, which contributes to 34% of global greenhouse gas (GHG) emissions and has become one of the biggest drivers of global climate change. This paper adopts the literature analysis method to review recent progress in research on GHG emissions from food systems from four aspects: evaluation methods, systematic evaluation, emission reduction strategies and uncertainty analysis. This paper proposes that the accuracy of evaluation results needs to be improved in three aspects: accurate evaluation of the dietary consumption of residents in each country, improvement of the boundary of the carbon footprint accounting system, and use of regionally localized carbon footprint parameters, so as to provide a basis for the low-carbon and sustainable transformation of food systems.