Towards circular nitrogen use in the agri-food system at village and county level in China

CONTEXT: Increased nitrogen (N) losses from linear agri-food systems result in severe environmental issues. These problems can be mitigated by circular N use. Yet, circularity is a scale-specific problem, and the feasibility of pathways towards N circularity at different scales is unclear. OBJECTIVE: This study aimed to 1) evaluate N circularity of a complete agri-food system, including household compartment, at both the village and county scale; and 2) assess potential pathways towards N circularity. METHODS: We used the county of Quzhou (China) with 342 villages as a case study and applied the modified version of a nutrient flow model (NUFER) to calculate N flows, using national statistical data and own survey data collected from farms and households. To evaluate N circularity, we selected four key performance indicators: N import, N loss, N use efficiency and N recycling rate. RESULTS AND CONCLUSIONS: Our analysis showed significant variation at the village scale, depending on local production and consumption patterns. At county level, total N import was 546 kg ha(-1) yr(-1), of which 54% was lost to the environment. The N use efficiency of the agri-food system and N recycling rate of excreta were both <30%. We investigated scenarios to increase N circularity, including application of good management practices in crop and animal production; household dietary change to more plant protein; recycling of organic waste; growing legumes instead of cotton; and reducing livestock breeding. All measures combined increased the system's N use efficiency by 172% and N recycling rate by 87%, while reducing N import by 68% and N loss by 77%. Recycling of organic waste was the most effective and most feasible strategy to promote circularity. SIGNIFICANCE: Our study bridges the gap between village and county level N cycles, illustrates possibilities to transition towards circular N use, and can help policymakers worldwide to achieve more sustainable agri-food systems.