Assessing agro-food system circularity using nutrient flows and budgets.

Nutrient reuse and recycling is a key strategy towards more circular and sustainable food systems and depends on the specific conditions of the area under study, such as geography and the type of agricultural system. In this study we analysed nutrient flows and assessed the circularity of a livestock-dominated and export-oriented agro-food system at different system levels and spatial scales. We quantified the nitrogen (N), phosphorus (P) and potassium (K) flows and soil balances in the Belgian agro-food system at the sub-regional, regional and national scale, and assessed five P-based indicators that capture different aspects of circularity: total inputs, phosphorus use efficiency, share of reused to total input, recycling rate, and losses. We found that nutrient soil balances depend on the type of agricultural system: areas with intense livestock production accumulate up to 108 kgN/ha, 4.8 kgP/ha and 150 kgK/ha in their soil annually, whereas areas of mostly arable production have low N and K surpluses of <20 kg/ha and P deficits of < -10 kg/ha. We further found that Wallonia, the southern region of the country that is characterized by lower livestock densities and a partial reuse of sewage sludge, outperforms the Flemish region in the North in all five indicators. The food system in the whole of Belgium has a 34% phosphorus use efficiency rate and a 63% overall recycling rate, while 84% of the total inputs in agriculture are from secondary sources. Our results show that the type of production system is the most crucial determinant for circularity, and highlight the benefit of working at different levels and spatial scales to capture all aspects of circularity in agro-food systems.