Impacts of international food and feed trade on nitrogen balances and nitrogen use efficiencies of food systems

International trade of agricultural products has greatly increased over time, but its impacts on sustainable development are debated. It may contribute to food security in importing countries, increases the dependency between countries, and has been implicated in displacement of environmental pollution and resource depletion. There is also discussion about the relationships between trade and nitrogen (N) balances and N use efficiencies (NUE). We explored relationships between changes in the trade of food and feed and in N balances and NUE of the food supply systems through simulation modeling and an analysis of empirical data of 115 countries (representing 91% of global population) for the period 1961–2011. In the empirical analysis, 64 main importing countries and 14 main exporting countries, were distinguished. Importing countries had on average a higher population density than exporting countries but rather similar protein intake and GDP per capita. The empirical analysis indicate that main importing countries had on average higher N fertilizer inputs to their food supply systems, and also higher N surpluses and higher NUE than main exporting countries. The overall mean NUE of the food supply system of main importing countries decreased with increasing import, but the relationships between import and NUE were diverse when these countries were grouped according to population density and GDP per capita. We compared N balances and partial N balances, and three methodologies commonly used for estimating NUE. We observed that NUE2 provides an unbiased estimate for both importing and exporting countries. Our study contributes to the understanding of the diverse relationships between international trade, N balances and NUE of food systems.