Global phosphorus flows through agricultural trade

The global phosphorus cycle has been transformed in recent decades through increased use of mineral phosphorus fertilizer in agriculture and losses to water bodies, leading to risks of fossil phosphorus resource depletion and freshwater eutrophication. By moving phosphorus resources across world regions, international trade of agricultural products (food, feed, fiber and fuel) may contribute to these changes in the global phosphorus cycle, including critical nutrient imbalances. However, we lack a comprehensive, quantitative understanding of the role of agricultural trade in the global phosphorus cycle. By combining detailed data on international trade and the phosphorus content of agricultural products, we demonstrate that phosphorus flows through trade increased nearly eight-fold from 0.4 Tg P/yr in 1961 to 3.0 Tg P/yr in 2011, leading to an increase in the fraction of phosphorus taken up by crops that is subsequently exported from 9% in 1961 to 20% in 2011. The P flows in traded agricultural products was equivalent to 27% of the P traded in mineral fertilizers in 2011. Agricultural P flows were mostly driven by trade of cereals, soybeans and feed-cakes, with 28% of global phosphorus traded in human food, 44% in animal feed and 28% in crops for other uses in 2011. We found a strong spatial pattern in traded phosphorus in agricultural products, with most flows originating from the Americas and ending in Western Europe and Asia, with large amounts of phosphorus moving through trade within Western Europe, in strong contrast with the pattern of the mineral P fertilizer trade. We demonstrate that international trade of agricultural products has affected the domestic phosphorus cycle within many countries, making phosphorus exporters susceptible to the volatility of the mineral phosphorus fertilizer market. Overall, these results highlight the importance of trade as key component of the global phosphorus cycle.