Manure, food waste and similar sources could be recycled to curb reliance on imported phosphate rock used for agriculture.

Phosphorus is crucial for fertilizing crops. Because its supply could be limited in the future, researchers have mapped out the potential for an alternative source: recycling.

Most phosphorus fertilizer is derived from phosphate rock mined in China, the United States, Morocco and the Western Sahara. This is a non-renewable resource: at today’s rates of extraction, China and the United States are estimated to each have about a 30-year supply in their known, recoverable phosphate-rock reserves. Most nations are net importers of the mineral.

Stephen Powers of Washington State University in Pullman and his colleagues mapped the places where crop cultivation occurs in close proximity to areas with large populations of livestock or people — regions replete with manure, food waste, sewage or wastewater that could be recycled. The team’s analysis found that 72% of manure-rich cultivated areas and 68% of populous cultivated regions are in nations highly dependent on phosphorus imports, including India, Brazil and much of Europe.

This suggests, the authors say, that these countries could move towards agricultural independence and food sustainability by recycling phosphorus from their own waste.