To what extent our food production depends on anthropogenic phosphorus?

Agricultural productivity has dramatically increased in the last sixty years, with undeniable benefits for global food security. Yet, our agricultural production systems have been built on the use of non-renewable resources, thereby altering their sustainability. Agriculture depends on fossil fuel energies – mainly to produce nitrogen fertilizers - but also on another non-renewable resource: phosphate rocks. Here we propose to quantify the reliance of our global food production on the use of fertilizer and additives derived from phosphate rocks, referred to as anthropogenic phosphorus (P). To do so, we simulated the evolution of the soil available P for 132 countries during the 1950-2017 period, with a distinction between both anthropogenic vs. natural soil P stocks. Natural P refers to P that is not derived from mined phosphate rocks. We also explicitly simulated the international trade of feed and food products, given that these fluxes participate in the transfer of anthropogenic P between countries. Finally, for each country, we calculated the P anthropogenic signature of their food production by dividing the anthropogenic P content of agricultural products by their total P content. Our results show that in 2017, the global P anthropogenic signature of food production was ~37%, with large variations across world regions. North America displayed the largest anthropogenic signature (63% ±9% in 2017), followed by Western Europe (55% ±10%), Asia (47% ±7%), Eastern Europe (35% ±10%), South America (33% ±6%), and Africa (20% ±5%). Also, the temporal evolutions of the P anthropogenic signatures reflect the dynamics of agricultural intensification observed in the different world regions. Overall, trade had a negligible effect on the P anthropogenic signature of food production, even when it contributed significantly to increase the soil P fertility of some countries (e.g. The Netherlands). Our estimates of soil P anthropogenic signatures were associated with large uncertainties, raising questions about the best way to estimate soil P legacy and about the data availability to calibrate the models. Eventually, our results highlight the large dependence of global food production to the non-renewable resources that are phosphate rocks. They suggest the urgent need to engage the transition of our food production systems toward more sustainable, input-free and circular agriculture.