The use of mineral phosphorus (P) fertilizers, often referred to as anthropogenic phosphorus, has dramatically altered the global phosphorus cycle and increased soil phosphorus fertility and crop yields. Quantifying agriculture’s reliance on anthropogenic phosphorus requires estimates of its contribution to agricultural soil fertility. Here we present a model of soil phosphorus dynamics simulating phosphorus availability in agricultural soils for individual countries from 1950 to 2017. Distinguishing between anthropogenic and natural phosphorus pools and accounting for farming practices, agricultural trade and crop–livestock recycling, we estimate that the global anthropogenic contribution to available phosphorus in agricultural soils was 47 ± 8% in 2017. Country-level anthropogenic phosphorus signatures vary according to cumulative fertilizer use and phosphorus availability in soil inherited pre-1950, with negligible influence of the trade of feed and food products. Despite different historical trajectories, we find that Western Europe, North America and Asia are similarly reliant on anthropogenic phosphorus, with nearly 60% of the total available phosphorus of anthropic origin in 2017. Conversely, anthropogenic phosphorus inputs in Africa remained low over the study period, contributing only around 30% of available phosphorus. The unequal reliance of agricultural soil fertility and food production systems on anthropogenic phosphorus resources highlights the need for a fairer management of the world’s remaining phosphate rock resources.