Managing the reduction of soil phosphorus can prolong global reserves of fertilizer phosphorus and improve water quality

Abstract

Excess phosphorus in agricultural soils threatens freshwater quality and long-term fertilizer security. Globally, 27% of soils exceed crop phosphorus needs (plant-available soil test phosphorus as Olsen phosphorus), contributing to runoff that degrades water quality for 3 billion people. Reducing surplus phosphorus through fertilizer cessation (“drawdown”) is low cost, but rates remain poorly understood. We analyzed ∼12,700 observations from 225 trials in 21 countries to model the time for Olsen phosphorus to reach optimal agronomic thresholds across major crops and improved grassland. Drawdown rates ranged from 9 (Oceania and Asia) to 14 (Europe) years. Our model suggests that global drawdown could save ∼190,430 kt of fertilizer, 10 times the annual global use. These findings highlight opportunities to maintain yields, improve water quality, and deliver economic benefits, supporting better-informed agricultural practice and environmental polices worldwide.