Soil potassium depletion in global cereal croplands and its implications.

Nitrogen (N), phosphorus (P) and potassium (K) are of the most essential nutrients for crop production, and inputs of their fertilizers have been a direct and effective way to replenish their removal from crop harvest. However, the global soil K status is scarcely documented. This study attempts to evaluate the soil K deficit in global cereal croplands and potential effects of better K fertilizer management. We hypothesized that historical records of cereal yield and K fertilizer use rate (K-FUR) can be used to understand how soil K deficit is related to the cumulative insufficient K replenishment. Evidently, the cereal production has been depleting soil K at a rate much higher than its replenishment, resulting in soil K deficit across 61 % of the global cereal harvest area with an average K-FUR (kg ha) of 7.1 which is much lower than the ∼27 required to balance N and P supply for an optimal grain yield. Replenishing K for all K-deficit areas based on current K-FUR classes could potentially add about 601 Mt. grains to the global food production: 386 Mt. from 153 M ha croplands with K-FUR class 10-20 kg ha; 90 Mt. from 131 M ha with K-FUR class 3-10 kg ha; and 126 Mt. from 158 M ha with K-FUR class <3 kg ha. Global soil K deficit is a long-standing and ubiquitous issue, and to replenish K for all K-deficit areas as proposed herein can be a feasible way for improving cereal yield by about 49 %. Increasing awareness of public and policy-makers about this threat and potential will help lead to a judicious allocation of limited potash resources and to a better return on any financial and humanitarian aids for eradicating poverty and hunger worldwide while also advancing global food security and agricultural sustainability.