Extreme legacy phosphorus accumulation in agricultural soils of South Korea: A global comparison of plant-available phosphorus

South Korea has the second-highest phosphorus (P) surplus among OECD countries due in part to long-term overapplication of P fertilizer. However, the consequences for soil P accumulation under different cropping systems remain poorly understood because South Korea uses a unique soil-test P method (modified Lancaster P) that confounds international comparison. To address this, we first developed regression equations to convert plant-available P from the modified Lancaster method into two widely used procedures (Mehlich-3 P and Olsen P) based on 118 agricultural soils under a variety of cropping systems. We then used these equations to convert thousands of modified Lancaster P data from the South Korean national soil database into Olsen P for comparison with global datasets. The estimated Olsen P concentrations in Korea are highest in greenhouse soils (233 ± 106 mg P kg -1 , mean ± standard deviation), followed by orchard soils (158 ± 77 mg P kg -1 ), upland soils (a mixture of vegetables and fruits: 147 ± 86 mg P kg -1 ), and paddy soils (45 ± 37 mg P kg -1 ). These values are substantially greater than in all other major agricultural regions of the world. These findings link the high national P imbalance in South Korea to an extreme accumulation of legacy P in agricultural soils, stressing the urgent need for a nationwide strategy to reduce P inputs, draw down legacy P reserves, and reduce the environmental impact on water bodies.