Spatial distribution and drivers of cropland-phosphorus runoff in China

The unidirectional flow of phosphorus (P) from mineral reserves to croplands, freshwaters and ultimately to marine environments surpasses sustainable limits for human development. Addressing the dual challenges of rising food production and mitigating P pollution necessitates spatially explicit assessments. However, significant uncertainties persist regarding the spatial patterns of cropland-P runoff in China, largely due to inadequate methodologies for accurately estimating P runoff that incorporate climate variability, soil characteristics, and P fertilization rates. Here, we conducted a fine-gridded estimation of cropland-P runoff across China, using a data-driven artificial intelligence model in conjunction with county-level P fertilization data. Results indicated that cropland-P runoff in 2018 totaled 109.9 kilotons P yr −1 , representing 0.79% of China's mineral P fertilization, aligning with national surveys from 2017. Notably, P runoff fluxes from uplands exhibited an inverse relationship with latitude, highlighting hotspots in regions south of the Yangtze River, driven by lower soil pH, intensive crop ration, and elevated soil organic matter. In rice paddies, hotspots were concentrated in the Pearl River Delta, Yangtze River Delta and western Sichuan basin, linked to higher irrigation and P fertilization. These patterns suggest that mineral-fertilizer-induced cropland-P runoff hotspots mainly occur where high P input coincides with runoff-prone soil, climate and irrigation conditions. This study provides a spatially explicit basis for prioritizing future monitoring and management of cropland-P runoff in these vulnerable regions.