Nitrogen and phosphorus losses and eutrophication potential associated with fertilizer application to cropland in China

Increased application of nitrogen (N) and phosphorus (P) fertilizer has significantly improved crop yields and food security in China over the past several decades. However, this has also led to serious problems of aquatic eutrophication in inland and coastal waters. This study analyzed N and P losses from major cropping systems across China using the China Pollution Source Census dataset. The associated eutrophication impacts, including freshwater eutrophication potential (FEP) and marine eutrophication potential (MEP), were then quantified using spatially-explicit characterization models. Large spatial and crop specific variations in N and P loss were identified. For example, net N leaching varied from 0.78 to 23.66 kg ha−1 for vegetable cropping in open fields and covered systems. Provinces with large cropping areas contributed the largest total nutrient loads. However, the application of spatially-explicit characterization factors (CFs) led to the identification of eutrophication hotspots that were not simply correlated with the inventory of nutrient emissions. Hainan, Yunnan, Guangdong, Guangxi and Fujian, with high global CFs for P, contributed the most (79.9%) to the total global FEP. China's breadbasket provinces with high losses and local CFs for both P and N, such as Hunan, Hubei and Sichuan, contributed significantly to both local FEP and MEP. Hunan, Hubei and Sichuan accounted for 10.1%, 9.8% and 9.2% to the total local FEP, respectively; and accounted for 7.7%, 8.4% and 9.0% to the total local MEP, respectively. Strategic actions in these hotspot regions would be most beneficial in addressing aquatic eutrophication challenges.