Spatial variability of the nutrient balance and related NPSP risk analysis for agro-ecosystems in China in 2010

Abstract The nutrient budget is an effective indicator of non-point source pollutions (NPSP). The increasingly serious NPSP in China highlights the need for a method to estimate the nutrient balance on a macro level to provide technological support to politicians and policy makers. In this paper, a mathematical model and a comprehensive nutrient database were built on a county level in China. For 2010 in China, more than 196,000 data items with 2464 records and 80 fields exist in the calculation. Coupling the land use data in 2010 with an original resolution of 30 m, the spatial variability of the nitrogen (N) and phosphorus (P) balances were mapped and analysed by resampling to 250 m. The results demonstrated that the total N and P input for China was 42.7 and 10.6 million tonnes, respectively, with outputs of 35.7 and 3.8 million tonnes, respectively. The estimation of the nutrient balances revealed that the total amount of N surplus was 6.95 million tonnes, equivalent to an average of 5.96 t N km−2 and ranged between −25.90 t km−2 and 89.63 t km−2 for individual counties. Additionally, the total P surplus was 6.75 million tonnes, and the average P surplus of 5.27 t km−2, which ranged between −9.71 t km−2 and 77.44 t km−2 for individual counties. With the farmland and orchard information interpreted by remote sensing data, the spatial distribution of the nutrient balances demonstrated that both the agricultural land and nutrient balance were uneven, and the surplus of N and P were largest in the east and northeast parts of China. The relationship between the chemical fertiliser inputs, outputs and nutrient balances indicated that chemical fertiliser inputs positively correlated with the nutrient balances, and at present in China, chemical fertiliser effectively managed the agricultural eco-environment, especially the P fertiliser. Thus, reducing the rate of chemical fertiliser applied and enhancing the nutrient use efficiency should help reduce the risk of NPSP.