Bottom-up estimates of reactive nitrogen loss from Chinese wheat production in 2014

The excessive use of synthetic nitrogen (N) for Chinese wheat production results in high loss of reactive N (Nr; all forms of N except N2) into the environment, causing serious environmental issues. Quantifying Nr loss and spatial variations therein is vital to optimize N management and mitigate losses. However, accurate, high spatial resolution estimations of Nr loss from wheat production are lacking due to the limitations of data generation and estimation methods. Here, we applied the random forest (RF) algorithm to bottom-up N application rate data, obtained through a survey of millions of farmers, to estimate the Nr loss from wheat production in 2014. The results showed that the average total Nr loss was 52.5 kg N ha-1 (range: 4.6–157.8 kg N ha-1), which accounts for 26.1% of the total N applied. The hotspots for high Nr loss are the same as those for high applied N, including northwestern Xinjiang, central-southern Hebei, Shandong, central-northern Jiangsu, and Hubei. Our database could guide regional N management and be used in conjunction with biogeochemical models.