Net anthropogenic nitrogen inputs (NANI) index application in Mainland China

Abstract This study provides a new understanding to sources of nitrogen (N), and may serve as a foundation for further exploration of anthropogenic effects on N inputs. Estimation of net anthropogenic nitrogen inputs (NANI) was based on an inventory of atmospheric N deposition, N fertilizer use, N in human food and animal feed, seeding N and N fixation. This study took a step forward to calculate NANI in detail on a regional scale, and analyzed its temporal variations and geographic differences. Over the past 28 years, NANI increased significantly in Mainland China, from 2360 kg N km− 2 yr− 1 to 5013 kg N km− 2 yr− 1. On a geographical basis, NANI was higher in southeast where Chinaʹs eight major watersheds are located than in northwest, and the largest NANI, 26160 kg N km− 2 yr− 1, appeared in Shanghai. The administrative regions corresponding to Haihe watershed, Huaihe watershed and Tai lake watershed have the largest NANI. N input of fertilizer is the largest source of NANI, followed by atmospheric N deposition and N fixation. The primary factor in relation to the change in NANI is total population density, followed by cultivated land area and total grain yield. In those densely populated large cities and watersheds, reasonably allocating the social resources to reduce the existing population density is the most effective way to address the problem of high N inputs, while in those agriculture-dominated regions and watersheds, the most effective way for reducing NANI is to improve fertilizer utilization efficiency in agriculture.