Effects of atmospheric inorganic nitrogen deposition on cropland ecosystems and implications for fertilizer application in China.

Excessive fertilizer use is widely recognized as a primary driver of nitrogen pollution in China's croplands, while the critical role of atmospheric inorganic nitrogen deposition (AIND) as an underutilized nutrient source remains underexplored. Current agricultural management strategies largely neglect AIND's dual identities-both as a contributor to environmental degradation and as a potential substitute for synthetic fertilizers. Our study addresses this gap by quantifying the spatial distribution of AIND in croplands and evaluating its untapped potential for reducing fertilizer dependence. From 2017 to 2019, the average AIND on croplands was estimated at 33.83 ± 13.06 kg N ha-1 year-1, ranging from 3.54 to 77.90 kg N ha-1 year-1. When AIND was considered an additional nitrogen input to cropland ecosystems for major staple crops, 30.58% of the total sown area experienced increases in grain yield due to AIND, while the remaining area showed no beneficial effect on grain yield. To fully utilize AIND for crop growth in areas where it provided no direct yield benefit, nitrogen fertilizer application could be reduced by 22.52 ± 15.87 kg N ha-1 year-1 on average across the seven representative cropping systems, without affecting current grain yields. Nationally, this reduction represents 5.59%-12.23% of current nitrogen fertilizer application. These findings underscore the potential of AIND as an environmental nutrient resource and support the development of targeted environmental policies.