Regional variation of net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI) across the continental US: 1987-2022

Net Anthropogenic Nitrogen (N) and Phosphorus (P) inputs (NANI/NAPI) are estimated from available county-level US census and USDA ag census data and other sources.  The recent update of the USDA ag census data to 2022, along with newer US census data and N deposition estimates, has allowed new estimates of corresponding NANI and NAPI values, comprising up to four terms: mineral fertilizer inputs, net food/feed inputs to a region (calculated as the balance between local crop production and livestock and human food demand) and, for NANI, atmospheric N deposition and crop N fixation. Strong regional variations can be seen, depending on the balance of crop production, livestock production, and human population density, with implications for the N&P loads of riverine and coastal waters. Both NANI and NAPI are dominated by fertilizer inputs in some of the large agricultural regions of the country, but livestock nutrient demands and corresponding manure availability also can have regional impacts. Crop N fixation is a major component of NANI in agricultural areas with no corresponding term in NAPI. NANI and NAPI in urban centers are strongly driven by net food inputs with implications for local sewage loads to urban streams; in contrast, crop-dominated agricultural regions export crop nutrients to other regions.   Changes over 35 years are evident, including the increasing dominance of heavily-fertilized energy crops and regional shifts in livestock production.  Regional variation in NANI:NAPI and riverine N:P has implications for managing the Nation’s rivers and coastal waters.

Primary Presenter: Dennis Swaney, Cornell University (dps1@cornell.edu)

Authors:

Dennis Swaney, Cornell University  (dps1@cornell.edu)

Robert Howarth, Cornell University  (howarth@cornell.edu)