Nitrogen Partial Balance, Use Efficiency by Corn, and Flux From the Mississippi River Basin to the Gulf of Mexico: An Update.

Previous work by scientists at the University of Illinois has documented the net anthropogenic nitrogen balance and relationship to the flux of nitrate-nitrogen to the Gulf of Mexico from 1997 to 2006, which was estimated by the U.S. Geological Survey. These reports did not address changes in nitrogen balance or their relation to changes in nitrogen flux across a range of years. This paper will relate partial nitrogen balances, corn partial factor productivity for nitrogen (PFP_N), and flux of nitrogen to the Gulf of Mexico using data for the USDA Agricultural Census years, 1987 to 2007. Partial nitrogen balances will be estimated using the Nutrient Use Geographic Information System (NuGIS), which has been developed for the U.S. at the county, state, and 8-digit hydrologic unit level by the International Plant Nutrition Institute.  Recent nitrogen flux trends reported by the U.S. Geological Survey for major river sub-basins will also be discussed in relation to these balances.