Submitted to: Association of American Geographers
Publication Type: Abstract Only
Publication Acceptance Date: March 29, 1998
Publication Date: N/A
Nitrate is one of the nutrients transported through the Mississippi River basin related to hypoxic conditions in the Gulf of Mexico. Agricultural practices in watersheds surrounding tributaries are major contributors to the nitrogen load. This poster defines the geographic distribution, by hydrologic unit, of major agricultural sources of nitrogen in the basin and dominant losses of nitrogen. Sources include imported nitrogen as inorganic fertilizer and manure, and sources generated in situ such as potentially mineralizable nitrogen from soil organic matter and nitrogen fixed by legume crops. Distributions are shown of the dominant nitrogen sinks that can be readily quantified including crop harvests, loss through plant senescence, manure volatilization, and atmospheric losses from fertilizer. National data bases used in the analysis include the State Soils Geographic Database, 1992 Census of Agriculture, and the National Atmospheric Deposition Program/National Trends Network. Animal manure and mineralizable nitrogen in the organic rich soils in the upper Mississippi River basin constitute the major source of nitrogen remaining after fertilizer additions and nitrogen losses during crop harvest. Nitrogen inputs from inorganic fertilizers are less than losses to crop harvest and plant senescence in most hydrologic units, and the difference is greatest in the Midwest cornbelt where crop productivity is largest. The balance between all sources and losses shows the greatest excess nitrogen in areas with large concentrations of soil organic matter, and parts of the Tennessee and Red/Arkansas hydrologic regions.