Submitted to: International Conference on Diffuse Pollution
Publication Type: Abstract Only
Publication Acceptance Date: 10/28/2004
Publication Date: 10/28/2004
Citation: Burkart, M.R., James, D.E., Liebman, M., Vanouwerkerk, E. 2004. Integrating principles of nitrogen dynamics in a method to estimate leachable nitrogen under agricultural systems[abstract]. Proceedings of the 8th International Conference on Diffuse Pollution. 1:175
Technical Abstract: Excess nitrogen in ground and surface water are of concern to land users and downstream water users in intensive agricultural regions such as the Midwest United States. Excess nitrogen is available for leaching during lengthy periods without crop cover in annual crop systems used in many temperate regions. The periods without crop cover frequently coincide with periods of precipitation and snow melt resulting in substantial infiltration and ground-water recharge potential. The purpose of this paper is to present a method for estimating the amount of excess nitrogen potentially available for leaching to ground water beneath agricultural systems. The method was developed to utilize georeferenced data on soils, crops, and livestock so that the results can be applied to watersheds covering a wide range of areas. The method links stocks of nitrogen within the agricultural system including soil, crops, and livestock and external stocks representing fertilizer and atmospheric sources. External stocks include fertilizer application and atmospheric flows to and from soil, crops, and livestock. Atmospheric exchanges include volatilization from soil, manure, and senescing crops, direct atmospheric deposition, denitrification, and symbiotic fixation. Nitrogen flow is centered on exchange between the soil inorganic and organic nitrogen stock. Differential nitrogen mineralization and immobilization rates are defined for three soil organic matter pools, and two pools of crop residue and manure based on carbon:nitrogen ratios in each pool. These rates are adjusted to account for soil temperatures and moisture conditions. Inorganic nitrogen flowing through the soil stocks cycles through crops and ultimately livestock. Nitrogen exports from the system are accounted for by harvesting crops and animals in addition to losses to the atmosphere. The method is applied to small watersheds in an intensively cropped part of the Midwest to demonstrate its utility.