ANALYSIS OF NITROGEN MANAGEMENT STRATEGIES USING EPIC

This paper illustrates a method of using a hydrologic/water quality mo del to analyze alternative management practices and recommend best man agement practices (BMPs) to reduce nitrate-nitrogen (NO3--N) leaching losses. The study area for this research is Tipton, an agriculturally intensive area in southwest Oklahoma. We used Erosion Productivity Imp act Calculator (EPIC), a field-scale hydrologic/water quality model, t o analyze alternative agricultural management practices. The model was first validated using observed data from a cotton demonstration exper iment conducted in the Tipton area. Following that, EPIC was used to s imulate fertilizer response curves for cotton and wheat crops under ir rigated and dryland conditions. From the fertilizer response functions (N-uptake and N-leaching), we established an optimum fertilizer appli cation rate for each crop. Individual crop performances were then simu lated at optimum fertilizer application rates and crop rotations for t he Tipton area, which were selected based on three criteria: (a) minim um amount of NO3--N leached, (b) minimum concentration of NO3--N leach ed, and (c) maximum utilization of NO3--N. Further we illustrate that by considering residual N from alfalfa as a credit to the following cr op and crediting NO3--N present in the irrigation water, it is possibl e to reduce further NO3--N loss without affecting crop yield.