OPTIMIZING NITROGEN AND IRRIGATION INPUTS FOR CORN-BASED ON NITRATE LEACHING AND YIELD ON A COARSE-TEXTURED SOIL

A study was conducted on a Verndale sandy loam soil (coarse loamy over sandy, mixed, frigid Udic Argiboroll) during 1991 and 1992 at Staples , MN, to assess the influence of irrigation scheduling and N source an d rate on corn (Zea mays L.) yield and nitrate leaching. Nitrogen sour ces were urea and turkey manure. Soils were irrigated to field capacit y (i) at a fixed trigger deficit throughout the season, or (ii) at a v ariable trigger deficit based on crop growth stage. Leaching losses we re calculated from measured daily fluxes of water percolation and soil water NO3-N concentrations and from a seasonal N mass balance. Based on yield response curves, maximum corn grain yields were obtained at 2 02 and 234 kg N ha(-1) urea in 1991 and 1992, respectively. This resul ted In growing season leaching losses of 72 and 55 kg N ha(-1) in 1991 and 1992, respectively. The Fate at 95% of the maximum crop yield is suggested to substantially reduce nitrate leaching past the root zone. Using this guideline, nitrate leaching would be reduced by 35% compar ed with nitrate leaching at the maximum yield. When a variable availab le water deficit was used to schedule irrigation compared with a fixed deficit schedule (at 95% of maximum yield N rate), nitrate leaching w as reduced 46%. At equivalent N rates, turkey manure produced equal or greater crop yields as that from urea applications; however, nitrate leaching was equal to or less than urea.