NITRATE LEACHING FROM NITROGEN-FERTILIZED AND MANURED CORN MEASURED WITH ZERO-TENSION PAN LYSIMETERS

Excessive N fertilization increases the potential for nitrate (NO3-) l eaching, but no research has evaluated NO3- leaching from corn (Zea ma ys L.) receiving economic optimum N rates (EON). This study assessed ( i) how-weighted average concentration and mass of nitrate-N (NO3-N) le ached from nonmanured and manured corn treated with five fertilizer N levels and at EON, and (ii) the relationship between NO3-N mass in the 1.2-m soil profile following harvest and the flow-weighted average le achate concentrations. Following application of liquid dairy manure ea ch April, the field was chiseled and dished prior to planting. Ammoniu m nitrate was broadcast at planting (0-200 kg N ha(-1) in 50-kg increm ents and 0-100 kg N ha(-1) in 25-kg increments) in the nonmanured and manured corn. Eighteen (0.465 m(2)) pan lysimeters were placed 1.2 m b elow the soil surface in zero, intermediate, and high N treatments. Ze ro-N plots had 3-yr average flow-weighted leachate concentrations less than 10 mg NO3-N L(-1). At EON, the 3-yr averages were 18.8 and 19.3 mg NO3-N L(-1) for nonmanured and manured corn. Nitrogen rate influenc ed mass of NO3-N leached only when collection efficiency estimates wer e used to account for pan bypass how. In the nonmanured corn, the 3-yr average amount of NO3-N leached was 107 kg ha(-1) or 36% of the N app lied at EON. Total mass of NO3-N in the 1.2-m soil profile following h arvest was useful to predict annual flow-weighted average leachate NO3 -N concentrations, but this is not practical in most soils of the Nort heast.