Soil Nitrate Accumulations following Nitrogen-Fertilized Corn in Pennsylvania

Nitrate (NO⁻₃-N) contamination of surface waters and groundwater in Pennsylvania has made it necessary to evaluate the impact of N fertilization practices for corn (Zea mays L.) on the accumulation of NO⁻₃-N in the soil. This study was initiated to (i) determine soil NO⁻₃-N accumulations following the harvest of corn fertilized at various N rates in Pennsylvania, (ii) estimate the soil nitrate accumulation at the economic optimum N rate under a range of conditions, and (iii) estimate changes in soil NO⁻₃-N over the winter. Soils in nine N response experiments in central and southeastern Pennsylvania and in a long-term N source experiment in central Pennsylvania were sampled in 30.5-cm increments to 122 cm following corn harvest in the fall of either 1986 or 1987. Five of these experiments were sampled again the following spring. All experiments were located on limestone-derived silt loams classified as either Duffield (fine-loamy, mixed, mesic Ultic Hapludalfs), Hagerstown (fine, mixed, mesic Typic Hapludalfs), or Murrill (fine-loamy, mixed, mesic Typic Hapludults) soils. Soil NO⁻₃-N accumulation to 120 cm in the N response experiments, averaged over N rates, ranged from 36 to 295 kg NO⁻₃-N ha⁻¹. Sites with a history of manure applications generally had greater NO⁻₃-N accumulation. At economic optimum N (EON) fertilizer rates, estimates of soil NO⁻₃-N accumulation to 120 cm ranged from 41 to 138 kg N ha⁻¹. Accumulations at the EON averaged 74 kg ha⁻¹ in nonmanured sites and 94 kg ha⁻¹ in responsive, manured sites. Soil NO⁻₃-N accumulation in two check treatments on manured sites where no yield response to N occurred averaged 169 kg NO⁻₃-N ha⁻¹. In the longterm experiment, soil NO⁻₃-N accumulation at the economic optimum N rate in the manured system was greater (135 kg N ha⁻¹) than in the nonmanured system (115 kg N ha⁻¹). Changes in soil NO⁻₃-N accumulations between fall and spring were variable, but often a substantial accumulation was still present in the spring. The results of this study indicate need for careful N management in manure-based systems, identification of nonresponsive and potentially polluting sites, and consideration of soil NO⁻₃-N accumulation in N fertilizer recommendations. Paper no. 8150 of the Journal Series of the Pennsylvania Agric. Exp. Stn.