Fertilizer source influenced nitrous oxide emissions from a clay soil under corn

Synthetic N fertilizers are a major source of N 2O emissions from soil. A field experiment was conducted during three growing seasons (2004-2006) on a clay soil (fi ne, mixed, frigid Typic Humaquept) under corn (Zea mays L.) to evaluate the impact of N fertilizer source and application rate on N 2O emissions. Treatments consisted of three sources of N fertilizer (urea-NH 4NO 3 32% [UAN], Ca-NH 4NO 3 [CAN], and aqua NH 3 [AA]) at four diff erent rates (0, 100, 150, and 200 kg N ha -1). Fertilizers were banded 5 cm below the soil surface between corn rows at the six-leaf stage and N 2O emissions were measured weekly. For all 3 yr of this study, cumulative N 2O emission decreased in the order UAN ≥ CAN ≥ AA. Averaged across years, fertilizer-induced post-sidedress emissions were greater than the Intergovernmental Panel on Climate Change default factor (0.01 kg N 2O-N kg -1 N), with values of 0.038, 0.033, and 0.027 kg N 2O-N kg -1 N for UAN, CAN, and AA, respectively. The N 2O emissions increased linearly with N rate, even at rates exceeding the optimum level for grain yield. Peaks of N 2O fl ux occurred on the days following fertilizer application and in early fall when the soil was re-wetted. Emissions of N 2O were higher at water-filled pore space >0.57 m 3 m -3 and were also related to soil inorganic N and water-extractable organic C contents. Our results confi rm that N fertilizer source and application rate can impact N 2O emissions but these effects are modulated by soil environmental conditions.