Fertilizer Source Influenced Nitrous Oxide Emissions from a Clay Soil under Corn

Synthetic N fertilizers are a major source of N2O emissions from soil. A field experiment was conducted during three growing seasons (2004-2006) on a clay soil (fine, mixed, frigid Typic Humaquept) under corn (Zea mays L.) to evaluate the impact of N fertilizer source and application rate on N2O emissions. Treatments consisted of three sources of N fertilizer (urea-NH4NO3 32% [UAN], Ca-NH4NO3 [CAN], and aqua NH3 [AA]) at four different 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 N2O emissions were measured weekly. For all 3 yr of this study, cumulative N2O 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 N2O-N kg(-1) N), with values of 0.038, 0.033, and 0.027 kg N2O-N kg(-1) N for UAN, CAN, and AA, respectively. The N2O emissions increased linearly with N rate, even at rates exceeding the optimum level for grain yield. Peaks of N2O flux occurred on the days following fertilizer application and in early fall when the soil was re-wetted. Emissions of N2O 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 confirm that N fertilizer source and application rate can impact N2O emissions but these effects are modulated by soil environmental conditions.