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

Synthetic N fertilizers are a major source of N 2 O 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 N 2 O emissions. Treatments consisted of three sources of N fertilizer (urea–NH 4 NO 3 32% UAN, Ca–NH 4 NO 3 CAN, and aqua NH 3 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 N 2 O emissions were measured weekly. For all 3 yr of this study, cumulative N 2 O 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 2 O‐N kg −1 N), with values of 0.038, 0.033, and 0.027 kg N 2 O‐N kg −1 N for UAN, CAN, and AA, respectively. The N 2 O emissions increased linearly with N rate, even at rates exceeding the optimum level for grain yield. Peaks of N 2 O flux occurred on the days following fertilizer application and in early fall when the soil was re‐wetted. Emissions of N 2 O 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 N 2 O emissions but these effects are modulated by soil environmental conditions.