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

Abstract

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 m3 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.