Fertilizer Source and Tillage Effects on Yield‐Scaled Nitrous Oxide Emissions in a Corn Cropping System

Management practices such as fertilizer or tillage regime may affect nitrous oxide (N2O) emissions and crop yields, each of which is commonly expressed with respect to area (e.g., kg N ha−1 or Mg grain ha−1). Expressing N2O emissions per unit of yield can account for both of these management impacts and might provide a useful metric for greenhouse gas inventories by relating N2O emissions to grain production rates. The objective of this study was to examine the effects of long‐term (>17 yr) tillage treatments and N fertilizer source on area‐ and yield‐scaled N2O emissions, soil N intensity, and nitrogen use efficiency for rainfed corn (Zea mays L.) in Minnesota over three growing seasons. Two different controlled‐release fertilizers (CRFs) and conventional urea (CU) were surface‐applied at 146 kg N ha−1 several weeks after planting to conventional tillage (CT) and no‐till (NT) treatments. Yield‐scaled emissions across all treatments represented 0.4 to 1.1% of the N harvested in the grain. Both CRFs reduced soil nitrate intensity, but not N2O emissions, compared with CU. One CRF, consisting of nitrification and urease inhibitors added to urea, decreased N2O emissions compared with a polymer‐coated urea (PCU). The PCU tended to have lower yields during the drier years of the study, which increased its yield‐scaled N2O emissions. The overall effectiveness of CRFs compared with CU in this study may have been reduced because they were applied several weeks after corn was planted. Across all N treatments, area‐scaled N2O emissions were not significantly affected by tillage. However, when expressed per unit yield of grain, grain N, or total aboveground N, N2O emissions with NT were 52, 66, and 69% greater, respectively, compared with CT. Thus, in this cropping system and climate regime, production of an equivalent amount of grain using NT would generate substantially more N2O compared with CT.