Influence of urea fertilizer placement on nitrous oxide production from a silt loam soil
Received for publication April 8, 2009. Urea placement in band or nests has been shown to enhance N use efficiency, but limited work has been done to assess its affect on N2O emissions. This study compared N2O emissions from urea prills applied to an Amsterdam silt loam (fine-silty, mixed, superactive, frigid Typic Haplustolls) using broadcast, band, and nest placements. Experiments were conducted in greenhouse pots (200 kg N ha–1) and in canola (Brassica rapa L.) seeded fields using rates of 100 kg N ha–1 (recommended) and 200 kg N ha–1. Urea placement affected N2O emission patterns and cumulative N2O losses in the greenhouse and field. Urea prills placed in nests, and sometimes bands delayed N2O production with peak flux activity occurring later, and elevated emission activity being more prolonged than for broadcast applications. Differences were more obvious at 200 kg N ha–1. These effects were attributed to a delay in urea hydrolysis and inhibition of nitrification. The fraction of applied urea-N lost as N2O for broadcast, band, and nest placements applied at the recommended rate averaged 2.0, 2.7, and 5.8 g N kg–1 N, respectively. The fraction of applied urea-N lost as N2O averaged 2.9, 10.4, and 9.2 g N kg–1 N for broadcast, band, and nest placements when urea-N rate was increased from 100 to 200 kg N ha–1, respectively. Greater N2O production with nest placement may in part be due to significant soil NO2–N accumulations. Potential benefits to crop fertilizer use efficiency that come with placement of urea in concentrated zones may lead to enhanced N2O production.