Nitrogen Losses From Application of Side-Dress UAN: Near-Continuous NH3 and N2O Emissions.

The environmental consequences of applying urea-ammonium nitrate (UAN) fertilizer on maize fields include volatile loss of N as NH3 and N2O after application. The additional application of nitrification inhibitors is believed to reduce N2O losses.� Continuous measurements of gaseous concentration, turbulence, and ancillary weather and crop variables were made to determine NH3 and N2O emissions over 20 d starting 3d after UAN 28 and UAN 28 with Instinct(TM) side-dress applications of 180 lbs N/ac on separate portions of the same field in June 2012.� Gas concentrations were derived from open-path Fourier Transform Infrared Spectrometer measurements continuously scanned along five paths across the two treatments. �Emissions were calculated assuming three distinct sources: the UAN only treatment area, the UAN+Instinct nitrification inhibitor (UAN+I) treatment area, ��and the grass strip along a drainage swale between the treatments.� Emissions were calculated at � h intervals using a backward Lagrangian Stochastic model.� During the 3 to 10 d period after application, the maximum N2O emissions were 30 mg N2O m^-2s^-1 and 5 mg NH3 m^-2s^-1� for the UAN treatment� and 4 mg N2O m^-2s^-1 �and 4 mg NH3 m^-2s^-1 for the UAN+I treatment.� Emissions were nonlinearly correlated with wind speed and high rates in general did not last for many hours during a day.� Maximum daily NH3 emissions declined through the week suggesting the volatilization of the gas continued a full seven days after the UAN application.� The proportion of N2O to NH3 emissions was higher for the UAN treatment than the UAN+I treatment. The N volatilization loss as N2O was generally greater than that as NH3 for the UAN treatment and similar in magnitude for the UAN+I treatment.� On the third day after treatment, 53% of the N loss from the UAN treatment and 18% of the N loss from the UAN+I treatment was a result of N2O emission.