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.