Streaming Urea Ammonium Nitrate with or without Enhanced Efficiency Products Impacted Corn Yields, Ammonia, and Nitrous Oxide Emissions

Surface streaming urea ammonium nitrate (UAN) into corn (Zea mays L.) at side-dress (v4-v6) or later in the season (v12-v14) is an emerging N fertilizer application method as it is rapid, reduces soil disturbance, and allows for flexible application times. In 2013 and 2014, side-dress N application (130 kg N ha(-1)) using three streaming UAN sources was evaluated for their ability to maintain grain yield, reduce ammonia (NH3) volatilization, and mitigate nitrous oxide (N2O) emissions. The products included streaming of urea ammonium nitrate (StrUAN), urea ammonium nitrate with a urease inhibitor (StrUAN-UI), urea ammonium nitrate with urease inhibitor plus nitrification inhibitor (StrUAN-UI+NI), and a control (no N). The efficacy of streaming relative to traditional shallow-injected urea ammonium nitrate (InjUAN) was also assessed. Delayed NH3 sampling related to wind-tunnel installation in 2013 and 2014 led to additional NH3 measurements in 2015 and 2016. Average yields from StrUAN were 11% lower relative to InjUAN. The use of inhibitors did not improve yields relative to StrUAN. Ammonia volatilization was not significantly different between StrUAN and InjUAN losing 14 and 20% of applied N (2-yr average), respectively. However in 2015 and 2016, NH3 volatilization from StrUAN was 3.6-fold greater than InjUAN when measurements were started immediately after application. Hence lower yields in 2013 and 2014 from StrUAN likely reflect N loss to rapid volatilization during or shortly after application. The StrUAN-UI treatment increased 2-yr average N2O emissions by 17.3 to 18.7% relative to StrUAN or StrUAN-UI+NI. For humid-temperate clay loam soil, UAN streaming with/without inhibitors was not effective for maintaining yields or reducing NH3 volatilization.