Surface Streaming UAN at Side-Dress Is Ineffective at Improving Corn Grain Yields with/without Urease and Nitrification Inhibitors and Can Increase Ammonia Volatilization Losses As Compared to Injected UAN.

Improvement of nitrogen (N) use efficiency in field crops is connected to mitigating fertilizer N losses by appropriate fertilizer placement, as well as through the use of nitrification (NI) and urease inhibitors (UI). In 2013 and 2014, an N placement and inhibitor field study was established for grain corn on a clay loam soil in Southwestern Ontario. Placement treatments compared nozzle spraying streams of UAN between corn rows and shallow knife injected UAN at the V6-V8 stage. In addition, the effectiveness of using UI and UI+NI inhibitors in the surface streaming treatment was evaluated. Ammonia volatilization was measured for 28 d after N application using wind-tunnels. Delayed ammonia sampling related to wind tunnel installation in 2013 and 2014, led to additional measurements in 2015 and 2016 where volatilization was measured immediately after application. In both 2013 and 2014, the injected UAN treatment had significantly greater (12%) corn grain yields than the streaming treatment (12 vs ~10.7 t ha^-1). The use of UI and UI+NI did not improve grain yields as compared to UAN alone in the streaming treatments. Ammonia volatilization of streaming UAN was not significantly different from the injected treatments, with average losses of 18 kg N ha^-1 and 26 kg N ha^-1, respectively. In 2015 and 2016, the streaming of UAN exhibited 3.6 fold larger losses than the injected UAN at 11.5 kg N ha^-1 and 2.5 kg N ha^-1, respectively. Suggesting that the poorer yields measured in 2013 and 2014 were likely due to significant ammonia volatilization loss occurring immediately after application. In this region, streaming UAN appears to be an ineffective placement method for improving corn yields and mitigating ammonia volatilization losses.