Estimating ammonia volatilization losses from urea fertilizers using a simplified micrometeorological sampler

The large amount of unincorporated, urea-containing fertilizer that is used on no-till corn (Zea mays L.) makes it imperative that we know the magnitude of NH3 volatilization loss from these fertilizers. Although there have been numerous studies to estimate these losses, in almost none of them were the losses measured under undisturbed field conditions. A simplified, micrometeorological method with NH3 samplers placed at the center of three replicates of 25-m-radius circular plots was used to estimate NH3 volatilization losses from 134 kg N ha(-1) of surface-applied, unincorporated urea, sprayed urea-ammonium nitrate (UAN) solution, and dribbled UAN. The average NH3 volatilization losses during the first 10 to 20 d after application for a 3-yr period were 40, 22, and 17 kg N ha(-1) from urea, sprayed UAN, and dribbled UAN, respectively. The losses from sprayed and dribbled UAN were not significantly different from each other and were, on average, significantly less than from urea. The rainfall in the first 6 d after application was <5 mm for all 3 yr of the experiment. Corn yields and N uptake generally reflected the measured NH3 volatilization losses, but were considered to be much less precise indicators of NH3 volatilization loss. One drawback of the simplified micrometeorological method is that large areas are needed to accommodate the 50-m-diam. plots and 100-m buffers between plots.