Effects of Field Methods and Soil Cover on Estimating Ammonia Loss from Nitrogen-15-Urea
- C. M. Reynolds and
- D. C. Wolf
Ammonia loss from urea fertilizers is difficult to measure accurately in the field. In a field study we compared two methods for measuring NH3 loss from 15N-urea surface applied to bare and bermudagrass (Cynodon dactylon L.) covered Captina silt loam (fine-silty, mixed, mesic, Typic Fragiudult). The two methods were semiopen chambers and open microplots using 15N recovery. Labeled urea was applied at 100 kg N ha−1, and chambers and microplots were shaded and protected from rainfall. Estimates of NH3 losses from the bare soil after 357 h were 24.6 and 48.0% of the applied N from the semi-open chambers and open microplots, respectively. Estimates of NH3 losses from the bermudagrass after 357 h were 34.5 and 42.7% of the applied N for the semi-open chambers and open microplots, respectively. In the bermudagrass microplots, 78.6% of the applied 15N either remained in the plant-thatch layer above the soil or was volatilized 18 h after urea application. Transport and transformations in the soil had little influence on NH3 loss from bermudagrass plots. These data indicated that measured NH3 loss from bare soil in semi-open chambers was significantly less than NH3 loss in open microplots using 15N recovery techniques. Cumulative NH3 losses from urea retained on bermudagrass and thatch above the soil were similar in the semi-open chambers and open microplots.
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