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Effects of Field Methods and Soil Cover on Estimating Ammonia Loss from Nitrogen-15-Urea

Dep. of Soil Science, North Carolina State Univ., Raleigh, NC 27695-7619

D. C. Wolf

Dep. of Agronomy, Univ. of Arkansas, Fayetteville, AR 72701

*Corresponding author.

ABSTRACT

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.

Research leading to this report was approved by the Director of the Arkansas Agric. Exp. Stn. Contribution from the Dep. of Agronomy, Univ. of Arkansas.