Ammonia Volatilization from Surface Applications of Urea in the Field and Laboratory

Few attempts have been made to directly measure ammonia losses from surface applications of urea under field conditions. The objective of this research was to measure NH 3 volatilized from urea in the field and to compare these losses to (i) losses measured in the laboratory, and (ii) losses estimated by crop response in the field. Direct field measurements were made using an automated apparatus designed to collect NH 3 lost without significantly altering environmental conditions on the treated area. Laboratory measurements were made using an apparatus similar to systems described previously by other workers. Ammonia losses were estimated from crop response in the field by measuring N uptake by Coastal bermudagrass ( Cynodon dactylon L.). Losses of NH 3 in the field measured directly were small (0 to 9% of the applied N) compared to those obtained in the laboratory (13 to 31% of the applied N) and those estimated in the first year of the N uptake study (0 to 39% of the applied N). However, in the second year of the field plot study, N uptake by forage from several urea fertilizer treatments was greater than from Ca(NO 3 ) 2 . When the results were combined for both years, N uptake by forage was similar from Ca(NO 3 ) 2 and urea treatments. Considering the small ammonia losses measured directly in the field, differences in crop response between urea and Ca(NO 3 ) 2 may have been due to some factor other than NH 3 volatilization. Results indicate that losses of N by NH 3 volatilization under field conditions may not be as severe as previously thought, at least under the soil and environmental conditions of this study. Results also demonstrate the importance of directly measuring NH 3 losses in the field.