Evaluation of Ammonia Volatilization from Stabilized Urea Sources Via Continuous Measurement.

Urea is the predominant form of nitrogen fertilizer used worldwide due to its relatively high nitrogen content and low cost.  Once in contact with moist soil, surface applied urea is hydrolyzed to ammonium (NH₄⁺) via the activity of soil urease and subject to volatile loss. Considerable ammonia volatilization could occur following urea surface application, resulting in reduced fertlizer nitrogen use efficiency by crop plants as well as increased potential environmental concerns. To address this issue, various physical and chemical mechanisms have been incorporated into granular urea. The use of polymer coatings to slow the release of urea is one way to curtail the acute loss of nitrogen due to volatilization, and incorporation of urease inhibitor such as N-(n-butyl)thiophosphoric triamide (NBPT) is another strategy proven effective. In this study, ammonia volatilization was determined for plain urea and several stabilized urea sources in a customized environment chamber experiment system utilizing an optical method. With day/night soil surface temperature controlled at 11/21⁰C, plain urea and three urease inhibitor incorporated urea sources were surface applied to soil columns with and without the presence of surface residue. After fertilization, ammonia emission from soil surface was continuous measured for a period of 10d. The temporal patterns of ammonia emission following fertilization and the cumulative loss from these urea sources were examined. These information presented detailed emission profiles and allowed evaluation of the relative effectiveness of these stabilized urea sources to suppress ammonia volatilization following surface applicaiton.