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NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Ammonia Volatilization from Urea-Based Fertilizers Applied to Tall Fescue Pastures in Georgia, USA

^a 3111 Plant Sciences Building, Crop and Soil Sciences Dep., Univ. of Georgia, Athens, GA 30602
^b Agricultural and Environmental Services Labs., Univ. of Georgia, Athens, GA 30602
^c Central Research and Education Center, Univ. of Georgia, 1508 Godfrey Rd. NW, Eatonton, GA 31024

^* Corresponding author (mcabrera{at}uga.edu).

The use of urea fertilizers in grasslands is likely to increase in areas with concentrated animal feeding operations as restrictions on manure applications are implemented. Concerns have been raised about the economic and environmental impacts of NH₃ loss from these urea fertilizers. This study evaluated NH₃ losses from Nitamin (a urea polymer), urea–NH₄NO₃ (UAN), and granular urea applied to tall fescue (Festuca arundinacea Schreb.) plots at 50 kg N ha^–1 in fall and spring for 2 yr. Fertilizers were applied to circular plots (30-m diameter) and NH₃ loss was measured by the modified passive flux method for 69 to 120 d after application. In a separate laboratory study, Nitamin, UAN, and urea were surfaced applied to fescue thatch at 100 kg N ha^–1 and treatments were incubated at 24°C and 90% relative humidity for 31 d. In fall applications, urea lost more NH₃ (19% in 2004, 46% in 2005) than UAN or Nitamin, which were not different from each other (6% in 2004, 34% in 2005). In contrast, there were no differences among fertilizers in spring applications, with average losses of 13% in 2005 and 17% in 2006. In the laboratory study, urea lost significantly more NH₃ (24%) than UAN or Nitamin, which were not different from each other (average 9% loss). These results indicate that Nitamin and UAN undergo similar NH₃ losses, and that both fertilizers may lose less NH₃ than urea under conditions favorable to volatilization.

Abbreviations: CRH, critical relative humidity • RH, relative humidity • UAN, urea–ammonium nitrate