Bermudagrass Forage Yield and Ammonia Volatilization as Affected by Nitrogen Fertilization.

Nutrient management for hay production is changing due to poultry litter use restrictions, decreased NH₄NO₃ availability, and increasing fertilizer costs which demand evaluation of fertilization strategies that maintain soil productivity and minimize N losses. Our research objectives were to i) compare yields of common bermudagrass [Cynodon dactylon] receiving a range of N rates from four N sources and ii) measure potential NH₃-N losses. Experiments were conducted in 2006 and 2007 on a Captina silt loam. Pelleted poultry litter (PPL), NH₄NO₃, urea, and urea plus Agrotain (urease inhibitor) were applied at 0, 100, 200, 300, 400, and 500 kg N/ha/year in split applications.  Ammonia volatilization was measured using a semi-closed chamber method in which NH₃-N is trapped by sorbers that were changed 3, 6, 9, 12, and 15 d after fertilization. Bermudagrass receiving no N produced yields of 3,987 and 5,169 kg/ha in 2006 and 2007, respectively. For all N sources, forage yields increased at a common linear rate in 2006 and a common nonlinear rate in 2007. Within each year, N source, the intercept term, differed among N sources. In 2006, intercepts were similar among all inorganic N sources which were numerically or significantly greater than PPL. A similar trend occurred in 2007, with the exception that the intercept for NH₄NO₃ was greater than all other N sources.  The intercept for PPL was 78 to 89% of the intercept values for inorganic-N sources. Cumulative NH₃-N losses by 15 d averaged 14% of applied N for urea, declined to 3% for urea+Agrotain, and were <1% of N applied as NH₄NO₃ and PPL. Results indicate that urea produced similar to slightly lower forage yields as NH₄NO₃ and volatile losses of urea-N can be reduced by using Agrotain.