The Effect of Enhanced Efficiency Nitrogen Fertilizer Products On the Nitrate Concentrations of Bermudagrass Hay.

Enhanced-efficiency nitrogen fertilizer formulations may reduce potential environmental losses, but their affect on nitrate concentrations in bermudagrass hay has not been evaluated. The objectives of this research were to compare the yields of bermudagrass hay of Agrotain^® (ATU), Environmentally Smart Nitrogen^® (ESN), or Nutrisphere-N™ (NSN) treated urea to conventional applications of urea and ammonium nitrate (AN).  Plots (2.1 x 3.7 m) were delineated within a previously established stand of bermudagrass (cv. ‘Russell’) at UGA Agricultural Experiment Station facilities near Calhoun and Eatonton, GA. Soil types were a silt loam and loam, respectively. The experiment was a randomized complete block design with four replicates and was conducted in 2007 – 2009. The treatment combinations included one rate of 336 kg actual N ha^-1 yr^-1 of ATU, ESN, NSN, or urea applied once or split among two applications during the season; urea or AN split equally across regrowth periods; and a 0 N control. ATU was not included in 2007. Herbage samples from each harvest were analyzed for nitrate (NO₃-N) concentration by the University of Georgia Feed and Environmental Water Lab (colorimetric analysis of nitration of salicylic acid). Rainfall during the growing season (Mar-Sept) was severely drought stressed in 2007 and 2008 (2008 and 2009 data will be presented at the conference). In 2007, potentially toxic NO₃-N concentrations (2500 ppm or more) were observed in the second and third harvests at Calhoun and the third harvest in Eatonton. Applications of ESN resulted in NO₃-N levels of 4400 and 4570 ppm in the second and third harvests (respectively) at Calhoun in 2007, and applications of NSN resulted in NO₃-N levels of 3860 and 3020 ppm in the third harvest at Calhoun and Eatonton (respectively) in 2007. Splitting unadulterated urea into just two applications of 168 kg actual N ha^-1 resulted in high NO₃-N levels (3800 ppm) only in the third harvest at Calhoun in 2007. In 2007, all other treatments resulted in NO₃-N levels that would be considered safe for use as the sole feedstuff in ruminant rations. We conclude that the slow-release of N from enhanced-efficiency fertilizers may not prevent the accumulation of high nitrate levels in bermudagrass under drought-stress.