Comparison of Enhanced-Efficiency Nitrogen Fertilizers for Reducing Ammonia Loss and Improving Bermudagrass Forage Production

The efficacy of enhanced-efficiency (EE) nitrogen (N) fertilizer formulations in reducing N loss and improving the efficiency of urea-based fertilizer products in forage production is unclear. This study compared ammonium nitrate (AN), urea, four EE urea N formulations [N-(n-butyl) thiophosphoric triamide (NBPT)-treated urea, NBPT and dicyanamide-treated urea, a polymer-coated urea (PCU), and a maleic-itaconic copolymer-treated urea (MICPU)], urea-ammonium nitrate (UAN), and two EE UAN formulations (NBPT-treated UAN, NBPT and dicyanamide-treated UAN) in forage bermudagrass [Cynodon dactylon (L.) Pers.] production. The experimental design was a randomized complete block design with four replications in each of two sites and 2 yr (2008-2009). Treatment applications were made at the rate of 168 kg N ha(-1) spring dormancy-break (ca. 30 April) and after the second harvest (ca. 25 July; total of 336 kg N ha(-1) season). Response variables included trapped ammonia (NH(3)) and forage yield, production efficiency, N concentration, N uptake, recovery of applied N, and nitrate concentration. Urea treated with NBPT reduced NH(3) volatilization and, in some situations, increased agronomic response relative to urea. Addition of NBPT produced results similar to AN and UAN, and it was never detrimental relative to untreated urea. The MICPU treatment was ineffectual relative to urea alone. The PCU reduced NH(3) volatilization and improved N concentration in the forage but did not improve other agronomic characteristics. Use of UAN solutions produced results that were generally intermediate in response between urea and ammonium nitrate and were not improved by NBPT addition. Adding NBPT can reduce NH(3) volatilization and increase the efficiency of urea, but further research is necessary to understand the limits of this additive.