Bermudagrass forage yield and ammonia volatilization as affected by nitrogen fertilization

Bermudagrass [Cynodon dactylon (L. Pers.)] managed for hay production requires significant amounts of N fertilizer to meet forage yield goals. Concerns over phosphorus (P) runoff and soil accumulation from repeated poultry litter application, the decreasing availability of NH ₄NO₃, and the increasing cost of inorganic fertilizers are changing nutrient management practices for forage production. Research objectives were to (i) compare yields and nutrient uptake of common bermudagrass receiving a range of N rates from four N sources, (ii) measure potential ammonia (NH ₃)-N losses from four fertilizer-N sources, (iii) determine the NH ₄NO₃-N equivalence of fresh (FPL) and pelleted poultry litter (PPL), and (iv) evaluate the effect of urea-N rate on bermudagrass yield and uptake of selected nutrients. Experiments conducted from 2006 to 2008 on a Captina silt loam evaluated urea, and urea+NBPT [urease inhibitor, N-(n-butyl) thiophosphoric triamide], PPL, and NH₄NO₃ applied at 0, 100, 200, 300, 400, and 500 kg N ha−1 year −1. Ammonia volatilization from each N source was measured 3, 6, 9, 12, and 15 d after each fertilization event using a closed-chamber method to trap NH₃. Urea can be a suitable inorganic-N fertilizer alternative to NH₄NO₃. Forage yields fertilized with urea were not benefited by the addition of a urease inhibitor, but potential NH₃ volatilization losses from urea were decreased by NBPT. The NH₄NO ₃-N equivalence factors for FPL and PPL tended to increase across time with annual application, and ranged from 0.59 to 0.74 for FPL and 0.59 to 0.81 for PPL. Recovery of the total urea-N applied ranged from 38 to 70% depending on harvest and year, and season total P and K were maximized with 436 and 400 kg urea-N ha−1 yr−1. Bermudagrass receiving 300 kg N ha−1 yr−1 removed 24.5 kg N, 3 kg P, and 20 kg K Mg−1 of harvested forage.