Bermudagrass Response to High Nitrogen Rates, Source, and Season of Application

High N rates and source of N have been thoroughly evaluated in bermudagrass [Cynodon dactylon (L.) Pers.] forage production, but less is known concerning season of application and estimated fertilizer N recovery in these systems. Two field studies (Ardmore, OK: Wilson silt loam, Vertic Haplustalfs; Burneyville, OK: Minco fine sandy loam, Udic Haplustolls) were conducted at two locations over two years to evaluate the effects of rate, timing, and source of N on bermudagrass forage yield, total N, NO3 concentration, and estimated fertilizer N recovery. Nitrogen was applied at rates of 112, 224, 448, 672, and 1344 kg N ha−1 as NH4NO3 or urea in early spring (March) and late summer (August). Fertilizer N recovery can be maximized at rates of 112 and 224 kg N ha−1 applied in the early spring and late summer, respectively. Even when N rates of 1344 kg N ha−1 were applied annually, bermudagrass forage NO3‐N was seldom above 2000 mg kg−1, which is below published toxic levels (2400–4500 mg kg−1) for cattle (Bos taurus) consumption. Early‐spring applied N increased yields, N removal, and fertilizer recovery compared with late‐summer applied N. Fertilizer N recovery was higher for NH4NO3 than for urea, especially when applied in late summer. Late‐summer applications of urea should be avoided, due to increased NH3 volatilization losses. Nitrogen applied at 112 kg N ha−1 in early spring can result in fertilizer recoveries in excess of 85%. These high recoveries in forage production systems are possibly a result of continuous preanthesis forage harvesting when gaseous plant N losses are small, but which increase following anthesis.