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 concern ing season of application and estimated fertilizer N recovery in these syst ems. Two field studies (Ardmore, OK: Wilson silt loam, Vertic Haplustalfs; Burneyville, OK: Minco fine sandy loam, Udic Haplustolls) Here conducted at two locations over two Sears to evaluate the effects of rate, timing, and source of N on bermudagrass forage yield, total N, NO3 concentration, and e stimated fertilizer N recovery. Nitrogen was applied at rates of 112, 224, 448, 672, and 1314 kg N ha(-1) as NH4NO3 or urea in early spring (March) an d 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, respec tively. Even when N rates of 1344 kg N ha(-1) were applied annually, bermud agrass forage NO3-N was seldom above 2000 mg kg(-1), which is below publish ed 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 a pplications of urea should be avoided, due to increased NH, volatilization losses. Nitrogen applied at 112 kg N ha(-1) in early spring can result in F ertilizer recoveries in excess of 85%. These high recoveries in forage prod uction systems are possibly a result of continuous preanthesis forage harve sting when gaseous plant N losses are small, but which increase following a nthesis.