SPRING NITROGEN FERTILIZATION PRACTICES IN OREGON’S WILLAMETTE VALLEY GRASS SEED CROPS

W.C. Young III, T.B. Silberstein, M.E. Mellbye, G.A. Gingrich,
J.M Hart and T.G. Chastain
Department of Crop and Soil Science, Oregon State University,
Corvallis, Oregon, 97331

Optimum levels of spring applied N for seed production were 150-200 kg N ha^-1 for perennial ryegrass, 100-150 kg N ha^-1 for tall fescue, 56 kg N ha^-1 for fine fescue, and 150 to 200 kg N ha^-1 for annual ryegrass as determined from site averages over several years. Results are summarized over three years for perennial ryegrass and tall fescue, four years in fine fescue, and two years in annual ryegrass. The study was designed to provide data and recommendations over the productive stand life of the three perennial crop species. The use of N rates above the recommended levels increased soil and plant N, but did not improve yield. Lower N rates resulted in reduced seed yield, which became more pronounced as the stand aged. These data are being used to rewrite OSU Extension fertilizer guides.