Spring-applied nitrogen and productivity of cool-season grass seed crops

Understanding effects of spring N rates and application timing on seed yield and yield components of cool-season grass seed crops will help improve N fertilization management. We tested effects of 90, 120, 150, 180, and 210 kg N ha(-1), applied at the double-ridge (DR) stage of development on seed yield and yield components of Chewing's fescue [Festuca rubra L. subsp. fallax (Thuill.) Nyman; syn. F. rubra var. commutata Gaudin], tall fescue (F. arundinacea Schreb.), and orchardgrass (Dactylis glomerata L.) in 1985 and 1986. In a second study, effects of 120 kg N ha(-1), applied either at DR, at spikelet initiation (SI), or equally split between the two stages, were tested. Soil type for both experiments was fine-silty, mixed, mesic Aquultic Argixerolls. Chewing's fescue seed yield was not affected by N rates in 1985 and was the greatest at 90 kg N ha(-1) in 1986. Averaged across years, orchardgrass seed yield was the greatest at 120 kg N ha(-1). Nitrogen rates did not affect seed yield of tall fescue. Seed yield of all species was most closely correlated with the number of seeds produced per unit area. Seed number per unit area was primarily correlated with the number of seeds produced per panicle in all species; in orchardgrass, the number of panicles per unit area also contributed to total number of seeds produced. Seed yields of all three species were the greatest when N was applied at DR. Split application was not better than application of all N at DR or SI. We concluded that in western Oregon spring application of 90 kg N ha(-1) for Chewing's fescue and tall fescue and 120 kg N ha(-1) for orchardgrass should be adequate for seed production. For all species, spring N should be applied in one application at DR.