Field and controlled environment studies were conducted to evaluate the effects of certain environmental factors on the persistence of buried seed of annual ryegrass (Lolium multiflorum Lain.), a free‐volunteering species; and perennial ryegrass (Lolium perenne L.), nonpersistent species. Buried seed of annual ryegrass persisted in both nondormant and dormant condition. Buried seed of perennial ryegrass lost virtually all viability after 60 days of burial in the field. This dissipation occurred largely via in situ germination. Dormancy was induced in annual ryegrass when seeds were buried in cold, wet soils. High soil temperature associated with intermediate soil moisture level was effective in depleting viable seed through in situ germination. Loss of buried seed viability increased with soil temperature and moisture.

A model describing the parameters of persistence and depletion within buried seed populations is presented. This model provides a conceptual framework for problems involving buried seed persistence and depletion which are often encountered in weed control and crop seed certification. Them model may also find use in studies where the ecology, physiology and genetics of buried seed persistence and depletion are being evaluated.

Spring application of N generally increases seed yield of perennial ryegrass (Lolium perenne L.). Understanding the influence of N rates and timings on seed yield components can be used to improve N use efficiencies and seed yield. Field experiments during 1982 and 1983 at Oregon State University studied the effects of 60, 90, and 120 kg N ha−1, applied either at double‐ridge stage (DR) or at spikelet initiation stage (SI), on seed yield and yield components of the cultivar Pennfine. Control plots with no spring‐applied N were also included. Little lodging was observed in 1982, but all plots severely lodged by maturity in 1983. Timing of N application did not affect seed yield in either year. Compared with the control, spring N increased seed yield 43% in 1982 and 39% in 1983 when averaged across rates. In 1982, seed yield did not vary with N rates applied at DR, but 120 kg N ha−1 produced greater seed yield than 60 kg N ha−1 when applied at SI. In 1983, seed yield was maximized by 90 kg N ha−1 applied at DR, and by 120 kg N ha−1 applied at SI. Nitrogen application did not affect the number of spikes per unit area, but increased seed number per spike in 1982 and weight per seed in 1983. Averaged across rates and timings, N increased total number of seeds produced per unit area 43% in 1982 and 30% in 1983. Seed yield was correlated with the number of seeds per spike in both 1982 (r2 = 0.68) and 1983 (r2 = 0.72). In 1983, seed yield was also correlated with weight per seed (r2 = 0.55). We concluded that in the absence of severe lodging, 60 kg N ha−1 applied at DR is adequate for achieving maximum seed yield. If fertilization is postponed until SI, however, higher rates of N may be required. Results also suggest that modifications in N fertilization should focus on improving seed set per spike and seed growth rather than increasing the number of spikes per unit area or floret sites per spike.

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.

Spring grazing annual ryegrass (Lolium multiflorum Lam.) seed fields with sheep (Ovis aries) is a common practice. The effects of grazing duration in early stages of stem elongation on seed yield and its components are not well known. We studied four durations of spring grazing annual ryegrass with sheep over a 2‐yr period on an Argiaquic Xeric Argialboll soil. Grazing was begun before onset of stem elongation. Treatments were no grazing (G0) and grazing until one‐third (G1), two‐thirds (G2), or all (G3) primary tillers had their apical meristems removed. Leaf area was progressively reduced by grazing duration. The number of fertile tillers increased with grazing duration in the first year, but the effect was not significant in the second year. Grazing did not affect the number of spikelets per spike or florets per spikelet in the first year. In the second year, G2 and G3 reduced spikelets per spike and had no effect on the number of florets per spikelet, whereas G1 did not affect either character. Both G2 and G3 decreased seed weight in the first year, while G1 had no effect; treatments did not affect seed weight in the second year. Grazing treatment did not affect total herbage dry matter at seed maturity, seed yield, or seed quality in either year. We conclude that, in western Oregon, grazing annual ryegrass in late winter and early spring up to the time when the apical meristem of all primary tillers are removed (G3) does not reduce seed yield. Grazing until about one‐third of primary tillers lose their apical meristem (G1) may actually improve seed yield.