RESPONSE OF FORAGE YIELD AND YIELD COMPONENTS TO PLANTING DATE AND SILAGE PASTURE MANAGEMENT IN SPRING SEEDED WINTER CEREAL SPRING OAT CROPPING SYSTEMS/

Spring-planted mixtures of spring and winter cereals in a silage/fall pasture system have been shown to extend the grazing season in the Par kland of the Canadian prairies. Experiments were conducted at Lacombe, Alberta to determine the effects of planting date on yield and yield components of spring-seeded spring oat (Avena sativa L.), winter wheat (Triticum aestivum L.), winter triticale (X Triticosecale Wittmack) a nd winter rye (Secale cereale L.). The cereals were grown as monocrops or as binary mixtures of the oat and winter cereals. Treatments were planted in early May and mid-June and harvested twice for forage. The initial harvest for early and late planting dates occurred when oat re ached the early-milk and heading stages, respectively. Regrowth was ha rvested in mid- to late September. The planting date x treatment inter action did not affect(P < 0.05) annual yield(initial + regrowth) even though oat was harvested at different developmental stages. Averaged o ver treatments, late planting reduced annual yield by 42%. The annual yields ranked: mixtures = oat monocrop > winter cereals. Late planting date reduced the initial yield of all treatments, but the winter mono crops were reduced less than oat. Oat dominated the initial yield of a ll mixtures. Although oat tiller density was lower in the mixtures tha n monocropped oat at the initial cut, oat constituted a greater propor tion of the mixture than would have been expected from the seeding rat io (1:1). A larger tiller weight in the oat mixture vs. the monocrop m ay have compensated for low tiller density in the mixture. Mixture reg rowth yields tended to be greater in late-planted treatments and were dominated by the winter cereals. Although the winter cereal component of the mixture had more tillers at the regrowth cut, they still had lo wer yields when compared with their respective monocrops. Thus, late p lanting reduced annual yields of mixtures and monocrops, but did not l imit regrowth of winter cereals in mixtures given equal regrowth perio ds.