ADAPTATION OF WINTER CEREAL SPECIES TO SHADE AND COMPETITION IN A WINTER SPRING CEREAL FORAGE MIXTURE/

Spring planted mixtures of spring and winter cereals maximize dry matt er yield and provide fall pasture by regrowth of the winter cereal. Ho wever, delay of initial harvest may reduce the winter cereal component and therefore subsequent regrowth yield. Research was conducted at La combe, Alberta to investigate the effect of time of initial cut (stage ), winter cereal species (species) and cropping system (monocrop and m ixture) on winter cereal shoot weight, leaf carbon exchange efficiency and shoot morphology. These parameters may be related to adaptation o f winter cereals to growth and survival in the mixture. Winter cereal plants were grown in pails embedded in monocrop plots of fall rye (Sec ale cereale L.), winter triticale (X Triticosecale Wittmack) and winte r wheat (Triticum aestivum L.) and in binary mixtures with Leduc barle y (Hordeum vulgare L.). The plants were removed when the barley reache d the boot (B), heads emerged (H), H + 2, H + 4 and H + 6 wk stages. S hoot weight was generally smaller in the mixture than in the monocrop and wheat was reduced more than fall rye and triticale in the mixture compared to the monocrop. Dark respiration rate (r = -0.54) and carbon exchange (r = 0.36) under low light intensity were correlated (P < 0. 05) to shoot size in the mixture. Fall rye and winter triticale had lo wer dark respiration rates than winter wheat. Leaf area index (LAI) wa s closely correlated (r = 0.83 and 0.84) with shoot weight in both the mixture and monocrop. While species failed to exhibit clear cut diffe rences for LAI, fall rye and winter triticale were reduced less than w inter wheat in the mixture relative to the monocrop. Stage was the dom inant factor affecting winter cereal growth in both cropping systems, but fall rye and triticale exhibited superior morphological features, and their carbon exchange responses to light were more efficient than wheat, which should allow them to be sustained longer under the shaded conditions of a mixture.