Adaptation of winter cereal species to shade and competition in a winter/spring cereal forage mixture

Abstract

Spring planted mixtures of spring and winter cereals maximize dry matter yield and provide fall pasture by regrowth of the winter cereal. However, delay of initial harvest may reduce the winter cereal component and therefore subsequent regrowth yield. Research was conducted at Lacombe, Alberta to investigate the effect of time of initial cut (stage), winter cereal species (species) and cropping system (monocrop and mixture) on winter cereal shoot weight, leaf carbon exchange efficiency and shoot morphology. These parameters may be related to adaptation of winter cereals to growth and survival in the mixture. Winter cereal plants were grown in pails embedded in monocrop plots of fall rye (Secale cereale L.), winter triticale (X Triticosecale Wittmack) and winter wheat (Triticum aestivum L.) and in binary mixtures with Leduc barley (Hordeum vulgare L.). The plants were removed when the barley reached the boot (B), heads emerged (H), H + 2, H + 4 and H + 6 wk stages. Shoot 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 lower dark respiration rates than winter wheat. Leaf area index (LAI) was closely correlated (r = 0.83 and 0.84) with shoot weight in both the mixture and monocrop. While species failed to exhibit clear cut differences for LAI, fall rye and winter triticale were reduced less than winter wheat in the mixture relative to the monocrop. Stage was the dominant 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. Key words: Delayed harvest, shade, spring and winter cereal mixtures, adaptation, carbon exchange, respiration