Grass and Legume Effects on Nutritive Value of Complex Forage Mixtures

Dry matter productivity of complex forage mixtures is typically influenced by a dominant species, but nutritive value may be a function of multiple components. Two experiments were conducted in Pennsylvania and Wisconsin during 2 yr. Each experiment consisted of 15 mixtures and monocultures of orchardgrass (Dactylis glomerata L.), quackgrass (Elymus repens (L.) Gould), alfalfa (Medicago sativa L.), and white clover (Trifolium repens L.), or of meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.], reed canarygrass (Phalaris arundinacea L.), red clover (Trifolium pratense L.), and kura clover (Trifolium ambiguum M. Bieb.). Vegetative-stage mixtures and monocultures were harvested five times each year. Botanical composition was used to calculate the additive effect of each species, or the expected change in nutritive value associated with a change in proportion of a species in the mixture from 0 to 100%. Nutritive value differences among mixtures attributed to abundance of sown species were evident the first year, but except for monocultures, had largely disappeared in the second year. White clover and meadow fescue had a positive additive effect on forage digestibility (range of 36 to 80 g kg(-1)), but alfalfa and reed canarygrass had no additive effect on digestibility. Legumes generally had a negative additive effect (range of -179 to -81 g kg(-1)) and grasses a positive effect (range of 81 to 166 g kg(-1)) on forage neutral detergent fiber concentration. The results suggest that species with high nutritive value relative to other species within the same functional group have a disproportionate effect on nutritive value of complex mixtures.