Herbage Nutritive Value in Relation to Plant Species Diversity of Pastures.

Planting forage mixtures may benefit pasture herbage production; however, changes in botanical composition could cause unstable nutritive value. Data from two grazing studies and a farm survey were used to examine how plant species diversity influenced herbage nutritive value. In one grazing study, four mixtures (two, three, six, and nine species of grasses, legumes and chicory, Cichorium intybus L) were established in replicated pastures and grazed for two years. In a second grazing study, three mixtures (two, three, and 11 species) were compared under on-farm grazing for four years. In the survey, pastures from several farms were sampled to determine plant species composition and analyzed for nutritive value. In most instances, nutritive value of herbage was influenced most by functional group composition (e.g., proportion of grasses, legumes, and forbs) than by plant species diversity. Crude protein concentrations seemed to be controlled by the legume proportion in the herbage, whereas fiber and digestibility were controlled by the grass proportion. There was no evidence that complex forage mixtures were more variable in nutritive value than a binary mixture.