Effects of functional traits of perennial ryegrass cultivars on forage quality in mixtures and pure stands

Abstract

Plant breeding has brought about improvements in the herbage yield potential, forage quality and functional traits of perennial ryegrass (Lolium perenne L.). Under conditions of low external inputs, grassland swards based on perennial ryegrass often contain dicotyledonous species (legume and non-legume). Cultivar-specific functional traits such as growth form or phenology affect the competitive ability and yield in mixtures, but the extent to which cultivars with different functional traits affect forage quality in mixtures compared with pure stands is unknown. Therefore, we analysed four perennial ryegrass cultivars, each representing a combination of two functional traits with respect to phenology (early v. late heading) and growth form (upright v. prostrate) on forage quality, in a field experiment over 5 years. Each cultivar was grown in binary-mixtures with Trifolium repens L., as four-species mixtures with Taraxacum officinale L. and Plantago lanceolata L., and as grass monocultures. The effect of functional traits was dominant in the primary growth and persisted in pure stands but not in the mixtures from the third year onwards. Prostrate cultivars allowed the development of a greater proportion of clover and forbs within the mixtures, resulting in increased protein and energy and reduced fibre contents. In mixtures, forage quality was generally higher in the last regrowth. In conclusion, the indirect effects of growth form on forage quality due to modifications of botanical composition were more important than direct effects on forage quality.