Relationships between the yield of perennial ryegrass and of small-leaved white clover under cutting or continuous grazing by sheep

Seven varieties or advanced breeding lines of white clover (Trifolium repen s L.), all of small leaf size, were grown separately in mixtures with peren nial ryegrass (Lolium perenne L.) in an experiment encompassing three harve st years. Harvestable dry-matter (DM) yield measurements were taken of thes e mixtures and of perennial ryegrass monocultures under two management regi mes: cutting and continuous sheep grazing. Considerable differences were ob served in the harvestable DM yields of white clover, perennial ryegrass and total yields of the mixtures between plots containing different white clov er varieties. White clover yields were generally higher under cutting, and perennial ryegrass yields were higher under grazing. The difference between perennial ryegrass yield in monoculture and in mixture was variable. in th e second harvest year, a significant interaction effect was seen between ma nagement and white clover variety for white clover yield but not for perenn ial ryegrass yield. The relationship between clover yield and grass yield d iffered between the two management regimes. Under cutting, a negative corre lation was observed, indicative of competitive effects. However, under graz ing, no such correlation was seen. Possible mechanisms underlying these out comes are discussed.