FORAGE YIELD AND QUALITY INTERACTIONS BETWEEN WHITE CLOVER AND CONTRASTING RYEGRASS VARIETIES IN GRAZED SWARDS

The impact of white clover on seasonal yield and nutritive value trait s in perennial ryegrass was investigated using six ryegrass varieties which expressed contrasting levels of water soluble carbohydrate (WSC) . These were sown in an upland environment at Syfydrin, near Aberystwy th, in mixtures with white clover and in monocultures. Plots were graz ed by sheep and sampled during 1991-93. Grass yields in mixtures and m onocultures were similar except during mid to late summer when clover contents were high. White clover had a considerably lower WSC content but a much higher crude protein (CP) content than the ryegrasses. The WSC content of grasses in mixed swards was consistently lower than in monocultures and markedly so during mid to late summer. Use of ryegras s varieties with a relatively high WSC content can compensate for this depletion. Consequently high WSC grasses may reduce the amounts of ni trogen excreted by ruminants grazing mixed swards by increasing the ef ficiency of protein use from clover.