A field experiment was established at the Institute of Grassland and Environmental Research (IGER), Aberystwyth, to compare the seasonal growth and annual yields of two white clovers when grown with each of five perennial ryegrasses. Swards were subjected to two contrasting defoliation managements, namely cutting only and continuous grazing with sheep. In addition to data recorded on dry matter yields of the swards, the effect of management on growth and development of white clover stolons and tillering of ryegrasses was also studied in the third harvest year. The management of the swards had a significant effect on ryegrass tiller number and on the ingress of weed grasses. Differences in persistency and tillering among the ryegrasses were significantly greater when continuously grazed by sheep than when swards were cut. It is argued that ingress of weed grasses under grazing could be used as an indicator of ryegrass persistency. Among those studied, only two of the ryegrasses were able to provide dense persistent swards under continuous sheep grazing. The white clovers included in this experiment differed in leaf size with Gwenda smaller than Ac 3785. Greater differences existed between white clover components when grazed than when under cutting management. Under continuous sheep grazing there were large differences between the clover varieties in stolon length, stolon weight, number of growing points and root weight.

The data indicate the importance of the persistence of mixture components under continuous sheep grazing and, since ryegrass is the main component of a clover/grass seed mixture, greater emphasis in breeding and evaluation programmes should be given to persistence, especially under grazing.