Interactions between variety and the timing of conservation cuts on species balance in Lolium perenne-Trifolium repens swards

The effects of two periods of rest from grazing by sheep (either April-May or May-June) on the composition of swards of both an early-flowering (Aurora) and a late-flowering (Melle) perennial ryegrass variety grown with cither a small-leaved (Kent) or a medium-leaved (Milkanova) white clover variety are described. Compared with a continuously stocked treatment, the early rest period did not affect the mass of clover in the swards (expressed as a proportion of the total) but resulted in a subsequent decrease in its population density. The late rest period doubled clover mass in the swards at the time of cutting but did not affect the subsequent population density of clover. The magnitude of the change in mass during the late rest period depended on ryegrass variety, but not on clover variety. The adverse effect of the early rest period on the subsequent population density of clover was associated with the degree of shading experienced by clover laminae at the end of the rest period. Temperature may also have had an effect here as mean temperatures were cooler during the early rest period than during the late rest period. It is concluded that the effects of the two rest periods on the clover content of the swards were primarily due to timing, and less to inherent differences between ryegrass varieties.