Winter growth of varieties of perennial ryegrass (Lolium perenne L.)

The growth of eight varieties of perennial ryegrass (Lolium perenne L.) was compared during the winter to determine their potential for extending the grazing season. The varieties varied in heading date and ploidy. Five of the varieties were on the Irish Recommended List and three were in Recommended List trials. Growth was measured under a cutting regime designed to simulate grazing. Measurements of growth were made during three seasons for the three periods - September to November, November to March and March to April. There were no significant differences between varieties in the September to November period. Significant differences between varieties occurred in both the November to March and March to April periods and were associated with heading date. Early varieties out-yielded late varieties by a factor of 1.54 in the first year, by a factor of 1.36 in the second year and yielded the same as the late varieties in the third year. Full exploitation of the potential offered by the early varieties will depend on a better understanding of the factors responsible for the failure of early varieties to persist and for their decline in quality in mid-season.