SPRING DEFOLIATION OF WHITE CLOVER SEED CROPS .1. INFLORESCENCE PRODUCTION OF CONTRASTING WHITE CLOVER CULTIVARS

Three white clover cultivars, S 1 84 (small-leaved), Menna (medium-lea ved) and Olwen (large-leaved), were sown at a seed rate of 3 kg ha-1 u nder spring wheat cv. Tonic. In the spring of the two following years, there were three pre-bud emergence mechanical defoliation treatments on which were superimposed four post-bud emergence treatments giving a total of twelve cutting treatments. Pre-bud emergence, plots were eit her cut twice (at approximately two weeks before bud emergence and at bud emergence), cut once at bud emergence or not cut. To each treatmen t were applied four post-bud emergence treatments: plots were not cut or cut once (one, two or three weeks after bud emergence). Counts of t he total number of inflorescences and of the proportions in various ri peness categories were made throughout the period of seed crop develop ment to determine the pattern of inflorescence development and optimum harvest date. Overall, inflorescence numbers were greatest in cv. S 1 84 and least in cv. Olwen. Defoliation before bud emergence had no ef fect on inflorescence production; however, it was significantly influe nced by defoliation after bud emergence. Although delaying the initial development of the crop, inflorescence numbers of all cultivars were highest in both years following cuts two and three weeks after bud eme rgence. Optimum harvest date was not affected by defoliation or cultiv ar, numbers of ripe inflorescences in both years reaching a peak at th e end of August. The number of brown inflorescences, which may also co ntribute to seed yield, reached a peak in both years in late July. Sea sonal differences in inflorescence production were again observed, emp hasizing the difference between first and second year crops and import ance of climate in white clover seed production. The implications of t hese differences in numbers and proportions of inflorescences in vario us ripeness categories under different defoliation regimes are discuss ed in relation to seed crop management in the UK.