EFFECTS OF TIMING AND INTENSITY OF DEFOLIATION ON GROWTH AND DEVELOPMENT OF WHITE CLOVER SEEDLINGS

The effects of different defoliation regimes on the growth and develop ment of three contrasting white clover cultivars (S184, Menna and Alic e) were assessed in three experiments in the glasshouse. Experiment 1, with clover growing on its own, investigated the effects of three tim es of onset x two intensities of defoliation. In Experiment 2, clover was grown with grass and there were two times of onset x two heights x two frequencies of defoliation. Experiment 3, also with grass, invest igated the effects of changing defoliation frequency at different inte rvals from sowing. All clover cultivars responded similarly to the var ious treatments and there were no interactions between time of onset a nd subsequent defoliation regimes in Experiments 1 and 2. Without comp etition from grass (Experiment 1), defoliating early at the three leaf -stage of clover decreased the number of growing points by 32% and sto len weights and lengths by 50% compared with delaying defoliation unti l the nine leaf-stage. Maintaining one compared with two leaves pet gr owing point had similar effects. Over 17 weeks undefoliated seedlings produced ten times more stolen than early defoliated or intensively de foliated seedlings. In competition with grass (Experiment 2) delaying defoliation significantly decreased all aspects of stolen growth. Seed lings growing in swards defoliated frequently and closely had most gro wing points whereas those defoliated infrequently had least. Stolen le ngths and weights were larger for seedlings growing in swards defoliat ed frequently than for those defoliated infrequently at both heights o f cutting. Mean weight of stolen per unit length was greater when swar ds were defoliated at 6 cm than at 2 cm height. Changing defoliation f rom every 2 weeks to every week (Experiment 3) decreased stolen growth slightly when the change was made early but increased it when the cha nge was made late, although similar amounts of stolen were produced by seedlings continuously defoliated throughout every week and every 2 w eeks. The results are discussed in relation to the seedlings' leaf com plements and growth habit; the over-riding influence of grass competit ion is highlighted. The possibility of devising optimal defoliation st rategies and the need to test these in the field are also outlined.