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 development of three contrasting white clover cultivars (S184, Menna and Alice) were assessed in three experiments in the glasshouse. Experiment 1, with clover growing on its own, investigated the effects of three times 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, investigated the effects of changing defoliation frequency at different intervals from sowing. All clover cultivars responded similarly to the various treatments and there were no interactions between time of onset and subsequent defoliation regimes in Experiments 1 and 2. Without competition from grass (Experiment 1), defoliating early at the three leaf-stage of clover decreased the number of growing points by 32% and stolen weights and lengths by 50% compared with delaying defoliation until the nine leaf-stage. Maintaining one compared with two leaves pet growing point had similar effects. Over 17 weeks undefoliated seedlings produced ten times more stolen than early defoliated or intensively defoliated seedlings. In competition with grass (Experiment 2) delaying defoliation significantly decreased all aspects of stolen growth. Seedlings growing in swards defoliated frequently and closely had most growing points whereas those defoliated infrequently had least. Stolen lengths and weights were larger for seedlings growing in swards defoliated frequently than for those defoliated infrequently at both heights of cutting. Mean weight of stolen per unit length was greater when swards were defoliated at 6 cm than at 2 cm height. Changing defoliation from every 2 weeks to every week (Experiment 3) decreased stolen growth slightly when the change was made early but increased it when the change was made late, although similar amounts of stolen were produced by seedlings continuously defoliated throughout every week and every 2 weeks. The results are discussed in relation to the seedlings' leaf complements and growth habit; the over-riding influence of grass competition is highlighted. The possibility of devising optimal defoliation strategies and the need to test these in the field are also outlined.