Competition in perennial ryegrass white clover mixtures under cutting. 2. Leaf characteristics, light interception and dry-matter during regrowth

The effect of defoliation interval on growth patterns of contrasting perenn ial ryegrass (Lolium perenne)-white clover (Trifolium repens) mixtures was studied. The dynamics of increase in leaf area, light interception and dry- matter (DM) production were measured within successive regrowth periods. No N fertilizer was applied. During 1995 six mixtures were cut eight (F1) or six times (F2) at a stubble height of 5 cm. The stubble composition was sta ble throughout the growing season: after harvest about 50 g DM m(-2) (with a white clover proportion of 0.52) was present with a leaf area index (LAI) of 0.5 (0.38 white clover). The percentage of intercepted radiation after cutting was 20-30% and increased during 3 weeks to about 95%. The relative growth rate of leaf area and DM was higher for white clover th an for perennial ryegrass, with the proportion of clover in the LAI and DM increasing during each regrowth period. Mixtures with large-leaved white cl over cv. Alice had a lower initial clover content after harvest, but a more rapid increase in clover LAI and DM than mixtures with the smaller leaved cvs Gwenda or Retor. Alice had the highest total and clover LAI and DM at h arvest. Cutting frequency affected the change in white clover-perennial rye grass ratio during regrowth. This was significantly higher in mixtures with Alice than in mixtures with Gwenda, but only under less frequent cutting ( F2). In spring there was a mean white clover proportion of about 0.55 in the LAI and 0.45 in the total harvested DM. In summer the white clover proportion in the LAI and DM increased to 0.70-0.75. There was a decline during autumn , especially in F2 and in the mixtures with the small-leaved white clover c v. Gwenda and the medium-leaved cv. Retor. In contrast, grass DM and LAI de clined from spring to summer. The decline in clover LAI in autumn was simil ar in Alice and Gwenda at frequent cutting (F1), but stronger in Gwenda in F2. Retor had the lowest clover specific leaf area (SLA). The SLA values of Alice and Gwenda were similar, SLA being similar between cutting treatment s. No differences were found for leaf weight ratio (LWR) among the three wh ite clover cultivars or between the grass cultivars, and LWR was not affect ed by cutting treatment. Defoliation interval had limited effects on the gr owth pattern and leaf characteristics of perennial ryegrass-white clover mi xtures.