The influence of defoliation on vegetation growth in swards of three strains of subterranean clover

Abstract

Three defoliation regimes—uncut, defoliated every 14 days at 1.5 cm, and defoliated every three or four days (alternately) at 1.5 cm—were imposed on dense swards of Blackwood, Dwalganup and Daliak subterranean clover. The swards were grown in boxes, out of doors, at Perth from 1 June to 29 August. Mean daily solar radiation ranged from c. 1050 to 1450 J/cm²/day, and the average daily maximum and minimum temperatures were about 17° and 8.5°C respectively.

The main finding was that defoliated swards yielded considerably less than uncut swards; averaging strains (and the two defoliated treatments) the decrease was c. 20% at day 33 and more than 40% at day 89. The lower yields of defoliated swards were associated with lower leaf area indices. During the first half of the experimental period, defoliation depressed growth in Blackwood more than in Dwalganup and Daliak.

Uncut swards maintained the original plant density (28 plants/dm²), though some dead material was recorded in harvests at day 61 and (more particularly) day 89. Leaf area index exceeded 9 at day 89, with no clear optimum. Defoliated swards—especially those cut every three or four days—had more but smaller leaves, and higher branch numbers than uncut swards.

In some respects these results conflict with those of previous reports, and explanations are proposed for apparent inconsistencies, mainly in terms of the temperature conditions.