WHITE CLOVER MORPHOLOGY AND PHYSIOLOGY IN RESPONSE TO DEFOLIATION INTERVAL

Yield response of white clover (Trifolium repens L.) to defoliation varies with leaf size. Our objective was to determine how specific aspects of plant morphology and physiology are responsible for differences in growth of diverse white clover cultivars in response to defoliation interval. Individual plants of 'Aberystwyth S184' (small-leaf), 'Grasslands Huia' (medium-small-leaf), and 'Osceola' (large-leaf) were clipped to remove all fully expanded leaves and petioles 55 d after sowing in the greenhouse and then clipped every 7, 14, or 28 d for the next 28 d. Plant fraction dry matter (DM) accumulation and morphological and physiological characteristics were measured 1, 3, 7, 14, and 28 d after the final clipping. Stolen growth rate was inverse to leaf size classification (Aberystwyth S184, 7.6 cm d(-1) > Grasslands Huia, 5.8 cm d(-1) > Osceola, 3.6 cm d(-1)). In contrast, maximum stolen weight/length ratio of Osceola increased 31% vs. a 1% increase for Grasslands Huia and Aberystwyth S184 as defoliation interval Increased to 28 d, which resulted in greater stolen DM accumulation by Osceola at the 14- and 28-d intervals. Stolen and root carbohydrate concentration of Osceola was greater than and leaf carbohydrate concentration was less than the other cultivars at all defoliation intervals, indicating greater reliance on stored carbohydrates for regrowth by Osceola. Although plant leaf area of Osceola was greater than that of Grasslands Huia and Aberystwyth S184 at the 28-d interval only, forage DM accumulation of Osceola was greatest at all intervals due to petiole length. In grazed swards, however, greater petiole length would likely increase accessibility to and removal of leaf tissue, subsequently reducing new leaf and stolen growth.