Studies on the Regrowth of Tropical and Sub-tropical Grasses : I. Effects of cutting height and defoliation of basal leaves on the regrowtn of Dallis grass (Paspalum dilatatum Poir)

For the purpose of knowing the effects of the presence or non-presence of leaves of the basal part of plants after cutting at different heights on the regrowth, trials were conducted in the following design. Plants of Dallis grass were grown in 1/5000 a plastic pots. About 8 weeks after sowing, they were cut at three different heights, i.e. 1, 5, and 10cm above ground level. Each of the three lots were divided into two. 1) In the first lot, the basal part of the plants rimaining after cutting were left with leaves intact, while 2) in the second lot, the leaves were completely removed. In each treatment, replications were made 4 times. And the effects of the presence or non-presence of the basal leaves on the regrowth were studied: ^<14>CO_2 was fed to plant immediately after, 2 days, 5 days and 11 days after defoliation, using ^<14>CO_2 assimilation chamber under the condition of artificial light of 40 klux, 25-30℃, ^<14>C4μCi/each plant. One day after ^<14>CO_2 treatment, the plant of both lots were harvested, making a series of dates of harvest 1 day, 3 days, 6 days and 12 days after the dates of difoliation. The harvested plants were separated into stubble, root and the part of regrowth ; and dry weight, TAC content, and radioactivity of each component were measured. In another series, plants were harvested, dipped in boiling water for a few seconds, dried, mounted and then their radioautographs were made. The major results and interpretation were as follows: 1) In all the pairs of lots, regrowth was faster in those with the leaves left on the stubble than those defoliated, the effect of undefoliated leaves of basal parts being apparently favourable. 2) Increment of dry weight of newly grown leaves was the fastest in the lot of combination of highest cutting height and undefoliation of basal leaves, showing the sharpest upward curve ; whereas it was the poorest in the lot of combination of lowest cutting height and defoliation of basal leaves. 3) Reduction of dry weight of stubble and root after cutting was the smallest, its duration being shortest, and the recovery started earliest and rose most rapidly in the lot of combination of highest cutting height and undefoliation of basal leaves ; while the reduction was heavy, lasting longer and the recovery started slower in the lot of lower cutting height and defoliation of basal leaves. Basal leaves apparently acted to keep the reduction smaller at each level of cutting. 4) Translocation of ^<14>C-assmilates to roots after defoliation started earlier in the plants cut at high levels and in the plants which had undefoliated basal leaves than in the plants cut at low levels and whose basal leaves were thoroughly removed.