EFFECT OF DEFOLIATION FREQUENCY ON AN IRRIGATED PERENNIAL PASTURE IN NORTHERN VICTORIA .2. INDIVIDUAL PLANT MORPHOLOGY

The effect of 5 winter and 2 post-winter defoliation frequencies on th e morphology of medium-leafed and large-leafed white clover and perenn ial ryegrass plants in an irrigated perennial pasture in northern Vict oria was investigated. Measurements included leaf appearance rates, ax illary bud development and survival, stolen elongation and survival, a nd tiller production and survival. White clover leaf appearance rate w as affected little by either defoliation frequency or cultivar, rangin g from 0.4 leaves/week in July to 1.1 leaves/week in February. In cont rast, perennial ryegrass leaf appearance rate in the same period range d from 0.35 to 0.7 leaves/week. Axillary bud production on clover stol ons was highest in winter and spring and lowest through summer, and wa s usually greater in the medium-leafed than in the large-leafed cultiv ars. When the swards were not defoliated through winter, the rate of b ud production was reduced in late winter; this was followed by a high rate of bud production in early spring, resulting in little treatment difference in the number of buds per stolen by mid spring. Bud surviva l was greater when initiated in winter than in summer. The rate of sto len death in spring was higher in the swards not defoliated during win ter and higher in the large-leafed than in the medium-leafed cultivar. These effects were associated with the stolen elongation rate in late winter; the medium-leafed cultivar was unaffected by defoliation freq uency, whereas in the large-leafed cultivars the rate of stolen elonga tion increased as the defoliation interval lengthened and canopy shadi ng increased. Perennial ryegrass tiller production was greater with fr equent than infrequent winter or post-winter defoliation, but never ex ceeded 1.2 daughter tillers/tiller, with 44% of the reproductive tille rs failing to replace themselves. The low leaf appearance rate and til ler production of the perennial ryegrass may contribute to its poor co mpetitiveness and persistence in this environment.