Ar. Lawson et al., EFFECT OF DEFOLIATION FREQUENCY ON AN IRRIGATED PERENNIAL PASTURE IN NORTHERN VICTORIA .2. INDIVIDUAL PLANT MORPHOLOGY, Australian Journal of Agricultural Research, 48(6), 1997, pp. 819-829
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.