EFFECT OF DEFOLIATION FREQUENCY ON AN IRRIGATED PERENNIAL PASTURE IN NORTHERN VICTORIA .1. SEASONAL PRODUCTION AND SWARD COMPOSITION

A field experiment was carried out to investigate whether changes in w inter and post-winter defoliation frequency would increase the white c lover content of an irrigated perennial ryegrass-white clover pasture in northern Victoria. Pastures defoliated every 4 weeks during winter had higher white clover growing point (stolen apices with at least 2 n odes) density at the end of winter than pastures defoliated every 8 we eks or those receiving a single defoliation after 16 weeks, but these differences did not affect the clover content in the spring. Reasons f or this are suggested. Pastures defoliated at 8-week intervals in wint er were the most productive over winter-early spring. Less frequent de foliation (4 v. 2 weeks) during the post-winter, September-May period reduced white clover growing point and perennial ryegrass tiller densi ties. However, the white clover growth rate during this period was inc reased by less frequent defoliation, whereas the ryegrass growth rate was reduced, resulting in an increase of 10% in the white clover conte nt, and a 1.9 t dry matter (DM)/ha increase in total DM produced. This higher clover content and pasture yield during spring-autumn with les s frequent defoliation has important implications for the management o f irrigated perennial pastures for the dairy industry in northern Vict oria.