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The botanical composition of high rainfall pastures in south-western Victoria

G.N. Ward and P.E. Quigley

Department of Agriculture, '78 Henna Street, Warrnambool VIC 3280 P0 Box 180, Hamilton VIC 3300

The pastures of the high rainfall areas of south-western Victoria are one of the regions greatest assets, producing amongst other things some 20% of Australia's total dairy production. Observations have suggested that many of these pastures are now in a botanically degraded condition. To determine the actual condition of pastures in these areas a survey of pasture botanical composition was undertaken in November 1988.

Methods

The survey area consisted of a 600 km' segment of the dairying areas (750-950 mm annual rainfall), of the Shires of Heytesbury and Hampden. A total of 156 pasture sites (86 being dairy milking and 70 beef, sheep or dairy out paddocks) were selected from randomly generated points on topographical maps. In the field, an area of approximately 0.5 ha of pasture at each site was assessed. All plant species present were recorded. The proportions of the major species in the pasture were determined using the dry-weight-rank method (1). Further management and physical data was collected.

Results and discussion

Only 7% of dairy milking arid 4% of other pastures had been resown in the previous two years. Some 73% of dairy milking and 82% of other pastures were greater than eight years of age indicating a comparatively low rate of pasture resowing. Some 36% of all sites were considered to have good improved pastures, (arbitrarily set as containing >20% of a legume and >20% of an improved pasture grass). Some 40% of all sites contained less than 20% legume, while 52% of sites had less than 20% of an improved pasture grass. Dairy pastures were generally in better condition than the other pastures.

Of the sown species perennial ryegrass, Lolium perenne, was the most abundant occurring in 94% of pastures. White clover, Trifolium repens, occurred in 85% and subterranean clover, Trifolium subterraneum, in 63% of pastures. The most prevalent species were a group of volunteer, low fertility adapted perennial grasses. Of these, fog grass, Holcus lanatus, was the most abundant occurring in 89% of pastures with 26% of the pastures containing greater than 20% of this species. Other major grasses and their occurrence were sweet vernal, Anthoxanthum odoratum (52%); crested dogstail, Cynosurus cristatus (45%); meadow foxtail, Alopecurus pratensis (36%), and bent grass, Agrostis capillaris (28%).

It is clear that whilst one third of pastures contain a good composition of improved pasture species, the majority of the pastures in the survey area have a degraded botanical composition. Such pastures often have an inadequate legume content and are usually dominated by less desirable, volunteer perennial grasses.

Reference

T Mannetje, L. and Haydock, K.P. 1963. J. Br. Grassld Soc. 18, 268-275.

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