Effect of synthetic windbreaks on pasture growth in south-western Victoria, Australia

The impact of a synthetic windbreak on the growth of subterranean clover and perennial ryegrass pasture in the cool-temperate zone of south-western Victoria was investigated over 2 years. Four square plots (10 m sides) at each of 2 sites were fenced with wire mesh 1.2 m tall in 1996 and 1997. Two plots at each site were sheltered with synthetic mesh of 50% porosity attached to the wire mesh. The open wind speed averaged 3.6 m/s in 1996 and 3.1 m/s in 1997. Winds exceeded 6 m/s for 4-23% and 2-8% of the time in 1996 and 1997, respectively. There were small but significant differences in temperature between the sheltered and open plots. The mean daily temperature was 0-0.4degreesC warmer with shelter. Temperatures in the shelters were always higher from 0900 to 1800 hours, the differences ranging from 0.1 to 0.9degreesC. Conversely, lower temperatures (a maximum difference of 0.4degreesC) usually occurred in the shelters from 1800 to 0600 hours. The mean daily relative humidity was 1.4-3.1% greater in shelter than in the open and the maximum difference was 3.8%. There was a significant (P<0.01) effect of shelter on pasture growth in both years. In terms of total production over both years, the results indicate a small but consistent increase in pasture growth of about 9% for sheltered v. open plots at both sites. There was a clear seasonal effect of shelter, with greater production in autumn-winter, and a trend towards greater production in open plots during very wet periods. The results indicate that responses of pasture plants to shelter in the cool-temperate zone of Australia may be modest, and difficult to determine in field experiments, but shelter should contribute significantly to animal production because of improved plant growth in times of scarcity and reduced expenditure of energy for maintenance. Artificial shelters may provide the best means of testing the likely response to shelter of other pasture species or crops.