The effect of time of planting on yield attributes of wheat varieties in the Ord River valley

At Kimberley Research Station six wheat varieties, three Australian and three South African, were sown under irrigation at four dates from April 24 to August 6 in the 1964 dry season. Data from four varieties are presented. The highest grain yields were obtained from two Australian varieties, Gamenya and Gabo. These two, the earliest varieties, attained maximum yield at the second sowing on May 30. The slightly later South African variety Penkop reached maximum yield at the first and second sowings, and the late South African variety Wit Spitskop declined in yield from the first sowing onward. Observations on phenology and analysis of yield components showed that changes in grain yield with date of sowing were the result of environmental effects on a number of plant attributes. The most important effect appeared to be that of steeply rising spring temperature, which accelerated maturation and reduced crop performance by its influence on the later processes of yield accumulation. The results suggested that for the varieties sown there is a common optimum temperature of 75-80�F for these processes. The practical conclusion from this experiment is that maximum wheat yields are attained when crops are sown so as to come into anthesis at the end of July or early August.