Eleven field trials were sown in the north-eastern wheatbelt of Western Australia to test the hypothesis that if wheat cultivars with suitable maturity are sown earlier than current practice, then higher grain yields will be achieved.
The experiments included time of sowing treatments that ranged from early May to late June in 1988, 1989 and 1990. Seven commercial cultivars with a wide range of developmental patterns and maturities were used.
Sowing between mid May and early June produced the highest grain yields. For plantings after early June, yields declined by approximately 250 kg/ha (15%) per week. Delayed sowing caused a decrease in dry matter and kernel number (per m2). In general this reduction in kernel number was not compensated by an improvement in kernel weight.
At early times of sowing, the medium-long season cultivars generally had higher yields than short season cultivars. The short season cultivars were the highest yielding cultivars at the late times of sowing. These results suggest that cultivars should be chosen to suit the seasonal break, which may vary from late April to mid June. As a consequence, farmers should be encouraged to retain a number of cultivars with differing maturities suited to a range of planting times.