INFLUENCE OF GENOTYPE, SOWING DATE, AND SEEDING RATE ON WHEAT DEVELOPMENT AND YIELD

A 3-year study was conducted to measure the effect of sowing time and seeding rate on the development and yield of wheat (Triticum aestivum L.) grown under high-yielding conditions in north-eastern Victoria. A range of wheat cultivars with different development responses, includi ng 'winter' types, was used in 2 experiments in each season. High grai n yields for dryland wheat were measured in the first 2 seasons (1985- 86), and in 1985, near-optimal water use efficiencies (>18 kg/ha.mm ef fective rainfall) were obtained. In the third season (1987) grain yiel d was limited by adverse climatic conditions in the pre- and post-anth esis period. In each season, grain yield declined with delay in sowing time. In 1985 there was a loss of 200-250 kg grain/ha for each week's delay in sowing time. In 1987, yield loss with delayed sowing was 50- 110 kg grain/ha. In each season, cultivars with late or midseason matu rity development gave the highest mean yields, and the use of these ma turity types allowed earlier sowing, in mid April. However, with late sowing of wheat there was a trend for early maturity types to give hig her yields, and so the use of 2 wheat cultivars with distinct maturity development responses to climate is recommended. If only 1 wheat cult ivar is to be used, then a late maturity type is recommended. Higher w heat yields were also obtained as spike density increased, as a result of higher seeding rates. Our data suggest that in the higher rainfall region of north-eastern Victoria, a spike density of about 500 spikes /m(2) is required to optimise wheat yields.