GENOTYPE, SOWING DATE AND PLANT SPACING INFLUENCE ON HIGH-YIELDING IRRIGATED WHEAT IN SOUTHERN NEW-SOUTH-WALES .1. PHASIC DEVELOPMENT, CANOPY GROWTH AND SPIKE PRODUCTION

Sowing date, sowing rate and row spacing effects were studied on high input crops at Griffith, N.S.W., between 1983 and 1985 using 25 bread wheats (Triticum aestivum L.) and 3 triticales (X Triticosecale Wittmack). The aim was to identify improved management practices and genotypes through a better understanding of development and growth of irrigated wheat grown under high-yielding conditions. The genotypes were chosen to represent a wide range in genetic background, maturity and stature. Growing period durations were between 208 days and 100 days for early April and mid-August sowings, respectively, with differences in anthesis dates within sowing dates of up to 45 days. Genotypes were classified into six major maturity groups. There was no maturity type that could flower close to 1 October from a wide range of sowing dates since anthesis was delayed by 0.3 to 0.5 days per 1-day delay in sowing. Increased daylength sensitivity tended to delay anthesis relative to the timing of floral initiation and terminal spikelet formation. The end of tillering was generally associated with the attainment of 50-60% light interception rather than a given development stage of the inflorescence. Spike density was not closely related to maximum tiller number but depended on genotype, but was independent of spike development. For a given final leaf number, internode elongation started at a later leaf number for later sowing dates, resulting in reductions in both node number and height. Crop height decreased by up to 5 cm per 1-week delay in anthesis date. The period of full light interception decreased from 133 days to 43 days between April and August sowings, respectively. The timing of reproductive development determined the green area duration, but the initial development and size of the canopy was less affected by it, because of adjustments in number and type of tillers, and size and thickness of leaves. The development and maintenance of an adequate canopy was not restricted by earliness, shortness or low sowing rates (50 kg seed/ha) for April-July sowing dates.