The effects of soil type, temperature, and moisture on the survival and seasonal germination of seeds of A. fatua and A. ludoviciana, buried at five depths in the soil, were studied in a glasshouse experiment. Seeds of both species germinated only when mean weekly minimum temperatures were below 20°C and mean weekly maxima below 28°. A. fatua germinated better than A. ludoviciana in the 20–30° range and was therefore the dominant species in autumn germinations of wild oats. Both species germinated throughout winter. Only 30% of the seeds sown produced seedlings. Of these 90% emerged in the first year after seeding and the remainder in the second year. Only 2% of the seeds sown remained viable after 18 months. The depth at which the seeds were buried, seed type, soil type. and moisture regime all affected the survival of seeds and the percentage that produced seedlings. An explanation is offered for the dominance of A. ludoviciana in the northern wheat-belt of eastern Australia.

Seeds of Avena ludoviciana after-ripened more rapidly with increasing temperatures up to 30°C and with increasing relative humidities between 16 and 100%. In continuous light, these seeds after-ripened more rapidly than in the dark. Seeds of different species and strains of wild oats after-ripened at different rates; primary seeds after-ripened more rapidly than secondary. One week after anthesis 60% of the viable primary seeds of A. ludoviciana were dormant, compared with 100% at maturity. The importance of these findings to studies on the physiology of dormancy and to the control of wild oats in the field is discussed.

The effect of CCC m controlling plant height during internode elongation and assimilate accumulation, during grain filling and at grain maturity, was investigated in plants growing under three temperature regimes. With increasing temperature the plants matured earlier and the maximum height achieved became smaller. The effectiveness of CCC in controlling internode elongation was reduced. Analysis of the distribution of 14C-labelled compounds assimilated as 14CO2 by the flag leaves after ear emergence, showed no difference between the control and CCC-treated plants. It is suggested that the early application of CCC has a limited effect on metabolism of the plant during grain filling.

A simple soil water budget model was used to estimate weekly changes in available soil water as affected by plant density, time of sowing and level of available fallow water for spring wheat cultivars grown on a black earth in northern New South Wales. Estimated values of available water were mostly within �10 mm of observed values (ranging from 50-270 mm) obtained at four intervals during the growing season. The results are discussed in relation to both the interpretation of agronomic field experiments and use of the model in regions where conserved fallow water contributes significantly to cereal production.

A study was made of the effects of plant density, time-of-sowing and level of fallow water on profile changes in soil water content and potential during the growing season of spring wheat. The pattern of soil moisture extraction was affected by all treatments although water depletion occurred chiefly in the 0-90 cm zone. The results are discussed in relation to limitations of a simple soil water budget model and to wheat cropping on the north-west slopes and plains of New South Wales.