Genotype, sowing date and plant spacing influence on high-yielding irrigated wheat in southern New South Wales. III. Potential yields and optimum flowering dates

Abstract

Experiments were undertaken at Griffith, N.S.W., using a range of genotypes, sowing dates and plant spacing to identify management strategies and genotypes that would increase irrigated wheat yields and minimize lodging risk. Results are used in this paper in an analysis of potential yield and optimum anthesis date, as influenced by temperature, irradiance, sowing date and genotype. Lodging duration was used to predict potential yields in absence of lodging from the lodging-affected yields in the study. Lodging duration between 7 days after mid-anthesis and maturity was found to best explain early and late lodging effects on yield. Yield reductions due to lodging were up to 45%. Predicted potential yields (Yp) were 800-950 g/m2 and the end of the optimum anthesis period varied from year to year. Average temperature (T, ¦C) and total irradiance (+R, MJ/m2) for a preanthesis period of 500¦C days (>3¦C) or a maximum of 60 days explained 61% of the variation in Yp: Yp=981 - 53.4T+ 0.51 +R (g/m2). Using historical weather data and frost risk restrictions indicated an optimum anthesis period between 22 September and 10 October when average predicted yields were reasonably stable. Flowering after mid-October caused reductions in average predicted yield of 70 g/m2 or 11 % per 1-week delay in anthesis. Kernel weights decreased by 5% per 1¦C above 14¦C, but this decrease was also associated with increased kernel numbers. High-yields under irrigation can only be achieved consistently and efficiently with lodging resistant (short, stiff stems) or avoiding (early maturing) genotypes. Very early maturing types for late sowing dates are currently not commercially available. Adjusted management practices (e.g. relatively late sowing) and lower target yields are recommended for current lodging susceptible varieties.