Response of canola and Indian mustard to sowing date in the grain belt of north-eastern Australia

Abstract

Sowing date is an important determinant of yield in canola. The arrival at an optimum sowing time will depend on trade-offs between lowered frost risk with delayed sowing and lowered yield potential. A comprehensive analysis of response to sowing date has not been conducted for northern environments, a new region for canola production. The aim of this study was to analyse the response of phenology, yield and oil content of current cultivars of canola to sowing date (April–September) in north-eastern Australia, using 17 sowings from Tamworth (31.09°S) to Lawes (27.55°S). Three cultivars were studied: an early and late flowering canola and an advanced breeding line of Indian mustard. For all 3 genotypes, a delay in sowing shortened the time to 50% flowering and to maturity, while differences among the genotypes in time to flowering for sowing dates around 15 May reflected their known differences in phenological development. For sowings at Tamworth beyond 15 May, a 1 day delay in sowing delayed flowering by 0.42, 0.42 and 0.37 days in Indian mustard, Monty and Oscar, respectively. Delay in maturity was 0.58, 0.56 and 0.54 days per day delay in sowing date. Yield and oil content penalties due to delayed sowing were similar to those found previously in other Australian environments. The decline of grain yield with delay in sowing date could be largely explained by the decline in biomass at maturity, while for oil content it could be related positively to harvest index and seed size, and negatively to temperature conditions post-anthesis. Indian mustard had a lower harvest index, grain yield and oil content than both canola cultivars. Oil content exceeded 40% in canola in half of the sowings. Information on the response of oilseed Brassicas to sowing date can be used to quantify the trade-offs between frost risk and crop productivity with sowing date for different cultivar types.