WA canola growers can refer to new research to identify the optimum sowing window to maximise crop yields, the AusCanola 2018 conference in Perth was told last week.
The research and the modelling behind it was undertaken by the Department of Primary Industries and Regional Development (DPIRD) with co-investment from the Grains Research and Development Corporation.
DPIRD used the Agricultural Production Systems Simulator (APSIM) to compare canola yields for a range of sowing dates across 24 locations, three soil types and three canola varieties.
DPIRD research officer Imma Farre said as a rule of thumb, the optimum sowing window to maximise canola yields for low and medium rainfall zones was in April, while for high rainfall locations the best yields could be achieved by sowing before the end of May.
Dr Farre said the modelling confirmed field research that the “sweet spot” was based on temperature, radiation and water availability that achieves the crop’s biomass at flowering that maximised final yield.
“Typically, crops sown very early encounter a yield penalty when temperatures are high and the crop grows rapidly and biomass at flowering is low,” Dr Farre said.
“Similarly, late-sown crops have a shortened period from sowing to flowering, reducing the biomass at flowering and the yield potential.”
Dr Farre said the sowing time also influenced the crop’s exposure to the risk of frost and heat at the crucial flowering time.
“Sowing very early increases the risk of frost damage, if the crop experiences frost stress during early grain filling,” she said.
“Later sown crops also risk greater exposure to heat stress during this growth stage, resulting in yield penalties.”
The research is also designed to help canola growers to evaluate the likelihood of achieving a target yield or break even yield for a given location if the sowing opportunity is late.
“For example, the chances of a target yield from a late sown crop at the end of May varies significantly throughout the grainbelt,” Dr Farre said.
“According to the simulation, for end-May sowing there is only a 15 per cent chance of achieving at least 1.5 tonnes per hectare at Kellerberrin, but a 45pc chance at Mingenew, while at Kojonup there is a 95pc probability, based on 41 years of climate data.”
There has been a growing trend towards sowing canola earlier and earlier in WA in recent years due to variability in the break of the season during autumn.
“Very early plantings are at risk of lower yields than the optimum time but sometimes there are good reasons to sow earlier than the optimum sowing date,” Dr Farre said.
“Early autumn rains have been known to be followed by long dry periods and if the early opportunity to plant is not taken, another may not occur until after the optimum sowing window has passed.
“This can be the case in low rainfall, short growing season environments, where it may be better to sow earlier than risk missing the opportunity to sow at all.”