Delays bad for yield outcome

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Cally DupeThe West Australian
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A graph showing optimum canola sowing times.
Camera IconA graph showing optimum canola sowing times. Credit: Department of Agriculture and Food WA

Canola growers holding off planting because of dry conditions are facing a narrowing window of opportunity.

Department of Agriculture and Food WA development officer Jackie Bucat said circumstances varied according to location and rainfall.

She said farmers in low rainfall areas had until roughly the start of June to plant canola before potential yields dropped too low.

“(Areas) such as the Lakes district, probably only have until the start of June to sow canola before potential yields drop too low,” Ms Bucat said.

“In high-rainfall areas, where a cooler finish to the season is more likely ... modelling shows canola is still a good proposition until the end of June.

“After that, pasture might be a better option.”

The variable start to the season has some farmers feeling jittery that newly sown crops might not germinate after low or null and void rainfall in April and May.

Some farmers, Ms Bucat said, would turn their attention to other crops, pastures or fallow rotations.

“The opportunity to plant canola in low-rainfall areas north of Merredin has most likely passed,” she said.

“There could be more profitable crops to sow than canola — keeping in mind the impact of changing the crop rotation — or giving paddocks a rest.”

Canola sowing was delayed in parts of the grain belt, particularly in the eastern and northern regions, this year.

The impact of delayed sowing on canola yields has been analysed by DAFWA, which evaluated previous “time of sowing” canola trials from across WA.

It compared canola yields sown at 10-day intervals from May 10 to June 29 at Mullewa, Wongan Hills, Merredin, Kojonup, and Gibson from 1976-2016.

Research was refined to model the differences for five locations across the grain belt, using historical rainfall data and this year’s rainfall up to mid-May.

Ms Bucat said results showed a similar rate of yield loss across the field trials after mid-May.

“Average yield losses were 15 kilograms per hectare per day for the last week of May, increasing to 25kg/ha/day in June,” Ms Bucat said.

“I expect these results to be reasonably robust because of the similar rate of loss in most trials.”

Ms Bucat urged growers to carefully consider a canola crop’s yield potential.

She said growers should compare it to the returns from an alternative cereal crop or options, including leaving paddocks fallow or return to pasture.

DAFWA senior research officer Bob French said modelling showed there was little benefit gained for most growers from leftover stored soil moisture.

He said substantial yield losses occurred later and estimated yields were higher in longer season environments, including Kojonup and Esperance.

“Current yield losses are likely to be greater in low-rainfall environments,” Mr French said said. “About 30kg/ha/day at Wongan Hills and Mullewa, 12kg/ha/day at Kojonup.”

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