Continuous croppers Andrew and Karly Dumaresq say grading their retained open-pollinated canola and only sowing the largest seed available is a worthwhile risk management strategy.

Andrew and Karly, who crop 1600 hectares at Gregadoo, New South Wales, started having their canola sized by Hart Bros Seeds four years ago in response to research findings and encouragement from Riverina Co-op agronomist Nigel Clarke.

The findings from former NSW Department of Primary Industries research agronomist Rohan Brill, with GRDC investment, showed seed size matters for canola establishment.

"When it comes to retaining open-pollinated canola, growers should target a seed diameter of two millimetres," Mr Brill says.

"Research from 2012 to 2014 showed the largest seeds improved early vigour, which followed through to increased grain yield."

Before sowing each year, Andrew sends a semi-trailer load of ATR Wahoo (PBR) to Hart Bros Seeds north of Old Junee.

There, for about $100 a tonne, an aspirator is used to remove trash, weed seeds and debris, before the grain is sieved and put on to a gravity table to separate the heaviest seed (usually more than 1.8 to 2mm in diameter, depending on seasonal conditions) from the lightest.

Andrew Dumaresq holds some canola seed that has been graded to more than 1.8 to 2.0mm in size. Photo: Nicole Baxter

Andrew picks up the large seed earmarked for sowing and sells the remaining small seed to Riverina Oils & Bio Energy, a canola crushing plant north of Wagga Wagga.

In 2019, 28t of canola was sent for sizing, which yielded about 2.8t of seed.

Early sowing

Sizing the canola allows 500 to 550ha of the slow-developing variety ATR Wahoo (PBR) to be sown from early April, depending on subsoil moisture and forecast rainfall.

The couple like to sow early on the basis of research by Mr Brill, which showed a yield loss of five per cent per hectare per week where sowing is delayed.

"Having our seed sized allows us to sow early and deeper - down as far as 30mm beneath the soil surface," Andrew says.

"Sowing larger seeds deeper to chase moisture means the seeds have the vigour to punch out of the ground after germination."

Andrew says sizing open-pollinated canola also means his seed cost is significantly lower.

"I think we are getting a larger seed than what we would buy," he says.

Although many people have thrown out ATR Wahoo (PBR), Andrew says the variety suits the couple's environment. But he stresses that it needs to be sown early so it flowers during September to October.

Sowing rates

Using an Excel disc seeder set on 300mm row spacings, Karly sows the canola at 2.8 to three kilograms/ha to establish 50 to 60 plants per square metre.

"We sow at a higher rate because we have the potential to lose seedlings due to slugs or other pests," Andrew says. "Slugs can be a problem if there is a wet autumn."

A sow-by-the-calendar approach is taken, provided there is subsoil moisture and rain is forecast.

"The advantage of our zero-tillage system is that if we can get 10mm of rain, the canola will germinate and push through the soil," Andrew says.

"If there was no subsoil moisture we'd either reduce our canola hectares or not plant any at all.

"In the past, canola could be sown dry because spring rainfall was reliable - but now we don't seem to get seasons with finishing rain."

Moisture critical

In 2019, Andrew says subsoil moisture underneath a 2018 failed lupin crop meant that with a little bit of March rain, the canola could be established in early April.

And the benefits of sowing large open-pollinated canola early can be seen in Andrew and Karly's 2019 yield results.

Last year their average canola yield was 2.3t/ha - the best result they have had for 260mm of in-crop rainfall.

Andrew says this is because parts of the farm can become waterlogged in wet seasons.

For example, in 2016, he says their lowest canola yield was 0.3t/ha on average, because it was grown on country that became too wet.

"We now embrace the wet years, because when the dry years come we tend to record better yields because our soil holds the moisture," he says.

During 2019, Andrew and Karly grew a bag of the hybrid canola SF Ignite TT, which yielded 2.6t/ha, a good result compared to an adjacent crop of ATR Wahoo (PBR), which yielded 2.4t/ha.

"But if our country became too wet and the SF Ignite TT yielded poorly, we would have lost $60 to $70/ha worth of seed versus about $15/ha for the ATR Wahoo (PBR)," Andrew says.

"If we have an early autumn break and there's plenty of subsoil moisture, we might venture more into growing hybrids, but when you lose confidence in the seasons, growing large open-pollinated canola seed is just about managing risk."

GRDC Research Code DAN00129

More information: Andrew Dumaresq, 0418 223 855, dumaresqs@bigpond.com.au