Deep-rooted canola holds on in the dry

Deep-rooted canola holds on in the dry

Cropping News
CSIRO farming systems agronomist John Kirkegaard has been investigating canola's deep roots and agronomy to capture benefits during the growing season. Photo by Nicole Baxter/ GRDC.

CSIRO farming systems agronomist John Kirkegaard has been investigating canola's deep roots and agronomy to capture benefits during the growing season. Photo by Nicole Baxter/ GRDC.

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Research over the past couple of years has shown that early sown, longer-season varieties of canola have the potential to perform well during a dry finish, largely due to their root depth.

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RESEARCH over the past couple of years has shown that early sown, longer-season varieties of canola have the potential to perform well during a dry finish, largely due to their root depth.

The 2018 and 2019 seasons showed researchers from CSIRO that stored moisture from summer rain could be capitalised on by sowing canola earlier with varieties that will still flower at the right time to miss heat and frost.

The past two years have confirmed observations from the Optimised canola profitability project, a collaborative study between CSIRO, the Grains Research Development Corporation and others.

The project had suggested that earlier sown, slower-maturing varieties had a yield advantage over later varieties in seasons where there is stored soil moisture but it turns dry in the spring.

CSIRO farming systems agronomist John Kirkegaard said they found that a range of canola varieties were growing down at about two centimetres per day from sowing to flowering.

"After flowering they were slowing to about 1cm per day, so that was getting them well down to three to four metres when they were on soils that had that depth," Dr Kirkegaard said.

"We were getting roots taking up significant water down to around three metres, it was often 25 to 30 millimetres of water from down there that these earlier sown varieties were capturing.

"They were often converting that into up to one tonne of yield, so you're looking at very high water usage efficiencies, up to double what you'd expect from a total seasonal water point of view."

On average, across about 20 trials, in yield ranges from 1.5 to 3.5t, the research team was getting a 0.4 tonnes a hectare advantage from the earlier sown varieties.

However, there are agronomic issues to consider, especially the impact on deep stored soil moisture that may no longer be available to the following crop.

Dr Kirkegaard said while it's great to be able to sow one of the early varieties, capture that soil moisture and make quite a bit of profit, that canola is going to use a lot of water and nitrogen.

He said if growers then went into a very dry summer and a very dry autumn, they may need to rethink what the crop sequence was going to be.

"Starting the season with a completely dry profile, for some of the options growers might have been looking at, is risky," he said.

"What we suggest is to think about crops that might be more successful from a later sowing to give yourself time to capture some soil moisture, things such as barley or grain legumes which can be sown later with success.

"One of the other considerations to keep in mind is how much cover is left.

"If you've got a lot of cover, maybe a grain legume is an option because they don't tend to produce a lot of cover.

"Whereas if you don't have cover you may well want to lean towards a barley or a cereal, something that is going to produce more cover and get that crucial level of cover back up."

Another agronomic issue is that canola is a big user of nitrogen, so longer season, earlier sown crops will not only use the water but also use the nitrogen.

Dr Kirkegarrd said sequencing into these crops with something like a grain legume was a good option as they stored water and nitrogen.

"Those two resources are then available to the canola crop," he said.

"Canola needs about 80 kilograms of nitrogen per tonne of grain expected, so that supply needs to be there."

While yield is the main advantage of the earlier sown crops, in an Australian system there is the added bonus that generally they produce a lot more biomass early and through the autumn

"If growers have animals in their enterprise, they can graze those crops in the winter, providing they get the animals off at the right time, they won't have an impact on the grain yield, so that biomass just contributes to profit," Dr Kirkegarrd said.

"The winter canola will, from a March sowing for example, put on a lot of biomass which provides good grazing in the autumn, allows you to get the animals off the pasture and give them a rest."

Overall, a lot of summer rain and stored soil moisture gives growers both the opportunity and the confidence to sow canola early, with a slower maturing variety, knowing they've got a bank of water at depth for the roots to access.

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