Northern region grain growers who have good stored soil moisture levels after autumn rain are likely to benefit later in the year from early-sown, longer season canola varieties.
New research has demonstrated the capacity of these crops to utilise deep water to yield well in a tough finish.
CSIRO researcher Dr John Kirkegaard, presented the findings from this project - 'Canola's deep roots and agronomy to capture benefits and manage legacies' - at this year's GRDC Grains Research Update in Wagga Wagga.
The specialist farming systems researcher has also shared his Update presentation in a new GRDC podcast, detailing the results from the key research - which for the first time accurately measured the maximum depth and efficiency of canola roots.
What lies beneath
Dr Kirkegaard says long season canola has proved it can yield well in dry seasons, thanks to root systems capable of accessing soil moisture at depths of three to four metres.
But he urges growers who might be deliberating about whether to try longer season varieties to consider their agronomic and crop rotation consequences - in particular how much moisture would be available to subsequent crops.
"What we found during trials in the very dry periods of 2018 and 2019, where we had some summer fallow rain pre-crop but limited falls during the season, was that we could capitalise on stored moisture by sowing canola earlier," he says.
"These earlier sown varieties have time to develop deeper roots that can capture stored moisture late in the season, which is really important for yield.
"But, importantly, these varieties will still flower at the right time to miss the heat and frost.
"In the past four or five years, these slower maturing varieties have really come into their own in terms of their yield advantage, because we have had some summer rain giving us deep stored moisture, while our springs have been hotter and drier."
The trials built on work conducted as part of the Optimised Canola Profitability project - a collaborative research project with co-investment from the GRDC, CSIRO and the New South Wales Department of Primary Industries - which investigated the potential for early sown canola - from northern NSW to the Eyre Peninsula.
How low can they go
Dr Kirkegaard says brassicas had a reputation for deep roots. But, until now, research in Australia had not accurately quantified their maximum depth and water uptake.
"We found a range of varieties were growing roots down at a rate of about two centimetres per day from sowing to flowering, and after flowering the rate slowed to about 1-1.5cm/day," he says.
"These roots ended up growing down to about three to four metres in soils of sufficient depth."
Dr Kirkegaard says in drier seasons, deep stored water had proven to be 'liquid gold' in farming systems and the long season canola varieties had shown they were capable of accessing deep water with high efficiency.
"We have seen longer season canola drawing up 25-30 millilitres of water from a depth greater than 2m below the soil surface, generating yield increases of up to one tonne per hectare," he says.
"This is really impressive water use efficiency (30-40 kg/ha/mm) for that deep water, and is around double the efficiency we would expect from a total seasonal water (10-15 kg/ha/mm).
"Longer season canola grown in more than 20 trials in 2017 and 2018 achieved, on average, an 0.4t/ha yield advantage from this early sowing system - with total yields ranging from 1.0 to 3.5 t/ha."
We have seen longer season canola drawing up 25-30 millilitres of water from a depth greater than 2m below the soil surface, generating yield increases of up to one tonne per hectare.
Yield performance potential
Dr Kirkegaard says shorter season canola, sown in the ideal window (early May), was also able to match the yield performance of longer season varieties - but only in wetter seasons when deep water was not called upon to support high yields.
"Shorter season canola roots grow at a similar rate to those of longer season varieties, yet because they are growing for a shorter time they don't get as deep," he says.
"However, the depths of about 2m reached by the shorter season canola varieties is still impressive when compared with crops like cereals and pulses."
Yet, Dr Kirkegaard warns the trade-off for planting canola varieties with deep seeking roots is drying out the soil profile at depth - and growers needed to understand the legacy effects.
"If the profile fails to fill up over summer, the dry soil following early-sown canola can be managed by growing crops such as barley, grain legumes or shorter season wheats that perform with a later sowing, allowing time to capture additional moisture," he says.
"If you have dry soil following early canola you may need to think about changing your crop sequence and your sowing date."
Dr Kirkegaard says other agronomic considerations were ground cover levels.
He says if cover is adequate, a grain legume could be a sowing option. If cover is limited, a barley or cereal crop might provide an adequate level of ground cover to protect the soil and preserve moisture.
GRDC Research Code: CSP00187
More Information: Toni Somes, GRDC Communications Manager - North, 0436 622 645, firstname.lastname@example.org