Optimum canola densities tested for lower-rainfall zones

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A man standing in a paddock of canola

Mark Seymour, leader of the GRDC-DAFWA tactical break crop agronomy project in WA, at a trial site examining canola plant density at Salmon Gums in 2013.


Research into plant density is helping to piece together the agronomy jigsaw for canola production in Western Australia’s medium and low-rainfall zones.

This is part of the new five-year ‘Tactical break crop agronomy in Western Australia’ project, a joint project between the GRDC and the Department of Agriculture and Food, WA (DAFWA).

The aim is to finetune tactics for profitable production of non-cereal break crops, focusing on areas where these are not traditionally grown.

Project leader Mark Seymour, of DAFWA, says break crops reduce the risks of vulnerability to weeds, disease and declining nutrition in continuous wheat rotations.

He says canola is a highly profitable break crop in many areas of the wheatbelt, but establishment rates fluctuate widely (from 30 to 80 per cent) with changes in soil moisture, soil temperature and variety.

In 2013, 12 trials were set up in low and medium-rainfall areas from Mullewa to Salmon Gums to assess plant density responses in different herbicide-tolerance systems.

Varieties used in these trials were:

  • open pollinated (OP) triazine-tolerant (TT) Telfer (low-rainfall zone) and ATR-Stingray (medium-rainfall zone);
  • hybrid TT Hyola® 450TT;
  • OP Roundup Ready® (RR) GT Viper; and
  • hybrid RR Hyola® 404RR.

There were eight plant density levels assessed, from five to 80 plants per square metre.

The project team found Telfer – which is the most popular variety in WA’s lower-rainfall areas – had higher economically optimum plant density levels (31 plants/m2) than hybrids or RR canola.

Mr Seymour says RR hybrid Hyola® 404RR had the lowest economic optimum plant density levels of 20 plants/m2 on average across the trial sites.

He says at a cost of about $31 per kilogram for seed and relatively high yields at low plant densities, the yield and economic response from Hyola® 404RR flattened out after reaching that density level.

“The TT hybrid Hyola® 450TT and the OP TTs Telfer and ATR-Stingray had higher average economically optimum plant densities ranging from about 23 to 31 plants/m2,” he says.

“This equates to a seeding rate of about 2kg/hectare for OP TT and RRs and hybrid RRs and 1.5kg/ha for hybrid TTs.
“If 1.5kg/ha is risky or too low for seeding equipment to handle, the extra cost of bumping this up to 2kg/ha is about $12/ha.”

Mr Seymour says the RR hybrid Hyola® 404RR produced the best gross margins at most trial sites.

He says both hybrids tended to outperform the OP varieties in yield and gross margin at the same plant density at many of the 2013 trial sites in southern regions.

For example, Hyola® 450TT had the highest gross margin of $473/ha at Salmon Gums, compared with $343 to $389/ha for other varieties.

However, in central and northern wheatbelt areas, the RR hybrid outperformed the TT hybrid.

Mr Seymour says, overall, the trials highlighted that economic optimum plant density for canola differs for each variety and herbicide-tolerance system and adjustments need to be made according to the rainfall zone.

But, in general, a density of 20 plants/m2 was adequate in the trials for hybrid varieties and 30 plants/m2 optimal for OP TT varieties in most medium and low-rainfall areas to achieve canola yields of about 1 to 2t/ha.

“Above this level, there was a significant drop in yields at Mullewa and at other sites there was no economic gain, due to high seed costs,” he says.

“And at lower plant densities of five to 15 plants/m2, there was a tendency to produce plants that were less competitive with weeds and grew thick stems, making harvest more difficult.

“The optimum levels we uncovered in these trials are probably at the lower end of what most growers would use.

“So there may not be much economic benefit in increasing canola plant densities above these levels in low and medium-rainfall parts of the wheatbelt.”

More information:

Mark Seymour
08 9083 1111

A fact sheet on Growing Hybrid Canola is available at: www.grdc.com.au/GRDC-FS-GrowingHybridCanola


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