- Mallee trials investigate improving canola establishment
- Seeding rates, depths, hybrid varieties and summer herbicide residues researched
- Results show a 1kg/ha seeding rate increase provides positive returns
- No significant effect on yield was observed for other variables
While canola has taken off in recent years as a break crop in the Mallee, due to its usefulness in controlling weeds and diseases, grower surveys by Dodgshun Medlin in 2011 and 2012 found 20 per cent of canola did not establish with sufficient density. This cost the 42 growers surveyed $1.4 million a year in lost yield and additional outlay where resowing was required.
The GRDC funded the research to investigate simple agronomic practices to improve establishment at sites at Paruna in South Australia, and Walpeup and Manangatang in Victoria. The trial investigated seeding rate, seeding depth, variety and the effect of summer herbicide residues on plant establishment.
Dodgshun Medlin R&D leader Ivan Mock says the trials found the most effective way to improve establishment was to increase seeding rate.
Dodgshun Medlin R&D leader Ivan Mock has found that increasing seeding rate can improve canola yields in the Mallee.
PHOTO: Sandra Goodwin
“We know from previous work that 25 to 50 plants per square metre will give the best result in terms of yield,” he says. “In this trial we saw that at 1.5kg/ha, on average the sites achieved 22.7 plants/m2, which was below the target plant establishment.
“When we increased seeding rate to 2.5kg/ha, the establishment increased to 39.2 plants/m2 on average, which is within the target range. Further increasing to a 3.5kg/ha seeding rate gave a mean establishment rate of 52.2 plants/m2.”
In addition to increasing yield, achieving a higher establishment rate would more quickly increase plant density and ground cover, reducing the risk of erosion and providing more competition with weeds.
“Where growers have low plant densities, they should consider increasing the seeding rate. Based on the trial results, the increase would be expected to more than cover the costs of the extra seed in an average year. When growers are expecting low establishment due to sandy or heavy soils, or a dry start to the season, increasing the seeding rate by around 1kg/ha can make a significant difference to yield,” Mr Mock says.
The other three factors tested did not give such significant results. A shallow sowing depth was found to increase establishment where the season started with light showers and less rain; however, this is not always a benefit.
“As most growers will sow canola dry, there’s a risk that any showers that come before the season break will start it growing without enough follow-up rain. It might be better to sow deeper so the plant doesn’t germinate until a more definite season break wets the seedbed,” Mr Mock says.
Varieties did not provide significantly different results in the year trialled (2013), with hybrid varieties providing increased early biomass, but no increase in yield.
Summer and autumn were dry: as little as half the average rainfall was received at some sites. This was not enough rain to deactivate herbicides used in summer weed control. Herbicides evaluated in the trials for carryover effects on canola were 2,4-D ester, 2,4-D amine and Intervix®. However, there was no yield decrease caused by herbicide residues in the trial.
The control plot, where there were no summer herbicides, saw increased plant establishment and ground cover, but negligible difference in yield. There was a slight decrease (0.2 to 0.4 per cent) in oil content from the sites where herbicides had been applied.
“Surprisingly, we didn’t see any difference in the result where we used an imidazolinone-tolerant variety (Oasis Clearfield®). The response to the Intervix® was the same as the non-tolerant variety (Hyola® 450). This may have been different in a higher-yielding year,” Mr Mock says.
“With optimal seeding rate, adequate nutrition, effective weed and pest control and timely operations, two of the three trial sites yielded more than 1t/ha in a season that started with virtually no available stored soil moisture. These yields support the confidence growers have shown for canola as a rotational crop in the Mallee.”
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