Three years of trials by the Grains Orana Alliance (GOA) in the central-west region of New South Wales have consistently failed to demonstrate a canola yield or oil response to the addition of sulfur, which challenges the current recommended practice for canola.
GOA established four trials in 2010 to fine-tune its sulfur fertiliser programs by investigating the timing of application and the form of sulfur fertiliser and its impact on yield and oil percentage. Three of these sites were on red loam soils identified as highly responsive situations.
Maurice Street, GOA chief executive officer, says: “None of these trials resulted in any response to sulfur fertiliser, regardless of form or timing. Given that most canola growers apply 20 kilograms of sulfur per hectare as a matter of course this is likely to be reducing growers’ profitability.”
Following these initial results, GOA established numerous trials during the past two years to investigate sulfur nutrition in canola crops. None of these trials responded to sulfur in oil or yield. A number of trials run by other organisations also failed to demonstrate any benefits from sulfur fertiliser application.
“More than 20 trials have been run over the past three years and none have responded to sulfur,” Mr Street says. “This does not exclude deficiency and yield penalties from occurring but does highlight that the frequency and the likelihood is not high.”
A standard recommendation emerging from 1992 trials was to apply 20kg/ha of sulfur to all canola paddocks and to apply 30kg/ha where the soil was lighter and sulfur deficiencies had previously been seen. This recommendation was widely adopted and is still accepted today as quoted in the 2009 Canola best practice management guide for south-eastern Australia.
“Our trials show that the frequency and predictability of sulfur deficiency may not be as high as suggested by the 1992 trials,” Mr Street says.
While GOA’s trials showed no response to sulfur, there was often a strong response to increased rates of nitrogen fertiliser application.
“Within the original reports the overwhelming message was that nitrogen was paramount to achieve maximum profitability for canola in nearly all cases. However, when thinking about fertilisers most growers think of sulfur before nitrogen,” Mr Street says. “Growers need to think about reducing their rates of sulfur application to that which more closely matches their crop removal rates, but also consider boosting their nitrogen fertiliser application.
“Nitrogen applications are much more reliable in yield responses than sulfur and will in turn be more profitable.”
Decisions on fertiliser application are very much dependent on the individual paddock and situation. Deep soil tests are recommended before making a decision based on this research.
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