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Canola’s role in wheat yield increases shows out

Canola’s role in wheat yield increases shows out

The inclusion of canola in crop rotations is being linked to significant increases in wheat yields - and not only in those wheat crops sown immediately after canola.

According to Dr John Kirkegaard of CSIRO Plant Industry, analysis of 26 trials involving canola in south-eastern Australia has shown that, on average, wheat after canola yielded 20 per cent more than when a wheat crop was sown after wheat.

“The two-year gross margin was 25 per cent higher for canola/wheat than for wheat/wheat and much of this benefit derived from improvements in the following wheat crop rather than canola itself,” he said at a Farmer Research Update held at Birchip.

Dr Kirkegaard and his CSIRO colleagues attribute the yield improvements in wheat following canola to the oilseed’s ability to suppress wheat root diseases and to improvements in soil structure following a canola crop. They say that this leads to increased water and nitrogen uptake, particularly from the subsoil, which also often results in improved grain protein levels of wheat.

At the Update, which was supported by growers and the Federal Government through the Grains Research and Development Corporation and the Birchip Cropping Group, Dr Kirkegaard said canola’s influence on wheat yields also occurred “further down the rotation”.

“Field studies show that second and third wheat crops in a sequence can yield up to 13 per cent more when the sequence commences with canola rather than wheat,” he said.

In some cases these residual benefits could be explained by the continuing benefits of lower levels of root disease. However, a recent study near Rutherglen by Rob Harris of Victoria’s Natural Resources and Environment Department showed benefits to a wheat crop in the fourth year of a rotation, which commenced with canola even though the break crop, lupin, had been included in the sequence. The reasons for this were unclear.

Reporting on other canola-linked research Dr Kirkegaard said:

- There had been reports of poor wheat crops in southern NSW grown after canola where direct drilling and sulfonylurea herbicides had been used but zinc applications had alleviated these problems. Recent research by the CSIRO’s Dr Megan Ryan suggested that the problem was worse in some defined areas such as the Wimmera and that it was associated with conservation farming, sulfonylurea herbicides and inadequate fertiliser applications.

- Work by the CSIRO’s Ms Sarah Bruce had shown that where wheat stubbles of more than 2t/ha were spread evenly across paddocks, canola growth and yield could suffer but canola could be successfully grown after wheat if the stubble was pushed into the inter-row space before seeding.

- The Best Bet Canola Management Project in southern NSW, managed by Harden Agricultural Consultants, had shown in 2001 that the disease sclerotinia was the major yield-limiting factor, reducing yields by 0.2 to 0.9t/ha depending on the area, sowing date and the variety.

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