Crop rotation impacts canola yields

A new Ag Canada study finds that increasing the number of years in your rotation between canola crops can raise your average canola yields

Canola is one of the biggest crops in Canada and it’s only getting bigger. In the five years from 2008 to 2013 Canadian farmers went from growing 10 million to 18 million metric tonnes, nearly doubling the canola harvest. With market demand anticipated to only increase in years to come, driven by a rising global demand for vegetable oils and other canola products, the same land is going to have to yield ever more bushels per acre.

Raising canola yields on the same land requires more intensive cultivation as well as rotating canola more frequently than in the past. This strategy carries significant risk of heavy losses as many canola pests and diseases are capable of overwintering in fields and on surrounding vegetation making them harder to control.

To test out the possible effects of this more intensive cultivation, researchers from Agriculture and Agri-Food Canada undertook a series of trial to see what happens. This team, which includes Neil Harker of the Lacombe Research Centre in Alberta, recently published their results in the Canadian Journal of Plant Science under the title “Canola rotation frequency impacts canola yield and associated pest species.”

The research

To study the effects of more intensive cultivation the scientists conducted six years of trials at five sites across the Prairies using glyphosate and glufosinate resistant canola, treating them with the recommended amounts of herbicide each season. Each field had previously grown no-till wheat, barley, or oats. In different fields, they tested different rotation rates, alternating canola with various crops on one- and two-year intervals. After five years, researchers collected and analyzed the data, looking for the effects of temperature and precipitation, weed densities, blackleg disease levels, root maggot damage and canola yield.

“In terms of the number of sites,” Harker told us, “and the way it was conducted there hadn’t been a study quite like this before. To make this more useful we conducted an all-phases study, which means that if we had wheat in one year and canola the next we also had canola in that first year and wheat the next.” The all-phases nature of the research helped the research team eliminate single-year effects, like weather that may have just been, by chance, better for one crop rather than another.

The results

Among the major results of the study was the finding that canola seed yields were not hurt significantly by decreasing the years of rotation between crops. At the same time, canola yields always improved when wheat or field pea were followed by barley between canola plantings. So while there was not significant loss with intensive cropping, yields were higher with rotations, as was expected. “What stood out to me the most,” Harker said, “was how consistent the improvement in production was with years between canola crops. In other words as you go from zero years (between crops) or continuous canola you had yield improving constantly as you put both one year and then two years between them.”

As for diseases and pests, the study confirmed what was long suspected, that growing canola intensively invites increased yield losses due to predation. “As you went from zero to two years,” Harker said, “you had pests, whether they were insects or disease, decreasing.”

Without a year or two of rotation between canola persistent pests proved highly resilient and hurt yields significantly. Another result of interest was that higher yields were produced at sites that had relatively uniform precipitation (no extremes of wet or dry) and generally cooler temperatures. If you live in a region that regularly experiences cooler than provincial average temperatures this may be another reason to consider canola planting.

While high frequency rotation of canola may be profitable in the short term it will be highly risky in the long term. To ensure sustainable production (and a profitable farm) the researchers recommend that farmers balance high immediate-income low diversity cropping with lower immediate-income, higher diversity systems. This can be accomplished by not using your entire farm for intensive cropping but only a portion, retaining one area in longer-term canola rotation. Managed over several years, rotating the areas of higher intensity cultivation, can yield strong returns for the careful farm manager.

Harker and his colleagues plan to continue the study for three more years. In addition to seeing how the trends they’ve identified continue they will be working with economic specialists to calculate the effects of different rotation strategies on a farmer’s bottom line.

About the author

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Michael Flood is a business writer and columnist. You can reach him at [email protected]

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