Canola rotations and sustainability

Key result: A nine-year AAFC study compares canola in continuous, two-year and three-year rotations and finds that continuous canola costs more and yields less than canola in rotation with other crops. Whole-rotation revenue is similar, but continuous canola is the less sustainable option.

Project title, Principal investigators: “Canola Sustainability – Risk Mitigation,” Neil Harker (retired) and Breanne Tidemann, AAFC Lacombe

Funding: Growing Forward 2

Continuous canola yields less than canola in a two-year or three-year rotation. That yield gap can be narrowed with added inputs, but the questions then are whether the economic cost to manage a continuous canola rotation is worth the risk to the farm and whether continuous canola presents other longer-term risks to sustainability.

This nine-year rotation study compared continuous Liberty Link canola, continuous Roundup Ready canola, canola in a two-year rotation with wheat and canola in a three-year rotation with peas and barley. Trials were repeated at five locations across the Prairies and “all phases” were repeated each year. For example, for the canola-barley-peas rotation, every phase of the rotation – canola, peas and barley – were grown each year to eliminate the confounding effect of different environmental conditions each year.

When all sites and years are averaged, canola yield improved 5 bu./ac. with a one-year break and another 5 bu./ac. with a two-year break. While this is an average, Tidemann notes that results were quite different year to year and site to site. In Melfort, Sask., for example, there was no yield difference between rotations in 2012, but in 2016, canola yields were 17 bu./ac. higher with a one-year break and 34 bu./ac. higher with a two-year break.

When looking only at high-input results for continuous canola, the yield gap between continuous and rotation canola narrowed, suggesting that farmers can rescue most of the lost yield with continuous canola by investing more in crop inputs.

Canola’s selling price per tonne is higher than peas, wheat and barley, and even with lower yields, continuous canola can still pencil out better on some farms. This does come to light in economic analysis for this study. Even with higher input costs and lower yields for continuous canola, net returns, when averaged across all years and all locations, were similar for all rotations. From the farmers perspective, the question is whether spending more on inputs to make the same money is worthwhile.

In a related recently-published study, (“Attempts to rescue yield loss in continuous canola with agronomic inputs,” Harker et al, Canadian Journal of Plant Science, 2018) the researchers investigated whether it was possible to compensate for yield losses in continuous canola by increasing inputs. Blackleg resistance was a priority. “Other possible strategies to rescue yield that declines under continuous canola would be to apply inputs at levels higher than “standard practice” (SP), to increase tillage, or to remove chaff. Our objective was to determine if higher fertility levels alone or in combination with a higher seeding rate, tillage, chaff removal, or additional fungicide could increase continuous canola yield compared with SP. We hypothesized that additional inputs and some nonstandard practices in continuous canola would increase yields compared with SP and would recover yields to levels similar to canola yields in rotation with other crops. Furthermore, we hypothesized that yield recovery would be greater after two or three years of consecutive treatments.”

These hypotheses were confirmed with the results. Continuous canola, when given fungicide to manage blackleg and 50 per cent higher fertilizer rates, could achieve yields comparable to canola in rotation. But the paper concluded that “higher fertility regimes in continuous canola may not be as economically viable as simply rotating to other crop species.” And added: “Aside from blackleg monitoring, we did not address additional continuous canola production risks from other pests; these might well impact canola’s long-term sustainability.”