Crop rotation: Economics and agronomy

Estimates are for another rise in canola acres in 2018. This will add further short- and long-term yield and agronomy pressure on fields that are already in tight rotations.

AAFC researchers in Lacombe led a nine-year rotation study that 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.

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, results were quite different year to year and site to site. In Melfort, Saskatchewan, 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.

Net returns for each site each year were highly variable, but when averaged across all sites and years, net returns were similar for all rotations.

A concluding document for the study had this statement: “These data refute the notion of continuous canola being the most profitable rotation. Furthermore, these data do not account for increased disease, insect pest and weed threats [from continuous canola] that are likely to threaten sustainable canola cropping over the long term.”

When doing their own analysis, farmers will want to consider how each crop can benefit the other. With peas in the rotation, for example, the positive contribution to canola yield ends up being represented in the canola year, when this contribution should actually be added to the pea economics or be considered as whole-rotation economics.

Further reading:

Rotations and risk management
Canola Digest Science Edition: Year-6 summary for AAFC study noted above
Tips on rotation for clubroot management