To determine the long term impact of continuous or short rotation canola on weed, insect, and disease pressures, as well as effects on soil microbial diversity and the economic impact of these rotational choices.
Canola is a popular and profitable crop for Canadian farmers. The ability to profit means some farmers have increased the proportion of canola in their rotation leading to canola being grown continuously or every second year. This study was the final three years of a 12 year long study comparing yield as well as pest risks from growing canola continuously compared to every second year or every third year. The results from these three years are consistent with the results throughout the study in that canola yield increases when not grown continuously. Previously, statistics suggested that for each year out of canola there was an equal increase in yield (i.e. 5 bu/acre yield increase for each year out of canola). These final three years suggest that the yield benefit is highest moving from continuous canola to every second year (~7 bu/acre) and is less moving from every second year to every third year (~2 bu/acre). Additional exploration into the data is needed to explain why this is the case.
Weed pressures were highest in continuous canola prior to spraying, but in the canola every second year rotation post-herbicide application. Root maggot damage decreased with each year out of canola but the overall range of damage was quite low. Frequency of canola in a rotation did not impact days to crop maturity, although the Liberty Link variety matured about 1 day earlier than the RoundUp Ready variety.
Additional analyses still need to be conducted including on blackleg incidence, and quality, which was interrupted by the Covid pandemic. In addition correlation analyses will be used to determine if there is a relationship between some of the data such as weed density and yield (i.e. perhaps weed density is impacting the canola yield). Economic analysis looking at profitability of the rotations is just getting underway and analysis of microbial biomass samples is also ongoing. We will also be conducting analyses across the entire twelve year study, as well as the final six years to look at trends and changes over the entire course of the study. There is a lot more information to be gained from this study with additional in depth statistics to be run.
The information from this study will help to identify the most sustainable ways to grow canola in terms of agronomic aspects like yield and weed pressures, but will also look at the economics involved. Key messages for producers right now is to extend the number of years between canola crops to reduce risks associated with weeds (and possible selection for herbicide resistance), insects and decreases in yield.