Willenborg: Exploring the Ecological Impact of Canola-Inclusive Cropping Systems in Western Canada
Date: May 2013
Term: 3 years
Status: Completed
Researcher(s): Christian Willenborg, University of Saskatchewan, Ted Chastko, University of Alberta, Julia Leeson, Agriculture and Agri-Food Canada (AAFC), Saskatoon SK
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Researchers in Saskatchewan led a three-year study to assess the potential effects of increasing the frequency of canola in rotation on weed abundance, species distribution, community diversity and function in canola-inclusive rotations across western Canada. Using a combination of existing weed survey data and field surveys, the study results showed that herbicides play a major role in shaping the weed community, although there was no indication that increased frequency of canola or herbicide systems had any effect on weed species diversity. However, the risk of developing herbicide resistant weeds under continuous canola production is high and extreme caution must be used when incorporating a risky practice such as this into a cropping system.
In order to meet increased canola production demands and the needs of emerging markets, canola growers will be enticed to grow more canola more often. As producers shorten rotations and reduce cropping system diversity to grow more canola more often, the sustainability of the cropping system is likely to be reduced and the pest management impacts are expected to amplify.
Researchers at the University of Saskatchewan in collaboration with Agriculture and Agri-Food Canada (AAFC) in Saskatoon, led a three-year project to assess the potential effects of increasing the frequency of canola in the rotation (decreased rotational diversity). The main objective of the research was to study weed abundance, species distribution, community diversity and function in canola-inclusive rotations across western Canada and their relationships with management practices, frequency in the crop rotation, and diversity of the crop rotation.
The research included a combination of data mining of existing weed survey data with “ground-truthing” by assessing species diversity and composition in field trials. Extensive data mining of existing weed survey data was conducted, including crop management practices and weed species abundance, for Saskatchewan between 1976 and 2012, and for Alberta and Manitoba between the years of 1995 and 2010.
Field data was collected during the growing seasons of 2011 and 2012 from two sites at Lacombe and Lethbridge, Alberta, part of a collaborative trial led by Neil Harker, AAFC (Canola Rotations Study) comparing crop rotations with 0-, 1-, and 2-years intervening since the previous canola crop was grown. Two canola varieties were used, (Liberty Link L150 and Roundup Ready 73-45), with rotation 0 comprised of the same variety of canola grown continuously each year, rotation 1 consisted of canola followed by wheat, while rotation 2 was comprised of canola-pea-barley. In 2012, field data was also collected from 464 canola fields surveyed in Saskatchewan.
The final study results indicated that specific weed species are associated with increased frequency of canola in the crop rotation. The field survey results showed that wild buckwheat (75% of fields) was the most frequently found species, followed by green foxtail and wild oat (almost 50% of fields). Dandelion, shepherd's-purse, Canada thistle, lamb's-quarters, spiny annual sow-thistle and volunteer wheat were found in 40 to 45% of fields. (See Table 1). The existence of relatively few weed species consistently found in canola fields throughout the province is attributable to restricted geographic distribution of species and varying efficacy of management.
Table 1. Top twenty abundant species in 2012 Saskatchewan canola (464 fields).
Uniformity Density Relative
Rank Species Frequency All Occurrence All Occurrence Maximum Abundance
Taken together, the results suggest the majority of weed species community composition can be explained by site, however the effects of time (herbicide application) and rotational diversity were also significant. However, there was no indication that increased frequency of canola or herbicide systems had any effect on weed species diversity. The results of two Saskatchewan field surveys, where the majority of the canola surveyed was grown using HR systems, had contrasting weed diversities. Under the dry conditions of 2003, weed species richness was lower than ever previously recorded and under the wet conditions in 2012 weed species richness was higher than ever previously recorded. This indicates that weather has a larger impact on weed diversity than management system.
Figure 1. Number of species per field in each survey year.
The data also suggest that volunteer canola was the major weed issue associated with continuous canola cultivation, along with relatively few other weed species. This can be attributed to the high efficacy of the herbicides used in herbicide-tolerant canola production, which provide excellent weed control on a consistent basis. However, the risk of developing herbicide resistant weeds under continuous canola production is high and extreme caution must be used when incorporating a risky practice such as this into a cropping system.
Full Report PDF: n/a