Rotational Effects

Canola and wheat plots in Ritzville, WA.

Canola is considered the most promising oilseed crop for diversifying wheat-based cropping systems in the Inland PNW. Acreage planted to canola in the Inland PNW has increased each year for the past 15 years. Canola serves as a break or non-host crop for many important soilborne pathogens of wheat and helps farmers control weeds. Most studies in the literature report that canola has a positive effective on subsequent wheat yield Degree of influence on soil biological properties and crop productivity is, however, crop specific.Long term cropping systems studies on wheat performance when canola was the previous crop have been conducted near Reardan and Ritzville, WA. Results show that wheat after canola generally has significantly less grain yield compared to wheat after wheat. Analysis of surface soils sampled every year revealed that canola led to decreased microbial biomass compared to wheat. Notably, mycorrhizal fungi and other fungi were reduced following canola. Canola is not a host of mycorrhizal fungi. Declines in viable microbial biomass could interrupt key microbial processes related to nutrient and water acquisition essential for optimal crop productivity.

DNA has been extracted from soil samples collected in 2020 and 2021 at the Ritzville site and will be analyzed for bacterial and fungal communities to identify differences following canola vs wheat. This will complement the phospholipid fatty acid analysis which is concurrently underway. The goal is to understand how canola may impact soil health, both positively and negatively. By understanding the cause of this phenomenon, we can understand the conditions under which it is a problem and possibly how it can be mitigated.

Extension Publications

Cover of winter canola feasibility in rotation with winter wheat.

Winter Canola Feasibility in Rotation with Winter Wheat

Winter wheat-summer fallow rotations are predominate in the dryland cropping region (< 12” of annual precipitation) of eastern Washington. Farmers in this region rely heavily on continuous applications of Group 2 herbicides for winter annual grassy weed control and suppression (see sidebar). This repeated application of Group 2 herbicides that includes Beyond, Maverick, Olympus, Olympus Flex, Osprey, and PowerFlex increases the potential for herbicide-resistant populations of winter annual grassy weeds such as downy brome (Bromus tectorum L.) and jointed goatgrass (Aegilops cylindrica) (Campbell 2011).

Click here to see all the CSS Field Day Abstracts. 

  • Young, F.L. 2012. Synching Chemical Rotation with Crop Rotation. Oral presentation in Pacific Northwest Oilseed Crop Adaptation session. Northwest Bioenergy Research Symposium. Seattle, WA. Nov. 13, 2012.
  • Kennedy, A.C., T.L. Stubbs, W.F. Schillinger, and T.A. Smith. 2010. Soil Quality Differences Among Long-Term No-Till Irrigated Crop Rotations to Replace Burning and Plowing Continuous Wheat [CD-ROM]. Soil Science Society of America annual meeting, 31 Oct. – 3 Nov., Long Beach, CA. ASA, CSSA, and SSSA Abstracts.
  • Young, F.L. and K.E. Sowers. 2010. Introducing Winter Canola in the Wheat-Fallow Region of North Central Washington. American Society of Agronomy annual meeting, 31 Oct.-4 Nov., Long Beach, CA. ASA, CSSA, and SSSA Abstracts 253-8.

For more information on rotational effects contact:

Aaron Esser
Phone: 509-659-3210

PDF Accessibility

If you require an alternative format for any of the content provided on this website, please contact us:

Samantha Crow
Program Specialist 2