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Physiology Matters: Adjusting Wheat-Based Management Strategies for Oilseed Production

Physiology Matters: Adjusting Wheat-Based Management Strategies for Oilseed Production

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Taylor Beard, Crop and Soil Sciences, Washington State University, Karen Sowers, Crop and Soil Sciences, Washington State University, William Pan, Crop and Soil Sciences, Washington State University
For more than a century, growers have honed their management practices to meet the needs of the wheat-dominated Inland Pacific Northwest. As a result, even though we have a broad range of soil types and environments, the region lacks crop diversity. Oilseeds, however, are recognized as potential rotational crops due to their ability to extract deep soil moisture in arid environments. For growers interested in adjusting wheat-based management strategies for oilseed production, this publication describes the physiological differences between crops and recommends modifications based on those differences.
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The Washington State Oilseed Cropping Systems Research and Extension Project (WOCS) is funded by the Washington State Legislature to meet expanding biofuel, food, and feed demands with diversified rotations in wheat based cropping systems. The WOCS fact sheet series provides practical oilseed production information based on research findings in eastern Washington. More information can be found at:


Funding and support for the WOCS provided by:

Washington State Legislature, Washington State Department of Agriculture, Washington Department of Commerce, and the Washington State University Energy Program.



The wheat-dominated inland Pacific Northwest (iPNW) has a broad range of environments and soil types; however, the region lacks crop diversity. Many other semi-arid wheat-growing regions throughout the world have successfully included oilseeds in their rotations for decades (Conley et al. 2004; Kirkegaard et al. 2008; Zentner et al. 2002). While interest in oilseed crops in the iPNW dates back to the 1970s (Divine et al. 1977) production has lagged due to socioeconomics, unique environmental conditions, and agronomic reasons (Pan et al. 2016a).

Growers in the iPNW have fine-tuned their agronomic management practices to meet the needs of wheat production for more than a century. Agronomic approaches to oilseed production require adjustments to account for physiological differences between the two types of crops. By coordinating production practices with growth stages and growing conditions, the impacts of moisture and temperature stress can

be minimized. The iPNW has a winter precipitation pattern with high amounts of snow and rain occurring over frozen soils and less than 40% of total annual precipitation during the spring and summer (Schillinger et al. 2008). This requires crops to be more reliant on stored water and nutrients in the subsoils for sustaining growth and development due to greater water and heat stress during reproductive stages. Some of the greatest production challenges for iPNW crops are (1) plant establishment, (2) winter and early spring frost survival, and (3) water and nutrient use during the summer months.

Oilseeds are recognized as potential rotational crops due to their ability to extract deep soil moisture in water-limited environments more effectively than wheat or peas (Merrill et al. 2004). Opportunities for integrating oilseeds into traditional cropping sequences in the iPNW include (1) substituting spring canola or camelina for either spring wheat or legumes in high rainfall areas (>18”), (2) planting winter or spring oilseeds instead of winter or spring wheat in the intermediate rainfall zone (12–18”), and (3) replacing winter wheat with winter canola every fourth year in the low rainfall zone (<12”).

Crop management is typically tailored to the physiological and morphological traits of each crop. Farm equipment, timing of farm operations, and agrichemical management are also designed in consideration of these traits. While canola producers can take advantage of wheat-based farm machinery and equipment, farm operations need to be tailored specifically to canola physiology and morphology to optimize yield and quality. A review of these differences between crops from planting to harvest, in the context of iPNW environmental stressors, provides insight into recommended modifications of wheat management strategies for canola production.

Seed Size

Wheat has a much larger seed size compared to canola and camelina (Figure 1; Vollmann et al. 1996) resulting in a lower number of seeds per pound and ultimately a higher seeding rate (lb/acre; Table 1). Seed size is affected by both variety and seed production environment (Lamb and Johnson 2004). When deciding on a seeding rate, both seed size and number of seeds per pound become an important factor when targeting specific population goals. Seven to fourteen plants per square foot are recommended to meet yield goals of spring canola (Canada Council) and 4–15 plants per square foot for winter canola (Boyles et al. 2009). In comparison, optimum spring wheat populations range from 30–32 plants per square foot, and



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