Suitability of Winter Canola (Brassica napus) for Enhancing Summer Annual Crop Rotations in Iowa

Project Overview

Project Type: Graduate Student
Funds awarded in 2013: $10,000.00
Projected End Date: 12/31/2015
Grant Recipient: Iowa State University
Region: North Central
State: Iowa
Graduate Student:
Faculty Advisor:
Dr. Mary Wiedenhoeft
Iowa State Univ

Annual Reports


  • Agronomic: canola, corn, rapeseed, soybeans


  • Crop Production: cover crops, crop rotation
  • Production Systems: general crop production


    Winter canola (Brassica napus) could be a good candidate for enhancing cropping systems in Iowa because of its potential to provide environmental benefits and produce a marketable crop compatible with existing grain production and distribution schemes. However, it is still uncertain whether this crop would be suitable for helping balance environmental and financial goals of conventional cropping systems under the environmental and market conditions unique to Iowa. The work conducted during this project was an effort to assess the suitability of winter canola for providing environmental benefits while fitting within the logistic and economic constrains of current cropping systems. Based on observations from experimentation in field plots, it is determined that canola can be successfully established in the fall, survive the winter, and regrow in the spring, but adequate conditions during fall growth are crucial. It is estimated that seeding by 31 Aug in the north to 12 Sep in the southeast will allow enough time for adequate growth of canola during the fall in at least half of the years in Iowa. Because these seeding date requirements will likely conflict with standing crops during most years, adjustments to the rotation schemes of conventional rotations are needed. Therefore, two alternative systems were proposed, and their economic profiles were studied. Findings from this economic analysis suggest that these rotation alternatives produce relatively less net returns than the conventional corn-soybean rotation, throughout a range of market and canola yield scenarios. Based on these results, it is determined that although winter canola can provide some environmental and economic enhancements to summer annual crop rotations in Iowa, the specific situations in which canola can fit these rotations are limited. Nonetheless, more research is needed to fully understand the productivity of winter canola, before counting these as feasible alternatives for Iowa producers.


    Fields under conventional summer annual crop rotations in Iowa often remain bare with no living plants between the harvest of corn and soybeans in the fall and emergence of the next crop in the spring. This renders soil susceptible to erosion, loss of nutrients, and degradation of soil health, and damages surface water quality with nutrients and sediment. Establishing overwintering annual crops (i.e. cover crops) between the harvest and planting of corn and soybeans can be done to ameliorate these negative environmental impacts. Cover crop shoots and roots protect the soil from erosion, add organic matter to the soil, and actively take up water and nutrients, which prevents their movement into waterways. However, this practice has not been widely adopted among producers in this state; cover crops have been planted in only about 1 – 2 % of all Iowa corn and soybean acres during the last few years. A possible reason for their low adoption may be that the costs associated with planting cover crops do not reliably translate into short-term economic benefits that justify their use. Thus, conservation strategies that demonstrate economic advantages along with the agronomic and environmental benefits may be better positioned for wide adoption.

    We hypothesized that including winter canola (Brassica napus) into Iowa summer annual crop rotations could enhance the environmental sustainability of these cropping systems, while providing agronomic and economic benefits that would incentivize their adoption. Being a winter annual crop, winter canola could provide ground cover to reduce erosion and living roots to uptake nitrates during the winter fallow period. In addition, Iowa-grown canola could produce a marketable crop compatible with existing grain production and distribution schemes. Thus, the need for additional machinery and infrastructure might be limited.

    Previous studies in Iowa[1] had observed that winter canola seeded in the early fall (late August or early September) achieved good survival and produced acceptable oilseed yields. However, if included into summer annual rotations, this seeding timeframe would likely conflict with standing corn and soybeans because these crops are typically harvested well into October. It is known that timing of seeding can greatly affect winter canola’s fall growth and its ability to successfully overwinter. If the winter canola grows poorly during the fall and fails to adequately overwinter and regrow in the spring, its environment benefits and economic potential would be limited. Therefore, there is a need to determine whether delaying seeding of winter canola until it could be planted after corn or soybeans is a feasible alternative for Iowa farmers.

    Project objectives:

    The main objective of this research project was to assess the suitability of winter canola for providing environmental and economic enhancements to the conventional summer annual cropping systems. We divided our efforts into three goals:

    • Determine the agronomic feasibility of growing winter canola in Iowa and characterize the effect of seeding date on its ability to provide winter cover benefits, and produce an oilseed crop
    • Establish reliable seeding dates for this crop in Iowa
    • Assess the economic feasibility of integrating winter canola into summer annual rotations

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.