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

2014 Annual Report for GNC13-176

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

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



In the fall of 2012, we initiated research on the agronomic and economic feasibility of extending conventional Iowa summer annual rotations with winter canola (Brassica napus), used as a cover crop and as a cash crop frost-seeded with red clover (Trifolium pratense L.). Winter canola was established at various seeding dates in the fall in a field following a soybean crop. In the spring, one half plot of winter canola was terminated and corn was planted, while in the other half winter canola was allowed to mature, and harvested for seed in mid summer. With the support of the NC-SARE, we were able to complete the first cycle (2012-2013) of the research study, collecting data on the winter survival, canopy cover, biomass accumulation, nitrogen uptake and seed yield of winter canola, and grain yields of the subsequent corn crop. We also established test plots in a different location in the fall of 2013, in order to replicate the experiment a second cycle (2013-2014) in a different environment.

Objectives/Performance Targets



Preliminary findings from our field experiments suggest that winter canola should be planted in early September in order to achieve maximum agronomic performance and provide de greatest environmental benefits, either as a cover crop or as a cash crop. Only canola seeded in early September in 2012, and in early and mid September in 2013, produced sufficient AGB, canopy cover and N accumulation to provide adequate cover crop benefits during fall growth (Figure 1). This suggests that in order to maximize cover crop benefits during the fall in central Iowa, delaying seeded beyond early September should be avoided. Mid-September seeding may still provide a feasible cover crop, but the risk of uneven establishment and poor growth is substantial. However, we also observed that early seeding did not completely eliminate the risk of winterkill. This was the case in the 2013-2014 study, in which none of the seeding date treatments survived the winter despite achieving sufficient growth in the fall. This was presumably due to unseasonably harsh winter conditions experienced that year.

The data collected from these two field experiments was then used to determine reliable seeding dates for this crop in Iowa. We calculated the latest reliable seeding date for winter canola by estimating its thermal-time requirement for developing a healthy, robust rosette of at least five leaves that maximizes potential winter survival. Then we related this requirement to historical weather observations in 110 weather stations across the state, using spatial analysis software. The outcome of this analysis is a seeding date atlas for winter canola in Iowa (Figure 2). This information will be shared with peers, growers and other interest groups.


We are now in the process of analyzing the economic impacts of the proposed cropping system alternatives, which will serve us to better understand winter canola’s potential. The research team now also includes Dr. Kari Jacobs, associate Professor in the Department of Economics at Iowa State University, who is acting as support advisor for developing the economic assessment. We are using information gained through reviewing literature and our own field experiments to determine reasonable estimates of costs and productivity potential of the studied systems. We are confident that with the information generated from our research, we will be able to characterize this crop’s performance as a cover crop and as a cash crop, integrated into a corn soybean rotation.



Impacts and Contributions/Outcomes

Professional development activities:


The graduate student in charge of conducting this research was involved in several professional development activities. This student had the opportunity to attend the ASA, CSSA and SSSA International annual meetings in Tampa, Florida in 2013 and in Long Beach, California in 2014. During this conferences he attended several seminars and symposiums related to the field of soil and water conservation, crop science, and agricultural systems diversification. He also attended the Midwest Cover Crop Council meeting on April 8th and 9th 2014 in Warsaw, Indiana. During this meeting he interacted with other researchers involved in the evaluation and implementation of strategies to include cover crops into rotations. He also participated in the organization of the 2014 Graduate Minority Assistantship Program Research Symposium on September 20th , 2014, in which he coordinated more than a dozen student presentations and presented his own research.


In addition, an undergraduate assistant involved on this project developed her own side research project on the effect of establishing a canola cover crop on splash erosion. Her results were presented at an on-campus research symposium.


Dissemination of Results and Outreach:

The preliminary results of this project have been presented on campus at two departmental research symposiums, one interdepartmental research symposium and at the 7th annual Graduate Minority Assistantship Program (GMAP) research symposium sponsored by the ISU Graduate College. Results were also presented at the session no. 301: “Water, Nutrients and Conservation Systems” of the Soil Science Society of America Division of Soil and Water Conservation of the ASA, CSSA and SSSA 2013 International annual meetings, and at the Canola Research Poster session of the US Canola Research Conference in Long Beach, California. 

The research has been featured at a popular press article[1] and researchers have also met with Iowa farmers interested in the use of alternative crops to diversify their rotations. We believe that cultivating these relationships will enable us to establish a network of producers that would be interested in on-farm research at later stages of our project.

[1] Lucht, G. (2013, February 28). Researchers seek alternatives for traditional crop rotations. Iowa Farmer Today, Retrieved from




Mary Wiedenhoeft
Faculty Adviser
Iowa State University
1126 Agronomy Hall
Ames, IA 50011
Office Phone: 5152943274