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

Final 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
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Project Information


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


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  • Mary Wiedenhoeft


Materials and methods:

Field Experiments

Research trials were conducted to study winter canola’s ability to provide cover crop benefits and its yield potential in Iowa. Two field experiments were carried out during the 2012-2013 and 2013-2014 growing seasons in fields that are part of the Iowa State University Agricultural Engineering and Agronomy Farms in Boone County, Iowa (42.02°N, 93.74°W). In the 2012-2013 season, experimental plots were established in a field on the Sorenson Farm (SOR), and in a field on the Bruner Farm (BRU) during the 2013-2014 season. The two sites were located within 0.6 mi of each other. In both years and farms, a soybean crop had been growing during the summer and was removed in late August using a silage chopper. Then, fields were tilled with a tandem disk harrow, and fertilized by surface broadcasting 24 lb N acre-1, 80 lb P2O5 acre-1, 30 lb K2O acre-1, 20 lb S acre-1 and 2 lb Zn acre-1 at SOR and 20 lb N acre-1, 60 lb P2O5 acre-1, 20 lb K2O acre-1 and 20 lb S acre-1 at BRU. Fields were tilled a second time to incorporate the fertilizer. Experimental plots were established in a completely randomized block design with four repetitions at each farm.

Seeding Date Treatments

One of four seeding date treatments was randomly assigned to each plot: early September, mid September, early October, mid-October. At SOR, seeding dates corresponded to 31 Aug, 17 Sep, 1 Oct and 12 Oct, respectively. At BRU, seeding dates corresponded to 3 Sep, 13 Sep, 1 Oct and 14 Oct. On each seeding date, winter canola “Baldur” was seeded using a 10-ft wide grain drill in 7.5 in rows, at a rate of 5 lb acre-1 and depth of 0.75 in. Baldur (DL Seeds Inc. & Rubisco Seeds LLC) is a medium maturity, medium height and high yielding hybrid, with generally good winter hardiness.

Four indicators of cover crop performance were estimated for each plot: aboveground biomass (AGB) production, canopy cover, N accumulation, and winter survival. Samples and observations near the end of fall growth and near the cover crop termination date in the spring. Sampling dates were: 4 Nov and 20 May at SOR, and on 8 Nov and 15 Apr at BRU. Data and samples were collected from sample areas using a 30×26 in frame laid at three random points throughout experimental plots. The position of the frame was adjusted to contain four rows and the longest side was perpendicular to the rows. The average of the three areas was used as the estimate for the whole plot. Digital photographs of the areas were obtained and were used to estimate canopy cover. From each sample area, six plants were randomly selected and number of true leaves was counted. The number of plants was counted and plants were clipped at the soil surface. The aboveground portion of the plants was dried in a forced-air oven at 140°F until constant weight, and weights were recorded. Dry weights were used to estimate the AGB expressed in lb acre-1. Biomass samples were grinded using a Wiley mill (1 mm sieve) or a coffee grinder (home appliance) if the samples were too small. Biomass samples were analyzed at the Iowa State University Soil and Plant Analysis Laboratory to determine % N, which in turned was used to estimate total N accumulation in the biomass expressed in lb acre-1.

Percent canopy cover of each sample area was estimated by overlaying a 100-point grid object on top of the digital photograph. The grid was created using Microsoft PowerPoint, and was adjusted every time to fit entirely within the sample area. The number of grid intersections that were superimposed over living canola canopy were counted and expressed as percentage. The grid was repositioned within the sample area, and the process was repeated a second time. The average of the two counts was the estimate of the percent canopy cover of each image.

Number of plants per sample area was used to estimate plant density of experimental plots. Percent winter survival was calculated by dividing the estimated plant density of plots in the spring by the estimated plant density of plots recorded on the last sampling date in the fall. If spring density was greater than fall density, then winter survival was considered to be 100%.

Crop Rotation Treatments

Control plots were established in which soil was left fallow after soybean harvest, fall tillage and fertilization. Then, corn was planted in the spring and managed conventionally. Late spring nitrate test was performed 35 days after planting to ensure adequate fertilization rate. Additionally, corn stalk samples were collected at physiological maturity, and were analyzed for nitrate concentration. Corn was harvested 17 October 2013, and yield were determined.

Crop rotation treatments (Q1 and Q2) were assigned randomly to experimental subplots for each treatment plots (Table 1). In treatment Q1 subplots, winter canola was terminated in the spring, with an application of a tank-mix of 2,4-D and glyphosate, and then mowing seven days after herbicide application. Then, corn was established following the same protocol as described for the control plots.

In treatment Q2 subplots, red clover (Trifolium pretense L.) was frost seeded into the canola stand on 28 March. Nitrogen at a rate of 30 lb acre-1 was top-dressed as urea three days after frost seeding. Winter canola was allowed to mature, and was harvested by hand on 9 July and 24 July 2013 for for the early and mi Sep seeding treatments, respectively. Yield and yield components were determined. Red clover was left as groundcover and was terminated in the spring 2014 with herbicide applications and tillage. Then, corn was planted and yields determined upon harvest.

Table 1. Treatments for crop rotations

Treatment Q


Q1 (2yr rotation)

soybean => winter canola (cover crop) => corn

Q2 (3 yr rotation)

soybean => winter canola + red clover (cash crop) => corn


Research results and discussion:

Winter canola cover crop performance in Iowa

We found a general trend in which earlier seeding date tended to produce more biomass, accumulate greater amounts of N in the biomass and provide more ground cover by the end of fall growth (Figure 1). However, the pattern was different between the two years. While at SOR fall AGB production, N accumulation and canopy cover were clearly increased by earlier seeding dates, at BRU there was no difference in these three indicators between the canola seeded in early and mid Sep. This was most likely related to the delay in emergence that was observed in the early Sep treatment, which was about 8-10 days greater that most other treatments. A delay in emergence may affect the growth and development of the fall rosette because it decreases the amount of thermal time available before the onset of winter condition, and this can limit the successful establishment of the canola crop in the fall. At least 30% of ground cover is recommended to protect soil against wind and water erosion, and in our study, this was only exceeded for the early Sep seeding date at SOR and the early and mid Sep seeding dates at BRU by the end of fall growth. In summary, only winter canola seeded in early Sep at SOR, and in early and mid Sep at BRU, produced sufficient AGB, canopy cover and N accumulation to provide some cover crop benefits during fall growth. This suggests that to maximize cover crop performance in the fall in central Iowa, delaying seeding beyond early Sep should be avoided. Mid-September seeding may still provide a feasible cover crop, but the risk of inadequate establishment and poor growth is increased.

The effect of seeding date on winter survival was evident at SOR; a sharp decline in survival was observed when seeding was delayed. Winter survival was nearly 85% when seeded in early Sep, and decreased to 12% when seeded in mid Sep. Both early and mid Oct seeding dates winter killed. On the other hand, seeding date made no difference in the survival of canola at BRU. Extreme weather conditions were registered during the winter of 2013-2014, with 27 days in which minimum temperatures fell to or below -2°F, and two days with temperatures reaching -20°F. This likely caused winter canola plants across all treatments to winterkill. Thus, the overall effect of seeding date on canola winter survival in central Iowa is still questionable. Failure of the canola plants to survive at BRU impeded measuring the effect of seeding date on AGB, N accumulation and canopy cover in the spring. Only winter canola seeded in early Sep at SOR resulted in ample AGB production, N accumulation and canopy cover at sampling date in the spring(Figure 1).

Signs of increased performance of early seeding dates were detected in these field experiments, in spite of the great variation observed between the two years. As demonstrated here, a winter canola cover crop in Iowa can provide ample AGB production, N accumulation and canopy cover during the fall and spring, and achieve sufficient survival, if seeded in early September and adequate conditions for establishment, growth and overwintering are present.

Based on our field measurements of growth of canola during the fall and using historical weather observations from 1972-2011[2], we have estimated that canola planted by Aug. 31 in northern Iowa, by Sept. 4 in western and central Iowa, and by Sept. 12 in southeast Iowa will likely have sufficient time to establish and grow enough to maximize cover crop benefits and winter survival during at least half of the years in Iowa (Figure 2). Therefore, seeding beyond these dates is not recommended. Nonetheless, early seeding may not completely eliminate the risk of winterkill if winter conditions are too extreme, as was observed at BRU.

Yield potential and rotation effects

Because of complete winter kill at BRU. Here we only present results for the SOR experiment. 

When used as a cover crop under the Q1 rotation treatment, the yield of corn was decreased by about 35 bu acre-1 compared to the control, following a winter canola seeded on early Sep. Although the reasons for this decrease are still not entirely clear, we believe that it might be related to a reduced ability of the corn crop to uptake N during growth. LSNT results suggested adequate fertilization rates in all treatments, but fall corn stalk nitrate tested low in the early Sep treatment, while optimal in all other treatments. Calculated average C:N for the canola AGB residues was 19:1 which is lower than what is generally observed to trigger microbial N immobilization effects (>30:1). However, the 2013 growing season was characterized by cool and wet conditions in the late spring and early summer, and an exceptionally dry mid and late summer. So, it is possible that residues might have delayed corn emergence and growth enough to negatively affect N uptake in an environment challenged by unfavorable weather.

At SOR, winter canola under the Q2 rotation treatment and seeded in early Sep produced an oilseed yield of 3290 lb acre-1, while yield was reduced to 643 lbs acre-1 when canola was seeded in mid Sep. Neither seeded in early and mid Oct survived the winter. Red clover aboveground biomass achieved the following spring at termination was 276 lb acre-1 and 551 lb acre-1 for the early and mid Sep treatments respectively. These treatments were estimated to contain 7.88 lb acre-1 and 15.54 lb acre-1 of total N, respectively. Corn yields of canola following red clover were 148 bu acre-1 for P1 and 174 bu acre-1 for the early and mid Sep seeding dates, respectively, a yield advantage that could be attributed to the greater amount of red clover growth in the mid Sep treatment prior the establishment of corn.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Peer-reviewed publications

Martinez-Feria, R.A., T.C. Kaspar, and M.H. Wiedenhoeft. 2015. Seeding date affects fall growth of winter canola (Brassica napus L. 'Baldur') and its performance as a winter cover crop in central Iowa. Crop Forage and Turfgrass Management. Online. DOI: 10.2134/cftm2015.0181

Seminars and scientific presentations given by the student

Suitability of winter canola for enhancing summer annual crop rotations in Iowa (Thesis defense seminar). 26 May 2015. Available at:

An empirical approach to estimating seeding dates for winter canola in Iowa (Poster presentation). Session 109: Canola research poster session. U.S. Canola Association Research Conference. Long Beach, Calif. 4 Nov. 2013. Available at:

An empirical approach to estimating seeding dates for winter canola in Iowa (Oral presentation). 10th Annual Graduate Minority Assistantship Program Research Symposium. 13 Sep 2014.

Suitability of winter canola for enhancing summer annual crop rotations in Iowa (Poster presentation). George Washington Carver Life and Legacy Symposium. Ames, Iowa. 23 Apr. 2014.

Suitability of winter canola for enhancing summer annual crop rotations in Iowa (Poster presentation) Agronomy Graduate Student Research Symposium. 20 Nov. 2013.

Suitability of winter canola for enhancing summer annual crop rotations in Iowa (Poster presentation). Session 301: Water, Nutrients, and Conservation Systems. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America International Meetings. Tampa, Fla. 5 Nov. 2014. Available at:

Suitability of winter canola for enhancing summer annual crop rotations in Iowa (Poster presentation). 8th Annual Graduate Minority Assistantship Program Research Symposium. 14 May 2013.

Estimating reliable seeding dates for winter cover crops in Iowa using geographic information systems (Oral and poster presentation). Introduction to Geographic Information Systems (CRP551) final project. 1 May 2013.

Suitability of winter canola for enhancing summer annual crop rotations in Iowa (Poster presentation). 9th Annual Graduate Program in Sustainable Agriculture Research Symposium. 10 Apr. 2013.

Suitability of winter canola for enhancing summer annual crop rotations in Iowa (Poster presentation). Agronomy Graduate Student Research Symposium. 1 Nov. 2012


Research reports

Martinez-Feria R. 2015. Winter canola used as a cover crop in Iowa. Practical Farmers of Iowa Cooperators’ Program. Ames, IA. Available at:

Martinez-Feria R. 2015. Suitability of winter canola for enhancing summer annual crop rotations in Iowa (M.S. Thesis). Iowa State University. Ames, IA. 

Outreach to farmers and peers

The research has been featured at a popular press article [11] and researchers have also met with some 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. We have also reached out to farmers and farmer organizations to share our experience with this crop. For instance, in September 2014, together with personnel from the USDA-ARS, we hosted staff from the farmer group Practical Farmers of Iowa to visit our field plots and discuss potential alternatives for using canola as cover crop or third crop in rotations.

We also partnered with the Midwest Cover Crop Council and attended their meeting on April 8th and 9th 2014 in Warsaw, Indiana. During this meeting the graduate student interacted with other researchers involved in the evaluation and implementation of strategies to include cover crops into rotations. In addition, two undergraduate assistants involved developed their own side research projects: one on the effect of canola on splash erosion and another in the effect of red clover on the yield of corn. Their results were presented at on-campus research symposia and through research reports. 

Project Outcomes

Project outcomes:

Economic Analysis


To assess the economic feasibility of integrating winter canola into Iowa cropping systems, two cropping system alternatives are proposed and compared to a conventional corn-soybean system. The analysis of whole-farm net returns are conducted on a rotated hectare basis so that the analysis may be easily scaled up. The cash rent equivalent of land is included as a fixed cost throughout the analysis to account for the opportunity cost of land, at a rate of $273 acre-1 yr-1 annual cash rent. Likewise, labor costs are fixed at a rate of $13 hr-1 to account for the opportunity costs of labor. Federal subsidy payments are excluded from the analysis.

The cropping systems analyzed are:

  • System A: soybean (SRM)–winter canola/red clover–corn (3 yr rotation)

  • System B: corn silage–winter canola/red clover–corn (3 yr rotation)

  • System C: corn–soybean (2 yr rotation)

System C is the baseline scenario that represents a conventional Iowa corn-soybean system. In this system, corn plantings are expected in mid-April and harvest is expected in mid-October. Similarly, we expect soybeans are planted in early May and harvested in late September. For purposes herein, one half of the land is planted to each crop annually. System A is a rotation that includes winter canola planted in early September and harvested in mid-July. To allow sufficient time for establishment of canola, SRM soybeans are planted in mid-May and harvested in late August. A 20% yield loss of SRM (Relative Maturity= 0.5) is assumed compared to the full maturity varieties (Relative Maturity = 2.5), as indicated by Iowa State University (ISU) Extension’s Soybean Planting Decision Tool [3]. Red clover is frost-seeded into the canola stand in early spring, left as cover crop after canola harvest, and terminated with herbicides and tillage the following spring before corn planting. System B is a rotation in which corn is harvested for silage in late August, and then followed by winter canola. In this alternative, red clover is also frost-seeded as described above and terminated before corn planting. Red clover growth during the fall and regrowth in the spring in systems A and B may add value as forage for grazing or N fertilizer to the succeeding corn crop, but these potential benefits are not incorporated into the analysis. In both A and B systems, one third of the land is allocated to each crop annually.

Enterprise budgets for each crop are developed based on estimated costs of production published by ISU Extension’s Ag Decision Maker (AgDM) [4]. Default AgDM values are used for corn following soybeans, soybeans following corn, and corn silage following corn. A winter canola/red clover enterprise budget is constructed using available cost-return budget information for south central Kansas [5] updated with AgDM Iowa cost estimates, where they exist. The N requirement of canola is assumed to be 120 lb acre-1. Corn, soybean and corn silage yields considered are displayed on Table 2.

Winter canola/red clover labor requirements are calculated at 2.5 hours acre-1 based on published estimates on machinery field capacities [6]. In addition, winter canola crop insurance premium cost is assessed to be $12.2 acre-1, based on a determination from an insurer in the private sector. Variable costs of direct combining winter canola are assumed at $10.9 acre-1 because it is expected that harvest time is approximately 30% higher than those of soybeans. Haul and handling machinery costs are computed based on canola seed yields. For corn following winter canola/red clover, the same cost estimates as for a corn following soybeans are used except that N requirements are assumed to be equal to those of corn following corn (i.e. no red clover N credit).

The reference net returns for each system are computed using forecasted commodity prices. These are estimated using market information (i.e. future contracts, bases and $US/$CAN) collected on 6 March 2015. Based on these forecast analyses, canola prices are considered $16.80 cwt-1 at sale in July 2015, corn prices are $3.67 bu-1 at sale in December 2015, and soybean prices are $8.98 bu-1 at sale in November 2015. A reference yield of 1785 lb acre-1 for canola seed is expected, based on the average yield from the 2003 to 2012 National Winter Canola Variety Trials [7]. Corn silage prices are computed using the AgDM corn silage pricer tool [8], assuming 165 bu acre-1 expected corn grain yields, and 4.4 ton acre-1 expected stover yields. Silage is priced in the field (i.e. no storage cost) at the value of silage as feed (i.e. substitution price of grass hay plus corn grain), assuming the market price of grass hay substitute is $117.1 ton-1. This estimate is determined based on the averages from 2010 to 2014 of large round bale hay auction prices in early September at the Rock Valley, Iowa market [9].

To establish the yield level needed at which winter canola’s integration is economic feasible a sensitivity analysis is performed for each cropping system by varying canola seed yield while holding all other parameters constant. The factors used to perform the sensitivity analysis are canola seed yield. The range of yields used for the sensitivity analysis is 890 to 3570 lbs acre. Response curves of the effect of these factors on system net returns across the studied range are calculated as well as the curves of the differences in net returns between the alternatives and the baseline systems, which represent the value of adopting the proposed alternatives at different levels of the studied factor.

Table 2.
 Assumed crop yieds for the economic analysis 

Crop Yield  
  Corn 180 bu/acre
  Soybean  50 bu/acre
  Corn Silage  24 ton/acre
  Winter Canola 1785 lb/acre

Comparison to establishing cover crops

We also estimated cost of establishing winter canola as a cover crop based on published values[10] and compared with the cost of cereal rye under two seeding methods scenarios: direct seeding and aerial broadcasting. Cost of canola seed is assumed to be $5.5 lbs-1 while cost of cereal rye seed is considered at $0.31 lb-1. For direct seeding, 5 and 54 lbs acre-1 seeding rates are assumed for winter canola and cereal rye, respectively. Winter canola and cereal rye aerial seeding rates are doubled in respect with with drilling method. Aerial application rates used are $18 acre-1 for cereal rye, whereas because of its lighter seed weight, cost of aerial broadcasting for winter canola is considered to be $11 acre-1.

Results and Discussion

Table 3 provides the expected net returns for each of the three cropping systems, which are calculated based on estimated crop prices, yields and production costs. At the reference values used for the initial analysis, none of the systems produce positive net returns, but the baseline corn-soybean rotation generates the smallest net losses. These negative net returns are an artifact of the market conditions under which this analysis is performed, with historically high production costs and lower commodity prices. The high rental rates for land are especially burdensome for winter canola/red clover and soybean, in which budgeted land rent equivalents for these two crops represents roughly 45 to 50% of total production costs. Expensive land and input costs in Iowa may be linked to relatively high commodity prices during the past few years. As revenue continues to remain lower in the foreseeable future, it can be expected that farmland values and input costs will adjust accordingly, but the level at which they will stabilize, and when this will occur is still uncertain.

It is perhaps most useful to examine the relative returns of the alternative cropping systems compared with the standard rotation. This can be done by subtracting the expected net returns of the alternative cropping systems minus the expected net returns from the baseline system. The result represents the dollar value of adoption of these alternatives. Negative value of adoption may be considered as the additional losses incurred by adopting the system, while positive value of adoption may be considered as the economic advantages over the baseline system. According to computed estimates of system profitability (Table 3), the expected cost of adopting the canola rotations is $108 and $75.9 ha-1 for systems A and B, respectively.

An interesting finding is that total production costs of winter canola/red clover and soybean are comparable. Total production costs of winter canola are about 9% higher than for soybeans. The main differences between these two crops are observed in the variable costs, with the added cost of N fertilizer for canola, and the relatively lower cost of canola seed. However, commodity prices tend to favor canola, typically being 1.07 to 1.36 times greater than soybeans. Thus, the primary difference in profitability between these two crops is given by their yield potential.

Because of this, we conducted sensitivity analyses of winter canola yield to provide insights of its roll on the overall profitability of the production systems. To do this, seed yield is varied and the response curves of its effect on system net returns are calculated. These response curves are used to calculate the yield levels at which the net returns of the proposed system equal the net returns of the baseline rotation with all other factors set at the reference levels.

Based on this analysis, winter canola seed yield seems to have an important role in the net returns of the proposed systems. To increase returns by $100 acre-1, an increase of 1800 lb acre-1 in the yield of canola is needed. Because total revenue is computed as yield times the sales price, and net returns are total costs minus total revenue, a linear relationship between yield and net returns is observed. However, the changes in production cost associated with varying yield level (e.g. changes in the amount of inputs) are not included in this analysis, because at this moment, no information is available on this regard for Iowa-grown canola.

Under this scenario, the canola yields that are required for achieving the same net returns than those of system C baseline rotation are approximately 3170 lb ha-1 for system B and between 3750 lb acre-1 for system A. A recent study [7] estimated that winter canola’s yield potential with optimal weather conditions, best management practices, and the best available genetics is 6250 lb acre-1, although real yields usually range between 0 to 3570 lb acre-1. Moreover, winter canola yields tend to be greater in cooler environments with relatively stable amounts of precipitation throughout the year, and yields tend to be higher in northern and Midwest regions. In our field experiment, canola produced as much as 3290 lb acre-1, suggesting that these yield levels may be achievable in Iowa. However, because of the higher risk of winterkill, whether consistently achieving these relatively high yields in Iowa is possible is still questionable. 

Table 3. Expected net returns for studied cropping systems

   System:       A       B      C
Crop    ---------Net Return ($/acre)---------
  Corn   -101.5 -101.5 -74.7
  Corn Silage     -90.3  
  Soybean   -186.4   -97.7
  Winter Canola / Red clover   -294.4 -294.4  
System Net Return   -194.1 -162.1 -86.2


Alternative cropping economic returns compared to establishing cover crops

The partial budgeting analysis (Table 4) reveals that direct seeding is a lower cost alternative for establishing both winter canola and cereal rye; direct seeding is, on average, 34% less costly than aerial broadcasting. The analysis also suggests that cereal rye cover crops possess an economic advantage over winter canola. Establishing a winter canola cover crop is, on average, approximately 35% more expensive than cereal rye, with increased cost of 30% and 41% under aerial and direct seeding methods, respectively. It seems that the greatest disadvantage for using winter canola as a cover crop stems from its relatively higher seed cost when compared to cereal rye and most other species. Perhaps, substituting winter canola with brassica alternatives with lower seed cost such as winter rape (B. rapa) would be suitable for situations in which only the cover crop benefits are sought.

Nevertheless, when a 1785 lb acre-1 winter canola yield is considered, the costs of including any of these two cover crop alternatives into a corn-soybean rotation is typically lower than the cost of adopting both system A and B. This is with the exception of an aerially broadcasted winter canola cover crop and system B, and direct seeding a winter canola cover crop and system. In the former case, the costs of aerially establishing canola exceed the net returns given up by adopting system B. In the latter case, direct seeding winter canola in early September requires the inclusion of SRM soybeans, which results in a yield decrease compared to relative full maturity varieties. Thus, adopting system A is a more competitive alternative than establishing a winter canola cover crop under these conditions. This seems to indicate that planting these cover crops may be a less costly nutrient mitigation strategy than adopting these diversified rotations in situations when expected yields of winter canola are low. The opposite may be true if higher yields of winter canola are achieved.

Table 4.
Cover crop partial budgeting analysis

      Aerial Seeding   Direct Seeding
      Cereal Rye   Winter Canola   Cereal Rye   Winter Canola
Seeding Rate (lb/acre)   104   10   54   5
Seed Cost (per lb)   $0.31   $5.50   $0.31   $5.50
Total     $32.24   $55.00   $16.74   $27.50
Grain drill (fixed + variable)   $0.00   $0.00   $8.50   $8.50
Custom aerial broadcast   $18.00   $11.00   $0.00   $0.00
Sprayer (fixed + variable)   $4.40   $4.40   $4.40   $4.40
Chemical     $5.00   $8.00   $5.00   $8.00
Labor hours                
Drilling 0.2   $0.00   $0.00   $2.60   $2.60
Spraying 0.1   $1.30   $1.30   $1.30   $1.30
Total     $60.94   $79.70   $38.54   $52.30


Areas needing additional study

Project Conclusion and Further Study

Based on the findings from the performed agronomic and economic studies, it is determined that winter canola has the potential to provide some environmental and economic enhancements to summer annual crop rotations in Iowa, although the specific situations in which canola can fit these rotations are limited. Winter canola may be effectively used to provide ground cover benefits, but because it requires a late-August or early-September seeding date, direct seeding may not be a feasible method unless summer annual crops have been removed early (e.g. silage or SRM soybean varieties). Aerial broadcasting into standing crops could then be considered as an alternative for establishing canola under these circumstances, but this method may result in delayed and poor establishment if dry conditions are encountered. It is still unknown whether canola is well adapted for growing under a senescing crop canopy, or if harvest operations and crop residues would affect the crop’s ability to develop properly. Moreover, seeding rates and pre-plant N fertilizer application methods would likely have to be adjusted, if an oilseed harvest is sought. Thus, further investigation in this area is needed.

Another important aspect in need of more examination is canola’s ability to provide erosion control. Here we assumed that the canola canopy provides the same relative erosion protection as surface residue or grass cover crops. But preliminary research (not described in report) during the second year of our field experiment indicated that soil movement was greater in the cover crop plots than on untilled control plots. This may not be a completelyfair comparison, but it should be noted that in contrast to the fibrous roots and dense vegetative structures of grasses, the architecture of the canola rosette, with wide, limp leaves and deep but thin taproot, might not be entirely favorable to protect the soil. Perhaps, canola’s erosion mitigation potential could be improved by increasing plant populations or planting in binary mixes. On the other hand, winter canola’s potential for scavenging NO3 is well documented in the literature, but comparison to other cover crops grown under Iowa conditions would be useful to highlight its value as a tool for nitrate pollution mitigation tool. Thus, quantification of canola’s environmental benefits is necessary.

At this moment, the economic incentives for incorporating a winter canola cash crop frost-seeded with red clover into Iowa rotations seem to be limited. Until winter canola’s yield potential is fully understood, it may be premature to count this alternative as being financially competitive to conventional systems. Given that all the seeding date treatments in our field experiment at BRU winterkilled, we were not able to further explore the rotation effects of winter canola cover crops and cash crops on the yield of corn. Therefore, further investigation in this regard is needed. Perhaps, the next step could be the establishment of long-term cropping system studies at various sites across the state to provide evidence of the true productivity potential of these systems under Iowa conditions, as well as their ability for effectively mitigating nutrient losses. This information would be valuable in determining if the strategies proposed here would serve well to potentially mitigate some of the impacts of agriculture on water quality, while maintaining economic feasibility of Iowa cropping systems.


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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.