Agronomic factors such as seeding rates, hybrid maturity and harvest method contribute to optimal canola harvest and yield stability.
November 15, 2023 By Donna Fleury
Canola is widely grown across Western Canada, providing growers with high returns under the right conditions. However, expensive inputs such as hybrid seed and multiple pre-harvest operational steps can offset high canola commodity prices. Understanding how agronomic factors can contribute to optimal canola harvest and yield stability is key.
Researchers initiated a five-year project in 2018 across Western Canada to understand how manipulations to seeding rate, pod shatter reduction hybrid and harvest method alter canola seed yield and quality.
“We were interested in finding out how integrating agronomic factors such as seeding rate, cultivar selections, and timing of harvest methods impact canola production,” says Brian Beres, research scientist at Agriculture and Agri-Food Canada (AAFC). “Understanding the risks and benefits associated with an integrated system and the impacts those decisions have on straight-cutting and swathing harvest systems can help optimize canola harvest.”
Experiments were conducted at five sites across the Prairies between 2018 and 2022, including Lethbridge and Lacombe, Alta., Indian Head, Sask., and Brandon, Man. At Lethbridge, an irrigated site was added for comparison to the four dryland locations. Two pod shatter reduction hybrids, InVigor L233P (early-maturing) and InVigor L255PC (late-maturing) were seeded at rates of 60, 120, and 180 seeds/m², aiming for target plant densities of 40, 70, and 100 plant/m². The plots were swathed at either 60 per cent or 90 per cent seed colour change (SCC), and compared to straight-cutting (S/C) at either 10 per cent or five per cent seed moisture, which simulated a delayed harvest scenario. Pre-harvest desiccant was applied as needed to achieve uniform whole plant moisture and test the response of pod shatter reduction traits to factors associated with delayed S/C. The trial was suspended for the 2020 season due to COVID-19 restrictions. The four growing seasons of this experiment were characterized by a wide range of weather conditions across the Prairies.
“One of the strong findings from the study was the performance of the pod shatter reduction trait,” explains Beres. “The consistency and efficacy of how the trait was expressed were impressive as there was no notable seed loss in any of the treatments, including little difference between the early and late cultivar responses. Even though the shift to straight-cutting was a bit ahead of the availability of pod shatter reduction hybrids, the study shows this is a good tool for growers who choose to straight-cut. Although there will be times where swathing is needed, the ability of hybrids with that trait to withstand pod shatter was impressive.”
Overall, the highest seed yields were achieved with the higher seeding rates of 120 seeds/m² (~57 plants/m²) and 180 seeds/m² (~80 plants/m²). These rates typically displayed consistent high and stable yields across environments; however, there was no yield difference between the two rates. Both rates outperformed the lower seeding rate of 60 seeds/m² across all treatments, which appeared optimized with the early-maturing hybrid in terms of yield or yield stability. The lowest seeding rate produced the fewest plants, which often results in low yield stability. This suggests that, regardless of hybrid selection, both 120 and 180 seeds/m² appear to be biologically optimum seeding rates for canola in the Canadian Prairies. When comparing treatment combinations, the late-maturing canola hybrid (L255PC) seeded at 120 or 180 seeds/m² and managed with S/C was superior relative to other treatment combinations.
“Managing seeding rates is very important, and although there are reasons growers may choose lower rates, environmental considerations can be a significant risk,” adds Beres. “If there is an environment that guarantees a high percentage of emergence or if production is not in a water-limited environment, then lowering seeding rates may be less risky. For example, under irrigation, a high percentage of emergence is expected, and growers note that with the plasticity of the plant, lower rates can result in a thicker primary raceme or main stem that, in turn, is easier to straight-cut because the plant is likely to remain upright and not lodge. However, under a water-limited environment, there is no guarantee of a high rate of emergence, and environmental conditions can be variable over the growing season. Growers are reminded that low plant stands are associated with higher risk due to variable yield across growing environments, particularly in the presence of biotic and abiotic stress.
“Although high yields are often the goal, an equal emphasis should be on yield stability or achieving consistent yields across field-to-field and year-to-year. Yield tends to drive decisions because of economic considerations, but that overlooks the importance of yield stability. In our study, the management data suggests seeding at the moderate rate of 120 seeds/m² is guaranteeing about six plants/sq. ft. (~57 plants/m²), which will consistently lead to positive outcomes as opposed to rolling the dice at a lower rate. A canola production system of 120 seeds/m² coupled with timely straight-cutting assures high grain yield and yield stability with minimal seed loss. There were no significant differences in seed quality between the management treatments, which indicates seed quality was driven by variety selection over agronomics.”
Management is really the deciding factor of whether to straight-cut or swath. If the crop has been staged properly and managed in a way that provides optimal uniformity and timely pre-harvest applications, then straight-cutting can be a good option. However, if there are uniformity issues in the field caused by emergence issues, or pest and disease problems or nutrient gradients, then swathing may be preferred. Growers may also select varieties without the pod shattering trait if they are addressing other potential disease or pest issues, depending on stacked seed trait options. From an operations standpoint, being able to skip a step at harvest can be helpful. For those straight-cutting, being able to get into a uniform field quickly with a large sprayer and apply a desiccant in a timely manner means swathing can be avoided. However, the desiccant application step can be skipped if swathing is the harvest method. Other factors growers need to keep an eye on are things like MRL limits and market changes that may impact harvest method decisions.
The study estimated that the net return of the 180 seeds/m² was $46 per hectare less than the 120 seeds/m² and $29 less than the 60 seeds/m² when managed with the same harvest method, based on the daily canola commodity prices posted by Alberta Canola. This underscores the delicate balance between what is biologically optimal versus the economic realities of what is viable on the farm. Conversely, although the lower densities may provide acceptable net returns, growers must weigh the risks and consider intangible consequences such as greater yield instability, particularly if swathing and irrespective of hybrid, along with poor weed control, risk of greater selection for herbicide-resistant weeds, delayed maturity/harvest and compromised seed quality.
“The study reinforced the importance of a good harvest management strategy and timely operations that will drive success often irrespective of the hybrid,” says Beres. “One key takeaway was that a sustainable practice must be profitable. For example, while the highest seeding rate provided really good agronomics, it is virtually impossible to reconcile on the farm balance sheet. Another takeaway and reminder of the complexities of modern farming and decision making is that, while we learned moderation around seeding rates is key to high, stable yields and profitable returns, the sensitivity analysis showed us that when environmental stress is low, then pulling back on seeding rates may be an option. Growers have to carefully assess risks and be pretty confident in what they are predicting. This was a rewarding project for us and reinforced that integrating agronomic factors such as seeding rate, cultivar selections, and timing of harvest methods can create synergies that contribute to optimal canola harvest and yield stability.”