Seeding Rate

Table of contents

    Important tips for best management

    • Seeding rates should be adequate to achieve a target of 50-80 plants/m2 (approximately 5-8 plants/ft2). Yield potential tends to drop off with fewer than 3-4 plants/ft2, so a stand of 5-8 plants/ft2 will allow for some plant mortality during the growing season.
    • Seeding rates should be adjusted (from the target density) based on seed weight (measured in grams) and estimated emergence to account for the variability in these factors. If the seeding rates are measured by pounds per acre, the variation in seed weights (between seed bags) and estimated emergence (between fields) won’t be accounted, resulting in a plant density that may differ significantly from the desired target density.
    • Factors such as soil moisture, soil temperature, fertilizer toxicity, seeding speed, seeding depth, seed placement, seed to soil contact, seed vigor, seedling disease and dormancy can affect germination and emergence.

     

    Targeting a plant population

    Setting a canola seeding rate without first considering the thousand seed weight (TSW) means the variability in seed weights won’t be accounted for (despite the considerable variability that can exist between seed bags). One pound or kilogram of seed with a high TSW will contain fewer individual seeds than that same pound or kilogram with a lower TSW. Current varieties of herbicide-tolerant canola can vary between 3.5 grams per thousand seeds to 6.5 or more grams per thousand seeds.

    For example, a grower targeting 6 plants/ft2 (approximately 60 plants/m2) and expecting 60% emergence would need to seed 5.8 lbs./ac. to achieve their target density with 6 gram TSW seed, whereas a grower with the same target density and expected emergence that had 4 gram TSW seed would only require a seeding rate of 3.8 lbs./ac. to reach the same plant density (CCC 2019).

    Seeding rates should typically be set to achieve a minimum of 100 seeds per metre square (approximately 10 seeds/ft2), given that average seed survival rates are between 50 to 60%. This will produce a target seed density of 5-6 plants/ft2, which is within the recommended target of 50-80 plants/m2 (approximately 5-8 plants/ft2). Yield potential tends to drop off with fewer than 3-4 plants/ft2, so a stand of 5-8 plants/ft2 will allow for some plant mortality during the growing season  (Harker and Hartman 2017; Hartman unpublished; Kutcher et al. 2013).

    Canola crops can reach their yield potential with as little as 10 plants per square metre (1 plant/ft2) but the risk of yield loss or crop failure increases considerably when plant densities drop below 30-40 plants/m2 (approximately 3-4 plants/ft2) (Shirtliffe 2009 and Hartman unpublished).

    Seed weight becomes a key factor in yield potential when the number of seeds planted is not sufficient to provide a plant stand within this desired range (CCC 2002). For example, if seed weighs 6 grams per 1,000 seeds and a grower seeds at 1,800 grams (4 pounds) per acre, the seeding rate is 60 seeds per square metre (approximately 6 seeds/ft2). At 50% seed survival, which is common, the crop has only 30 plants per square metre (3 per square foot). 

    This does not leave much margin for competition with weeds or plant death (due to disease, frost, insects or other factors) before yield potential starts to drop. Therefore, considering seed size, seedling survival rates and target plant populations when setting seeding rates can minimize risk and save money. 

     

    To set a seeding rate based on seed size visit www.canolacalculator.ca/seeding-rate

    Canola Calculator - Seeding Rate

    An example:

    If the seed weight is 5 grams per 1,000 seeds, the target plant population is 5 plants per square foot (approximately 50 plants/m2), and estimated seed survival is 50%, then the seeding rate should be 4.8 pounds per acre.

    If the seed weight is 6 grams per 1,000 seeds, the target plant population is 5 plants/ft2 (approximately 50 plants/m2), and estimated seed survival is 50%, the seeding rate should be 5.8 lbs/ac (one pound per acre more than the previous example)!

    Follow up with plant counts after emergence to determine what population was actually achieved, so that an accurate seed survival percentage can be determined. Start looking for emerged seedlings at 10 to 14 days after seeding. At approximately 21 days after emergence, or when assessing a field for the timing of the first herbicide application, record plant populations from various location in the field. Doing this a few times per year and from year to year will give you a baseline for typical seedling survival on your farm with your seeding system. This information will be useful for setting seeding rates in the future, especially when trying to maximize efficiency of seed input investments without substantially increasing risk.

    To learn more from these sites, mark them and go back again before harvest to see how many plants survived to maturity.

    Seeding rate required at 20% survival

    Seeding rate required at 60-80% survival


    References

    Canola Council of Canada (CCC). 2002. Canola stand manipulation trial. (This study found that the contribution margin was higher for a seeding rate of 3 lb./ac. than for a seeding rate of 1 lb./ac. The lower rate had lower seed costs, but also much lower plant stands and lower yields). See the tables in the Appendix below for results.

    Canola Council of Canada (CCC). 2019. Canola Calculator. www.canolacalculator.ca/seeding-rate

    Harker, N.K. and Hartman, M.D. 2017. Nitrogen and seeding rate versus novel inputs for Western Canada canola production. Canadian Journal of Plant Science. Vol 97:32-43.

    Hartman, N.K. (unpublished)

    Kutcher, H.R., Turkington ,T. K., Clayton, G. W., Harker,  K. N. 2013. Response of herbicide-tolerant canola (Brassica napus L.) cultivars to four row spacings and three seeding rates in a no-till production system. Canadian Journal of Plant Science. Vol 93:1229-1236.

    Steve Shirtliffe. 2009. Determining the economic plant density in canola (published based on summary data from 35 experiments). University of Saskatchewan.

    Appendix

    Canopy Manipulation Trial – Western Canada Summary 3 year
    Treatment Yield
    (%)
    Yield
    (bu/ac)
    Contribution
    Margin ($/ac)
    Oil
    (%)
    1,000 Kernel
    Weight (g)
    Growing
    Degree Days
    Days to
    Maturity
    Grade
    Early Planting Date
    1 lb/ac 81 30 90 42.5 3.9 1118 103 1
    3 lb/ac 95 35 123 43.0 4.0 1061 99 1
    5 lb/ac 100 37 126 43.3 3.9 1051 98 1
    Normal Planting Date
    1 lb/ac 84 31 102 43.3 3.9 1140 100 1
    3 lb/ac 97 36 136 43.7 4.0 1091 98 1
    5 lb/ac (check) 100 37 130 43.8 4.0 1081 97 1
    LSD
    CV%

     

    Canopy Manipulation Trial – 3 year Western Canada Summary
    System Emergence Counts Plants/m2 Harvest Counts Plants/m2 Plant Height (cm) Lodging Ratio (%) # Primary Branches # Secondary Branches
    First Planting Date
    1 lb/ac 20 21 90 69 8 16
    3 lb/ac 50 52 98 77 5 5
    5 lb/ac 88 85 98 78 5 3
    Second Planting Date
    1 lb/ac 28 26 92 75 8 9
    3 lb/ac 59 58 100 78 5 4
    5 lb/ac (check) 95 90 98 77 4 2
    LSD
    CV%

     

    Date modified: March 12, 2019