Seed costs represent one of the largest input costs for growing canola. Due to its small seed size, canola has an average seed survival rate of around 60 percent, much lower than large-seeded crops like wheat and soybeans. This means, on average, for every two seeds planted, one will establish and grow to maturity. It’s important to ensure a good return on those invested dollars by optimizing the number of seeds going into the ground.
Studies show the plant stand to achieve optimal yield is 7-10 plants per square foot. Yet, many growers still use the traditional recommendation of 5 lb/acre. Canola seed size varies considerably between hybrids. By neglecting to consider thousand kernel weight (TKW), the seeding rate could be off by 50 percent or more.
Adjustments to canola seeding rates should be based on the seed weight and expected percent of seed survival. Seed weight is provided on the seed tag in TKW. Determining percent survival can be more challenging given the number of contributing factors, but a baseline of 50-60 percent can be used until on-farm data is obtained. To determine survivability, compare the initial seeding rate to the actual plant stand across several locations within the field. Fall stand counts, using the stubble after canola harvest, is typically the preferred method.
Seeding rate formula using seed size
Seeding Rate (lb./ac.) = [9.6 x desired plant density (plants/ft2) x TKW (grams)] ÷ estimated seed survival (%, expressed as a whole #)
It’s also important to consider spring planting conditions when using historic seed survival numbers. If establishment was 80 percent the previous year because of excellent planting conditions and the current year conditions are average, the previous season’s survivability is likely not realistic. Collect as many data points as possible each season to build a reliable, historical average.
Over-seeding to a higher plant stand increases input costs and provides minimal additional return. A high seeding rate creates unnecessary in-row competition for nutrients and space, increases the likelihood and spread of disease, and creates more risk of the crop lodging due to thin stems.
On the other end of the spectrum, under-seeding greatly decreases your opportunity for maximum yield potential and leaves very little room for in-season plant mortality due to canola pests, frost or disease. A low seeding rate presents additional challenges when managing late flushes of weeds and timing the harvest, due to uneven ripening of the big, bushy plants.
The canola plant is very elastic and can achieve good yields at a range of seeding rates. Growers should strive to maximize yield and manage seed costs by optimizing the planting rate to adjust for seed size and seed survival.