As a general rule, only 50 to 60 percent of open-pollinated and hybrid seeds will survive to produce viable seedlings. Other than weather conditions, most factors that affect survival can be managed to some degree.
Determining the appropriate seeding rate to achieve proper plant populations of seven to 14 plants per sq. foot requires a good estimate of seed and seedling survival for each field. Survival in the spring can vary greatly, easily ranging from 25 to 75 percent.
Twelve key factors affect seed and seedling survival:
- Seed size – In most cases, the larger the seed size, the better the vigour. The more vigour, the better the seeds and seedlings are able to cope with early stresses and survive.
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The following rating system, developed by Bob Elliott of Agriculture Canada in Saskatoon, estimates potential seed vigour:
Seed vigour index rating = (7 day germination %/100) X thousand seed weight (grams).
Typical seed vigour index ratings: open pollinated, three to 3.5; hybrids, 3.5 to 4.5.
If a seed lot has a rating below these ranges, the seed may be less vigorous and more sensitive to stress. Managing seeding to reduce stress on the seed will be more critical.
Growers should seed these lots into warm soils, keep seeding depth shallow and consider seeding at a little higher seeding rate.
- Seed chlorophyll – Higher seed chlorophyll content can reduce vigour and increase mortality. Testing should be done to ensure that the levels are below 35 milligrams per kilogram.
- Hybrids versus open pollinated varieties – Typically hybrids will have higher seedling vigour or growth than open pollinated varieties by 10 to 20 percent. Remember to adjust seeding rates to accommodate seed size, making sure the right amount of seed is planted to ensure a proper plant stand.
- Seedbed temperature – Soil colder than 5 C at seeding and for two weeks following seeding can increase mortality by 10 to 20 percent. The ideal soil temperatures for germination is at least 10 C. However, 5 C is a reasonable starting point.
- Frost – Early season frost can thin a stand, but in most cases a sufficient number of canola seedlings will survive. Keeping a field clean until the canola canopy closes the ground will be beneficial.
Most often reseeding a frost damaged field will fail to improve returns. If canola is being seeded early to improve yield potential, the increased risk of early spring frost may warrant an increase in seeding rates to ensure a stand within the range of seven to 14 plants per sq. foot. Research has shown that stands with a plant population as low as two plants per sq. foot can still produce a viable canola crop. However, yields are often lower than a canola stand that has at least seven plants per sq. foot.
- Seed depth – Optimum seeding depth is 11/4 to 21/2 centimetres below the press wheel furrow.
There are still too many cases of deep seeding. Increased seeding depth increases time to emergence, reduces plant populations, decreases seedling, plant and root growth, delays maturity and increases the risk of seedling diseases. All of this can increase seedling mortality and ultimately reduce yields.
- Seeding speed – Slow down. This will ensure uniform seed distribution and emergence and proper fertilizer separation in single pass seeding systems. If higher seeding speeds are needed to cover the required acres, recognize that seed survival will likely be reduced and increase seeding rates accordingly.
- Fertilizer in the seed row – Placing high rates of fertilizer in the seed row can greatly increase mortality if the seeding equipment has low seedbed utilization, especially in poor moisture conditions.
- Seeding equipment and seedbed quality – Seedbed quality depends on soil texture, moisture, tillage, openers and trash residue. Improper on-row packing can result in poor seed-to-soil contact and increased mortality, especially in dry springs.
Crusting on low organic matter soil can also increase mortality. Large amounts and uneven distribution of crop residue can cause seed placement problems, leaving seed stranded within the straw.
- Tight rotations and disease – Short breaks between canola crops of less than two years will increase the probability of mortality due to seedling disease. Other host crops for diseases or use of residual herbicides in the rotation may also cause stand establishment problems.
- Weeds – Heavy weed pressures in the field can increase mortality through competition with the canola seedlings for moisture, nutrients and sunlight. Denser canola stands will be more competitive and early weed removal will also improve crop performance.
- Insects – Heavy flea beetle pressures can thin the stand even with high seed treatment insecticide rates. The clue is the previous fall. If flea beetle numbers were high, the likelihood of flea beetle pressure the following spring is also high. Keeping seed rates up to obtain a dense plant stand will spread the damage over more plants. Cutworms and wireworms the previous year can also indicate a potential threat.
