Early seeding usually improves canola yield potential and quality, but these benefits depend on survival of a sufficient plant population — ideally 7 to 10 plants per square foot, and a minimum 4 to 5. An early-seeded crop that is thin and uneven because of a damaging frost will not meet yield and quality expectations.
Typically, the maximum yield benefit comes when canola is seeded in late April to mid May. The exact window depends on the region and the season.
Before making the decision to seed earlier than usual, consider:
Typical date of last killing spring frost. Canola seedlings can typically withstand some light frost (e.g. -2 C to -6 C) without significant mortality, but crop development may be delayed in those situations. Higher mortality occurs when the frost happens the morning after warm to hot spring days. Average dates of last spring frost in Alberta, Saskatchewan and Manitoba.
Soil temperature. Although 20 C is the optimal soil temperature for canola to germinate quickly and evenly, 10 C is a reasonable soil temperature to seed canola, and the general recommendation is that 5 C is a good place to start. Weather forecasts for the week after seeding will help indicate whether the seedbed will be warming or cooling during germination. Canola can germinate at soil temperatures of 2 C, but seeding into soils that are too cool can add significant stress to seedlings, extend the germination period, and reduce seedling survival. Determine average soil temperature by taking readings at 2.5 cm (1") depth at 8:00 am and 4:00 pm over several days. Alberta growers can also find soil temperature information here.
Soil type. Making use of available spring moisture may be more critical on coarse textured soils with less water holding capacity. Potential for compaction from heavy rains following seeding, which can increase stress on seedlings emerging in cool conditions, is lower on sandier soils.
Seed treatment. Seed that takes 2-3 weeks to emerge may not have much seed treatment protection left, so scout often for flea beetles.
Quality seed. No. 1 certified seed has a guaranteed germination rating of 90 per cent at the time of purchase. High germination ratings tend to coincide with higher vigour, so seed quality is rarely a concern if seed is treated gently and placed well.
Accurate seed placement. Seed at a speed that achieves uniform seed distribution and depth, and proper fertilizer separation in single-pass seeding systems.
Set a seeding rate that targets higher plant densities, perhaps 10 per square foot, if seeding very early. This cushions the impact of spring frost or diseases by allowing some plant mortality without an immediate effect on yield potential.
Use this time to control weeds. University of Saskatchewan research has shown that early application of preseed herbicide treatments provide greater yield benefits for later seeded crops than waiting until immediately prior to seeding.
April 2, 2015 By Canola Council of Canada