Growers don’t have to be in a rush to seed canola in early May. Other crops such as cereals and pulses that are more suitable for deeper seeding to reach moisture may be better choices if you’re waiting for rain. However, if the choice is to seed canola now into dry soil or wait until after it rains, seeding into dry soil is a workable option.
Seed no more than 1” deep — even if seed is placed in dry soil. When rains come, seeds will germinate and emerge fairly quickly. Even if seed waits two weeks in dry soil for rain, it should still be OK.
Seeding deep to reach moisture will increase seed mortality due to disease or decreased vigour. It may also result in more variable emergence dates. More considerations for shallow seeding in dry soil.
The risks of waiting until after a rain: (1) Seeding could be further delayed if rains are heavy. (2) Muddy conditions do not always result in ideal seed placement. (3) Moist conditions will increase the amount of soil — and potentially clubroot — spread around the farm.
Source : Albertacanola