Canola fields may benefit from a top-dress application of nitrogen or sulphur (or both) if logistics and weather prevented the full recommended application of fertilizer at or before seeding, and if improved weather conditions (rainfall, for example) have increased the yield potential of the crop.
If farmers decide to top dress, the ideal time for nitrogen is any time up to the five-leaf stage to make sure fertilizer in place before the crop needs it. Sulphur can be applied up to early flowering and still provide a yield benefit.