The most profitable results from a topdress will probably come from bolstering good areas of the field rather than trying to rescue poor areas where the primary stress is excess moisture rather than lack of nitrogen.
The strategy: Dribble band liquid nitrogen or broadcast ammonium sulphate at 20 to 30 pounds of actual N per acre on the better areas.
Results from a recent split application study found that in 2005, a wet year, the best yielding canola at two sites came from a split application of nitrogen fertilizer. Of the total 60 pounds applied in the trial, half was applied as a pre-seed band and half as a urea broadcast at bolting.
This strategy could work this year for many canola crops, especially those that recover well after weeks of wet weather. Rain will have leached a lot of applied and reserve nitrogen, and if the crop has good yield potential, nitrogen topdressing can make a difference.