From Canola Council of Canada

In a recent survey on agronomic practices, the Canola Council of Canada found that, on average, growers were applying 79.5 lb./ac. of actual nitrogen, 25.8 lb./ac. of phosphate (P2O5), 4.9 lb./ac. of potassium (K20) and 13.6 lb./ac. of sulphur to their canola fields.
This may not be enough for high yielding canola.
Canola that yields 35 bu./ac. removes 61-74 lb./ac. of nitrogen, 33-40 of phosphate, 16-20 of K2O, and 10-12 of sulphur. Average fertilizer rates are probably keeping up with removal for canola at that yield.
But many growers harvested higher canola yields the past couple years. A 50 bu./ac. canola crop removes 87-105 lb./ac. of nitrogen, 47-57 of phosphate, 23-29 of K2O and 14-17 of sulphur. If that 50 bu./ac. crop was produced from the average application rates above, the deficit would have come from available nutrient in the soil.
When canola achieves higher yields than targeted with a fertilizer application, it may be depleting soil nutrient reserves. Growers should evaluate the nutrient balance for preceding crops on each field to determine if this is the case. If so, soil testing may reveal lower than expected residual nutrient levels, and producers may need to increase fertilizer rates for 2011 if they want to maintain this higher yield potential.