Some reports suggest sulphur fertilizer supplies may be limited in some areas this spring. If growers have trouble getting all the sulphur they need prior to seeding, divide what you have across all your canola acres, then top up with an in-crop application of ammonium sulphate.
Post-emergence sulphur can be applied up to flowering and still provide a yield benefit, but the most efficient yield conversion comes from sulphur applied at the time of seeding or soon after. When doing an in-crop application, growers could target only those areas — such as hill tops — that tend to be sulphur deficient.
Elemental sulphur applied at the time of seeding will not be available in time for when the crop needs it, especially if it is incorporated. Elemental sulphur prills need time to break apart to increase the surface area, and then require bacteria to oxidize the sulphur into plant available form. These bacteria are most active in warm moist soils. It can take months for elemental sulphur to become available to the crop. Also note that any sulphate made available from the oxidation of elemental sulphur applied last fall may have leached down into the soil profile if fields were wet last fall and this spring, potentially delaying availability to the crop this year.
Does your canola need potassium? Unlikely. Only sandy and peat soils tend to benefit from potassium fertilizer. And wheat is more likely than canola to show a response when soil test levels are at 300 ppm or lower. So if soils are deficient, apply potassium to wheat and see if you get a response. Leave a check strip. For canola, the best return on investment for fertilizer is likely to come from nitrogen, phosphorus and sulphur.
Growers who plan to apply potassium on canola land could consider potassium sulphate (K2SO4) fertilizer to get the benefit of the sulphur as well, but they will need to consider the relative cost of this source.