Wet fields will have lost up to half of their applied nitrogen and soil reserves through leaching or denitrification the past couple weeks. But growers should make sure their canola has survived the wet conditions before investing in a fertilizer top up.
If the crop is in good shape, a small nitrogen top up may help the crop. Too much and the crop is vegetative longer and matures later, increasing the risk of fall frost damage.
Because sulphur deficiency can also occur after soil saturation, one top up product to consider is ammonium sulphate — which provides nitrogen and sulphur. Broadcast dry, it needs a shower shortly after application to wash it into the root zone.
Symptoms of nitrogen deficiency: Nitrogen deficiency symptoms first show up in older leaves as pale green to yellow colouring, and sometimes purpling. Click here for more details from the Canola Growers’ Manual.
Symptoms of sulphur deficiency: With sulphur, yellowing and leaf cupping tend to occur on new leaves first. Purpling of leaf edges can show up when deficiency is fairly severe. (See the photo below.) In many fields, there is enough sulphur available initially to get the crop past the early rosette stage without visible symptoms, and then problems show up at flowering. Click here to read an Alberta Agriculture factsheet on sulphur deficiency
and click here for details from the Canola Growers’ Manual.