Heavy rains in the past week left some Prairie canola fields under water. Canola is quite susceptible to water logging and shows a yield reduction after only three days with wet feet. Wet soils cause an oxygen deficiency, which reduces root respiration and growth. Root failure reduces nutrient uptake, and plants will eventually die unless drowned areas dry out quickly.
Wet conditions also increase soil nitrogen losses. Click here for a Manitoba Agriculture factsheet that explains how excess moisture reduces nitrogen reserves.
Reseeding: If only a small percentage of the field is lost, reseeding may not pay off — especially if that small percentage includes a bunch of pot holes all across the field. Reseeding may required if the whole field is lost, but by the time those low spots are read for seeding, it could be mid June — crop insurance cut off time for canola.
What to do about nutrient losses: Wait to see how the crop recovers from saturated soils before investing any more in fertilizer. Don’t do anything while soils are still wet. Roots cannot take up nutrient when soils are saturated. Applying nutrient direct to leaves doesn’t help. Most foliar-applied nitrogen is washed off and then goes into the root zone. Uptake through the leaves is minimal.
Even if soils do dry up quickly and the crop recovers nicely, think twice before applying high rates of nitrogen top dress this late in the season. Excessive nitrogen applied now will stimulate growth, and make the crop even later. That raises the risk of fall frost grade losses.
Click here for a detailed article on how waterlogging hurts canola.