Excess moisture restricts nutrient uptake, speeds N loss

Canola is quite susceptible to water logging and shows a yield reduction after only three days. The key is that wet soils cause an oxygen deficiency, which reduces root respiration and growth. Root failure reduces nutrient uptake, and plants can die. CCC senior agronomy specialist Derwyn Hammond provided this photo of his own canola field. His farm near Brandon got close to 4” on Saturday alone.

Wet conditions also increase soil nitrogen losses. “If growers still haven’t seeded and applied any fertilizer, extended wet conditions mean they’ve probably lost whatever nitrogen was in the soil profile,” says Murray Hartman, oilseed specialist with Alberta Agriculture. If they did apply nitrogen last fall or early this spring, then half was probably lost through leaching or denitrification in the past two or three weeks of wet weather, he says. “What’s more, losses will not be even throughout the field.” Click here for a MAFRI factsheet that explains how excess moisture reduces nitrogen reserves.

So what’s a grower to do? Wait to see how the crop recovers from saturated soils before investing any more in fertilizer. Certainly 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,” says Hartman.