Keep Canola Well Fed

Nitrogen is your best investment in terms of canola inputs, says Jim Bessel, senior agronomy specialist with the Canola Council of Canada. “If you’ve got the moisture and you don’t feed canola what it needs to reach its genetic potential — especially with hybrids — then you’re not going to be profitable,” he says.

Every bushel of canola needs 2.5 to 3.5 pounds of actual nitrogen, 1.25 pounds of phosphate, 2.5 pounds of K20 and 0.5 pounds of sulphur. Those numbers don’t change as the price of fertilizer changes. If you target a 35-bushel canola crop, you need at least 100 pounds of available nitrogen.

Bessel recommends you start with a soil test to determine nutrient reserves and get fertilizer rate recommendations. If you also send along a soil moisture estimate and a snowfall measurement, the soil test lab can use that information to adjust your yield potential up or down.

Canola needs three or four inches of available water to build biomass. Each additional inch of water adds three to five bushels of yield, Bessel says.


Bessel describes how to make your own soil moisture probe. It’s a length of half-inch rebar with a ball bearing welded to one end and a crossbar at the top to push on. Push the ball-bearing end into the soil as far as you can. When you can’t push any more, that’s where the water ends.

Say you can push it down three feet. Next, you need to know the water holding capacity of your soils. Sandy loam holds 1.25 inches of water per foot of moisture. So three feet of moisture equals 3.75 inches of water available to the crop. Clay loam holds 1.75 inches of water per foot of moisture, so three feet of moisture equals 5.25 inches of water.

You then add an estimate of precipitation for the season, including snow, and add that to the moisture in the soil. Finally, there is a formula to estimate canola yield potential based on this available water and your soil zone. For example, for the thin black soil zone, you multiply available moisture by a factor of 3.3 to get the canola yield potential.

If you have three feet of moisture in clay loam soil and you farm in the thin black soil zone and you expect to get seven inches of precipitation, here is the estimate: 5.25 inches of soil moisture plus seven inches of estimated precipitation times 3.3 gives you a target canola yield of just over 40 bushels per acre.

All of these numbers and detailed instructions are available at the Saskatchewan Ministry of Agriculture website at “Measuring subsoil moisture to determine stored water” in the search box. For a general estimate, see Les Henry’s moisture map on page 14 of the February 16 Grainews.

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