An Argument For High SBU

With the world of seeding equipment going to wide row spacing and narrow openers, this is putting our seed at higher risk of seed-placed fertilizer injury. Yes, the wide rows and narrow openers are reducing the horsepower required to pull the gargantuan drills that cover more ground and gain efficiencies of scale. And it does help the moisture-challenged areas produce higher yielding crops and protect soil from erosion. But we find that high seedbed utilization (SBU) works best on our farm.

A quick explanation: (SBU) is the amount of spread by the opener divided by the row spacing multiplied by 100.

We farm in the east central area of Saskatchewan, and seed with an 8800 Bourgault airseeder on eight-inch centres. Depending on the conditions and the fertilizer rate, we alternate between knock-on 11-inch shovels, four-inch spikes, and 1.75-inch hoe openers. Quick attach harrows and packers were added four years ago and are highly recommended from the standpoint of being able to respond to the soil moisture conditions.


When applying higher rates of phosphate and potash with our seed, we use the 11-inch shovels. While the shovels work the whole area, seed and fertilizer are actually placed in a four-inch spread behind the shovel. Four inches of spread on eight-inch centres equals a 50 per cent SBU.

When switching to the 1.75-inch openers, we are down to 22 per cent SBU, meaning that we can apply only 44 per cent of the fertilizer with the 1.75-inch opener as with the four-inch spread with the 11-inch shovel.

Using the Saskatchewan Ministry of Agriculture’s guidelines for safe rates of fertilizer placed with the seed, using a one-inch opener on nine-inch centres (11 per cent SBU) with good to excellent soil moisture, you can safely seed place 50 pounds of P2O5 (or 96 pounds of 11-52-0) with cereals, 25 pounds with canola, and 15 pounds for flax, pea and forages. Drier soil means this number drops. By using our four-inch spread on eight-inch centres, we can seed place 225 pounds of P2O5 (or 432 pounds of 11-52-0) on cereals, whereas the 1.75-inch opener we can seed place 100 pounds (or 192 pounds of 11-52-0). Most seeds are more sensitive to nitrogen.

On average, barley removes 0.40 pounds of P2O5 per bushel, where canola is 0.91, oats 0.25, and wheat is 0.50. So a 70-bushel barley crop will remove 28 pounds of phosphate, 35 bushels of canola remove

32 pounds, 100-bushel oats need

25 pounds and 40 bushels of wheat require 20 pounds of P2O5. So on average, most cereal crops can safely place P2O5 with the seed.

The canola is another story. There is a seven-pound deficit that needs to be addressed. That’s for a one-inch opener on nine-inch centres. With a one-inch opener on 12-inch spacing — an eight per cent SBU — the amount of phosphate per acre you can safely place in the seed row drops even further. With this scenario, you can only seed-place 19 pounds per acre of phosphate with canola seed. Cereals can have 37 pounds of P2O5, and flax, peas and forages can only have 11 pounds — and that’s under good moisture conditions. When you look at what the plants take up in the season, we do not come close to supplying the total required. Barley will take up 40 pounds of P2O5, canola 50 pounds, oats 40 pounds, and wheat needs 35 pounds.


When you add potash to your seed-placed blend, this reduces the amount of phosphate you can seed place. The rule of thumb is the total amount of P2O5 and K2O has to be less than the safe rate of P2O5. Based on the yields in our area, barley takes up 100 pounds of K2O, canola uses 80, oats 150, and wheat 75. (Note, a lot of that is returned to the field in straw and chaff. Of the total, barley will remove 25 pounds of K2O, canola 20 pounds, oat 20 pounds, and wheat 20 pounds in the seed.)

Having a paired row, side banded, or mid row will help with seed safety, but then the phosphate is located away from the seed and you will lose the pop up effect. Because of our high soil pH and high levels of free calcium in the soil, adding a high amount of phosphate in the soil is not effective unless in a tight band with the seed.


The other benefit of having a higher SBU is weed competition. High SBU will require a higher seeding rate, but will canopy up quicker, shading the ground, cooling the soil, and choking out weeds. Wider rows will allow the canopy to dry out and keep diseases more at bay but will take longer to canopy requiring a higher level of weed control which may be a big of deal under a high thatch condition.

The wider seed bed utilization does take more horsepower to pull, but is able to put more fertilizer down with higher rates of fertilizer use efficiency, with higher seed safety and higher plant counts per square metre. Wider row spacing is going to rely on higher mycorrhizae populations in the soil to work with the plants to obtain nutrients when the plant demands them due to low levels of seed placed fertilizer.

If direct seeding, the low disturbance seeding system is not going to allow the soil to warm up and will then further reduce the phosphate and potassium uptake from the soil. These are some of the implications of going to a low SBU seeding system.

Kevin Elmy operates Friendly Acres Seed Farm, along with his wife, Christina, and parents, Robert and Verene, near Saltcoats, Sask. You can contact him at 306-744-2779 or [email protected]

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