Bigger seed changes the canola seeding equation

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The best chance for maximizing canola yields is a plant population of eight to 10 plants per square foot and a minimum of five throughout the growing season, says Doug Moisey, an extension agronomist with the Canola Council of Canada.

“Typically when you have four to five plants per square foot or higher your yield goes up linearly until about 10 plants per square foot, and that gives you the best chance (for optimal yields),” Moisey said during a webinar May 3.

Yields decline 13 to 21 per cent in fields with a minimum of four plants per square foot, he added.

Seeding five pounds an acre doesn’t guarantee your field will achieve the ideal plant population, especially now with some canola seed being bigger. Bigger seed generally survives better, but when sown by the pound there are fewer bigger (heavier) seeds per square foot.

In a survey of 218 canola fields last year 34 per cent had less than four plants per square foot, Moisey said

“Forty-one per cent of those 34 per cent were seeded at five pounds per acre,” he said.

Probably about 50 per cent of those fields didn’t reach their optimal yields just because of inadequate plant stands.

Plants population depends on how many seeds are planted and how many emerge and survive to harvest. Precipitation is the single biggest factor affecting emergence, Moisey said, but since that’s beyond farmers’ control they should focus on the agronomics they can influence.

For starters, farmers should know their seed weight (grams per 1,000 kernels), seeding rate and plant stand from last year to serve as a guide for this year. But 75 per cent of western Canadian farmers don’t do plant counts, Moisey said.

“Going into this season with $10-a-pound seed with the potential for $14-a-bushel canola we have to know what we’re putting in the ground,” he said.

The canola council’s website (http://www.canolawatch.org/2012/04/25/wide-range-of-seed-weights/) has tables showing the plant populations per square foot expected when planting various seed sizes with survivability rates of 20 to 80 per cent.

The following formula can also be used: Seeding rate (lb./ac.) = [9.6 x desired plant density (plants/ft.2) x Thousand Seed Weight (TSW) (grams)] ÷ estimated seed survival (per cent, expressed as a whole number).

So if the TSW is six grams, the desired plant population per square foot is eight and the survivability is 70 per cent, the seeding rate should be 6.6 pounds an acre.

However, if survivability can be increased to 80 per cent, the seeding rate drops to 5.5 pounds an acre, saving the farmer $10 an acre.

There isn’t much room for error when striving for 80 per cent survivability, Moisey said.

Smaller seed can help. Plug four-gram canola into the formula and at 70 per cent survivability it takes just four pounds of seed an acre to get seven plants per square foot.

Moisey has some tips for improved plant emergence and survival:

  • Fine tune your air seeder. Make sure it’s balanced front to back and side to side.
  • Keep fertilizer away from the seed. Reducing seeding speed can help. Travelling too fast also results in uneven planting depths.
  • Seed one-half to one inch deep.
  • Seed when soil temperatures average 4 to 8 C at seeding depth.
  • Increase the seeding rate when planting into cooler soils.
  • Measure seeding depth continually.

Planting into soils cooler than 4 C will result in reduced and delayed emergence. Seed treatments only provide 21 to 28 days of insect protection. Seed that’s in the ground for 15 days might only have a week of protection after emerging.

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