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Plant density dilemma

Perplexed by the low plant density of the canola stand in two of his fields, John, who farms 3,000 acres of peas, wheat and canola northwest of Saskatoon, asked me to visit his operation. He wanted some answers.

It was the first week of June, and most of the 1,200 acres of canola John had planted that spring were progressing well. “There’s a problem with seedling emergence in two fields,” he said. “All of my other fields of canola have emerged fine.”

The plant stands of the affected fields were thin, and this low plant density was prevalent throughout the fields — except in low-lying areas. On average, the plant density was six plants per square foot, and it seemed thinner on the hillsides and hilltops than in the low-lying areas.

There were many possible reasons for this poor crop stand, such as damage from frost or insects, poor germination or vigour, or incorrect seeding depth.

However, all of these possibilities were quickly ruled out. There had not been a frost after the date the crop was sown, and we found no evidence to support cutworm activity, such as chewed stems or the presence of the insects when we dug in the ground. All of the canola seed used to sow John’s fields was from the same lot, so poor germination and vigour were also not causing the problem. When I checked the seed rows, I also noticed the seed had germinated, eliminating seeding depth as one of the possible causes of the damage.

The soil texture was sandy loam with low soil moisture content at the time of seeding. Because it had not rained from the time the seeds were sown until that first week of June, soil moisture content had remained low through the germination period.

I thought it was worth exploring John’s fertilizer rates. He told me soil tests had indicated marginal amounts of sulphur in these fields, a problem he thought he’d addressed by adjusting his fertilizer application rate. “I increased the amount of seed-placed fertilizer blend on these two fields,” said John.

He had thought he was simply correcting a mineral nutrient deficiency, but he’d actually walked into a complex set of factors that ultimately injured his crop.

What is causing the low plant density in two of John’s canola fields? Send your diagnosis to Grainews, Box 9800, Winnipeg, MB, R3C 3K7; email [email protected] or fax 204-944-5416 c/o Crop Advisor’s Casebook. Best suggestions will be pooled and one winner will be drawn for a chance to win a Grainews cap and a one-year subscription to the magazine. The answer, along with the reasoning which solved the mystery, will appear in the next Crop Advisor’s Solution File. †

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