In mid-May I got a call from David, who grows 2,000 acres of canola, wheat, soybeans and peas on his farm in southeastern Manitoba. It had been three weeks since David had planted his canola crop, but he was seeing very poor emergence in the field.
David had hoped for eight to 10 plants per square foot, but so far only two to four seedlings per square foot had appeared in the seed rows. With so few canola plants emerging, he suspected seed might be the issue.
“I think I received a bad seed lot, and that has caused poor germination,” David said.
He asked me to come out and have a look at his canola field. When I arrived at David’s farm, I was told the weather had been fairly dry in recent months, and that soils in these fields were a mixture of clay-loam and sandy-loam.
I performed a plant stand count right away and confirmed that relatively few seedlings had emerged. These findings were uniform across the entire field, and there were no signs of patchiness indicating some areas were affected worse than others.
Prior to visiting David’s farm, I had called the seed supplier to enquire about the canola seed lot. The supplier reported that no one else had experienced germination issues with this seed batch, ruling this out as a source of the problem. But if bad seed wasn’t to blame, what was?
I wasn’t sure, but I suspected the issue might have something to do with chemicals applied to the field. When I looked at the grower’s application records, I could see that no residual herbicide had been used the previous year, and that a glyphosate product had been applied that spring just prior to planting.
With respect to nutrients, David had applied a primary source of nitrogen as anhydrous at a rate of 100 pounds per acre the previous fall. A 36-50-0-20 fertilizer blend had also been applied at planting, in an effort to boost phosphorus levels in the field. I also learned that the fertilizer had been seed-placed with a narrow opener disc drill.
Crop Advisor’s Solution: Too much phosphorus
Looking at David’s nutrient blend sheet for the field, it was evident that he had exceeded the recommended rates of phosphorus and sulphur in the seed row. This had produced a high level of salt toxicity as well as some ammonium toxicity in the soil — both of which would have caused plant damage to occur and led to fewer canola seedlings surviving to make it above ground.
Unfortunately, there wasn’t much the grower could do to rectify the situation, and he ended up with a reduced yield for his canola crop that year. I urged David to be more careful with how he applied nutrients in the future and that he also consider using other rotational crops that are more tolerant of fertilizer as a better solution to increasing phosphorus levels in the field.
In addition, I recommended a number of changes in his nutrient program for the following planting season. These included putting less phosphorus down with the canola seed and using any leftover product with other crops better suited to handling higher quantities of seed-placed phosphorus. I suggested he try different sources of phosphorus fertilizer that aren’t as potentially toxic to canola plants, and I urged him to not to hesitate to ask for a second opinion when it came to crop nutrient plans.
David took my advice, and the following year he had a much better canola crop. The plant stand this time around was right on target, at eight to 10 plants per square foot.
Dan Friesen is a sales agronomist with Richardson Pioneer Ltd. at Starbuck, Man.