Crop Advisor’s Casebook: A canola conundrum confounds

A Crop Advisor’s Solution from the September 2, 2014 issue of Grainews

In early June I received a call from Wayne, a canola grower in Westlock, Alta. He told me a field of his canola was suffering from very poor plant establishment and vigour. The plants were purpling and dying.

“Only a few plants have come up,” Wayne said. “The ones that did are stunted and have very pinkish-purple leaves, which I noticed when the crop emerged.” He suspected the problem had something to do with poor seed quality, and he asked me to come out to see what I thought.

Rachelle Farrell is a crop inputs manager with Richardson Pioneer Ltd. at Morinville, Alta.

Rachelle Farrell is a crop inputs manager with Richardson Pioneer Ltd. at Morinville, Alta.
photo: Supplied

When I arrived at Wayne’s field the problem was evident, I could see uneven and stunted growth along with purpling and dying plants throughout the crop. I inquired into Wayne’s seeding practices; although a new disc drill had been used at planting, there were no issues initially and all the seed had appeared to go down at the right rate.

I could see the ground was extremely wet — almost saturated. There was a great deal of trash, or straw from the previous crop, covering the field and acting to hold moisture in. I pulled up some plant roots and had a look. While they were stunted, the roots didn’t appear to be infected with disease that often thrives in wet soil.

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My first guess was that some kind of nutrient deficiency might be to blame. However, when I inquired into Wayne’s fertilizer program, it appeared to be very comprehensive and a subsequent tissue test revealed all the necessary nutrients were in balance for canola plants at the two- to four-leaf stage.

When Wayne and I examined the plant stand more closely, I could see there wasn’t anything close to a decent canola crop here. Wayne needed at least five plants per square foot, but we were looking at a field with only about two to three plants per square foot.

Something had prevented many of the plants from germinating and emerging. Could it also be the source of the purpling and dying plants that had managed to emerge? Or were two separate problems at work?

Crop Advisor’s Solution: Phospate deficiency

It was early June when I got a phone call from Wayne, a canola grower at Westlock, Alta. He was worried about the canola in one of his fields, which was suffering from very poor plant establishment and vigour. The field was also rife with purpling and dying plants. Wayne thought poor seed quality might be to blame and he asked me to come out and have a look.

When I arrived the farm, I could see uneven and stunted growth along with purpling and dying plants evident throughout the entire field. I also saw the ground was extremely wet — almost saturated — and there was also lots of trash, or straw from the previous crop, covering the field and acting to hold moisture in. When I examined some plant roots, they were obviously stunted but didn’t appear to be infected with disease that often thrives in wet soil conditions.

I thought a nutrient imbalance might be the answer, but Wayne informed me that his fertilization program had been very comprehensive, and a subsequent plant tissue test revealed that all the necessary nutrients were in balance. I then inquired into Wayne’s seeding practices; he told me that although a new disc drill had been used at planting, there were no issues initially and all the seed had appeared to go down at the right rate.

Looking more closely at the plant stand, I noticed something important. To even be close to getting a decent crop, Wayne needed at least five plants per square foot. Here, we were looking at about only two to three plants per square foot.

I could see there were numerous seeds still sitting on top of the straw on the soil. The disc drill had obviously failed to penetrate the trash, causing a hair-pinning effect where the seed gets placed on top of the straw, instead of in the soil. This explained the poor plant stand, and for a moment I thought I had figured it out. But why were the plants that had emerged so small and discoloured? Something else was at work, too.

It had to be a nutrient imbalance, I told Wayne. “But we already did a tissue test and the results were good,” Wayne reminded me. However, that test showed the nutrients were in balance for the two- to four-leaf phase of canola plants, and did not take into account that the plants should have been at the rosette stage at this point in time.

To get to the bottom of the problem, I felt a soil test was in order. Lack of available phosphate often leads to severe stunting, and a standard tissue test alone does not tell the whole story. Phosphate is essential for root development; plant uptake is reduced in cold, wet soils, like that found in Wayne’s field. The wet soil would potentially be restricting root growth, further compounding a phosphate uptake issue.

Sure enough, a soil test found low levels of available phosphate. Unfortunately, nothing could be done to save Wayne’s crop. The damage was too severe; the crop was too thin and too far behind in the season to recover.

I advised Wayne that although his nutrient program had been comprehensive, there is much more to crop nutrition than fertilizer. Particularly with nutrients like phosphate, maintaining soil fertility, or the nutrient levels in the soil, is even more important. It is important to factor in how much phosphate is removed each year and that soil levels are not depleted over time. There are so many interactions happening in the soil profile that we cannot see which nutrients might play an important role in plant development.

My advice to Wayne was to ensure he improved his crop residue management in the future, to monitor his soil fertility over time and improve seed-soil contact.

Rachelle Farrell is a crop input manager for Richardson Pioneer Ltd. at Morinville, Alta.

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