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A nutrient-deficiency flare-up in canola

Everything goes along smoothly for decades, and the same old fertilizer combo produces the same old predicable results. Then soil levels for a particular nutrient dip below the critical threshold and plants grow funny and yields go askew. It happens

Jack Wood noticed strange patches of stunted canola in a field in 2013. By swathing time, those patches were clearly messed up. Pods were short and deformed. Stalks were skinny, and in the resulting windrows, the yield monitor dropped from 40 to just five bu./ac.

One adviser said it was heat blast. Wood wasn’t so sure because the field also had patches that were extra good. He also had a clue. He had grown flax the year before, and where he had gathered and burned the flax straw, the canola was in excellent shape.

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More pathetic patches appeared in Wood’s canola fields in 2014 and 2015. Again, the adviser suggested heat blast. In 2015, Wood got a second opinion from a local agronomist. She thought it might be a sulphur deficiency. Subsequent soil tests in these patches confirmed that sulphur levels were very low, so this was a possibility.

Wood had been growing canola for years with a 34-17-0-0 blend. As a test, he added sulphur to his canola fertilizer blend for two-thirds of one field in 2016.

While the field did show an overall improvement, results in those poor-growing patches were especially clear. Any time the line between sulphur fertilizer and no sulphur fertilizer passed through a patch, the difference was striking, Wood says. Plants on the sulphur side were normal and healthy. Plants on the no-sulphur side were stunted and “looked like they weren’t coming into flower,” Wood says.

In 2017, Wood will add sulphur to the blend for all his canola land. “I don’t know how I got along this long without adding sulphur fertilizer,” he now says.

Yes how?

Wood farms at Glenavon, Sask., in the dark brown soil zone. Brown and dark brown soils generally tend to have more sulphur than black or grey soils. So perhaps higher sulphur levels in the soil carried the load for longer than may have occurred in another soil zone.

The region has also been in a wet cycle. As Wood says, “2011 was a wreck” due to excess moisture. High rainfall can leach sulphur down in the soil profile, away from the root zone. Moisture also increases canola yields, and canola removes a lot of sulphur in its seed. The combination of high yields and leaching moisture could speed up a sulphur deficiency trend, making onset seem sudden.

Canola Council of Canada (CCC) agronomy specialist Warren Ward says more sulphur deficiency is showing up in lighter soils with higher rainfall.

Patches are fairly typical of sulphur deficiency. Of all the macronutrients, sulphur can have the most variation across a field, says University of Saskatchewan professor and crop nutrition specialist Jeff Schoenau. “In one field, you could have five pounds of sulphur per acre in the top six inches of soil on a hilltop and 10,000 pounds per acre in a salt-affected depression area,” he says.

As for areas looking better where flax straw had been burned, about half the sulphur that flax takes up remains in the plant biomass. Gathering up flax straw in one place can provide a rich localized source of sulphur as well as phosphorus and other nutrients. “However a hot burn can release nitrogen into the atmosphere and open up the soil to erosion,” Schoenau notes, “so burning is not really a good crop nutrition strategy. In time, nitrogen, sulphur and the other nutrients in biomass will eventually become plant-available again through natural microbial breakdown.”

Soils and sulphur

Sulphur deficiencies were first recognized in the grey soils, and they still tend to show the biggest response to sulphur fertilizer, Schoenau says. But more frequent production of canola and higher yields have been drawing down soil levels in all areas and soil types. Ross McKenzie, retired agronomy research scientist who worked 38 years with Alberta Agriculture, estimates that at least 25 per cent and possibly 40 per cent of soils across Western Canada are sulphur deficient.

“As a general rule, almost all brown and dark brown soils do have adequate sulphate-S in the subsoil and often the surface soil as well, but occasionally surface soil may be low in sulphate-S after growing a good high-yielding crop or after a wet fall or spring causing some leaching,” McKenzie says. “It will more frequently occur on sandy soils with low organic matter.”

Doug Schmunk farms north of Leader, Sask., and knows first-hand how brown soils can differ in sulphur content.
photo: Jay Whetter

Doug Schmunk farms the brown soils north of Leader, Sask. The brown soil zone has a broad spectrum of soil classifications, he says, and he knows where on his farm sulphur symptoms are most likely to show up.

He planted canola on Sceptre soil in 2016: “This soil is predominately clay lacustrine and is the best soil we farm. These fields do not vary much in soil type from corner to corner, and they are generally flat, so even after all the moisture we had in 2016, I did not notice a sulphur deficiency,” he says.

Schmunk also has hilly fields of Fox Valley loam: “I have planted canola on all these fields over the years and have noticed sulphur deficiency symptoms in various areas. This happens pretty much on the calcareous areas or eroded hills or poorly drained soil. In a year like the past one, I would expect the deficiencies to cover larger areas due to the prolonged saturation which would cause leaching of the nutrients.”

Agronomy tips

According to the Canola Encyclopedia, canola generally responds to sulphur fertilizer when the water-soluble soil sulphate content in the top 24 inches of soil is less than 20 lbs./ac.

McKenzie encourages growers to soil test for surface (top six inches) and subsurface sulphate-S separately. “When growing canola, if surface soil has less than 15 lbs./ac. of sulphur, I would suggest supplying 10 to 15 lb./ac. of sulphur regardless of subsoil sulphur level to avoid an early-season deficiency,” he says.

Keep in mind that a composite sample can include cores from deficient areas within the composite — given the variability of sulphur levels in some fields. “So growers targeting high yields in fields known to have sulphur variability may want to include some sulphur in the fertilizer blend, even if the test result shows sulphur levels above 20 lbs./ac.,” says the CCC’s Ward.

Growers will also want to know that applying high rates of nitrogen without sulphur in sulphur-deficient areas can actually create a toxic imbalance in the plant. “Without correcting the sulphur deficiency, yields can be worse than if you applied no fertilizer at all,” Schoenau says.

Among sulphur sources, those immediately plant available are ammonium sulphate and liquid ammonium thiosulphate. Add these to the nitrogen blend banded outside the seed row.

While Jack Wood seems to have solved his patch issue, one always has to be open to the possibility that multiple causes or entirely unexpected causes are at play. In that spirit, Wood is cautiously optimistic: “Hopefully this year I don’t see any patches,” he says.


Sulphur deficiency symptoms

Sulphur deficiencies often appear in patches, reflecting that soil sulphur levels can be highly variable across a field. In extreme cases, deficiency symptoms can start to show up fairly early in the season. In mildly deficient situations, symptoms may not appear until flowering.

Sulphur deficiencies tend to be more visually distinct than other nutrient deficiencies. With S deficiency, yellowing and leaf cupping tend to occur on new leaves first. At flowering, S deficiency will result in small pale-coloured flowers.

Common symptoms:

  • Top leaves are small and narrow, and are often cupped.
  • Pale yellow leaves.
  • Prolonged flowering if the crop is having trouble setting seed.
  • Small flowers with very pale yellow colour.
  • Short pods with little or no seed set.
  • Patchy look to the field. Sulphur is highly variable across a field, so deficiencies will usually show up in patches.

Sulphur deficiency is more typical in sandy soil with low organic matter, but even in higher-yielding soils, high removal rates will also eventually lead to deficiencies.

For more on sulphur management, read the “Fertilizer Management” section at canolaencyclopedia.ca.

About the author

Contributor

Jay Whetter is communications manager for the Canola Council of Canada.

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