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SULPHUR LOSS: MORE COMMON THAN YOU THINK

When Art, who farms 1,500 acres of canola, wheat, peas, oats and barley 10 miles east of Carrot River, Sask., noticed a problem developing in his oat crop in mid-June, he gave me a call right away.

Areas of Art’s field had deteriorated over a matter of days, and were showing patches of pale green leaves. Initially, Art thought it looked like an issue with the ammonia applicator, but quickly ruled out that idea, as the discolouration was irregular.

Another possibility was that rainfall — about 3-1/2 inches — had caused the nitrogen to leach below the root zone. When I headed out to Art’s field to see the crop, I found it in exactly the condition he had described. Irregular patches of light green leaves were discolouring an otherwise healthy-looking crop. But upon closer inspection, I found that only the newer leaves of many plants sported the pale green colour, meanwhile the older leaves had maintained their natural healthy green hue. In the case of a rainfall heavy enough to cause nitrogen leaching, the whole plant is affected, not just the new growth, so it couldn’t be nitrogen deficiency causing the discolouration.

“What did you grow on this field before oats?” I asked Art.

Art said he’d grown alfalfa for the local processor for three years prior to the oat crop. No fertilizer had been applied to the alfalfa field, although he had a fertility program in place for the oats, which included nitrogen.

A tissue sample confirmed what I suspected was the problem. Art’s oat crop was suffering from sulphur deficiency. Although highly mobile in soil, sulphur is relatively immobile in the plant, which resulted in the discolouration of the plant’s new growth. In the case of Art’s oats, the soil sulphur was adequate to maintain growth up to the 3- to 4-leaf stage. At that point, perhaps aided by the heavy rain, the plants ran short of sulphur, producing new leaves that were an unnatural shade of pale green.

By the time we received the tissue sample confirming our diagnosis, it was late in the season and Art’s oat crop was well advanced. Surprisingly, the crop recovered nicely. As conditions dried, the roots were able to reach the leached sulphur, and Art was fortunate to end the season with minimal loss. The damaged fields yielded about 100 bushels per acre.

While canola is recognized as a crop with high sulphur requirements, all crops, including oats, require sulphur. It should also be noted that alfalfa is a heavy consumer of sulphur.

Since then, Art has included a small amount of sulphur in his cereal blend. In general, eight to 10 pounds per acre added to cereal crops should safeguard them from future problems with sulphur deficiency — and yield loss. †

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