Evaluating sulphur
Wheat growers in the United States and Canada should evaluate sulphur management practices, according to a panel of eight soil specialists assembled at an American Society of Agronomy meeting.
“Without enough of it (sulphur), plants mature late, become spindly and both yield and quality are compromised,” said Donald Messick of The Sulphur Institute, Washington, D.C.
Several factors influence a crop’s sulphur supply. One is the type of soil, said Ray Lamond of Kansas State University. “Sandy soil is an example of one type of soil that tends to be low in organic matter and low in sulphur,” he said.
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Several other factors are increasing the need for sulphur in wheat crops, the agronomists said:
- Hardpans – Heavy farm equipment causes “hardpans” or areas of compacted soil that prevents roots from reaching subsoils, which may contain sulphate sources. Deep tillage may solve the problem and increase crop yield, said Jim Camberato of Pee Dee Research Station, Clemson University, Georgia.
- Crop rotation – Cynthia Grant of the Agriculture Canada research centre in Brandon, Man., cited the boom in canola, which drains sulphur reserves.
- Intensified production – With the focus on extended rotations, intense production and higher yields, Kansas’ Lamond said that naturally depletes sulphur soil reserves. A 50-bushel wheat yield removes approximately 10-15 pounds of sulphur per acre.
- Cattle grazing wheat pasture – “There are a lot of growers who plant wheat and intend to harvest as much as 2,000 pounds as forage, but who still have the expectation of coming back to get 40, 50 or 60 bushels of grain crop,” Lamond said.
- High-analysis fertilizers – Growers once routinely used fertilizers such as ammonium sulphate (21-0-0-24S), which provided significant sulphur. In recent years, many have switched to high-analysis forms of nitrogen, phosphorus and potassium, which contain little or no sulphur.
- Top-dressing with nitrogen alone – In some cases, sulphur deficiencies can develop in a wheat field when growers top-dress with nitrogen alone, said Messick. “The added nitrogen throws off the crop’s nitrogen-sulphur ratio and actually creates a sulphur deficiency.”
If producers suspect a sulphur deficiency during plant growth, they can confirm it with tissue or plant analysis. Another approach is to assess sulphur requirements ahead of planting with a soil survey or soil test.
– The Sulphur Institute
