Sulfur: A Secondary With Good ROI Promise
Terry Wendell doesn’t have hard research numbers to back it up, but he’s convinced that routinely adding sulfur for his dryland sunflower crop is a consistently worthwhile investment.
Wendell, who farms near Colby in northwestern Kansas, is predominantly a row-crop producer: sunflower, corn and a smaller acreage of milo comprise his rotation, with wheat being an exception rather than the rule. The Thomas County producer has been including sulfur as a standard part of his sunflower fertility program for a number of years — even when soil tests suggest it may not be necessary.
The sulfur goes on at planting along with the crop’s nitrogen and phosphorus needs, either on top or as a 2x2 treatment. “I’m on an all-liquid program: 32%, some 10-34-0 and then 12-0-0-26 (ammonium thiosulfate),” Wendell notes. He’ll apply about five gallons of the 12-0-0-26 at a cost of around $8 per acre. “But we’re getting some nitrogen there too, so we’ve probably looking at more like $5 to $6” in sulfur cost, he says.
“The sulfur in the combination works as a urease enzyme inhibitor,” Wendell points out, “so it tends to keep the nitrogen in a more-stable state. It doesn’t volatize as quickly when I’m putting it on top of the soil.” Some of his soils are high in magnesium, he adds, and “we know that by putting some sulfur on with the nitrogen in a high-magnesium soil, it tends to give us better nitrogen efficiency,”
Wendell has not conducted check strips to gain hard numbers on what the sulfur addition is doing for his sunflower yields. “But I think sunflower responds favorably late to nutrient uptake if there’s some sulfur out there,” he states. A confection grower, “I always have a high percentage of large seeds,” he adds. “Even in a year like  where we got dry during the tail end, I still had 85% larges. I think the sulfur affects that quality issue.”
Wendell became a sulfur advocate during his prior career in fertilizer sales (he logged 28 years in that business).
“I started selling it as part of a program when I was in Nebraska, and it seemed like we always saw good results,” he recalls. Now, on his own farm, “I feel comfortable enough that I just apply it as a standard practice.”
North Dakota State University soil fertility specialist Dave Franzen does not expect a good return on investment from most applied secondary or micronutrients for sunflower in his state. But he makes an exception for sulfur.
“Sulfur is different,” Franzen allows, noting that soil sulfur deficiencies in North Dakota are more common than they were 15-20 years ago. Why? One reason, ironically, has been tougher emission standards nationally, which has meant less sulfur being discharged into the air from industrial and transportation sources. Another factor has been the wet cycle experienced of late in much of the Northern Plains. But perhaps most important have been the higher crop yields compared to a couple decades ago.
“In a heavy clay soil and depression area, you’re not likely to see a sulfur problem,” Franzen says. “But on hills and slopes, where you tend to have coarser soils, you’re very susceptible in a wet year” due to leaching.
The current sulfur soil test is unreliable, the NDSU fertility specialist adds. “People use it because we don’t have anything better,” he says.
“So I suggest people do two things: First, look at where any coarser-textured soils — the sandy loams or loamy sands — are located. If they’re in depressed elevations, don’t worry — the water table is high, and it contains sulfates. But the hilltops and slopes need watching.
“The second thing [is precipitation history]: last fall’s rainfall amounts; winter snow amounts; early season rainfall. If any of those are high, you’ll likely need to put sulfur on those soils, because you will have a problem” due to leaching.
Price, availability and other nutrient needs will help determine the best source of sulfur. However, dealers should make sure that their customers use the right type of sulfur at the right time.
In general, elemental sulfur is converted over time to the sulphate form, which plants require. “The time involved in this conversion may be several months or more, depending on the specific sulfur source and the particle size,” Franzen points out. “Since most crops require sulfur in a deficiency situation rapidly, not slowly, elemental sulfur is not recommended for initial deficiency correction by itself, without most of the sulfur requirement being met by a sulfate-S form. “Sulphate sulfur is readily available to the crop and is most suitable for rapid correction of a sulfur deficiency.” - Don Lilleboe
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