Nitrogen may be making headlines in the New York Times and Wall Street Journal, but sulfur is what's turning some heads in northeast Iowa, southern Minnesota and other parts of the Midwest.

It started in 2005. After noticing pale green patches in alfalfa fields in the northeast corner of the state, Iowa researchers established a replicated sulfur study. Yields from healthy-colored alfalfa were unaffected by S, but yields from pale-green areas more than doubled in 2005 and nearly doubled in 2006.

Around the same time, deficiency symptoms began showing up in corn-a surprising trend because these soils had no history of sulfur deficiency. Yet results from 2006 and 2007 research would tell a dramatically different story. At two sites in 2006, 10 pounds of sulfur fertilizer increased corn yield by 15 bushels per acre. At six other sites, where previous visual symptoms or soil conditions pointed more strongly to a sulfur deficiency, application of sulfur fertilizer increased corn yield by 38 bushels per acre. In 2007, the average corn yield response was 15 bushels per acre on fine-textured soils (14 loam and silt loam sites) and 25 bushels per acre on coarse-textured soils (six loamy sand and sandy loam sites). The economic optimum rate of S was approximately 15 pounds S per acre for the fine-textured soil sites and 25 pounds S per acre for the coarse-textured soil sites.

According to John Sawyer, project coordinator, these studies in alfalfa and corn production indicate a considerable change in the need for sulfur fertilization in northeast Iowa.

"Loams and silt loams are not the traditional soil types where we would expect to see a sulfur response in corn," said Bob Schoper, agronomy services manager with Winfield Solutions LLC. "But the playing field for sulfur has changed dramatically in just the past few years. Across the Corn Belt, we're seeing sulfur responses in heavier soils with higher organic matter levels where corn is grown in high-yielding environments."

A 2004 corn study at Waseca is what "first opened our eyes to sulfur" on heavier soil types, said Gyles Randall, research professor with the University of Minnesota. Working with clay loams where organic matter ranged from 5 percent to 7 percent, Randall has measured an average annual yield increase of 10 bushels per acre from application of sulfur in corn starter over a three-year period from 2005 through 2007.

"These results pretty convincingly demonstrate that growers should be looking at sulfur when growing corn for high yield production on these soil types, which are dominant in southern Minnesota and northern Iowa," Randall said.

Dean Collamer, agronomist and CCA with Honeywell, says that sulfur's traditional market has been on sandy, low organic matter soils. Sandy soils get less sulfur from organic matter reserves and have a lower holding capacity due to leaching.

"Yield increases on these soil types are common and can be quite dramatic," Collamer said. "Sulfur response in heavier soils is a much more recent phenomenon that is picking up steam as more support comes in from university research results. In addition to Iowa and Minnesota, sulfur responses on more fertile soil types have been documented in Wisconsin, Kansas and Maryland."

Sawyer said a contributing factor is a reduction in sulfur coming from industry smokestacks. "Coal-fired power plants are installing scrubbers that remove sulfur dioxide, so there's less sulfur coming from the atmosphere," he said. From 1990 to 2006, the electric power industry has cut sulfur dioxide emissions by 40 percent.

Reduced tillage and earlier planting also play a role.
"It's not unusual to see farmers planting corn in mid to late April if the weather cooperates," Collamer said. "The trade-off is that cooler soils won't release as much sulfur. The same is true where reduced-tillage systems are in place, as they tend to keep soils cooler and wetter further into spring."

Researchers estimate that every one percent of organic matter releases anywhere from two to five pounds per acre of usable sulfur. But the mineralization required to release sulfur does not occur until soil temperatures warm up to about 60 degrees.

Randall's corn plots were planted in the latter half of April, with only a light spring field cultivation for tillage. "This is fairly representative of planting practices in this area and I think it explains to a large degree why we're seeing sulfur responses in soils where organic matter runs as high as 7 percent," he says. "Farmers are less concerned with soil temperatures than they are with getting their crop planted just as early as they possibly can."

A third piece of the puzzle is what Randall and Schoper call "high-yielding environments." These are areas where farmers are "matching the right genetics with the right soil types," Schoper explained. "It's where we're increasing plant populations and we're minimizing stress through weed, disease and insect control. In these situations, a key factor is having the right plant nutrients in the right amounts, and that's where sulfur comes in. It works together with all the other pieces of the puzzle to maximize yield."

Sulfur was a featured nutrient in last year's Answer Plots, a research and demonstration program sponsored annually by Winfield Solutions that encompasses 128 sites in some 12 states.

"Our objective was to demonstrate and educate retail agronomists on the role of sulfur in high yield corn systems," Schoper said. "We saw very visual responses to sulfur-not just in those traditional sulfur markets but at quite a number of locations on heavier textured soils and high yield environments."

Randall, likewise, is seeing very noticeable differences in his sulfur plots this year. "It's more pronounced than we've ever seen before," he said, "and it's probably because we got very little mineralization of organic matter due to a cool, wet fall followed by a cool, wet spring."

Adds Sawyer, "we haven't seen visual symptoms at all sites this year, but one site in north-central Iowa where corn was no-till planted following soybeans is showing sulfur deficiency symptoms in the control and response in plots where sulfur was applied."

The sulfur trend is still evolving, said Collamer. "As more power plants and other industries comply with sulfur dioxide restrictions, and as more crop production is practiced with reduced-tillage, we expect to see the geography of crop response to sulfur continue to expand."

Editor's Note: Linda Kane, a writer with Gibbs & Soell, Inc., wrote this article at the request of AgProfessional with editorial approval of content and sources.