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Sulfur gets mixed reviews

Sulfur fertility was a topic on many Midwestern crop meetings last winter. It's a do-all secondary plant nutrient that makes all other nutrients work better, say some. For as little as $10 an acre, you'll get several more bushels of $6 corn, they say.

Maybe. Farmers who have tried it and measured the response see some, sometimes. Most are intrigued enough to say they're going to keep fiddling with it. Few are ready to take over the whole bandwagon.

Here's what some Iowa farmers who have done replicated sulfur strip tests through the Iowa Soybean Association's On-Farm Network are saying.

Dennis Gerholdt, Cedar Falls, Iowa, had seen the classic sulfur-deficiency symptom in one cornfield: pale-yellow coloring and stripping in the upper leaves of corn plants. It's often confused with nitrogen deficiency, so the trick is to look closely at which leaves are yellow. New upper leaves = sulfur; lower leaves = nitrogen.

“I was sure what I was seeing wasn't nitrogen,” says Gerholdt. In 2009, he tried a foliar sulfur applied to that field just ahead of tasseling, including untreated test strips, and he saw no response at harvest. “I think it was too little, too late,” he says.

When that field went back to corn in 2011, he put sulfur on the field as a dry broadcast on the day of planting. It was a product called SuperCal SO4, a high-grade form of gypsum that is 17% sulfur, applied at about 300 pounds per acre, or about 50 pounds of actual sulfur. (For more information, see sidebar on the next page.) He worked with the On-Farm Network, which helps farmers use appropriate research protocol with replicated treated and untreated strips.

“You could easily see the strips all through the growing season,” says Gerholdt. “Everything was the same as for tillage and fertilizer, except for the SuperCal product. The treated strips were dark green; the untreated were yellow right up to harvest.”

The yield data showed a 7.8-bushel advantage for the sulfur, or about 6%. “That field is very light soil, and it didn't have enough rain,” says Gerholdt. “It yielded about 135 bushels. With a higher yield and a 6% advantage, it would have been even more bushels advantage, I think.”

The sulfur cost Gerholdt about $28 an acre. “It was an economic advantage to sulfur,” he says. “I'll use it again, particularly on my lighter soils. I'll get the soil tests, and if it calls for it, I'll use it. In this dry broadcast form, it's fairly easy for me to work with.”

Maybe yes, maybe no

Denny Friest, Radcliffe, Iowa, says he was never too concerned about sulfur deficiency because most of his acres get routine manure from his hog barns. Soils with high organic matter and routine manure applications are generally at less risk of sulfur deficiency.

“However, I've got some fields that are farther away from the hog barns where I don't spread manure,” says Friest. Three years ago, after hearing much talk about sulfur, he decided to try it on those fields with a fertilizer from Mosaic containing both sulfur and zinc. “I did get some response to sulfur for two years, not a lot, but a couple of bushels an acre, and it more than paid for the sulfur,” he says.

Last year, his fertilizer dealer changed suppliers, and he got no response to a generic sulfur. Other people in his area said the same thing, there was little response in 2011.

“I would have to say my results are mixed, and even when I got a response it was not very large,” he says. “At this point, I'm not very concerned that my fields need sulfur. If I could go back to the product I used three years ago, I might try it again.”

Rhonda Birchmier, Maxwell, Iowa, tried sulfur fertilizer on corn last year for the first time. It was a disaster – but not for anything to do with her and husband David's soil fertility program. They got hit with a devastating windstorm on July 11. The 100-mph straight-line winds ruined the sulfur experiment. Many of the stalks goosenecked back up, some as far as 30 inches, and yielded 160 bushels and higher. But it was such an uneven harvest stand and so difficult to actually follow rows that any yield response to sulfur was undetectable. Still, the Birchmiers are intrigued enough to try the sulfur experiments again in 2012, with a better growing season, they hope.

“I have seen the classic sulfur yellow striping sporadically, and it's been more common lately,” says Rhonda, who is a Pioneer seed dealer. One of her seed customers gives her reason to want to try for a sulfur response again. His field showed a very noticeable difference in the color and thriftiness of the treated areas before the wind damage. The Birchmiers will try some different approaches to sulfur in 2012, including broadcast sulfur on all types of soils and sulfur in the starter fertilizer on lighter soils.

“I'm still at the curious stage,” says Rhonda. “There are so many things going on out there that we don't know about and how they interact. Sulfur is just one of them.”

Dennis Lindsaym Masonville, Iowa, is a big fan of the On-Farm Network and how it helps farmers scientifically conduct replicated strip tests in fields. When he heard they were doing sulfur tests, he wanted to participate because he had seen the telltale yellow striping of sulfur deficiency. But after reviewing his yield maps, he cannot see a response.

“Maybe a little, but not as much as I expected,” Lindsay says. He's tried it on multiple fields over a couple of years without response.
“I know that one year is not enough to draw conclusions, so I'm going to stay at it and see if I can learn more. My perception is that sulfur is not an expensive thing to add.”

In some of his strips, he says the yellow striping has been very apparent – dark green where sulfur is applied and pale yellow in the control strips.

“But then I don't actually see any difference in yields,” he says. “It does make me wonder what's going on, and it's uncomfortable looking at the yellow strips. It varies by year and field, and that's why I can't just rely on one year and one trial.”

Tom Morris, University of Connecticut, gives these tips for monitoring sulfur deficiency:

Where is sulfur most likely deficient?
• Sandy soils with less than 1% soil organic matter content.
• Not much sulfur is mineralized from soils with low soil organic matter.
• Sandy soils don't retain much sulfur.
Where is sulfur most likely sufficient?
• Soils with greater than 1% organic matter.
• Soils with less than 80% sand.
• Manured soils usually have sufficient sulfur.

Sulfur Helps Convert Nitrogen to Protein

Craig Dick is the vice president of sales and an agronomist for Calcium Products, Inc., which markets a sulfur fertilizer called SuperCal SO4 ( The gypsum-based product is pelletized and can be mixed with other fertilizers and broadcast or applied in-furrow at planting. While much of the recent interest in sulfur has been for corn, he says it is also very useful for forage crops such as alfalfa for increasing tonnage and for improving protein content. “It's involved in every function of plants and is a catalyst nutrient for turning nitrogen into protein. It can increase protein in alfalfa by 1% to 2%. If you're growing any forage crop to feed to animals, you should consider fertilizing with sulfur for the extra protein,” says Dick.

His company's product is 17% sulfur, he explains, in the form most readily available to plants. He first encourages farmers to apply sulfur on eroded hillsides with low organic matter (1% to 2%), where they'll almost always see a yield response. Corn that yields 200 bushels an acre will remove about 16 pounds of sulfur per acre; he recommends applying at least 18 to 20 pounds. “And that may not be enough if you are making silage or removing the cornstalks from the field, which is like a double removal.” Some of his customers apply 240 pounds of the SuperCal product, which gives 40 pounds of sulfur. The cost varies from one retailer to the next, but it is approximately $9 per 100 pounds of SuperCal.

Alfalfa is a high remover of sulfur, and many growers apply 300 pounds of SuperCal. They often report an additional 1.5 tons of dry forage production, at 1% to 2% higher protein levels. Corn yields can be “all over the board,” says Dick, but a 5- to 8-bushel-per-acre response is typical. Wheat and soybeans respond, too, he says. While Iowa is the hotspot for sulfur interest for corn, the geography of its use is widespread, Dick continues. “They use it on small grains in Canada and on pastures in Missouri. A lot of golf courses use it to get a dark green color.”

Sulfur-based products can be applied in the growing season, but Dick would rather see farmers apply at planting or before. “If you wait until you see symptoms in the field and then get it applied, you can have a month of deficiency on the crop. All that time, you are losing yield.”

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