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Sulfur gets mixed reviews

09/05/2012 @ 3:20pm

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.

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