Nitrogen might be the king of yield, but if a corn plant is sulfur deficient, it won’t reach its maximum potential. Over the past 10 years, sulfur deficiency has become a significant issue.
“Farmers are measuring considerably less sulfur, depending on where you live, than they were just five to 15 years ago,” Farm Journal Field Agronomist Ken Ferrie says. “It’s time to revisit sulfur.”
At his farm in central Illinois, Ferrie says in the early ’80s testing for sulfate in late summer would have returned a reading near 30 parts per million (ppm). Today, the number is typically between 8 ppm and 12 ppm.
“On one sulfur service call this year we actually found a field at 1 ppm,” Ferrie says. “I’ve never seen sulfur that low in central Illinois.”
NUTRIENT DRAIN
The shift to lower sulfur seemed to start in 2008, according to Bob Nielsen and Jim Camberato, Purdue University Extension agronomists. The two have conducted 55 field-scale trials on yield response to sulfur in Indiana since 2017, including 15 in 2022.
“For the past five years or so, the number of soil samples coming back having tested low to very low for sulfate sulfur is consistently greater than half,” Nielsen says.
He attributes the drop to crops removing more sulfur from the soil to make higher yields, as well as reduced sulfur emissions from coal-fired power plants.
IDENTIFY SULFUR DEFICIENCY
Sulfur-deficient corn plants show delayed growth and maturity. The foliage turns light green to yellow and has a distinct striping on the leaves.
“This happens in the upper leaves because sulfur is not as mobile in the plant as nitrogen, and so there’s not much movement of sulfur from the lower canopy to the top,” Nielsen says.
Yellowing or striping on leaves can be caused by other nutrient deficiencies such as zinc. He recommends a tissue test to confirm it.
“Corn removes about 0.05 lb. to 0.1 lb. of sulfur per bushel of grain,” Nielsen explains. “A 200-bu. corn crop removes somewhere between 10 lb. and 20 lb. of sulfur.”
Nielsen says typically there’s about 100 lb. of organic sulfur for every one percentage point of organic matter. Usually between 2 lb. and 6 lb. becomes available to the crop every growing season. The rest needs to be supplied by the atmosphere, fertilizers or soil amendments.
MINERALS ON THE MOVE
A sulfur-deficient plant can be the result of its environment. Cold, wet or dry soils can all cause less mineralization and movement of sulfur.
“Soils that are excessively wet or excessively dry also impede the progress of mineralization and cause at least temporary sulfur-deficiency symptoms,” Nielsen says.
This year, Ferrie says, a lack of sulfur combined with dry conditions doubled or tripled the number of sulfur service calls his team answered.
“We need moisture to get sulfur in the plant,” he says. “As we continue to lower the sulfur load in the soil, drier weather makes that a bigger issue.”
No-till farms also often see sulfur deficiencies because those soils tend to stay wet and warm up more slowly than tilled fields.
While a yield response to sulfur remains difficult to calculate, Ferrie says it’s just one piece of the puzzle.
“When we see sulfur deficiencies in corn, you are almost always going to see a nitrogen deficiency,” he says. “If you have a sulfur deficiency, no matter how much nitrogen you put on, there’s a good chance you’re going to be deficient in nitrogen.”
That’s because the crop needs sulfur to metabolize nitrogen. At Purdue’s trials, Nielsen says nitrogen fertilization can trigger the development of sulfur deficiency in soils that are already borderline sufficient for sulfur.
ADJUST YOUR RATE
Purdue research suggests 10 lb. to 15 lb. of sulfur per acre, applied just before planting but no later than sidedress, is adequate in most sulfur-deficient situations.
Minnesota research shows an annual rate of 25 lb. of sulfur is adequate for corn production on sandy soils, while fields with more organic matter need less (10 lb. to 15 lb. per acre). The application can be done via broadcast or as sidedress.
The Role of Sulfur
Sulfate sulfur uptake happens at key time periods. “Only 10% of sulfur is taken up prior to V5 but this time frame is critical, and deficiencies early in the growing season can limit yield,” says Daniel Kaiser, University of Minnesota Extension specialist. Elemental sulfur can be applied in fall or early spring, but most of the mineralization won’t happen until the soils warm up in mid- to late summer.
- Sulfate: The only form absorbed by plant roots. It moves easily in the soil and can move past the root zone.
- Elemental Sulfur: This form can’t be used by plants, as it must be mineralized into sulfate. Only a small amount is mineralized naturally, depending on soil organic matter.
Farm Journal Editor Clinton Griffiths is a TV newsman turned magazine editor with a passion for good stories. He believes the best life lessons can be found down a dirt road.
