Fall gypsum likely won’t result in long-term sulfur
Corn growers looking for an additional spring growing boost of sulfur from applying gypsum to their soil in fall shouldn't expect to see any lasting sulfur in spring, an expert from Ohio State University's College of Food, Agricultural, and Environmental Sciences said.
While fall applications of gypsum, which is calcium sulfate, can be utilized by a fall-planted crop, growers shouldn't expect it to be available for future crops, said Ed Lentz, an Ohio State University Extension educator and associate professor who specializes in crop production and agronomy. OSU Extension is the outreach arm of the college.
While the agriculture industry has been promoting gypsum heavily for its soil benefits, the negative-charged sulfate component of gypsum can't bind to soils to ensure it will still be around for spring planting, Lentz said.
"I think when we have strong crop price, producers look for any way to get extra bushels," he said. "But the data hasn't shown that adding additional sulfur will improve the probability of increased yield for most Ohio soils.
"Historically, soils that are low in organic matter or are sandy will have the greatest potential benefit from adding sulfur. But those are more the exceptions for Ohio soils than the norm."
Some growers have sought the benefit of sulfur as a secondary nutrient that can benefit the plants, he said.
"But if we have enough organic matter naturally in soil, that should provide sulfur for crop needs," Lentz said.
Because gypsum is calcium sulfate, the sulfate will move with water and will likely not be present by spring planting if applied in fall, Lentz said. But growers who add elemental sulfur in fall could expect it to convert to sulfate by corn planting time, he said.
This is because the conversion of elemental sulfur to sulfate takes time. This chemical reaction will also release hydrogen ions, which may have an acidifying effect on the soil, Lentz said.
"The sulfate form of sulfur does not have an acidifying effect alone, but the reaction of the cation with it may, such as ammonium, where the hydrogen ions released by the conversion of ammonium to nitrate will gradually lower soil pH levels," he said.