Farmers who apply gypsum to their fields in the fall can increase sulfur and calcium in their soils for their next crop, an Ohio State University scientist explains.

Warren Dick, a soil biochemist in the university’s College of Food, Agricultural, and Environmental Sciences, says in a recent paper that  applying flue gas desulfurization (FGD) gypsum to crop fields in the fall after harvest can result in improved soils that lead to higher yields.

Gypsum is an abundant byproduct from coal-burning power plants, said Dick, who holds an appointment with the Ohio Agricultural Research and Development Center, the research arm of the college.

“Growers typically apply gypsum in the fall after harvest,” he said. “When the gypsum is applied to soils low in available sulfur or with poor physical properties, improved crop vigor and increased yields for corn, soybeans, alfalfa and wheat are commonly observed during the next growing season.

“Growers need to be aware, however, that the benefits are not always immediate, as time is needed for the reactions in soil to take place. As rain droplets contact gypsum-treated soil, the gypsum particles dissolve and begin to move slowly into the soil profile.”

FGD gypsum is powdery, resembles flour and generally can be applied using conventional farm spreaders designed for spreading ag-lime and/or litter. Growers apply it to soils for several reasons, Dick said, including supplying sulfur when the element is limiting crop yields, and improving soil chemical and physical conditions.

According to Dick’s research, sufficient sulfur from gypsum, applied at rates of 0.5 to 2 tons per acre commonly used by producers, remains present in the upper soil profile for several years after application.

“Gypsum is also used to improve soils high in sodium and in some cases magnesium, as such soils can become dense or crust,” he said. “Adding gypsum to these soils will improve water infiltration and aeration.”

A typical application rate is 1 or 2 two tons per acre every 1-2 or three years, Dick said. A growing number of farmer co-ops sell it. When applying gypsum to soils, there are several factors growers need to consider, he said, including:

  • Gypsum doesn’t dissolve all at once or move though all soils at the same rate. Its solubility is impacted by the source, particle size distribution and the environment surrounding the material once it is applied.
  • Gypsum movement into the soil profile is also influenced by soil texture, amount of organic matter, surface soil structure, residue, compaction, soil moisture condition, and the timing and volume of rainfall.
  • Crop nutrient needs vary depending on the type of plant, but most agricultural crops require 30-70 pounds per acre of applied sulfur. Most producers add more than this amount to their soil when applying gypsum.
  • Plants can use sulfur only in the sulfate form, the form supplied by gypsum.
  • Fall applications of gypsum to tight clay soils at recommended rates can be expected to provide adequate sulfate-sulfur and calcium to the following spring-planted crop. Over time, improvements to soil structure can also be achieved.
  • Gypsum contributes to a variety of improvements to soil quality beyond fertility, including increased water infiltration and reduced losses of topsoil and nutrients.

Dick said gypsum has multiple benefits, including the ability to reduce phosphorus runoff from high phosphorus soils. More details are available in an OSU Extension bulletin (Bulletin 945), “Gypsum as an Agricultural Amendment,” available for $7.50 here.

Dick recommends that growers research those benefits to decide if applying gypsum is the right choice for them.

“Applying gypsum in the fall can be worth it, but it is not a silver bullet,” he said. “It is a tool in the farmer’s toolkit that, if used properly on the right soils and with the right crops, can provide both economic and environmental benefits.

“The benefits depend on the soil and the crop, so growers should evaluate their soils and crop management options and goals.”