More growers are using calcium- and sulfur-rich gypsum on alfalfa and other forages and row crops.
Some have found that this soil amendment produces greener, leafier crops, gives faster regrowth, or that it improves soil structure. Others have discovered that it counteracts subsoil acidity or excess sodium. Scientific studies have backed up those benefit claims, says Malcolm Sumner.
“But it’s not a miracle product,” warns the former University of Georgia environmental soil scientist who has studied gypsum – calcium sulfate dihydrate – for 50 years. “It doesn’t work everywhere.”
Southern, Western, Atlantic-Coast and even Midwestern growers are applying the product. It comes from processed drywall gypsum, mined gypsum and a synthetic byproduct called flue gas desulfurized gypsum, which is derived from smokestack scrubbers at coal-fired power plants.
More soluble than lime, gypsum allows roots to enter Southern and Atlantic Coast states’ acidic subsoils and extract water from them, Sumner says. His Georgia work shows the product can increase alfalfa yield and quality. In the West it’s used to help reclaim sodium-affected soils.
“In the Midwest? They have had some success that I am at a bit of a loss to explain,” says Sumner. “It is not working exactly the same as it has worked in my experience. But many of the soils of the Midwest, as a result of being cultivated for 150-200 years, have become somewhat degraded.”
Applying gypsum to that region’s soils, which Sumner says turn “soggy” in winter, allows water to percolate through them quicker, giving roots a better environment in which to grow, he theorizes.
“Then, into the bargain, it’s a source of calcium and sulfur, which are two nutrients that are pretty important for the growth of crops.”
Recent research compared several rates of gypsum applied to alfalfa, corn and soybean fields – and found little first-year response, says Richard Wolkowski, emeritus Extension soil scientist, University of Wisconsin.
He and a colleague also looked at whether the byproduct improved soil structure at state research locations.
“We did some measurements of infiltration and bulk density and then aggregate stability to see how well the soil particles bound together. There were no measurable differences. Now, it is possible over a period of several years that a grower might see something, but we were looking at responses in the year of application.”
Some increases in plant-tissue sulfur were evident, although at his sites the plants already had enough sulfur available to them,
he says. With improved air pollution control, little sulfur is being supplied by precipitation and high-demand crops like alfalfa are becoming more responsive.
The added calcium from the application also wasn’t an advantage, as most Wisconsin soils already are calcium-sufficient, he says.
Wolkowski agrees that farmers have a lot of “testimonial evidence, although it’s not the type of research-based work that university folks would do where they replicate studies and statistically analyze data.”
At the same time, gypsum is relatively inexpensive; putting it on crops is better than dumping its sources into landfills, Wolkowski says.
And he reiterates that his gypsum study was looking only at the year of application.
“There may be a positive effect on soil properties to using gypsum for five or 10 years, but that research has not been conducted. Sumner showed in Georgia that responses to gypsum are more likely to occur after the first year – because considerable time is required for the gypsum to move in the soil and have an effect.”