Alfalfa producers could benefit from the current boom of new home construction, says Dick Wolkowski, a University of Wisconsin-Madison soil scientist. And crowded landfills need relief.
"Instead of shipping tons of scrap gypsum wallboard to landfills every year, it could be crushed and spread on alfalfa fields, where it's just as effective as commercial gypsum fertilizer," says Wolkowski.
"If there are materials that can be safely diverted from landfills and applied to the land to benefit crops, folks are interested in it."
Construction industry sources estimate that building a 2,000 square-foot house produces about a ton of clean wallboard waste. An estimated 2-3 million tons of gypsum wallboard scraps go into crowded U.S. landfills each year.
Gypsum wallboard is primarily calcium and sulfur with smaller amounts of other elements, such as magnesium. For years, extension soil specialists have advised farmers to keep a close eye on their crops' sulfur requirements, particularly in coarse-textured soils with low organic matter.
That now pertains to all soil types. Hay growers need to be especially careful, because forage crops tend to remove large amounts of sulfur.
"Where tests show sulfur is needed, we recommend applying up to 50 lbs of sulfur per acre for alfalfa," says Wolkowski. At four of the university's research stations, he studied how gypsum wallboard applied to alfalfa affected several factors, including stand density and yield.
Gypsum wallboard scraps were crushed with a hammer mill, screened to remove paper pieces and applied to alfalfa fields. They were spread at rates ranging from 1 to 16 tons per acre before seeding, or at lower rates on established stands.
Alfalfa stand density was not affected by the wallboard applications. Yields increased an average of 0.4 ton/acre at three of the sites, but decreased 0.4 ton/acre at the fourth site, reports Wolkowski. The yield increases recorded at the three sites are about what growers could expect from commercial sulfur fertilizer.
Do the results of Wolkowski's research have practical application for alfalfa growers?
"There's an obvious potential because of the large amount of material that's available. However, it's bulky and could be fairly expensive to transport. But alfalfa growers close to urban areas could see some benefit if they could get crushing and transporting logistics worked out. With the price of commercial gypsum fertilizer approaching $100/ton in some areas, it could possibly save them some money."
Crushed wallboard is about 13% sulfur, so 200-300 lbs/acre, applied every third or fourth year, should meet the needs of forage legumes. But commercial application equipment may not apply amounts that small, and higher rates would provide more landfill relief. Don't apply more than 1 ton/acre on sands and loamy sand, and 3 tons/acre on loams and heavier-textured soils, Wolkowski advises.
Before applying, however, check with your local Department of Natural Resources office. In Wisconsin, for example, application sites must be approved by the Wisconsin DNR.