Turning Wallboard Out to Pasture.

Building a 2,000-square-foot house leaves about a ton of gypsum wallboard waste from end cuts, window and door cutouts, and broken boards. In the United States, three million tons of gypsum wallboard waste is dumped in landfills each year. In addition to depleting space, microbial action can decompose gypsum to malodorous hydrogen sulfide gas, which at high enough exposures can cause irritation of the mucous linings, headache, dizziness, nausea, convulsions, coma, and death.

A study at the University of Wisconsin at Madison by soil scientist Richard Wolkowski, published in the January-February 2000 issue of Communications in Soil Science and Plant Analysis, found that clean scrap gypsum wallboard can be crushed and applied to alfalfa as fertilizer. Alfalfa covers over three million acres in Wisconsin and is fed to dairy cows and other livestock. This crop requires large amounts of sulfur as a nutrient. Although commercial gypsum fertilizer has existed for a long time, says Wolkowski, crushed gypsum wallboard waste provides a way to reduce construction waste while nourishing the soil.

For three growing seasons, crushed wallboard was spread on alfalfa fields at four University of Wisconsin agricultural research stations with different soil types and climates at rates ranging from 1 ton per acre to 16 tons per acre. Alfalfa yields were similar to those from fields treated with commercial gypsum fertilizer. "[Crushed wallboard] had neither a strong positive nor negative agronomic effects on alfalfa production," Wolkowski says. He concludes that there is thus a reasonable alternative to tossing the waste into landfills.

Larger amounts of crushed wallboard were no better for the alfalfa than smaller amounts. Wolkowski explains that the largest amounts of crushed wallboard raised concentrations of soil calcium and sulfur but lowered soil magnesium; the excess calcium from the wallboard displaces magnesium from the soil, allowing it to leach away. Alfalfa grown on magnesium-deficient soil could therefore become magnesium-depleted and potentially cause tetany if fed to cows (the muscular spasms and twitching of tetany result from insufficient minerals such as magnesium). Sandy soils are especially susceptible to magnesium deficiency because they have little natural magnesium and a low soil organic matter content. The magnesium content of alfalfa grown with crushed wallboard should be checked, says Wolkowski.

Finding a source of waste wallboard poses the greatest obstacle. Wolkowski teamed up with a local wallboard distributor who collected scraps from building sites. The material was hauled to a processing site, ground in a hammer mill, and sieved through a 12-millimeter screen. "It came out looking like lumpy flour," says Wolkowski.

Furthermore, state laws may stifle its application. In Wisconsin, for instance, wallboard is classified as a solid waste, and spreading it on agricultural lands requires a permit. Promoting the recycling of wallboard will probably require local effort. The ideal situation, says Wolkowski, would be for a "local fertilizer dealer who's open-minded about waste management to team up with a wallboard dealer." If anyone steps forward and takes up the challenge, Wolkowski's studies prove it can be done.