An Ohio State University (OSU) scientist says an abundant by-product from coal-burning power plants, if spread on farmers' fields, could help control phosphorus runoff that contributes to Lake Erie's harmful algal blooms.
Warren Dick , a soil biochemist in OSU’s College of Food, Agricultural, and Environmental Sciences (CFAES), says applying fluidized gas desulfurization (FGD) gypsum to crop fields can keep soluble phosphorus, the main nutrient feeding the algae, from getting washed from the soil by heavy rains, then running off into streams and rivers and eventually into the lake.
"FGD gypsum, which is a synthetic form of gypsum, can improve both the soil and the crops," he says. "Naturally occurring, mined gypsum has a long history as a soil amendment and fertilizer for farming."
A professor in CFAES's School of Environment and Natural Resources (SENR), Dick is part of a national program to develop agricultural uses for FGD gypsum, which comes from the air-emission scrubbers at coal-burning power plants. The scrubbers remove sulfur dioxide, which causes acid rain, from the plants' exhaust emissions. The process creates large amounts of quality gypsum as a by-product.
FGD gypsum is powdery, resembles flour, and can be applied using conventional farm spreaders. It costs about $35 to $50/ton spread on the field. Typical application rate is 1 to 2 tons/acre every two or three years. A growing number of farmer co-ops sell it.
Locally, Dick's research focuses on northwest Ohio's Maumee River Watershed, which is the largest watershed draining into Lake Erie and is the lake's largest contributor of nonpoint source pollution. His recently funded project in the Maumee watershed will test FGD gypsum on fields that have high soluble phosphorus levels. Soil and water samples will be collected from the fields to determine the material's effects and will compare crop yields from treated and untreated fields. The study's results will contribute to refined recommendations for farmers and should lead to wider and more-effective use of FGD gypsum, he says.
Excess soluble phosphorus is the primary cause of the sometimes toxic algal blooms that have plagued Lake Erie and other bodies of water over the past few years, experts say. The blooms come from fertilizer and manure runoff from farms, sewer overflow from storms, discharge water from wastewater treatment plants and leaking septic systems. Wide use of gypsum could slash the portion that comes from farms, Dick says.
"Based on various studies, gypsum can cut the amount of soluble phosphorus running off soils by 40 to 70%," he says. When spread on a field, gypsum binds in the soil with phosphorus to make calcium phosphate, a much less soluble form of phosphorus. This means it's less able to run off in water.
“Gypsum is also an excellent source of sulfur nutrition for plants for improving crop yields," Dick adds. "It interacts with nitrogen to make it more efficient. And it interacts with the soil itself. It aggregates the soil, which improves its structure and improves aeration and water infiltration, which reduces runoff. It allows water to move into the soil but doesn't keep the soil waterlogged so that air can move into the soil and allow the crops to grow well."
In previous studies, Dick has documented a nearly 7% increase in corn yields from using gypsum and an 18% jump in alfalfa tonnage.
"Plants are getting more and more deficient in sulfur," he explains. "If you continue to harvest huge amounts of alfalfa off a field, or if you harvest corn grain or soybean grain, you're removing a lot of sulfur every year. If you never put anything back, eventually you start to run deficits," he continues. Nitrogen-fixing crops, such as soybeans and alfalfa, have an especially high sulfur requirement, he adds.
"(FGD) gypsum is a readily available, less-expensive source of sulfur," Dick said. "And there's a lot of research now across the United States showing that crops are becoming more responsive to sulfur as a nutrient fertilizer input. Gypsum also provides calcium, which can stimulate plant root growth and help crops reach more water and nutrients.
Dick says using gypsum on corn could increase yields by about 5 bu./acre. At a conservative price of $5/bu., it would almost pay for itself the first year, he notes.
An OSU Extension bulletin that Dick co-authored, "Gypsum as an Agricultural Amendment," can be purchased through OSU Extension's eStore at http://go.osu.edu/Qzu  or downloaded free at http://go.osu.edu/gypsumforfarms  in pdf form.