UF Researcher: Cut Phosphorus To Help Lake Okeechobee Water Quality

Ed Hunter (352) 392-1773 x 278

Jack Rechcigl rechcigl@mail.ifas.ufl.edu, (941) 751-7636

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BRADENTON, Fla. — To help reduce algae levels in Lake Okeechobee, a University of Florida researcher says ranchers can eliminate phosphorus fertilizer without reducing the healthy growth of forage grasses.

Jack Rechcigl, director of UF’s Gulf Coast Research and Education Center, said grasses used in beef and dairy cattle grazing fields are capable of using phosphorus found deep in the soil. Plus, he said, phosphorus in grass animals eat is naturally recycled.

Based on research with stargrass, UF’s Institute of Food and Agricultural Sciences may soon change its phosphorus recommendations for this type of grass, Rechcigl said. His research at UF’s Range Cattle Research and Education Center in Ona resulted in a 1990 recommendation that ranchers not add phosphorus to bahiagrass fields.

Findlay Pate, director of the Ona facility, said the change in fertilizing practices saves the Florida beef cattle industry about $10 million annually.

But more importantly, eliminating phosphorus fertilizer will help keep Lake Okeechobee water clear by limiting the algae’s main food supply, Rechcigl said.

“We have found that the best way to control algae on lakes is to reduce the most limiting nutrient it needs,” Rechcigl said. “In the case of Lake Okeechobee, that limiting nutrient is phosphorus.”

While there are other sources for phosphorus found in the lake, Rechcigl said water managers believe runoff from pasture grasses can be controlled. Their task was simplified when researchers discovered forage grasses used phosphorus located three feet below the soil surface, he said.

“Normally when you sample soil in a field, you only test the first 6 inches which generally is very low in phosphorus,” Rechcigl said. “What people didn’t realize is that these perennial grasses have roots that go deep enough to get phosphorus where it exists naturally.”

Leaving phosphorus out of their fertilizer mix has resulted in cost savings for the Williamson Cattle Company, the Okeechobee-area ranch where most of Rechcigl’s research is being done.

“This is a practice that saves money and helps the environment at the same time,” said Sonny Williamson, one of the ranch’s owners. “Phosphorus in the lake comes from many areas other than agriculture but it’s very true we have some problem with agricultural phosphorus runoff.

“Obviously, if you can reduce phosphorus fertilizer or eliminate it, that’s a win-win because it costs less money and it also helps solve the problem,” he said.

Steffany Gornak, a senior environmental analyst with the South Florida Water Management District, said the research benefits both ranchers and the general public.

“The positive thing for the landowners is that they are able to meet our phosphorus regulations and realize a cost savings in the process,” Gornak said. “This will help ensure better quality surface water going into Lake Okeechobee, which is better for the environment and the public.”

Rechcigl said researchers also are looking into other ways to minimize phosphorus runoff. The addition of limestone or gypsum effectively locks the element in place while keeping it available to the grass, he said.

“The calcium in these two compounds mixes with the phosphorus and forms calcium phosphate, effectively putting the phosphorus in an immobile state that won’t run off,” Rechcigl said. “This method stores the phosphorus in the soil and allows the plant to get it like a slow release vitamin.”



Posted: August 15, 2001

Category: UF/IFAS

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