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What a Waste!
| Article
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10459 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
2 / 1993 |
758 Words |
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Doris Stanley
Doris Stanley writes for the Agricultural Research Service,
U.S. Department of Agricultural, at the Beltsville
Agricultural Research Center-West, in Maryland. |
The huge, unsightly mounds stretch across hundreds of acres. Some covered, some uncovered--these mountainous stacks are an eyesore on the flat, sandy Florida skyline. Whitish gray in color, with a crusty surface, they look like massive heaps of table salt that tower up to 200 feet high.
This is Florida's stockpile of phosphogypsum. More than 600 million tons of it are already on the ground and an additional 30 million tons accumulate yearly.
When phosphate rock is treated with sulfuric acid, the result is phosphoric acid, which is used to make fertilizer. Phosphogypsum (PG) is a by-product of the process.
Phosphogypsum has been used in construction materials and as a base in building roads. Its largest value, however, might be agricultural.
"This material could be used beneficially as a soil amendment," says Stanley Nemec. "We applied it for three years, at up to a ton per acre, on three orange groves with good results."
Not only did PG improve overall tree health, but it also increased the calcium and manganese levels in the fruit juice and calcium levels and bark. "Citrus is a heavy user of calcium, needing more of it than many other plants," says Nemec.
An Agricultural Research Service (ARS) plant pathologist with the U.S. Horticultural Research Laboratory in Orlando, Florida, Nemec Collaborated with University of Florida scientists Don Myhre and Ron Sonada.
"One finding was surprising: PG can probably reduce root rot, a major citrus disease in Florida that causes cankers on tree trunks and rots the roots," Nemec says.
"This unexploited source of calcium could also help avoid drought stress by facilitating deeper penetration of calcium and consequently, of roots into the acid subsoils of the Southeast," says Doral Kemper, ARS national program leader for soil management.
But the use of phosphogypsum has been controversial because it contains a small amount of radium. The U.S. Environmental Protection Agency has been cautious. Under a section of the Clean Air Act, it banned the use of phosphogypsum in April 1990, but then issued a waiver for agricultural use
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