ONTARIO, Ore. - One of the byproducts of American's national lust for French fries is a toothpaste-thick sludge that leaves potato processing plants by the truck load.

Oregon State University agricultural scientists are trying to recycle this sludge as fertilizer in order to keep it out of settling ponds and landfills and to save processors disposal fees.

Making potatoes into fries and hash browns is a major business in eastern Oregon and western Idaho. The processed potato industry creates a lot of potato peels and waste water - about 40,000 tons per year in the Boise-Ontario area alone, according to Lynn Jensen, chair of the Malheur County office of the OSU Extension Service.

Currently, beef feedlots take most of the potato sludge off the hands of area processors, explained Erik Feibert, research assistant at OSU's Malheur Agricultural Experiment Station in Ontario.

"The processors are happy to get rid of the sludge because previously they had to pay to dispose of it," said Feibert.

The feedlots also get culled French fries from the processors. Cattle gain weight easily on the fries, said Jensen. But sludge is a problem because of its low feed value, so its disposal is still a problem.

"We think the sludge has potential to be a good fertilizer, but we're still unsure at what rates it needs to be applied," said Jensen. "We're running field trials at various amounts of sludge per acre. We want to determine the nitrogen release rate of sludge to determine how it fits with crop fertilizer needs."

Clint Shock, professor of crop and soil science and superintendent at the OSU Malheur Experiment Station, is studying the nitrogen release rate of potato waste on local soils. The researchers have bags of carefully mixed soil and sludge buried in test plots so that they have the same temperature conditions as the field.

"We dig them up every three weeks to test for nitrogen release rates," explained OSU research assistant Feibert.

Potato sludge as a fertilizer has a lot of advantages over other organic fertilizers, claim the researchers. They are testing sludge as a fertilizer for onions at the Malheur Experiment Station.

"Potato sludge has only about two-thirds the nitrogen content of manure," explained Jensen. Unlike some industrial or city waste products, potato sludge does not contain heavy metal that could contaminate the soil. By the time the sludge arrives at the farm it 's in a gel-like consistency that can be easily applied to the fields with a modified manure spreader."

Despite its apparent benefits, there are still some obstacles to the wide spread use of potato sludge as a fertilizer.

"The Oregon Department of Environmental Quality (DEQ) isn't ready to allow unlimited use as a fertilizer until we have some more data on nitrogen release rates," said Jensen.

Growers have also expressed some concern about the spread of plant disease such as late blight with the sludge.

"The spread of disease should not be a problem since the sludge is treated at 350 degrees and is sterile of any potato disease organisms when it leaves the processing plant," he said.

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Clint Shock, 541-889-2174