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Researchers study biosolids' benefits for growers, 'yuck factor'


Capital Press

LIND, Wash. -- Researchers say growers may want to weigh the benefits of applying biosolids -- treated Seattle sewage -- as fertilizer on their fields.

Washington State University soil scientist Craig Cogger, based in Puyallup, has researched the use of biosolids for 20 years, including on dryland wheat.

Cogger provided an update on the results of the second year of an eight-year research project with WSU Dryland Research Station director Bill Schillinger in Lind, Wash., at the station's field day June 13.

A major ingredient in biosolids is dead insect bodies. It is rich in organic matter and such nutrients as nitrogen and phosphorus, Cogger said. Biosolids are like an organic fertilizer, as they rely on bacteria in soil to slowly release nitrogen, Cogger said.

"We have to separate out the yuck factor from the fact that biosolids are really very clean materials," Cogger said. "There's not a whole lot of difference between biosolids and (animal manure)."

Biosolids fall under the Clean Water Act. Permits are required as part of the process, but farmers don't need to go through the permitting process themselves, Cogger said. That falls to the wastewater treatment plant or private company that applies biosolids.

Wastewater treatment plants subsidize the application of biosolids, and farmers pay for the nitrogen, Schillinger said.

"It would be a huge waste to consider it a waste product, because of all the nutrients in it," he said.

In Douglas County, biosolids could recently be applied for $1 per dry ton or $5 per wet ton. Typically two to three dry tons per acre or 10 to 15 wet tons per acre are applied on a wheat field, Cogger said.

"For the farmer, it's a good deal," he said.

Biosolids are treated to meet standards for land application, including measuring for levels for potential contaminants. Cogger said this is not an issue today, but there are potential issues with pathogens.

Farmers would need to post notification for a year that biosolids were applied to the field, to avoid "low-risk" scenarios such as someone's dog rolling in the field while out hunting, Cogger said.

Schillinger said the research experiment will explore whether biosolids will boost yields when applied on top of the crop without tillage into the soil.

Cogger said biosolids will work across rainfall zones but have a bigger potential for yield boost in higher rainfall areas.

Wheat is a good crop for biosolids, but he does not recommend biosolids for fields that already have high nitrogen levels or for carrot or lettuce production, due to the waiting period.

It's been thoroughly tested to show that the wheat will be completely safe, Schillinger said.

He expects mixed interest from farmers, those drawn by the economics and those put off by it.

"From an economic standpoint, I think it's a no-brainer," he said. "There will probably be others that are interested, and there's probably going to be farmers that aren't so interested, 'I don't want to have anything to do with it. That's poop.'"


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