By JOHN O'CONNELL
New University of Idaho research suggests copper concentrations in some sandy-soiled Idaho farm fields treated with dairy lagoon water may be nearing levels that could stymie potato root growth.
In both 2011 and 2012, U of I Extension soils specialist Amber Moore raised potted potato plants in a greenhouse, adding six different rates of copper. Most dairies use copper sulfate for foot baths that protect the hooves of cattle from problems such as foot rot.
In the initial year, plant survival was too low for Moore to draw specific conclusions about copper toxicity in potatoes, aside from observing that the element tends to bind with loamy soils, affecting plants less than in sandy soils.
Based on the 2012 results, Moore detected stunted potato growth in loam soils beginning at 90 parts per million of copper. In sandy soils, plants were affected at levels as low as 25 parts per million. Though her research didn't utilize actual field trials, she consulted an expert who creates dairy nutrient management plans, who reported seeing copper levels in fields treated with lagoon water ranging from 2-36 parts per million.
"In general, I would encourage (growers) if they're working on a field they know has any kind of manure or lagoon water history to start including a copper or soil test," Moore said. "(Copper contamination) could happen to potato fields for sure."
Moore's plants also produced their first tubers in 2012. She found copper levels in potato roots at concentrations 10-17 times greater than in tubers or stems. Even at dosages sufficient to turn her potted soil blue, copper levels in tubers were too low to raise a human health concern.
Moore, whose research was funded by the Idaho Potato Commission, said she wants to study the health issue more closely with a broader tuber sample size.
Her collaborator on the research, Jim Ippolito, a soil scientist with the USDA ARS in Kimberly has also researched copper's effect on corn and alfalfa, finding alfalfa is especially sensitive and corn is slightly more sensitive than potatoes.
Moore acknowledged copper levels generally aren't a problem in Idaho fields but warned "it could take a century to get that copper out of your field to where it's not a problem."
American Falls dairyman Greg Andersen said copper sulfate is the most effective foot treatment, though he also uses some formaldehyde. He applies lagoon water to his own land and provides manure and compost to three other area farmers, rotating between use of manure and chemical fertilizer. Annual testing has raised no copper concerns.
Declo grower Mark Darrington protects himself by doing his own analysis of dairy nutrients, in addition to test results they furnish.
Rupert farm agronomist Mike Larsen has seen no elevated copper levels in soil tests of his fields with a long history of manure application, but he's had issues with high salt levels.
"We have not seen real high copper levels at this point, but it is something we watch," Larsen said. "You'll probably have salt-affected crops prior to having super high copper levels."