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.
SOURCE: John O'Connell, Capital Press
http://www.capitalpress.com/newsletter/JO-CopperResearch-011713