Foot baths that use copper sulfate increase the copper content of manure applied to fields.

Concern about what this could do to crop yields and forage quality led researchers at the W.H. Miner Agricultural Research Institute in Chazy, N.Y., to conduct a survey of changes in copper sulfate use on 17 dairy farms in northeastern New York and Vermont.

The results show that the copper content of corn silage and haylage decreased over a three-year span. For instance, in 2005, the copper content of corn silage fell to 5.1 milligrams per kilogram — down 7.6 mg per kg versus 2002.

It’s difficult to say what may have contributed to the decrease in forage copper levels because the researchers did not collect data on crop yields, copper concentrations in manure, manure-application rates or soil copper content.

This decrease is good news because preliminary research at the institute shows that the copper concentration in manure may cause significant yield decreases in forage grasses. A study also is under way to determine the effect on corn silage.

“While we develop research data, we’re encouraging farmers to use less copper sulfate, both by decreasing the concentration and by lessening the frequency of use,” says Ev Thomas, vice president of agricultural programs at the Miner Institute.