Copper sulfate could be hurting your forages

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Copper sulfate use in foot baths is commonplace on many dairy operations. Once emptied, the contents of a foot bath travel through the manure-storage system and onto farm fields. None of this is a surprise, but what it could be doing to crop growth and quality may call for some changes in how you manage foot baths treated with copper sulfate.

Scientists at the William H. Miner Agricultural Research Institute in Chazy, N.Y., have taken a close look at the potential impact of copper sulfate from dairy manure on forages. It is a work in progress, but here is what they have learned so far.

Copper concentrations under scrutiny

“The reason we got interested in the copper issue was the extremely high amount of copper arriving on farms via copper
sulfate for foot baths and the trivial amount leaving farms via milk,”
says Ev Thomas, vice president of agricultural programs at the Institute.

This was driven home in a survey of copper sulfate use on dairy farms in northeastern New York and Vermont. The results suggest there may be a connection between the amount of copper used on farm and copper levels in corn silage and haylage.

In 2001, the surveyed farms imported an average of 1.7 pounds of copper per acre. This level declined to 1.2 pounds per acre in 2004. The copper content of corn silage and haylage did the same thing during that three-year span. (Please see “Copper concentrations from surveyed farms.”)

A look back at the concentration of copper in manure slurry at the Miner Institute farm also piqued the researchers’ curiosity. Copper concentrations in the slurry before use of copper sulfate in foot baths was 4.8 grams per 1,000 liters. In 2000, when the farm began using foot baths, the concentration of copper sky-rocketed to 88.6 grams per 1,000 liters of slurry.

Implications for forage quality

Concern about what this could do to crop yields and forage quality led the researchers to conduct a two-phase project at the Miner Institute. It had two objectives in mind:

1. Study the impact of copper sulfate from dairy manure on the quality and growth of forage grasses and corn.

2. Determine the fate of excess copper in the soil.

During the first phase, the researchers grew three cool-season grasses under greenhouse conditions. The three forages included orchard grass, timothy and reed canary grass.

The results showed that increased copper application levels decreased plant shoot yield and dry root weight. The research has not gone far enough yet to show the impact of this on forage quality and yields, though a decrease in overall stand longevity and yields is possible.

Corn not as affected 

The researchers looked next at actual corn field plot data. The results show a one-time high copper application rate is not as detrimental to corn as it is to forage grasses.

A soil analysis of those fields showed that a one-time application rate of 16.3 pounds of copper from dairy manure resulted in 14 pounds more copper per acre than soil that did not receive copper application. (Please see the table “Changes in soil copper concentrations” below.)

However, this application rate did not affect corn plant dry matter at harvest or concentrations of nutrients like neutral detergent fiber and crude protein. There also was no effect of copper treatment level on the concentration of copper in the corn plants. Concentrations also were much lower than those measured in the grass shoots.

The researchers say more work is needed to study the effects of multiple, high-copper-application rates on corn. A field trial using the same three forage grasses and three different application levels of copper also is under way. Sally Flis, a PhD student at the Institute, is currently spearheading this research.

“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,” Thomas says. At the very least, it could help prevent growth and yield losses in your grasses harvested for forage.



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