May 10 2010 08:00 AM

Good crop and hoof health are possible with copper sulfate use. However, future regulations remain the wildcard.

The author is a crops and soils agent with the University of Wisconsin Extension, Fond du Lac County.

When making farm decisions, what might seem like a good idea for cows might not be advisable for the crops.

Copper is an essential element for plant growth, but like most micronutrients it is needed in very small amounts. Most crops remove less than 0.1 pound per acre of copper per year from the soil.

The copper ion (Cu++) is held very tightly by soil minerals and organic matter. In fact, it is held so tightly that most soil copper remains unavailable for plant uptake. Once soil copper concentrations are increased through manure applications containing high copper levels, soil test copper levels will remain high for a long time. On the flip side, instances of plant copper toxicity and deficiency have been rare historically.

Calculating copper application rates . . .
Ev Thomas reported on the Miner Institute's experience in Chazy, N.Y., with land applications of spent copper sulfate foot bath solutions in Hoard's Dairyman's July 2001 issue (page 458).

The farm was using about 254 pounds of copper sulfate per week for their 160-cow herd. On an annual basis, they were applying about 7 pounds of copper per acre. The farm took several remedial actions and reduced the amount of copper being applied to cropland to about 2 pounds per acre.

A 2003 herd hoof health survey of 27 Fond du Lac County, Wis., dairy farms revealed copper sulfate usage averaged 77 pounds per week with a range of 12 to 200 pounds. Of course, that is only part of the story because we need to know how many acres that the solution is being applied to and how often an individual field receives manure. Table 1 shows calculations from several Wisconsin dairy farms based on the premise that copper sulfate contains 25 percent copper.

Knowing how much copper is being applied per acre is important. Indications are that it is not uncommon for rates to fall between 5 and 10 pounds of copper per acre per year. Table 2 can be used to estimate annual copper loading on a per acre basis. These estimates do not include the normal background amount of copper found in manure without any copper sulfate solution additions (about 150 ppm d.m. or 0.06 lb./1000 gal).

In the late 1990s, Wisconsin researchers reported on the trace element content of manure samples submitted to soil testing labs across several U.S. regions. The copper concentrations for dairy, swine, and poultry manure are presented in Table 3. The study did not distinguish farms adding spent copper sulfate solution to the manure.

Nevertheless, it is interesting to note that liquid swine manure was over three times greater and poultry manure was over two times greater in copper content than dairy manure.

Swine are routinely fed higher levels of copper in their diet. Several research studies have been done evaluating high soil copper loading rates with swine manure. In some cases, up to 250 pounds of copper per acre were added to the soil with no crop yield decreases and only a small increase in plant copper concentration. Much of the copper applied was converted to an unavailable form but was still present in the soil.

Penn State researchers reported checking the copper content of corn silage from fields with three to five times normal total soil copper but finding no increase in the forage copper concentrations. Even so, total soil copper concentrations will build up over time and are virtually irreversible.

Copper is sometimes used as an algicide in ponds, a fungicide for plants, and is a known bactericide. The latter has implications for dairy producers. High manure copper concentrations have been shown to have a detrimental effect on the operation of anaerobic manure digesters which depend on bacteria for the digestion process.

Regulation of copper land applications . . .
The Environmental Protection Agency (EPA) has guidelines for copper loading to agricultural land when sewage sludge or other biosolids are applied. Although most state enforcement agencies do not monitor copper applications from dairy manure, standards set for biosolids offer a guide and perhaps an indication of future regulations.

The EPA is beginning to take a closer look at practices and procedures followed on dairy farms. Recently, a large New Mexico dairy farm was cited as being in violation of their NPDES permit by Region 6 EPA for discharging copper sulfate into a manure storage unit. The citation stated that: "discharges to containment structures must be composed entirely of wastewater from the proper operation and maintenance of the animal feeding operation."

A clean water foot wash ahead of the copper sulfate bath can extend the useful life of the copper sulfate solution.

The EPA 503 standard for application of biosolids to agricultural land cites a maximum lifetime loading limit for copper as 1,339 pounds per acre and an annual application limit of 66 pounds per acre. Neither of these guidelines is severely limiting for typical manure applications even where above average amounts of spent copper sulfate are added to the manure slurry. It should be noted that specific states may have more restrictive regulations. For example, Thomas reported New York has a lifetime cumulative loading limit of 75 pounds per acre and Illinois has a lifetime application limit of 250 pounds per acre.

What you should do . . .
It would seem the best approach regarding the use and management of copper sulfate for herd hoof health is to not use more than is absolutely necessary to maintain acceptable results. This can be accomplished by reducing the concentration in the foot bath solution, reducing the frequency of use, and substituting noncopper-containing hoof care products from time to time. Some veterinarians also suggest using a clean water foot wash bath ahead of the copper sulfate bath to extend the useful life of the latter.

Producers need to know how much copper is actually being applied to their soil. A buildup to high levels is essentially irreversible. For this reason, don't concentrate spent copper sulfate foot bath solutions in small-volume holding facilities and then spread the waste on a relatively small land area.

At this point in time, dilution is the best solution for the disposal of the spent foot bath effluent. Analyze manure, soil, and feed copper levels to set a benchmark. Where high amounts of copper are being applied to land (more than 10 pounds per acre), continue to monitor copper levels every few years.

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