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October 2005
Volume 14, Number 6
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Copper Sulfate Footbaths and Soil-Crop Levels of Copper |
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Introduction
Copper is an essential element for plant and animal growth, however, it is only needed in trace amounts. The requirement for the cow varies by stage of lactation from 0.5 milligrams to 2.0 milligrams per day. For crops, most remove less than 0.1 pound per acre per year from the soil.
The copper ion is held very tightly by minerals and organic matter in the soil and therefore most of the copper in soil is unavailable to plants. Soil pH has an impact on availability of copper with higher availabilities at lower soil pHs. As a result, once soil copper levels are elevated, they stay there for a long time. Plants have varying ability to tolerate high level of copper in soils. A general thumb rule is to avoid soil test copper levels above 20-30 ppm as toxicity may occur in plants.
Copper sulfate has been used extensively during the past decade as a management strategy to treat hoof related issues in dairy cattle. The amounts of copper that are used in footbaths and subsequently go into manure lagoons is far above that need for crop use. A report from Wisconsin of 27 dairies indicated that annual use of copper sulfate averaged 77 pounds per week with a range of 12 to 200 pounds. These amounts translate for four selected dairies to range from ~ 4,000 to 13,000 pounds of copper sulfate per year (Rankin, 2005). This level of use resulted in a range in copper application per year of ~ 8 to 10 pounds per acre per year.
Copper sulfate use and Soil and Forage Copper Levels in a NW Washington County
During the summer of 2005 we conducted a survey of six dairy producers that were willing to participate in a small study to look at copper sulfate use and its relationship to copper in soil and grass forage. A written survey was developed to collect information on the use f copper sulfate and soil and grass forage samples were taken on one field at each cooperating dairy. Results are shown in Table 1.
The producers indicated that they had been using copper sulfate footbaths for 5 to 15+ years with a range in annual use this past year of 250 pounds to 3250 pounds. If all the copper from the footbaths was collected in their manure lagoon and was uniformly applied across all forage acreage, the level of copper application would range from 0.3 pounds to 2.6 pounds per year per acre. The levels of soil and forage copper increased in a linear fashion as the amount of annual copper applied increased.
None of the levels of soil copper were high, however farm 6 did have levels that were ~ 9 ppm, a level that indicates significant accumulation over time. If all the copper were plant available, a 7 - pound application of copper would raise soil test copper 3.5 ppm per year.
The forage levels of copper were in a normal range with the exception of farm 4, with grass copper levels of 32 ppm, about 3 times what would be considered normal.
Limits of application
Some states have defined limits of life-time application of copper to soil. Most often these are associated with the regulation of application of biosolids. These limits have been reported to be in a range of 75 to 1339 pounds.
Recommendations
It would be wise to monitor soil and forage copper levels every few years when the amount of copper addition is expected to be more than 10 pounds per year.
References
Rankin, M. 2005. Copper sulfate use may bite us. Hoard’s Dairyman. May 10, 2005, page 338.
Davis, J. and B. Wailes. 2002. Copper levels affect lagoons, crops, and cows.
Hoard’s Dairyman. June 2005, page 438.
Thomas, E. 2001. Foot bath solutions may cause crop problems. The Progressive Dairyman. October 2001, pp 52-55.
Moser, L. 2000. Hoof baths…a simple solution to a serious problem. Hoard’s Dairyman. August 25, 2001. page 551.
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Joe Harrison and Lynn VanWieringen, WSU Puyallup |
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jhharrison@wsu.edu |
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