Copper Sulfate Soil Accumulation

By Steve Mason on

bag of copper sulfate Copper sulfate (CuSO4) has been used in cattle footbath solutions for many years and is usually the standard to which alternative products are compared. Typically, CuSO4 solution is considered effective for 150 to 300 cow passes through the bath. Spent solution is mixed with manure waste and ultimately disposed by land application.

Regulators in several US states have expressed concern that soil copper (Cu) could be increased to an unhealthy level by this practice and have established maximum (lifetime) loading rates of Cu. An 8 ft x 2.5 ft x 5 inch foot footbath will contain approximately 62 US gallons of water and 26 pounds of CuSO4 (charged at the 5% concentration). Since CuSO4 is 40% copper, each time the footbath is dumped, 10.4 pounds of copper are added to the disposal burden.

The environmental effect of this Cu depends on the volume of footbath solution disposed (a function of cow number and frequency of footbath use), concentration of CuSO4, and the land area of application. Without careful attention, maximum soil Cu loading rates may be exceeded by dairy producers in relatively short times (5 to 30 years). Plants require very little Cu—annual removal rates are less that 0.5 lb/acre for typical grain and forage crops.

When CuSO4 is applied to soil, the Cu has a high affinity for organic matter and accumulates in the upper soil layers. In the period 1994 to 2004, the W.H. Miner Institute (Chazy, NY) estimated that, in approximately one year out of 5, greater than 4 lb/acre of Cu was applied to their agricultural land. A preliminarily report suggests that 4 lb/acre of Cu supplementation may affect root development in certain grass plants under experimental conditions, though corn yields under similar circumstances were not affected (ref 1).

A survey of Vermont dairy farms estimated that 1.4 lb/acre of Cu was applied to farm land in 2005, which was down from 2.1 lb/acre of copper in 2002. Investigation of three central NY dairy farms showed varying levels of CuSO4 use, Cu content in manure and estimated Cu loading to soil ranging from 3.6 – 8.9 lb Cu / acre / year. Soil Cu was approximately 3 times greater than normal background levels at the farm applying 8.9 lb Cu / acre but was not increased at the farms applying ≤ 3.6 lb Cu / acre (ref 2).

It is clear that copper disposal from dairy farms can result in accumulation of soil copper in a short time, while soil copper will be naturally removed over several very long lifetimes.

References:
1. S.A. Flis et al., The effect of CuSO4 from dairy manure on the growth, and composition of cool season forage grasses and corn.
2. R. Stehouwer et al., Fate and bioavailability of soil-applied Cu from dairy hoof baths.
3. W. Epperson and L. Midla, Copper Sulfate for Footbaths – Issues and Alternatives.

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