Many of Idaho’s dairy cows wade through copper sulfate baths like this to help prevent foot infections. Photo by Ernest Hovingh, Penn State University.

Getting a head start on stopping soil copper buildup will now be a bit easier, thanks to studies by USDA scientists. This research could help Pacific Northwest farmers develop long-term irrigation management strategies to protect crops from potentially dangerous soil copper levels.

Scientists with USDA’s Agricultural Research Service (ARS) conducted a laboratory investigation to assess how copper levels in wastewater used for irrigation affected crop performance and soil microbial activities.

Copper sulfate baths are used to prevent foot infections in dairy cattle, and the discarded foot bath is often recycled to irrigate corn and alfalfa crops. The scientists surveyed alfalfa growth and development in soils containing different levels of total copper. Copper sulfate at soil levels of up to 250 parts per million (ppm) had no effect on alfalfa growth, but alfalfa growth stopped when soil copper sulfate levels exceeded 500 ppm.

The team also discovered that beneficial soil bacterial activity declined when test soils accumulated available soil copper levels above 50 ppm. Further analysis indicated that soil levels above 63 ppm of plant-available copper resulted in alfalfa copper concentrations that could potentially harm grazing livestock

Read more about this research here.