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.