Tracing Copper Derived from Pig Manure in Calcareous Soils and Soil Leachates by ⁶⁵Cu Labeling

Copper is used as a growth promoter in animal husbandry, resulting in high Cu concentrations in animal manure. We tested whether Cu would be mobilized in soils receiving excessive loads of manure, both from recently added and from aged fractions. To discriminate between these Cu sources, manure was labeled with ⁶⁵Cu. After soil application of 0, 15, and 30 Mg manure ha^–1, leachate was collected in free-draining lysimeters (40 cm depth) under undisturbed soil over a 53 day period. Determining the total amounts of Cu and the fractions of ⁶⁵Cu in leachate and the soil profile enabled us to trace the translocation of Cu derived from labeled manure. More than 84% of the applied Cu was retained in the top 2 cm of soil. Less than 0.01% of the applied Cu was detected overall in the leachate. Of this amount, however, 38% (±8.9 SE) was leached within 8 days after application. The total Cu concentration in leachates (32–164 μg L^–1) frequently exceeded the Chinese groundwater quality standard of 50 μg L^–1. The added ⁶⁵Cu, however, accounted for less than 3.6% of the total Cu leaching load, suggesting that Cu from older sources and/or geological background controls contamination, regardless of current land management