Copper and zinc accumulation in poultry and dairy manure-amended fields

Application of animal manure to meet the nitrogen (N) requirements or phosphorus (P) removal rates of agronomic crops can lead to accumulation of micronutrients in soil. The objective of this study was to determine the accumulation, depth distribution, and bioavailability of copper (Cu) and zinc (Zn) in fields amended with liquid dairy (Bos taurus) manure (DM) or solid poultry layer (Gallus domesticus) manure (PM) for up to 40 years using 109 fields of a case study farm in Southern New York. Soil total Zn contents in the plow layer (0-17.5 cm) increased with total P at a rate of 0.02 to 0.03 mu g Zn g(-1) soil for each mu g P g(-1) increase in total P. For Cu, the rate of increase was 10 times greater for DM fields (0.02 mu g Cu g(-1)) than that for PM fields (0.002 mu g Cu g(-1)). In the PM field with the longest manure history, Mehlich-3 extractable Zn levels were elevated (> 10 mg Zn kg(-1) soil) to a depth of 30 cm. For all other fields, Cu and Zn accumulated in the plow layer only. Leachate sampled from intact soil cores (50-cm depth) showed low dissolved Cu and Zn concentrations (< 0.12 mu g Cu mL(-1) and < 0.21 mu g Zn mL(-1)) and plant bioavailability, expressed as 0.01 M CaCl2 extractable Cu and Zn of plow layer samples, also suggesting no risk of toxicity to most agronomic crops. Implementation of the P runoff index will discontinue manure application on high P fields and thus prevent buildup of Cu and Zn to concentrations of environmental concern.