Metal Depth (cm) Control soils (0 yrs)a (mg/kg)
Soils treated for 10 years (mg/kg)
3.59 (2.77)a 0.86 (0.46)a 7.87 (4.67)c 1.33 (0.41)d a Mean Cu and Zn concentrations after 0 vs. 10 years' effluent application were tested by depth using a t-test and means followed by a different letter were significantly different at a P < 0.05 level of rejection.
Source: Novak, J.M. and Watts, D.W., Trans. ASAE (in review), 2004.
The leaching of Cu and Zn to subsoil depths has been explained by metal chelation with soluble organic compounds from the litter [80,81]. It appears that the highest trace metal concentrations in manure-treated fields are measured in topsoil. By extracting subsoils and finding an increase in Cu and Zn concentrations, scientists have suggested that some downward leaching of Cu and Zn can occur in manure-treated soils. Measured subsoil concentration increases are, however, small. Nevertheless, lack of substantial Cu and Zn concentrations in subsoil depths cannot exclude the fact that soluble forms of trace metals can leach through the soil profile and could cause enrichment in shallow ground water. Trace metal enrichment of shallow ground water as a result of leaching has not been sufficiently documented in soils treated with animal manures. Additional studies examining trace metal concentrations in shallow ground water beneath manure-treated fields should be conducted to determine whether trace metal leaching is a significant water quality issue.
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