Dynamic transformation of sewage sludge and farmyard manure components. 2. Copper, lead and cadmium forms in incubated soils

An incubation experiment was conducted with farmyard manure (FYM), a Russian and a Swedish municipal sewage sludge (SSR and SSS, respectively) suing a sandy loam soil (pH water 6.8) at 25°C for 6 weeks to study the Cu, Cd and Pb contents of soils. The metals were sequentially extracted with 1 M NH 4NO 3 (available forms) and 0.1 M Na 4P 2O 7 (organically bound forms). There was a shift from the pyrophosphate-soluble pool to the NH 4NO 3-soluble pool, regardless of treatment. Thus, incubating soils increased available metal forms and decreased organically bound forms. SSS and FYM did not cause marked changes in the two metal fractions, whereas SSR application significantly ( P = 0.05) affected them. The two pools were positively correlated ( r = 0.993, P = 0.001), indicating that the pools did not change at the expense of each other. The increase in metal solubility in the 1 M NH 4NO 3 solution is important from both plant nutrition and environmental viewpoints.