Evaluation of a soils suitability to apply sewage sludge

We simulated the chemical composition of the soil solution of an agricultur al soil under the assumption of an annual application of sewage sludge. Our goal was to estimate both the consequences of long term sludge application and the time frame available to exhaust the trace metal retention capacity of the soil. Our scenarios included changes in soil pH as consequence of l and use change. At low soil pH (pH = 3) a substantial portion of lead and c opper was tied up in organic complexes, whereas cadmium and nickel remained in solution as free ions; at high pH (pH = 7) even cadmium and nickel form ed complexes with organic ligands. The trace metal retention capacity of th e soil was high and allows a continuous application of sewage sludge for ma ny decades. Concentrations of trace metals in the soil solution are rising, but deep soil profiles make the retention capacity apparently inexhaustibl e. These conclusions apply for the chosen parameters in our study. preferen tial water flow is not considered in our models and may cause deviations be tween simulations and field measurements. Based on our results we consider modeling a valuable tool to evaluate the human impact on soil processes.