Copper (Cu) input to agricultural soils results from Cu containing pesticides and or that in soil amendments, such as manure or sewage sludge. Soil and soil solution properties influence the adsorption and desorption of Cu by the soil, which in turn determines its plant availability and/or phytotoxicities. Effects of different anion enrichment in the equilibrium solution on Cu adsorption by different soils (pH range of 6.2-9.9) were investigated in this study over a range of Cu concentrations. With Cu concentrations in the range of 0-100 mg L(-1) in the equilibration solution, 95-99% of applied Cu was adsorbed by all three soils. The adsorption of Cu was similar regardless of using either 0.01 M CaCl2 or Ca(NO3)2 as the equilibration solution. When the Cu concentration in the equilibration solution was further increased in the range of 500-2000 mg L(-1), the adsorption of Cu decreased from 60 to 24% of applied Cu in two soils with pH 6.2-7.9. In a high pH soil (pH=9.9), the Cu adsorption decreased from 77 to 34%. Addition of incinerated sewage sludge (ISS) to a Palouse silt loam soil (pH = 6.2) increased the Cu adsorption as compared to that by unamended soil. This was, in part, due to an increase in the soil suspension pH with ISS amendment.