In the uncultivated soil, the germination of ryegrass seeds was totally inhibited over the Cd concentration range from 4000 to 8000 mg/kg (Figure 1). In the cultivated soil, measurable ryegrass yields were obtained until a Cd concentration of 5000 mg/kg. The different concentrations of Cd in the two soils studied that inhibited totally seed germination demonstrate the influence of soil characteristics on the toxic effect of Cd to plants as reported by other authors (He and Singh 1994). The cultivated soil had a higher content of clay, CaCO 3 , and Fe and Mn oxides and hydroxides than uncultivated soil (Table 1). These characteristics influence the Cd phytoavailability, so that a greater amount of soluble forms of Cd added to soil was necessary to inhibit the seed germination of ryegrass.