The approach we have adopted in this study is different because it involves the addition of plant residues to soils where Cd is the only contaminant rather than the incorporation of metal-contaminated organic residues to soils. However, plant material can bind heavy metals due to the presence of reactive functional groups, thereby reducing their availability (Tiemann et al., 1999) and this effect should be taken into account in assessing the adverse effects of Cd in the contaminated soils, where the addition of plant material might have reduced the heavy metal availability.