Effects of different wood ashes on the solubility of cadmium in two boreal forest soils

In this study the fate of wood ash-derived cadmium (Cd) in forest soils was monitored in a field experiment and in a subsequent incubation experiment in the laboratory. The aim was to assess the distribution of cadmium between various pools differing in their bioavailability. In the field experiment the manual application caused a large variation between the subsamples and resulted in hot spots. A three-week incubation experiment carried out with mineral and peat soils using five different kinds of ashes demonstrated that ashes of dissimilar origin differ markedly in their effect on pH and cadmium dissolution. Furthermore, peat and mineral soils differed in the distribution of cadmium. Water-soluble and exchangeable cadmium, considered to represent bioavailable pools, remained low in all treatments. The results indicate that the stabilization of ash and the liming effect of the material are factors limiting the mobility of cadmium in soil even if the increase in the total amount can be high.