Changes in phytoavailability and concentration of cadmium in soil following long term Salix cropping

Cadmium concentrations in Salix (willow) shoots are generally high and Salix can therefore potentially remove significant amounts of Cd from soil. The aim of this study was to investigate how long-term Salix cultivation had affected total and plant available Cd concentrations in agricultural soil. The study was made in 8 to 30 yr old plantations. Soil profiles down to 65 cm depth were sampled and conditions within the plantations were compared to those in nearby reference areas. When consideration was given to certain pH differences, concentrations of exchangeable Cd throughout the soil profiles were significantly lower in the Salix stands than in the reference areas. However, the effect on concentrations of total Cd was negligible. The yield levels proved not to be optimal and Cd concentrations in shoots were lower than average in the investigated stands. Data on exchangeable Cd show that uptake occurs throughout the soil profile and the Cd pool involved is thus large. These facts may explain why total concentrations were only slightly influenced. The conclusion reached was that Salix cultivation reduces the amount of plant-available Cd in the soil. However, more investigations are needed to evaluate how this effect can be optimized by choice of clone and other management measures.