Effects of nutrient supply and soil cadmium concentration on cadmium removal by willow

Abstract

This investigation studied the effect of an increased biomass production as a result of fertilization and an elevated Cd concentration in the topsoil on concentration and amount of Cd in two clones of Salix (81090 and 78183). The experiment was conducted over a three year period using 200-dm 3 lysimeters filled with clay soil. A liquid fertilizer containing all essential macro- and micronutrients in balanced proportions by weight was applied at two rates according to growth. The lower rate corresponded to 0, 20 and 20 kg N ha −1 during years 1, 2 and 3, respectively, while the higher rate was 30, 60 and 60 kg N ha −1 for the same period. The Cd levels in the topsoil were an initial content of 0.3 mg Cd (kg dw soil) −1 and 0.6 mg Cd (kg dw soil) −1 after addition of CdSO 4. Biomass production increased significantly due to fertilization. In general, this increase in biomass resulted in a higher Cd amount in the stem. However, the magnitude was small and only statistically significant in some cases, mainly because increased biomass also resulted in a lowered Cd concentration due to an effect of biological dilution. Addition of Cd to the topsoil resulted in higher Cd concentrations and total Cd amounts (concentration×biomass) in the Salix plants. In most cases the increase in total stem Cd amount was 40–80% of the increase in soil Cd concentration, although a directly proportional increase was observed occasionally. Clone 81090 had higher concentrations and total amounts of Cd in the stems than clone 78183, while clone 78183 produced more stem biomass. The leaves had the highest Cd concentrations, but the total amounts of Cd were largest in the stems.