Effect of different way of bottom ash and compost application on phytoextractability of cadmium in contaminated arable soil

There have been few studies evaluating the effect of bottom ash (BA) on immobilization of heavy metals and reducing their phytoavailability. Further, work has not been conducted to evaluate the effect of BA along with mature animal manure compost (CP) on immobilization of cadmium (Cd) in soil and phytoavailability of this metal in contaminated soil. Therefore, this study was conducted to determine the effect of application of BA and CP on Cd phytoextractability. To elucidate the mechanism of Cd immobilization with BA and CP, soil was mixed without BA and CP, with BA only, with CP only, and with BA and CP together in the incubation. Bottom ash was applied at rates of 0 and 30 Mg/ha under different application rates of CP (0 and 30 Mg/ha) 2 weeks before sowing lettuce (Lactuca sativa). Our first experiment clearly demonstrated that reduced extractability of Cd with addition of BA, CP, and BA + CP was mainly the result of Cd adsorption by an increase in pH and negative charge of soil. Concentration of bioavailable Cd fraction (F1) effectively decreased with BA, CP, and BA + CP from 1.33 mg Cd/kg in control to 0.98, 0.29, and 0.26 mg Cd/kg, respectively. Applying BA and CP alone or together effectively reduced Cd uptake by lettuce. Concentration of Cd in lettuce decreased from 13.9 mg Cd/kg in control to 10.3 and 7.6 mg Cd/kg with application of BA and CP alone, respectively. However, applying BA with CP increased fresh lettuce yields more than BA applied alone. Therefore, combined application of BA and CP might be a good management practice in Cd contaminated arable soil from the view point of Cd phytoavailability and crop productivity.