Effects of application of silicon and zeolite on chemical speciation of cadmium in soil and its uptake by Tobacco

Abstract

This study was aimed to explore the effects of applying silicon (Si) or/and zeolite (Ze) on the soil pH, soil available cadmium (Cd) content, Cd speciation changes and Cd uptakes by tobacco using pot experiment with simulated exogenous Cd contaminated soil indoors. Results showed that soil pH increased and available Cd content reduced in different degrees with increase in the amount of applied silicon and zeolite. Compared with the control, separate application of silicon, zeolite and combined application of silicon and zeolite increased soil pH at 0.34-1.13, 0.21-0.72 and 0.89-1.07, respectively, and reduced the available Cd contents at 20.4-34.3%, 18.5-31.0% and 33.8-39.2%, respectively. In addition, soil pH had significantly negative correlation with available Cd content in each group (P < 0.05). Treatment with each modifier could effectively reduce Cd content in upper, middle and lower leaves and stems of tobacco, and the effect of each treatment on reducing Cd content in different parts of tobacco plants was in the order of silicon plus zeolite treatment > silicon treatment > zeolite treatment, and Cd content in all parts of tobacco plants was positively correlated with soil available Cd content. The content of exchangeable Cd (EXE) decreased to some extent with different treatments, while the contents of carbonates-bound (CAB), organic matter bound (OM), Fe-Mn oxides bound (FMO) and residual (RES) Cd increased in soil. Overall, combined application of zeolite and silicon significantly reduced the available Cd content in soil and Cd content in tobacco.