Interaction Effects of Zinc and Cadmium on Growth and Chemical Composition of Canola (Brassica napus cv. Hyola) in a Loamy Sand Soil

To investigate the interaction effect of Cd and Zn on growth and chemical composition of canola, a factorial greenhouse experiment in a randomized complete block design with two factors including Cd at eight levels (0, 5.0, 5.2, 5, 10, 20, 40 and 80 mg kg-1 soil) and Zn at eight levels (0, 5, 25, 50, 100, 200, 400 and 800 mg kg-1 soil) with three replications was conducted in a loamy sand soil. After 60 days, the dry weights and concentrations of Cd, Zn, Fe, Mn and Cu in shoots and roots were determined. At levels of 2.5 and 0.5 mg Cd per kg of soil, all levels of Zn increased shoot and root dry weights. At higher levels of Cd, applications of 5 and 25 mg Zn per kg of soil increased the shoot and root dry weights, but at higher levels of Zn, a decrease in these parts was observed. Moreover, at levels up to 5 mg Cd kg-1, application of Zn even at level of 25 mg Zn kg-1decreased Cd concentration in shoots in comparison with control. However, at higher levels of Cd, this decrease was achieved only at 5 mg Zn kg-1. Increasing the level of Cd at any level of Zn decreased the Zn concentration in shoots. Application of Zn at each level of Cd, first increased and then decreased the concentration of iron in shoots and roots. Zn supplementation at each level of Cd increased concentration of Mn in shoots and decreased its concentration in roots. In addition, Zn application at each level of Cd decreased the concentration of Cu in both shoots and roots.