Changes of chemical forms of Zinc in the rhizosphere of some turnip and radish cultivars

In order to study the changes in chemical forms of zinc in the rhizosphere of two tuber plants and their relationship to plant uptake in a polluted soil, sequential (Tessier et al., 1979) and single step extraction methods were used. In this research, three radish cultivars (Raphanus sativus) and two turnip (Brassica rapa) cultivars were planted in a complete randomized design pot experiment with four replications (20 pots) and 4 pots with no cultivation as blank. Results indicated that the largest forms of zinc include Fe and Al oxide bounded carbonates, and the residual forms respectively. The exchangeable and soluble forms comprise only less than one percent of total zinc in the rhizospheric soils of all plants. The zinc concentration of shoots for different cultivars of each plant did not show significant difference and in all plants the zinc accumulation factor and the translocation factor were less than unit. Sequential and single step extractions showed significant increase of Zn in the rhizosphere of both plants compared to bulk soil. Different cultivars of both plants could significantly increase the rhizosphere DOC up to 9 mg.L-, which consequently increased soluble and exchangeable Zn in this zone for both plants compared to bulk soil.