Effect of Plant Growth Promoting Rhizobacteria and Different Moisture Levels on Chemical forms of Cadmium in the Soil After Corn Harvesting

Cadmium (Cd) is known as one of the most dangerous elements for living organisms, and because of its easy availability for plant, is a major threat for the human food chain. In order to evaluate the effect of adding bio-fertilizers and inoculation of plant growth promoting rhizobacteria (PGPR) such as Micrococcus yunnanensis on chemical forms of soil cadmium, a greenhouse experiment was conducted with a factorial arranged in a completely randomized design with three replications. Treatments consisted of two levels of bacteria (with and without inoculation), four levels of Cd (control, 10, 20, and 40 mg kg-1), and three moisture levels (100, 80, and 65% of field capacity). After corn harvesting, amount of chemical forms of Cd were evaluated. Results indicate that increasing Cd levels significantly increased amount of all chemical forms of Cd. Application of bacteria decreased exchangeable (Ex), carbonate-bound (Car), organic-bound (Om), amorphous iron oxides-bound (AFe-ox) and manganese oxides-bound (Mn-ox) fractions but increased residual (Res) fraction. Reduction of soil moisture decreased Om and AFe-ox bound fractions in not inoculated treatments, but increased AFe-ox and Mn-ox fractions in inoculated soils. Highest contents of Cd were associated with Car-bound fraction, with the order being: Res > Mn ox-bound > AFe-ox- bound > Om -bound > Ex fractions.