Effects of Biological Fertilizers on Yield and Growth Indices of Tomato in Cd Contaminated Soil

Environmental problems associated with the excessive use of chemical fertilizers and abiotic stresses due to soil pollution by heavy metals have encouraged use of biological fertilizers in modern agriculture. In order to protect environment and reduce the tension caused by heavy metals, it is essential to use biofertilizer in crop production. To assess the effects of biofertilizers on yield and growth indices of tomato grown in cadmium contaminated soils, a factorial pot experiment was conducted using a completely randomized design with three replication. Factors investigated were levels of soil cadmium and the kinds of biological fertilizers used to inoculate tomato plant. The levels of soil cadmium were 0, 5, 10, 20, 40 and 80 mg Cd/kg soil and six combinations of biological fertilizers were used including: M₀: without inoculation, M₁: Phosphor solubilizing bacteria + plant growth promoting rhizobacteria + Azotobacter bacteria, M₂: Azotobacter bacteria+ Mycorrhizal fungi + Azosperillium bacteria, M₃: Plant growth promoting rhizobacteria + Azosperillium bacteria + Mycorrhizal fungi, M₄: Mycorrhizal fungi + phosphor solubilizing bacteria + plant growth promoting rhizobacteria + Azotobacter bacteria, M₅: Plant growth promoting rhizobacteria + Azotobacter bacteria + Mycorrhizal fungi. The results showed that application of biological fertilizers increased yield and growth indices when compared with the control, except fruit and stem diameter. The M₂ combination increased tomato yield by 179.8%, generating the highest yield of biological fertilizers that was significantly different from the other combinations. By contrast, the result of the combination of biological fertilizers M₁ was not significantly different from the control.