Effects of Combined Application of Cd and Zn on the Growth Characteristics of Rice Plant and Zinc, Cadmium, Iron and Manganese Concentration in Soil under Flooded vs. Nonflooded Conditions

Cadmium is one of the most toxic pollutants in the surface soil layer the accumulation of which in soils as well as in crops is of increasing concern. In addition, zinc is a micronutrient in rice nutrition which is in interaction with Cd. A pot experiment was carried out to study the effects of zinc and cadmium on rice growth and as well on concentrations of Zn, Cd, Fe and Mn in soil. A factorial experiment was conducted based upon a randomized complete block design of three replicates including two varieties of rice (Vandana and Hashemi), two water regimes (flooded vs. nonflooded), three levels of zinc and cadmium each (0, 5 and 10 mg kg-1). The results showed that flooded vs. nonflooded condition's shoot weight and root weight as well as root volume in the two varieties and in flooded conditions were greater than those in the nonflooded conditions. Dry matter, root volume and number of leaves inVandana variety were greater than those in Hashemi. By increasing Zn, shoot and root weight, root volume, number of leaves and tillers, stem height and water use efficiency increased but concentrations of DTPA-extractable Cd were diminished. By using Cd, the above said parameters and concentrations of DTPA extractable Zn and Fe were initially, and then decreased. By incease in Cd level, concentrations of DTPA -extractable Cd and Mn were increased. The effects of Cd and Zn levels on concentrations of Zn extractable by DTPA in soil were nonsignificant. By utilization of Cd in any level of Zn, shoot weight and water use efficiency firstly increased but then decreased.