Effects of Rice (Oryza sativa L.) Cultivation, Sewage Sludge and Chemical Fertilizers on Changes in Iron, Zinc, Copper and Manganese Concentrations in Soil Solution after Submergence

Micronutrients concentrations in soil solution affect nutrient uptake by plant. In this research, the effects of rice (Oryza sativa cv. Ali-Kazemi) cultivation and application of sewage sludge and chemical fertilizers on the changes in iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) concentrations in the soil solution after submergence were studied at greenhouse conditions. A factorial experiment based on randomized complete blocks design with two replications including duration of submergence at 10 levels (2, 11, 30, 37, 42, 49, 56, 63, 78, 92 days) and source and amount of organic and chemical fertilizers in six levels (control, 100% chemical fertilizers, 20g sewage sludge per kg of soil with and without 50% chemical fertilizers, 40g sewage sludge per kg of soil with and without 50% chemical fertilizers), with and without rice cultivation was carried out. The results showed that after submergence, Zn concentration of the soil solution decreased significantly in both of the cultivated and uncultivated treatments while Fe concentrations of the soil solution in all uncultivated treatments (except 100% chemical fertilizers) initially increased and then decreased significantly. After submergence, Mn concentrations of soil solution in all uncultivated treatments initially increased and then decreased. Application of sewage sludge and chemical fertilizers increased Fe, Mn and Zn concentrations of the soil solution in the cultivated and uncultivated treatments. In all treatments, Cu concentration in the soil solution was negligible. At the end of growth period, Fe and Mn concentrations of the soil solution in the cultivated treatments (rhizosphere) were significantly greater than the uncultivated treatments (non-rhizosphere), while Zn concentration of the soil solution showed no significant differences between cultivated and uncultivated treatments. In general, the rice plant cultivation (rhizosphere processes) and application of sewage sludge and chemical fertilizers can alter the micronutrients concentrations in the soil solution.