EFFECTS OF POST HARVEST MANAGEMENT PRACTICES ON THE STABILITY OF IRON MINERALS IN RICE CULTURE

Incorporation of crop residues in the soil results in the more reducing conditions as compared to other post harvest management practices. Understanding the nature and extent of reducing conditions and impacts of these reducing conditions on the iron minerals in the paddy soils is the focus of recent research. Two adjacent rice plots with different residue management practices were selected to measure the redox potentials and pH throughout the rice cultivation period. A thermodynamic approach, by constructing the pe-pH diagrams, was used to calculate the stability of iron minerals: Throughout the rice cultivation period a large variability between pe and pH values was observed such that -6 pe 11 and 6.8 pH 8.4. It was found that before flooding, in both paddy fields, all the iron should be stable in the form of Fe^3+ (system was oversaturated with respect to Hematite, Goethite, Lepidocrocite and Fougerite) and at the end of the rice cultivation period all the iron should be stable in the form of the Fe^2+ (system was under-saturated with respect to all mentioned iron minerals). The results also showed that incorporation of rice residues and rhizospheric activity have very determinant role in the dissolution of different iron minerals.