Distribution of Manganese Chemical Forms and its Relationship to the Availability of Plants Affected by Leonarditis

Supply of micronutrients is necessary for the improvement of plant biological processes. The total amount of elements in soil is not an appropriate indicator for plant availability, because main portion of nutrients are usually as unavailable forms. Humic substances can change the chemical forms of elements in soil. Therefore, this study was done to investigate the influence of humic substance on changes of chemical forms of manganese (Mn) in some cultivated soils of Urmia region. Twenty soil samples were collected of 0-30 cm from the fields of Urmia region. Some physicochemical properties of soils were measured by standard methods. DTPA extractable Mn and clay mineralogy of soils were also determined. FT-IR spectra were analyzed to determine the functional groups of leonardite. Laboratory evaluations were carried out as a factorial in a completely randomized design with three replications. Four different soil samples were selected and were treated by 200 mg kg-1 MnSO4.H2O and were incubated for two months at field capacity moisture. Different levels of leonardite (0, 2 and 4%) were added after incubation. Laboratory evaluations were carried out as a factorial in a completely randomized design with three replications. The concentration and chemical forms of the Mn were evaluated using DTPA and sequential extraction method respectively after 20, 60 and 120 days. The results showed that the quality and quantity of the clay minerals were different and the illite mineral was dominant in the studied soils. Results showed that the leonardite have different functional groups and showed significant effect on increasing plant available Mn (P