Conflicting results have been achieved by the evaluation of manganese availability in soil, largely a consequence of varying values denoted as available by different extractants. Knowledge on the element's chemical forms in the soil and on relationships with the available concentrations are important to predict its behavior in the soil-plant system. In this study, six Oxisol soil samples were analyzed to evaluate the influence of liming and different manganese doses on desorption, extraction and fractioning. These soil samples, with and without lime application, were treated with manganese doses (0.0, 16.0 and 32.0 mg dm-3) and then incubated for 30 days. Hereupon, Mn was extracted with Mehlich-1, Mehlich-3, DTPA and EDTA. and determined by atomic adsorption spectrophotometry. Additionally, the samples were fractionated for determination of manganese in the fractions: exchangeable (Ex), organic matter (OM), manganese oxides (MnOx), amorphous iron oxides (AFeOx), crystalline iron oxides (CFeOx), and residual (Re), as well as the total concentrations of the micronutrient. Micronutrient desorption was evaluated by successive extractions with cation exchange resin. Results showed that Mn was mainly retained in the exchangeable and organic matter fractions. In general, liming reduced exchangeable contents and increased the oxide fractions of amorphous iron and manganese. Without lime, the desorption order for Mn was Ex >> OM > AFeOx, where Mehlich-3 proved to be the best extractor for the determination of labile Mn concentrations. Liming caused a considerable decrease in Mn desorption. Under the same condition, Mehlich-1 proved to be inefficient to determine available Mn contents, while DTPA was the best extractant.
liming; soil analysis; micronutrient