The forms of occurrence of manganese in some acidic soils

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Abstract
SUMMARY: The forms of occurrence of Mn were examined in some acidic surface and sub‐soils from areas of permanent grassland using chemical extractants. Despite high total contents of Mn in some of the soils and low pH, only minor proportions occurred as exchangeable Mn2+. Much larger proportions were present as reducible hydrous oxides, e.g. up to 38% and 54% of the total contents in surface and subsoils, respectively, were present as hydroquinone extractable, or easily reducible, Mn. Reducible forms of Mn were poorly correlated with other more mobile forms. Large proportions of the total Mn contents were accounted for when estimates of different fractions were calculated from differences in amounts extracted by different individual extractants, i.e. M NH4OAc, 0.2% hydroquinone, 0.1 M pyrophosphate, and ammonium oxalate. The distribution of Mn amongst the different fractions as determined by a sequential fractionation scheme differed markedly from the distribution calculated by differences. In particular, there was a marked change in form after extraction with pyrophosphate.