STUDIES ON SOIL MANGANESE

Abstract

Summary1. While results of extractions, performed in the presence of reducing agents, of mineral soils low in organic‐matter content suggested that manganese higher oxides approaching the manganese‐dioxide type are present or formed by oxidation of added manganese, results obtained with other extractants lend support to the suggestion by Dion and Mann that hydrated manganese oxides may occur in such soils.2. From the distribution of manganese in various extracts of alkaline organic soils with or without added manganese materials, it was concluded that no difficultly reducible higher oxides of manganese are present or formed. Some evidence was presented for the view that manganese of a higher valency form may remain in combination with the organic matter or may be retained in this manner after oxidation of added manganese.3. Divalent manganese present as a complex of the organic matter of alkaline organic soils could be estimated by extraction with a monocalcium disodium versenate solution. It constituted 10–20 per cent. of the total manganese content. Manganese added to such soils and not present as readily soluble manganese was recovered by this extractant shortly after application; manganese did not, however, remain in this form after some weeks contact with soils.4. The organic matter of various soluble organic‐matter fractions migrated anionically over a wide pH range; that of lignin solutions remained at the iso‐electric point. Manganese already present in soluble organic‐matter fractions migrated anionically in contrast to manganese added and retained by such fractions that moved predominantly as a cation.5. The oxidizable carbon or total nitrogen content of soluble organic‐matter fractions was not closely related to the amounts of manganese retained by such fractions in a form that was non‐dialysable against potassium chloride. Some evidence was obtained that different types of complexing groups may be present in water extracts subsequent to extraction by sodium chloride of an alkaline fen and of an acid raw‐humus peat.