oxide generally at pH > 8.0 Manganese Cycle Fertilizer and Manure Mn2+ exchangeable (adsorbed cation or in solution) oxidation reduction reactions Biological oxidation Bacteria - Arthrobacter, Bacillus Fungi - Cladisporium, Curvularia weathering > pH 7.0 Organic complexes (predominantly soil organic matter) Precipitated Mn oxides Plant uptake residue Parent material Mn3+ as Mn2O3, unstable oxide Mn4+ as MnO2, very inert oxide generally at pH > 8.0 Foliar sprays (usually MnSO4) Deficiencies pH>7.0, <20 ppm Toxicities pH<5.5, >500 ppm Optimum availability at pH 6.2 to 6.4 diffusion