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This article in SSSAJ

  1. Vol. 50 No. 3, p. 588-593
    Received: June 29, 1984

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Manganese Phosphate Equilibrium Relationships in Soils1

  1. F. W. Boyle and
  2. W. L. Lindsay2



Solubility diagrams were developed using log K° values for MnHPO4·3H2O, Mn3(PO4)2·3H2O, Mn5H2(PO4)4·4H2O and MnPO4·1.5H2O. The latter mineral was found to be more stable than hydroxyapatite and thus capable of controlling soil-solution P at pH values <7.2 and pe + pH values between 13.5 and 17. Controlled redox cells were used to maintain suspensions of several soils at fixed redox levels above pe + pH = 13.5. After 28, 56, 84, and 140 d, samples were taken, and the clear filtrates were analyzed. The activities of Mn2+ and H2PO-4 were calculated by speciating total Mn and P in solution. Ionic activity products were calculated and compared to the activity products of pure Mn phosphates. This study helps to explain the beneficial effects of phosphate in alleviating Mn toxicities and the importance of Mn phosphates as reaction products of Mn and P fertilizers in soils.

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