Aluminum, Iron, and pH in Relation to Lime Induced Manganese Deficiencies
1957
Mehlich, A.
The effect of freshly precipitated Al- and Fe-oxide hydrates on Mn solubility and uptake by plant roots in relation to pH has been studied. Precipitation of Mn (as Mn (OH)₃ or Mn₂O₃ · XH₂O) from MnSO₄, by the addition of Ca(OH)₂, began at about pH 8.5, while in the presence of Al³⁺ and Fe³⁺ salts precipitation began at pH 5.8 and with Fe²⁺ salts at pH 6.8. Manganese in solution decreased with increasing pH and increasing cation/Mn ratios. In this regard, Fe³⁺ and Al³⁺ had a greater effect than Fe²⁺ while Zn²⁺ and Cu²⁺ had the least effect. It was concluded that freshly precipitated sesquioxide hydrates are effective in supplying OH ions for the precipitation of Mn at the lower pH values. Acid washed H-roots of soybeans and wheat adsorbed Mn and Al from freshly precipitated Mn- and Al-oxide hydrates. With increasing Al/Mn ratios adsorption of Mn decreased and that of Al increased. Solubilization of Mn and Al was thought to be the result of H ions on roots reacting with the OH groups of the Mn- and Al-oxide hydrates. Measurement of the nutrient content of soybean and corn tops of varying degrees of chlorosis showed Al and Fe to increase greatly with increasing chlorosis and increasing soil pH. Manganese content was not directly related to either severity of chlorosis or acid soluble soil-Mn. The Mn content in itself cannot be used, therefore, as a criterion for Mn-deficiency. It is concluded that excessive amounts of sesquioxide hydrates in soil may contribute to disturbances in the absorption and functional pattern of Mn as well as Ca in plants.
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