THE SOLUTION OF γ-MnO₂ BY SUBSTANCES RELEASED FROM SOIL AND FROM THE ROOTS OF OATS AND VETCH IN RELATION TO MANGANESE. AVAILABILITY

Water-soluble substances capable of dissolving γ-MnO₂ were readily extracted from an air-dried, manganese-deficient soil but they were not extracted from it after it had been moistened and incubated. Availability studies in pots showed that both oats and vetch utilized γ-MnO₂ with ease when grown in sand. The roots of both plants released substances which dissolved γ-MnO₂. These substances were readily decomposed by micro-organisms ; they became more effective as the pH fell below 7 and also as their concentration increased. The substances were different for each plant although the process of solution appeared similar. Polarograms of the dissolved manganese in mixtures of root washings and γ-MnO₂ were similar to that of manganous ion. Chromatographically, however, it did not behave like manganous ion. The availability of manganese to plants is discussed in relation to these findings.