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Interaction of Potassium in the Availability and Uptake of Iron From Ferric Hydroxide¹

ABSTRACT

The uptake of iron from ferric hydroxic by corn plants (Zea mays L.) was stimulated by the presence of increasing levels of potassium sulfate. Potassium nitrate had a much smaller effect. During the 48-hour absorption experiments, the pH of the SO₄ solution dropped from 9.2 to nearly 4, while that of the NO₃ solution dropped only from 8.4 to between 6.5 and 6.8. The different behavior of the two solutions must be due to different imbalances of cation and anion uptake. Nitrate is taken up at a rate similar to that of K, which is faster than that of SO₄. Thus NO₃ causes a smaller decline of the pH. Reduced pH has a favorable effect on Fe solubility. The phenomenon was also observed (i) in CaCO₃-buffered solutions, in which case the pH drop in the root boundary zone may have been important and different from that in the buffered bulk solutions, and (ii) when Fe was present together with a synthetic cation exchanger.

¹ Contribution of the Dep. of Soil Sci. and Agr. Eng., Univer. California, Riverside, Calif.

² Professor of Soil Science and former Graduate Student, respectively, Univer. Calif. at Riverside, Calif. 92502.

Received for publication September 26, 1973. Accepted for publication February 19, 1974.