Plant Nutrition and the Hydrogen Ion. I. Plant Nutrients Used More Effectively in the Presence of Hydrogen Ions

WM. A. ALBRECHT AND R. A. ScHROEDER NORMAL legume growth and successful nodulation, with the accompanying nitrogen fixation through the symbiotic activities of the plant and the bacteria, have regularly called attention to the dangers to them from the soil's deficiency in lime. The beneficial effects by liming, as they improve legume growth, increase nitrogen fixation, and favor growth of the bacteria in isolation from the host, have most commonly been ascribed to the fact that the concentration of the hydrogen ion in the soil was reduced by the lime treatment. Because we now know that the liming of legumes exerts its beneficial effects on both the legume plant and on the legume bacteria more because it supplies calcium than that it reduces the acidity, the question may well be raised whether the presence of the hydrogen is truly injurious to nutrient movement into the plant for its growth, as, to date, only inferences . rather than evidence have led us to believe. The use of the colloidal clay technic in growing plants makes possible the adsorption on the clay of the various nutrient cations in combinations with different anions, as hydroxides, for example, that reduce acidity or as chlorides, sulfates and other salts that are not effective in this respect. By careful choice of the kinds and amounts of anions as accompaniments of the cations, the latter were offered on clay in constant amounts per plant but in two series, one of which was "acid" or at pH 5.2 and the other "neutral" or at pH 6.8. That such a test might demonstrate the activity of hydrogen in encouraging the movement of cations in larger amounts into the plant was suggested by the greater exchange activity by cations in hydrogen presence when tested by simple chemical exchange methods. Jarusov has demonstrated that some exchangeable cations were taken off the clay in larger quantities if associated with acidity rather than neutrality of the clay. Careful examination of the work by Gedroiz offers similar suggestions and indicates greater effectiveness in connection with plants. On the basis of possible increased chemical activities by the cations under these conditions, it seemed plausible that the colloidal clay method might serve to test whether an acid series would give a larger share of its exchangeable nutrients to the plants than would the neutral series. Some legumes that, had been grown by the colloidal clay technic with complete balance of most nutrients in the soil and the seed at the outset against those in the soil and crop at the close, permitted examinations of some series in which variable amounts of calcium were accompanied by reciprocally varying amounts of hydrogen, or acidity, in contrast to other series in which barium was the reciprocal of the variable calcium and gave neutrality, or the absence of hydrogen. The data show that more calcium moved into the plants when it was accompanied by hydrogen than when hydrogen was absent. Here is a suggestion given by legume plant behavior, that there is a greater exchangeability from the clay and greater migration into the plant by the calcium when accompanied by hydrogen than when by barium. Since even legumes, which are commonly considered to be harmed by the hydrogen presence, suggest a value for hydrogen in their nutritional activities, it seemed logical to believe that the service of hydrogen in making cations more exchangeable or "available" would be even greater in case of the non-legumes, growing so commonly on the more acid soils. A crop of spinach was grown on two series of clay media, one of which was acid at pH 5.2 and the other at pH 6.8 and both constant relative to all the nutrients, except calcium. They were comparable rather than constant in the amount of calcium offered. This varied through the series of o, 3, 6, 9, 12 M.E. as additions of this cation per plant. Crop analyses and harvests demonstrated that the nutrient cations and anions were taken by the crop more effectively when they were accompanied by hydrogen ions than when these acidity conditions were Contribution from the Department of Soils, University of Missouri, Columbia, Mo. Professor of Soils and Assistant Professor in Horticulture, respectively. "JARUSOV, S. S. On the mobility of exchangeable cations in the soil. Soil Sci., 43:285-303. 1937. •"GEDROIZ, K. K. Exchangeable cations of the soil and the plant. I. Relation of plant to certain cations fully saturating the soil exchange capacity. Soil Sci., 32:51—62. 1931.