BASE CONTENT OF CORN PLANTS AS INFLUENCED BY pH OF SUBSTRATE AND FORM OF NITROGEN SUPPLY

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Abstract
Corn plants were grown in 2 types of nutrient soln., (1) containing N only in the form of nitrate and (2) containing nitrate-N and ammonium-N in approx. equivalent proportions, each adjusted to pH values ranging from pH 3 to pH 8. Plants were analyzed for total and soluble K, Ca and Mg and data for total and active acidity of the expressed sap of the plants are also given. The total base content of all the plants was higher than the usual base-content value for soil-grown plants. There was a direct correlation between high K content and the pH of the expressed sap. The plants grown with soln. of Type 2 showed lower total base content and lower pH of the expressed sap than did those grown with solns. of Type 1. Absorption of the ammonium ion evidently retarded the absorption of the other cations. The presence of ammonia in the nutrient soln. had the most depressing effect on C absorption and the least effect on Mg absorption. High K absorption apparently had a depressing effect on C and Mg absorption. The pH of the nutrient medium between the limits of pH 4 and pH 8 had little effect on base absorption and accumulation. The presence or absence of the ammonium ion had a much more marked effect on absorption and accumulation of basic nutrients than had the variation in the pH levels of the substrate. The pH values of the solution films adjacent to the absorbing plant roots in contact with soln. of Type 2 were apparently considerably lower than those of corresponding films on roots in contact with soln. of Type 1, regardless of the pH levels of the body of the solns. This phenomenon may be partially responsible for the difference in base content shown by these 2 series of plants.
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