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Growth and Nitrogen Distribution Patterns in Bean Plants (Phaseolus vulgaris L.) Subjected to Ammonium Nutrition: I. Effects of Carbonates and Acidity Control¹

ABSTRACT

Growth of bean plants was limited when nitrogen was supplied as (NH₄)₂SO₄ in sand culture in comparison to the growth of plants receiving nitrate nitrogen. Mixing relatively insoluble carbonates with the sand, using (NH₄)₂CO₃ instead of (NH₄)₂SO₄ or maintaining the pH of the nutrient solution near neutrality with NaOH all prolonged the life and increased the growth of plants. Experiments in which C¹³-labeled carbonate was used revealed no absorption or incorporation of C¹³ into the plant tissues. The changes in mineral element contents of plant tissue induced by the treatments did not account for the increased growth.

In the absence of pH control, ammonium, amide, and amino acid accumulation was very high in the leaves. Maintaining the pH of the nutrient solution near neutrality stimulated N assimilation in roots, especially the synthesis of amino acids and amides. Acidity control thus prevented the accumulation of ammonium in the tops and hence lessened the possibility of toxic effects from ammonium. The increased conversion of ammonium to nontoxic metabolites in roots is considered to be thedominant process by which acidity control improved the growth of plants on ammonium nutrition.

¹ Contribution from the Department of Soil Science, North Carolina Agr. Exp. Sta., Raleigh, N. C. Presented before Div. S-4, Soil Science Society of America, Nov. 1964. Published with the approval of the Director as Paper no. 2038. Investigation was supported in part by National Science Foundation Grant no. G21454.

² Former Post-Doctoral Fellow, Associate Professor, Professor, respectively. Department of Soil Science, North Carolina State University at Raleigh. Senior author is now Assistant Professor, Dep. of Plant and Soil Sciences, University of Massachusetts, Amherst.

Received for publication August 16, 1965. Accepted for publication October 29, 1965.