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The Critical Zn²⁺ Concentration for Corn and the Nonabsorption of Chelated Zinc¹

ABSTRACT

Corn (Zea mays) was grown in nutrient solutions of pH 5.2 and 7.5 with EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid) as chelating agents. At pH 5.2, corn plants were healthy and fully green, but at pH 7.5, the nutrient solutions with DTPA produced severely stunted, Zn-deficient plants. Spraying the foliage with Zn or increasing the level of ZnSO₄ added to the nutrient solution prevented Zn deficiency.

A concentration of 10^–10.6 M Zn²⁺ was sufficient to prevent Zn deficiency with corn. Even at 10⁵ times this concentration, chelated Zn was not absorbed by the roots. Equilibrium relationships of chelating agents in hydroponic solutions were extremely helpful in interpreting the results of this study.

The findings reported herein support the hypothesis that Zn²⁺ is the form of Zn absorbed by plant roots. Furthermore, plants can obtain adequate Zn from a nutrient media when Zn²⁺ is maintained at approximately 10^–10.6 M. This concentration is nearly 4,000 times lower than the 10^–7 M reported by Carroll and Loneragan. The hypothesis proposed herein is that chelation aids in the transport and movement of metal ions to plant roots, but only Zn²⁺ is absorbed.

¹ Contribution from the Dep. of Agronomy, Colorado State Univ., Fort Collins, CO 80523. Supported in part by Geigy Agric. Chemicals, Division of Ciba-Geigy Corp. and the Colorado State Univ. Exp. Stn., and published as Scientific Ser. no. 2163.

² Former Graduate Research Assistant and Professor of Agronomy, respectively, Colorado State Univ., Fort Collins. Senior author is now Soil Scientist, USDA-ARS, P. O. Box 1109, Sidney MT 59270.

Received for publication May 28, 1976. Accepted for publication January 12, 1977.

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