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Contribution of Metal-Organic Complexing Agents to the Transport of Metals to Roots¹

ABSTRACT

The movement of many cations in soils can be influenced by the presence of synthetic chelates and soluble organic matter capable of forming metal-organic complexes. To understand how these complexes may contribute to the nutrition of plants, a means is needed to interpret their thermodynamic properties and behavior in solution culture experiments in terms of their effect on roots growing in porous media such as soils. For this purpose, a theoretical model is proposed to describe the contribution of complexed species to the flux of nutrients to roots. The model is developed from considerations of diffusion in response to concentration gradients, mass flow of water to a simulated root, and chemical equilibria between complexing agents and competing cations, and is evaluated in terms of different boundary conditions. The model illustrates how metal-complexing can contribute more to the nutrition of plants grown in a porous medium such as a soil than in nutrient solutions. It also shows how competing ions can have a potentially beneficial effect, as well as the obvious deleterious effect, on the contribution of complexing agents to the nutrition of plants.

Contribution from the US Plant, Soil, and Nutrition Laboratory, ARS, USDA, Ithaca, N.Y. Presented at a symposium—Metal Chelation in Soils—Div. S-2, Soil Science Society of America, Washington, D.C., Nov. 8, 1967.

² Soil Scientist, USDA, and Associate Professor, Cornell University.

Received for publication March 29, 1968. Accepted for publication September 11, 1968.