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A Model of Zinc Movement to Single Roots in Soils¹

ABSTRACT

The movement of zinc in soils can be influenced by the pH of the soil and the presence of synthetic chelates or soluble organic matter capable of forming metal-organic complexes. To understand how these complexes and pH may contribute to zinc uptake by plants, the basic processes involved in zinc transport and absorption by a single root were formulated and the resulting differential equation solved simultaneously.

The model considers diffusive and convective flow of several zinc species, H⁺ and a chelating agent, flow of water to the root, and chemical equilibria between adsorbed and solution phase ions and between complexed and uncomplexed cations. The model assumes transient conditions with respect to water and ions and makes allowance for the adsorption isotherm and the biologically determined parameter relating flux of uptake to concentration to be concentration-dependent.

Within the range of studied cases, root permeability to ions and water is the most effective mechanism in controlling Zn uptake. Excretion of H⁺, and probably other means of reducing the pH near the root, are more effective in enhancing Zn uptake than excretion of complexing agents. A generalization of this conclusion is subject to improved experimental results of reactions between zinc-organic complexes and soils. Among the soil characteristics, which include maximum adsorption capacity and bonding energy related coefficients for the various ions, the maximum adsorption capacity is the most important one in determining Zn uptake.

¹ Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 140-E, 1980 series.

² Soil Scientist, Div. of Soil Chemistry & Plant Nutrition, A.R.O.

³ Biomathematician and Agricultural Economist, respectively, Div. of Statistics & Experimental Design, A.R.O.

Received for publication April 8, 1980. Accepted for publication July 21, 1980.