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A Computer Simulation of Fe(III) and Fe(II) Complexation in Limited Nutrient Solution: I. Program Development and Testing

Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506

W. L. Lindsay

Dep. of Agronomy, Colorado State Univ., Fort Collins, CO 80523

* Corresponding author.

ABSTRACT

The mechanism by which Fe-stressed roots increase Fe availability was determined with the assistance of a computer model (written in PASCAL) that predicted the effects of redox and pH on the stability of Fe chelates. The program solves a series of simultaneous equilibrium equations to calculate the concentrations of all species in a nutrient solution containing Fe, Ca, and two competing chelating agents as a function of pH and redox potential. Experimental data were used to test the model. Model calculations based on results published by other investigators supported the theory that Fe-deficient soybean [Glycine max (L.) Merr.] plants have the ability to lower the redox potential near their roots. It also showed that this phenomenon is the primary means by which iron-stressed plants are able to increase the availability of Fe. The redox potential of a nutrient solution at pH 5 must be below pe + pH 7 to account for observed trends in the stability of ferric chelates and the availability of Fe to soybean.

Joint contribution from Colorado and Kansas Agric. Exp. Stn. Kansas Agric. Exp. Stn. no. 88-183-J. Funded in part by the Tennessee Valley Authority.

Received for publication November 12, 1987.