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Diffusion of Iron and Iron Chelates in Soil¹

ABSTRACT

The importance of diffusion in moving Fe to plant roots was estimated by theoretical calculations. In plant studies chelates increased the diffusion and uptake of Fe by increasing the concentration gradient of diffusible Fe to sorghum roots (Sorghum vulgare). Uptake of Fe increased linearly with the concentration of Fe in solution.

Self-diffusion coefficients of Fe and Fe chelates were determined in both aqueous media and soil. In aqueous media, the diffusion coefficients were 6.2 x 10^-6 cm²sec^-1 for Fe, 5.4 x 10^-6 cm²sec^-1 for FeEDDHA, 4.2 x 10^-6 cm²sec^-1 for FeDTPA, and 3.9 x 10^-6 cm²sec^-1 for FeEDTA. In soil, a correction factor was used to adjust the apparent porous system self-diffusion coefficients. The corrected diffusion coefficients in soil were 1.5 x 10^-7 cm²sec^-1 for Fe and 1.85 x 10^-7 cm²sec^-1 for FeEDDHA.

¹ Contribution from the Department of Agronomy, Colorado State Univ., and Northern Plains Branch, Soil & Water Conserv. Res. Div., ARS, USDA. Part of a dissertation submitted by the senior author in partial fulfillment of a graduate program in Soil Science for the Ph.D. degree. Published with the approval of the Director of the Colorado Agr. Exp. Sta. as Scientific Series Paper no. 1556. This work was supported in part by the Division of Agricultural Development, Tennessee Valley Authority, Muscle Shoals, Ala.

² Graduate Research Assistant; Professor of Soil Science, Colorado State Univ.; and Research Soil Scientist, USDA, Fort Collins, respectively. Senior author is now Assistant Professor of Soil Chemistry at New Mexico State Univ., Las Cruces.

Received for publication July 7, 1970. Accepted for publication January 21, 1971.