THE MICRONUTRIENT CATIONS IRON, MANGANESE, ZINC, AND COPPER

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Abstract
Tomato plants, previously grown for 2 weeks in a dilute nutrient soln., were used in 24-hr. absorption expts. in which the roots were immersed in aerated suspensions of Ca-H bentonite containing micronutrient cations at low degrees of saturation. Fe55 59, Mn52, and Zn65 were used as tracers. For all 4 elements, uptake was approx. a linear function of the degree of saturation below approx. 0.1% saturation. Raising the Ca/H ratio on the clay from 25% Ca saturation (suspension pH 4.5) to 92% (pH 7), at constant levels of micronutrient cations, increased the uptake of Mn over the entire range, and of Fe except at the highest Ca/H ratio, and decreased the uptake of Zn. These findings are discussed in terms of complementary ion effects at both clay and root surfaces. Increasing Mn concns. at a fixed Fe level raised Fe uptake by the roots and diminished its transloca-tion to the shoot.