Sand culture experiments were conducted to evaluate the role of the plant and phosphorus substrate concentration in the possible phosphorus-induced changes in micronutrient availabilities. Beans, corn, tomatoes, and sour orange seedlings were grown 6 weeks or more under controlled sand culture conditions with P concentrations being maintained at 1 ppm. P, 10 ppm. P, and 100 ppm. P. The micronutrients were uniformly added to all P solutions in amounts calculated to produce concentrations of 0.25 ppm. of B and Mn, and 0.05 ppm. of Cu, Mo, and Zn. Iron, as magnetite, was incorporated with the sand.
No P-induced Zn or Cu deficiency occurred in any of the plants tested. In case of citrus, the levels of Zn within the plant actually increased with increasing substrate P. Of all plants tested for possible P-Cu antagonisms, only citrus exhibited a reduction in Cu uptake. Boron, Fe, Mn, and Mo were similarly studied. High P substrate concentrations may restrict the movement of Mo and Fe in some plants. Variable results were noted for B and Mn.
Regarding mechanisms of P-induced Zn or Cu deficiency, the experiments suggest that the plant is not exclusively involved; reactions occurring outside of the physiologically active root contribute to the induced deficiency.