Iron, the Limiting Element in a Chlorosis: Part II. Copper-Phosphorus Induced Chlorosis Dependent upon Plant Species and Varieties

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Abstract
Field and greenhouse expts. showed that the elements most consistently affected in a comparison of chlorotic and nonchlorotic leaves were Cu, P, and Fe. Cu and P were higher and Fe lower in chlorotic than in nonchlorotic leaves. Under the conditions of these experiments, increasing additions of P did not affect the absorption or utilization of Fe, to the extent that chlorosis developed, unless Cu was also present in the growth media. Copper and P were more effective in producing chlorosis if applied together, than if either element was applied separately. Plant species and varieties investigated differed in their susceptibility to this Cu-P induced Fe chlorosis. The concn. of P was higher in the sap of chlorotic than nonchlorotic soybeans. It did not differ appreciably in the residue of these plants. More P was absorbed by the plants as the rate applied to the growth medium increased. This resulted in a proportionately greater concn. of P in the sap than in the plant residue. Chlorosis-susceptible and nonsusceptible plants differed in their Fe requirements and deficiency symptoms when grown in soln. cultures with different kinds and rates of Fe as variables. Chlorosis-susceptible soybeans required a higher concn. of both inorganic and chelated iron in the soln. cultures than the nonsusceptible variety to prevent Fe-deficiency chlorosis. Several factors are discussed with reference to the cause and susceptibility of plant species to chlorosis.