Heavy-Metal Nutrition and Iron Chlorosis of Citrus Seedlings.

The recent widespread increase in iron chlorosis on acid, sandy soils in Florida has led to studies of the underlying causes. The leaves on affected trees are deficient in iron (10). Field observations show that tree condition can be substantially improved by liming. Additions of iron sulphate to the soil has not improved tree condition noticeably. Recently foliage condition improved when small quantities of chelated iron were used (12). It is not known yet whether soil applications of this material will promote the rehabilitation of the topsoil fibrous root systems, which have been severely damaged in all cases investigated. The heavy metals Cu, Zn, and Mn accumulate in the topsoil of citrus orchards despite its very sandy and acidic nature (8). This accumulation is independent of that of phosphate, which takes place simultaneously (8). These metals, as well as others, may interfere with Fe metabolism of plants (3, 5). Little is known about the fundamentals of heavy-metal nutrition of citrus. There is actually little information on the relative toxicities, antagonistic reactions, or the nature and extent of the accumulation of heavy metals in roots of any plant. Much additional research is needed to elucidate the processes of their absorption and accumulation. The present studies were made with the hope that some information on these aspects of nutrition could be gained and it is felt that the results presented will contribute toward this end.