Mineral Composition of Chlorotic Orange Leaves and Some Observations on the Relation of Sample Preparation Technique to the Interpretation of Results.

Certain types of chlorosis of leaves of green plants' are universally attributed to deficiencies or unbalanced conditions of one or more of the essential mineral elements. Agreement does not always exist, however, as to whether a specific type of leaf-symptom pattern is related to total content of the deficient element or only to a specific fraction of it. This is particularly true of the presumed deficiencies of iron and zinc where sample selection, contamination, and poor precision of analytical procedures are all complicating factors. An extensive review of all previous work is beyond the scope of this report. JACOBSON (8) and LINDNER and HARLEY (10) point out some of the more pertinent discrepancies with respect to iron content and iron chlorosis. More recently McGEORGE (11) reports the lack of any apparent relationship between total Fe or Zn and the appearance of the specific deficiency symptoms for these elements in citrus, pear, and several other plants. Other studies have occasionally shown this same result in the case of Fe; but JACOBSON (8) found that surface contamination was a factor of major importance in producing discrepant results. When pear leaves from trees grown in calcareous soil were carefully washed in dilute HCI, a correlation was found between the low total Fe values found and the iron chlorosis shown. BENNETT (1) confirmed this observation with further studies, although he found a stronger relationship of chlorosis to an acid-soluble, or "active"'Fe fraction than to the total. In Florida (6), New Zealand (7), and elsewhere citrus trees showing typical zinc deficiency symptoms have been found to contain less total zinc in their leaves than leaves from healthy trees. In Florida when the acidity of the topsoil of the Lakeland and related series drops below pH 5.0 (between 4.5 and 5.0) for a considerable length of time, citrus trees may become unthrifty in appearance, sparsely foliated, and show typical iron-chlorosis leaf patterns. This interveinal chlorosis condition strongly resembles the lime-induced iron chlorosis pattern (2) and that associated with poor drainage. Exploratory tests in small containers showed that reducing the acidity by treatment with the carbonates of Ca, Na, or K (or extracting the soil with NH4-acetate) all resulted in the disappearance of this symptom in young citrus seedlings. In connection with this general problem, some analyses were made to determine the mineral composition of leaves from trees affected with this type of chloro496