Comparison of different methods for diagnosis of iron deficiency in avocado

Iron chlorosis is a very common disorder of crops grown in calcareous soils. It is well known that the total iron concentration in leaves is not a valid index for iron nutritional status of crops and that the total iron concentration in chlorotic leaves are often similar or even greater than in the green leaves. In this study, we compare three extraction methods for iron deficiency diagnosis in young (two month old) avocado leaves: 1.5% phenanthroline (pH 3) extraction from fresh leaves, 1 N hydrochloric acid (HCl) extraction from fresh leaves, and 1N HCl extraction from oven-dry leaves. Relationships between the total and extractable iron concentrations in the leaves with the leaf color were examined by linear regression analysis. These regressions were statistically significant for the total iron and in the case of all three methods tested. However, the correlation coefficients suggest that phenanthroline extraction from fresh leaves was superior over other methods for diagnosis of iron deficiency in avocado.