The Evaluation of Iron Deficiency Using a Bioassay-type Test

Experiments to establish a bioassay-type pot test for the evaluation of iron deficiency in soils were performed. Peanut plants cv. Shulamit were grown in small pots (500 g of soil) for 5 weeks in six soils varying in CaCO₃ content from 3.6 to 63.0%. Control and FeEDDHA (ethylenediamine di-o-hydroxyphenylacetic acid) treatments were employed. Chlorophyll content of the leaves was measured at the end of the growth period. A significant linear correlation was found between the relative chlorophyll content of leaves (FeEDDHA = 100) and the total CaCO₃ or active lime content (r = 0.892 and 0.940, respectively). Chlorosis was completely remediable with the addition of FeEDDHA. A mountain rendzina soil containing 63% CaCO₃ caused the most severe chlorosis. An experiment was conducted in which the chlorophyll content of FeEDDHA-treated and untreated peanut plants grown on this soil was compared. This experiment was repeated at three different times of the year. Some variability was found in chlorophyll content of either treated or untreated plants when absolute numbers were compared. However, when chlorophyll content of the untreated plants was expressed as percent of that of FeEDDHA-treated ones, the resulting relative values for the three growth periods were as close as 46.8, 41.7, and 45.0%. The same soil was used for further experimentation with the screening test. Three genotypes of peanuts were tested for Fe-sensitivity: Congo Red, Virginia Bunch Improved, and Shulamit. Congo Red was found to be the most sensitive cultivar as known from former field studies. Iron-enriched peat was prepared in our laboratories and tested as a possible remedy for iron deficiency of Shulamit peanuts grown on the rendzina soil. A positive response curve of plant chlorophyll to iron-enriched peat dosage was obtained reaching levels comparable to FeEDDHA. The growth chamber pot test described provides a simple and efficient tool for the following purposes: (i) screening soils for potential chlorosis problems in peanuts and possibly other plants; (ii) screening peanut cultivars for iron efficiency; and (iii) screening iron-containing fertilizers, and roughly estimating their efficiency and application rates. The iron-enriched peat which was first tested in this work exhibited positive and promising effects.