Chemical forms of plant and soil iron as influenced by soil moisture

Abstract

Experiments were conducted to determine whether soil moisture content has an effect on the chemical forms of plant and soil iron. Soybean plants, variety Lee, were grown on Adelanto loam soil under greenhouse conditions. Two different moisture levels, 75 per cent and 120 per cent of the moisture equivalent, were maintained in soil samples placed in individual containers. The same moisture treatments were used for separate soil samples on which the test plants were grown. Soil iron forms were determined in the moisture-treated soil by using different extracting agents. A significant decrease in soil iron extracted with 10−4 M EDTA from soil at the high moisture level was attributed to a relative increase in the free calcium ion. Soybean plants grown under the high moisture level were chlorotic while those under the low moisture level were green in appearance. Plant samples were taken at two stages of growth for subsequent analysis. The chemical analysis of the leaf tissues have shown the presence of equal amounts of total iron and less amounts of water-soluble and “active iron” in chlorotic tissues as compared to non-chlorotic tissues. The difference found between chlorotic and non-chlorotic plants in the amount of iron in the water extract was in the trichloroacetic acid-soluble fraction. The water- and salt-soluble protein nitrogen was approximately the same in chlorotic and non-chlorotic leaves.