Influence of FeEDDHA and soil temperature on the growth of two soybean varieties

A greenhouse study was conducted to compare the growth of Lee and Bragg soybeans (Glycine max L. Merr.) on a calcareous soil at different soil temperatures (16 and 24°C) and FeEDDHA-Fe levels (0 and 2 μg Fe/g soil). Both varieties developed leaf chlorosis without the added chelate but Lee plants were more chlorotic. In addition, trifoliate leaves of Bragg without added FeEDDHA had crinkled leaf surfaces which were curled at the distal ends. This leaf distortion was worst on older leaves, was more pronounced at the lower temperature, and was completely absent in Bragg treated with FeEDDHA. In Bragg, some leaf distortion and associated cellular changes observed with scanning and transmission electron microscopy were not the same as the typical Fe deficiency syndrome found in Lee; these differences are believed to result from Mn toxicity in Bragg. High levels of Mn, 337 and 261 μg Mn/g in Bragg and Lee tops, respectively, accumulated without added FeEDDHA at 16°C; the corresponding values in the presence of FeEDDHA were 21 and 18 μg Mn/g, respectively. The visual symptoms and the Mn plant data support the hypothesis that the leaf distortion observed in Bragg without added FeEDDHA was due to Mn toxicity. The FeEDDHA x soil temperature interaction for plant Mn concentration was highly significant and reflected the fact that the lower soil temperature caused a decrease in plant Mn concentration only when FeEDDHA was applied. Bragg accumulated more Fe than Lee, especially when FeEDDHA was present.