Manganese and iron toxicities dependent on soybean variety

Tolerances to Fe and Mn were determined with Bragg and Forrest (Mn‐intolerant) and T203 and Lee (Mn‐tolerant) soybean (Glycine max. (L.). Bragg was Fe efficient; Forrest and T203 were equally Fe‐inefficient plants. The soybeans were grown in nutrient solutions with 1.0 and 2.0 mg Fe/liter, and with 0.33 and 5.1 mg Mn/liter as variables, respectively. Bragg soybeans developed Fe toxicity symptoms with 2.0, but not with 1.0 mg Fe/liter. Forrest, Lee, and T203 did not develop Fe toxicity symptoms on either treatment. Bragg and Forrest soybean developed more severe Mn‐toxicity symptoms than Lee or T203 soybean when grown on nutrient solutions with 5.1 mg Mn/liter. Approach grafts showed that Mn tolerance appears to be controlled in the plant tops. Both Mn‐intolerant and tolerant soybean tops contained about the same concentration of Mn, but Mn‐tolerant tops contained more K and roots contained less Fe than Mn‐intolerant tops and roots. When Fe and Mn toxicities are not economically correctable, tolerant soybean varieties may be selected in order to make the plant compatible with the soil.