ADDITION of chelating agents can increase Mn2+ activity (pMn2+). in soil solution and thus increase Mn uptake and plant growth. This study aimed at evaluating soybean growth and Mn2+ uptake in ethylenediaminetetraacetic acid (EDTA), or trans- 1,2-diamineciclohexane- tetracetic acid (CDTA) buffered nutrient solution. Varied levels (0.1, 0.32, 1.00, 3.16, 10.0 and 32.0 μM) of Mn, while constant concentrations of all other micronutrients, in combination with EDTA, or CDTA were imposed to soybean (Glycine max L.Merr.) in solutions with pH 6.0. Plant dry matter (DM) increased with increasing activity, not the total concentration of Mn and was highest at pMn2+ 8.0-8.1 in EDTA- and CDTA-buffered solutions. With pMn2+ >8.0, plant leaves accumulated higher Mn2+, but 80-87 mg Mn2+ kg-1 DM seemed sufficient for optimum plant growth. With pMn2+ < 8.0, the concentration remained at the optimum level in the CDTA-buffered solution, whereas in the EDTAbuffered solution leaf Mn2+ concentration was in the range 193-241 mg Mn2+ kg-1 DM. At pMn2+ < 8.0, leaf Ca2+ and Mg2+ were higher with MnCDTA than with MnEDTA. Leaf Fe3+ concentration remained constant and did not significantly change in response to Mn availability. Fe: Mn ratio decreased with increasing Mn availability in the EDTA and CDTA solutions. CDTA-buffered solution offers a strong control of plant uptake of Mn2+ due to its strong control of the free concentrations of Mn2+, Ca2+ and Mg2+ under conditions of limited Mn availability.