Aluminium (Al) is a major component of most soils and is a limiting factor to sustained crop production in many regions. The amelioration of Al toxicity is of theoretical as well as practical interest in our understanding of mechanisms of toxicity. The effect of Al and calcium (Ca) on root length, shoot and root dry mass of two soybean (Glycine max(L.) Merr) cultivars, Hill and Forrest, was evaluated in a nutrient solution culture experiment. The experiment consisted of a factorial design comprising varying levels of Ca (50, 250, 1 250 and 2 500 #x3BC;M Ca as CaSO4. 2H20), Al (0, 148, 296 and 588 #x3BC;M Al as AI2(SO4)3. 18H20) and the two soybean cultivars. At pH 4,0 these treatments resulted in predicted activities of monomeric Al species in solution in the range of 16#x2013;92 #x3BC;M for Al3+, 47#x2013;257 #x3BC;M for AISO4+, 1,6#x2013;9,3 #x3BC;M for AIOH2+and 0,1#x2013;4,6 #x3BC;M for AI(OH)2. Very poor correlations were observed between measured plant growth parameters and individual monomeric Al species in solution, this being ascribed to the interactive effect of Ca on Al phytotoxicity and the presence of the less phytotoxic species AISO4+. However, highly significant coefficients of determination were found where both the molar activities of Ca2+: AI3+and the ratios of Ca: AI on a concentration basis were considered. Increasing Al levels in solution significantly depressed Ca, Mg, P, Mn and Zn concentrations in the shoots. No relationship between Al concentration in the shoots and the activities of various monomeric Al species was observed. A highly significant quadratic function (R2= 0,956) was found between the Ca concentration in the shoots and the ratio of the molar activities of Ca2+: AI3+.
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