Calcium and Al interactions and soybean growth in nutrient solutions

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Abstract
The effects of Ca and Al on shoot dry mass and total root length of two cultivars of soybean (Glycine max (L.) Merr.) were evaluated in a nutrient solution culture experiment. The experiment consisted of a factorial design comprising varying levels of Ca (ranging from 50 to 2500 μM), and Al (ranging from 0 to 588 μM). Relatively poor correlations were observed between measured plant growth parameters and individual monomeric Al species, this being ascribed to the interactive effect of Ca and Al. However, highly significant coefficients of determination were found where both Al and Ca activities were considered simultaneously. The best fit of the data was obtained when plant response was plotted against Calcium Aluminum Balance (CAB = [2log(Ca2+)] ‐ [3log(Al3+) + 2log(AlOH2+) + log(Al(OH)2 +)]). Increasing Al levels in solution significantly depressed Ca, Mg, P and Mn concentrations in the shoots over all Ca treatments. There was no relationship observed between shoot concentration Al and the activities of Al3+, AlOH2+ and Al(OH)2 +. A highly significant relationship existed between Ca levels in the shoots and the derived CAB expression, indicating that the Ca content of soybean shoots is controlled by the interaction between Ca and Al monomeric species in solution.