Alleviation of aluminium phytotoxicity on soybean growth by organic anionsin nutrient solutions

The effect of aluminium (Al) phytotoxicity on the growth of soybean (Glycin e max (L.) Merr.) cv. 'Forrest' in nutrient solutions (pH 4.25) and its all eviation by organic anions has been investigated. Both 100 and 500 mu M Al caused significant reduction in root and shoot lengths and root dry weights over 15 days. Citrate, oxalate, tartrate, malate, malonate and lactate at 1000 mu M and humic acid at 1 g L-1 were used to alleviate phytotoxicity ca used by the presence of 500 mu M Al. The effectiveness of the organic anion s in alleviating Al phytotoxicity, measured by the change in root length, w as in the order oxalate > citrate approximate to tartrate approximate to ma late > malonate >> lactate. Humic acid at 1 g L-1 proved almost as effectiv e as 1000 mu M citrate. When the remaining fraction of phytotoxic aluminium was measured by the aluminon method and the results combined with calculat ed values obtained from stability constant data, the order of effectiveness of complexation was citrate > oxalate > tartrate approximate to malate app roximate to malonate >> lactate. It was concluded that benefits other than from simple complexation of phytotoxic aluminium were provided by the organ ic anions. Three of the anions were also used at different concentrations; these were citrate and oxalate (at 250, 500 and 1000 mu M) and humic acid ( at 0.01, 0.1 and 1.0 g L-1). For citrate and oxalate, it was found that the concentration of the organic anion must be at least that of the Al to redu ce phytotoxicity significantly, and twice as much oxalate as citrate was re quired to achieve the same reduction in phytotoxicity.