EFFECTS OF SILICON ON THE TOXICITY OF ALUMINUM TO SOYBEAN

The effects of soluble silicon (Si) on the toxicity of aluminium (Al) to soybean roots were investigated in solution culture. A weak nutrien t solution which included a low concentration of phosphorus (P) was sh own to be necessary to allow the full expression of Al toxicity. As so lution pH decreased below 6, reductions in root growth in the presence of Al became increasingly severe. Silicon alleviated the symptoms of Al toxicity, but the effective rate was dependent on pH. Greater conce ntrations of Si were required at lower pH where Al was more toxic. The se results support the hypothesis that the pH-dependent affinity of Si for Al in dilute solutions, and the consequent formation of sub-collo idal inert hydroxyaluminosilicate species, is the basis for the allevi ation of Al toxicity by Si.