Effect of increasing levels of aluminium on roots of rice grown in nutrient solution

Abstract

The effect of aluminium levels (0 ppm, 0.5 ppm, 1 ppm, 2 ppm, 4 ppm and 8 ppm) on the growth of rice (Oryza sativa L.) (IAC-25) was studied under greenhouse conditions. Treatments were applied fifteen days after seed germination. Weekly, pH and Al⁺⁺⁺ levels were measured, and the nutrient solution was changed. After three weeks plants were harvested, oven dried, and shoots and roots weighted. The dry weight of the shoots increased with increasing Al level in solution, reaching a maximum at the 8 ppm level. The dry weight of roots also increased but differences were not significant among the three highest levels of Al. Al levels did not affect the tiller number but led to an increase in root volume. Root cation exchange capacity (CEC) decreased significantly with increasing Al levels. At 8 ppm, CEC was only 48,6% in relation to control. There were positive correlations between shoot dry weights, solution pH (r = 0.960**) and root volume (r = 0.910*). Correlations were negative between root CTC, shoot dry weight (r = 0.970**) and root volume (r = -0.970**). The decrease of the CEC of roots may be due to the irreversible blocking of root charges by Al. The positive effect of Al on plant growth, was considered to be due to this blocking of charges on the activity of H₂PO^-₄ and NO^-₃ at the plasmalemma.