A sand culture experiment was conducted at the University of Agriculture, Makurdi, Nigeria, in 2001 and 2002, with the objective of determining the appropriate levels of aluminium activity to screen tropically adapted genotypes of soybean for aluminium stress tolerance. Fifteen genotypes of soybean constituted the main plot, while eight levels of aluminium activity (0, 50, 100, 200, 300, 400, 450 and 500 μMAl³⁺) constituted the subplots in a split-plot design. The experiment was replicated three times. Plants watered with the 500 μMAl³⁺ treatment got burnt after 3 to 5 days and were removed from the treatment. Data were taken on the root dry weight, shoot dry weight and relative root surface area at 25DAP. Aluminium, genotype and genotype × aluminium interaction effects were all highly significant. Aluminium activity at 300 μMAl³⁺ level along with the control (0 μMAl³⁺) were considered as appropriate for root dry weight, while the 450 μMAl³⁺ level along with the control (0 μMAl³⁺) were considered as appropriate for shoot dry weight and relative root surface area and recommended for the rapid screening of tropically adapted genotypes of soybean in sand culture in the tropics. The relative root surface area was the most sensitive in discriminating between levels of aluminium activity and should have preference in any selection programme.

Key words: Aluminium activity, sand culture screening, tropically adapted genotypes of soybean.