Evaluation of Differences in Tolerance to Aluminium Toxicity among some Tropical Cowpea (Vigna Unguiculata) Genotypes.
E. A. Akinrinde and K. N Ezeh. Agronomy Department, University of Ibadan, Ibadan, Nigeria, Otolowa village, Off Iwo Road, Ibadan, Nigeria
Aluminium (Al) toxicity is widespread in tropical and temperate acid soils. Eight cowpea (Vigna unguiculata) genotypes, G (Ife brown, IT87D-941-1, IT99K-1060, IT84S-2246-4, IT96D-610, IT93K-452-1, IT86D-719 and IT98D-810) were grown for 5 and 17 weeks (1st and 2nd experiments) and evaluated for their differential tolerance to 0, 20 and 50 ÁM AlCl3 levels applied prior sowing in an Alfisol (Typic Paleudalf). Plant height at weekly intervals (from 2 weeks after planting, WAP), yield and post-cropping soil chemical parameters (pH, extractable-Al, extractable-Mn and available P) were estimated. Except at 2WAP, Al effect was insignificant (P<0.05) on plant height, though extractable-Al differed greatly (P<0.01) among soils sampled after cropping, suggesting need to test higher rates and/or continuous application through irrigation water. On the contrary, G and G x Al interaction significantly affected plant height, yield, soil pH, P-availability and Al tolerance potential. Plants of IT93K-452-1 variety were taller (71.6 cm + 3.38) than individual plants of the other varieties at all Al application levels. Aluminium extracted from treated and untreated soils correlated linearly with Al addition levels, but not with the plant performance or other soil chemical parameters. Complexity in the soil environment increased with Al addition to the extent that crop performance became unpredictable and increasingly variable among the genotypes as tolerance to Al became more crucial. Biomass production (followed by pod weight) was the most sensitive parameter to Al addition while extractable Al changed maximally among the soil chemical parameters. The genotypes were categorized into efficient or non-efficient and tolerant or non-tolerant/susceptible types.