Abstract

The potential of the agroforestry species Gliricidia sepium, as a liming material needs to be investigated in the search for alternatives to slash and burn agriculture. Lime (CaCO₃) and organic residue in the form of Gliricidia sepium prunings, were incubated with an acid, P deficient ultisol from Sierra Leone at different rates to target pH values 5.0, 5.5, and 6.3 for 70 day. Although in several cases the target pH values were not met, the rates of application of the amendments, based on soil pH buffer capacity and neutralising value of the amendment, decreased the Al saturation from 89% to less than 10%. While CaCO₃ often decreased P, Mg and K availability in the soils, Gliricidia prunings increased these essential nutrients.  The Al-sensitive and Al-tolerant maize genotypes subsequently grown for 28 day in the amended soils following incubation decreased the soil pH, but also decreased the Al saturation by markedly increasing the effective cation exchange capacity of the soil.

Key words: Aluminium toxicity, soil acidity, maize growth, liming, aluminium tolerance, P availability, Gliricidia sepium, agroforestry.