Abstract
The study characterised and classified soils derived from coarse-grained granite and gneiss and assessed their suitability for cacao production. Four soil profile pits were established along a toposequence underlain by coarse-grained granite and gneiss and described following the FAO/UNESCO guidelines for soil profile description. Soil samples were collected from 18 identified genetic horizons of the profile pits and were subjected to routine physical and chemical characteristics determination. Land characteristics recognised on the field were combined with those determined in the laboratory to provide the land qualities in the study area. The land qualities obtained were matched with cacao requirements to obtain the soils' suitability classes. Suitability classes obtained were combined to produce aggregate soil suitability classes using the parametric approach. Results indicated that the soils are deep, well-drained, dark brown to reddish yellow in colour, varying from sandy-clay-loam to clay. The silt/clay ratio of the soils was > 0.15 indicative of young soils with high degree of weathering potential. The soils were strongly acidic, highly leached with low to moderate nutrients content. Soil organic carbon content and total nitrogen varied from low to high, ranging from 0.08 - 1.64% and 0.01 - 0.14%, respectively with low to medium available phosphorus. The high base saturation of greater than 50% by NH4OAc placed all the pedons in the order Alfisols (USDA Soil Taxonomy) and correlate as Lixisol (FAO/UNESCO). All the pedons had kandic subsoil with ustic moisture regime and isohyperthermic temperature. The soils were presently marginally suitable (S3) but potentially highly suitable (S1) for cacao production. Their major limitation to cacao production was low fertility (high soil acidity, low organic matter, Ca and Mg contents). The productive potential of the soil for cacao production could be enhanced through the application of appropriate fertilisers.
