ABSTRACT
The need to establish a sound scientific basis for subsoil studies using a geoelectric method for locating sites best suited for cocoa (Theobroma cacao) production is highly expedient considering recent scientific trends. An integration of geoelectrical and geological investigation was carried out with a view to assessing the relationship between subsoil parameters and cocoa production output on fifteen (15) selected farm-sites across different communities in Ondo State, currently ranking as highest producer of Cocoa in Nigeria. This is with the aim of delineating the subsurface geological sequences, determining their geoelectric parameters, identifying the composition of subsurface layers and soils best related for high yield of cocoa. The studied sites which are located on the Precambrian Basement complex and the Dahomey Basin, southwestern Nigeria, showed from the geoelectric sections a total of between three to five (3-5) subsoil layers comprising the topsoil, the weathered or fractured basement/cretaceous sediments layers, and imfinite depth basement bedrock. The well-drained clayey loam/loamy and clayey sand/sandy clay weathered/partially weathered subsoil groups coincided with high cocoa produce data zones. Granite Gneiss - Grey Gneiss and Charnockites rock groups make up the geology in these areas. While the weathered - partially weathered columns that are characterized as sands and plastic clay subsoils within the Schist/Granite Gneiss rock groups coincided with areas where cocoa are reported to have short life span and cocoa produce data is low. We concluded that fairly thick subsoil spectrum from the topsoil to weathered - partially weathered column, formed from the weathered products from rock units including Grey Gneiss - Charnockite rocks, make up the most important underlying lithologic units most suitable for optimal cultivation of cocoa crop in the study area.