Characterization and suitability assessment of the soils of Iwo series for cocoa production in rainforest area Southwestern, Nigeria

Abstract

Characterization and soil suitability assessment is a vital tool for understanding the nature and status of soils. It is one of the strategies for achieving food security as well as sustainable environment. This study was conducted to assess the suitability of the soils of Iwo series for sustainable production of cocoa. The study was carried out in 2022, in an area located approximately between 7°32' N and 7°33' N and longitudes 4°32' E and 4°40' E within the Teaching and Research Farm (T&R-F) of Obafemi Awolowo University (OAU), Kajola, Ile-Ife, Nigeria. Three profile pits were established, described and sampled with one at different physiographical units following the guideline for soil profile description according to FAO/UNESCO guideline. The soil samples collected were analyzed for particle size distribution, pH, total nitrogen, available phosphorus, exchangeable bases, and organic matter using standard method. Land characteristics obtained were matched with the crop requirements for cocoa to obtain the soils’ suitability classes using parametric method. The results showed that all the soils are well drained and deep. The texture of the soils ranged from sandy loam to sandy clay loam at the surface and sandy clay loam to clay at subsurface. Soil reaction ranged from highly acidic to slightly acidic (4.2-5.8 water and 3.9- 5.7 pHCaCl2) with low to moderate amounts of organic matter (0.4 to 1.74%) and available nitrogen (0.02-0.14%). Available phosphorus varied from 0.52-24.77 mg/kg in all the horizons in the profiles with the highest values at the surface soil horizons, an indication that soil organic matter contributes significantly to the available P in these soils. The exchangeable bases were low and the relative abundance of the exchangeable bases followed the order: Ca> Mg > Na>K at the exchangeable site. Suitability evaluation of the soils was carried out using parametric approach and the result showed that the soils of mapping units A and B are presently not suitable (N1) while mapping unit C is marginally suitable for cocoa production. With the appropriate fertility management, the soils of mapping unit A were classified as marginally suitable (S3) while soils of mapping unit B and C were classified as moderately (S2) for cocoa production. The limiting factors were mainly low soil fertility (low level of available phosphorus, macro-nutrients, nitrogen and organic matter). Therefore, combined application of organic fertilizer with inorganic fertilizers should be encouraged for optimum productivity.