Characterization and suitability assessment of soils underlain by mica-schist for yam and cocoyam production in rainforest area Southwestern, Nigeria

Abstract

This study was conducted to assess the suitability of the soils underlain by mica-schist for sustainable production of yam and cocoyam. The study was carried out in 2014, in an area located approximately between 7^o32′ N and 7^o33′ N and longitudes 4^o32′ E and 4^o40′ E within the Teaching and Research Farm (T&R-F) of Obafemi Awolowo University (OAU), Kajola, Ile-Ife, Nigeria. Four profile pits were established, described and sampled with one at different physiographical units following the guideline for soil profile description according to FAO/UNESCO (2006) 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 yam and cocoyam to obtain the soils’ suitability classes using parametric method. The result 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 3.8 – 5.4 pH KCl) with low to moderate amounts of organic matter (1.2% to 2.9%) and available nitrogen (0.07 – 0.2 %). Available phosphorus varied from 2.0 – 10.6 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. The result showed that all the soil mapping units were permanently not suitable (N2) for cocoyam and yam production for actual suitability evaluation. With the appropriate fertility management, the soils of mapping unit 2 was classified as moderately suitable (S2) for yam production while soils of mapping units 1 and 3 were classified as marginally suitable (S3) for yam production. Soils of mapping unit 4 was classified as presently not suitable (N1) for yam production. After improvement for cocoyam production, soils of mapping unit 1 and 2 were classified as marginally suitable (S3) while soils of mapping units 3 and 4 were presently not suitable (N1). The soils were limited by wetness, texture, shallow depth and low fertility (N, P and K). Therefore, Combined application of organic fertilizer with guided inorganic fertilizers (N-P-K) should be encouraged for optimum productivity.