Classification and evaluation of soils formed from diorite gneiss for sustainable land use in south western Nigeria

Abstract

The soils formed from diorite gneiss in Lagelu Local Government Area of Oyo State were studied and mapped for  sustainable land use. A flexible grid survey was used to map the soils. Soil units were determined and boundaries were  created for each unit based on morphological characteristics observed on the field using a soil auger. Representative  profile pits were dug, and soil samples were collected for laboratory analyses. The results showed that soils at the crest  and mid slope position have digenetic origin ranging from sand to sandy loam topsoil. The topsoil was underlaid with  saprolite separated by gravelly layer and waterlogged at the crest. The soil was moderately rich in cation especially at  the upper horizons compared to subsoil with CEC varying from 9.29 -14.21cmol/kg with high SAR in the saprolite. The  three soil units identified include Origo, Majerokun series (Lithic Epiaquepts and Gleyic Eutrudepts respectively) and  Matako series (Typic Fluvaquent). The suitability evaluation showed the units were suitable for lowland rice cultivation.  The upland was marginally suitable for arable crops except for cassava (not suitable). The management of the upland  for arable crops will include high ridge and basin drainage for removal of excess water. The nutrient maps showed that  pH varied from moderately acidic to neutral, N was low to moderate, P was low to medium, K was moderate to high, and  C was low to high. Thus, for sustainable land use, crop residue management and land use type that increase carbon  sequestration are recommended.