Slope-soil Relationships on an Aberrant Toposequence in Ife Area of South Western Nigeria: Variabilities in Soil Properties

Okusami, T. A. ; Oyediran, G. O. (1985)


Soils located on the upper-slope segment of a toposequence were studied to observe their properties and evaluate thc slope-soil variabilities thereof. In addition, the soils were classified. This toposequence has no middle-slope soils that normally occupy physiographic units between those soils formed in upper slope in-situ materials and Gambari series (Smyth and Montgomery, 1962). The soils studied occupy summit but crestal position (FBI), the lower crestal position (FB2), and the physiographically slightly sloping lower upper-slope segment (FB3, FB4 and FB6) of the landscape. They are located on 2%, 5%, 3%, 2.5% and 3% slopes respectively. All the soils belong to Iwo series with the greatest soil morphological variabilities expressed in the BC, and in C horizons. : Typically, the surface horizons (0-30cm) range from dark yellowish brown (10 YR 314 or 414 to dark brown (7.5 YR 518). A typical B horizon is strong brown (7.5 YR 518) with a depth range of 35-95cm. Soil physical and chemical properties mostly show statistically insignificant differences between soils located on different physiographic/slope positions. However, there are significant differences in chroma between FB3, FB4 profiles and others. Significant differences exist between some of the soil profiles for their silt content. Soils are mostly in the strongly acid to extremely acid range. Exchangeable Mg is the least variable (C.V. of 9.1%) of the exchangeable cations. These soils are classified as Paleustults in the USDA system with an equivalent of Ferric Acrisols and Ferric Lixisols in the FAO-Unesco system.