Department of Soil Science

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Department of Soil Science

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Browsing Department of Soil Science by Author "Okusami, T. A."

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    Hydromorphism - Its Definition and Correlation between Three Major Classification Systems with Reference to West Africa
    (Faculty of Agriculture, University of Ife, 1985) Okusami, T. A.
    Hydromorphic soils may be defined simply as any wetland soil that will not support crops (or plants), with aerobic edaphic requirements, during the peak of the groundwater recharge. The influence of the water-table is largely controlled by the texture of the profile. This is of significance because the capillary fringe of any water-table may be as saturated as those horizons under the water-table, and this tends to increase the height of the groundwater. A depth of 100 cm. to a saturated zone is suggested as the depth below which a pedon ceases to become aquic or show features associated with hydromorphism that could limit the environment to anaerobic crops. For a general landuse purpose, a probable depth of 150 cm. is suggested as the depth beyond which a pedon ceases to become hydromorphic. Because hydromorphism does not preclude those soil forming processes peculiar to the well-drained upland soils, classification as outlined in Soil Taxonomy (USDA) could be appropriate for the classification of hydromorphic soils. The aquic prefix points to the influence of the water regime on the pedogenesis and properties of the soils concerned. Attempt at correlating the three systems, viz. USDA, FAO - UNESCO and French was made.
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    Slope-soil Relationships on an Aberrant Toposequence in Ife Area of South Western Nigeria: Variabilities in Soil Properties
    (Faculty of Agriculture, University of Ife, 1985) Okusami, T. A.; Oyediran, G. O.
    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.