MORPHOLOGY, CHARACTERIZATION AND CLASSIFICATION OF SOILS OF API-RIVER FLOOD PLAIN IN OPI, SOUTHEASTERN NIGERIA

ABSTRACT

To achieve this purpose, six profile pits were studied on two selected physiographic units which were selected based on the differences in relief/physiography of the area after a reconnaissance survey. Soil samples were collected from the pits, horizon by horizon. Surface samples 0-15cm depth and subsurface samples 15-30cm depth, were collected from around the pits. The surface and subsurface samples were used for fertility evaluation. The chemical and physical properties of the soils were analysed in the laboratory. They were also analysed for heavy metals. Core samples were collected from inside the profile pits at the depth ranges of 0-25, 25-50, 50-75, and 75-100cm. The core samples were used to determine the hydraulic conductivity of the soils.

The colours of the moist soils ranged from dull yellow (2.5YR 6/3) to reddish brown (2.5 YR 4/3). The morphology of the profile pits differed. The pits closer to the river showed many layers indicating seasonal flooding of the area. Iron and manganese concretions were evident. Mottling was observed in almost all the pits. The result of the particle size analysis showed that the textures ranged from sand to sandy loam along the levee, and sandy loam to sandy clay loam on the back-swamps. Clay content was low ranging from 4-30% and increased with depth only in pit 5. Coarse sand which ranged from10-88% dominated fine sand which ranged from 10-85% in almost all the pits except in P2, and P3. The hydraulic conductivity was very slow (78.4-165.3cm/hr). Bulk density was low ranging from 1.46-1.65g/cm³. The chemical properties were low. The soil reactions ranged from  strongly acidic to moderately acidic with the pH ranges from 5.0-5.9. It had low Exch. Acidity 0.2-5.83, and low cation exchange capacity (C.E.C) ranging from 1.82-7.61. The clay mineral identified in the area was predominantly kaolinite using the C.E.C range.

The major pedogenic processes identified are elluviation, illuviatiion, and the soil was found to be young and still developing. The soils are classified as Entisols and Inceptisols using USDA Soil Taxonomy (2003) and correlated to FAO/WRB as Fluvisols and Gleysols. The following drainage practices were suggested, artificial, surface and subsurface drainage practices to suit land use. Use of organic matter was recommended to enhance the soils condition.

CHAPTER ONE

1.0 INTRODUCTION

The study of soil morphology is very important in characterizing and classifying soils. It is a very important attribute in determining whether a soil is a flood plain or not because soil morphology deals with the form and arrangement of soil features.  According to Marbut (2000), soil morphology is defined as the field observable attributes of the soil within the various soil horizons and the descriptions of the kind and arrangement of the horizons. He further stated that soil morphology is more reliable for soil classification than the theories of pedogenesis because theories of soil genesis are both ephemeral and dynamic.

The observable attributes ordinarily described in the field include the composition, form, structure, and organization of the soil, colour of the soil and features such as mottling, distribution of roots and pores, evidence of translocated materials such as carbonates, iron, manganese, and clay and the consistence of the soil. Field morphology starts with in-situ examination of a soil profile.

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