Title Page. ii

Certification. iii

Dedication. iv

Acknowledgment. v

Table of contents. vi

List of tables. vii

List of figures. viii

Appendix. x

Abstract xi


1.0 Introduction. 1


2.1 Development of Soils. 4

2.2 Characteristics of Floodplain Soils. 5

2.3 Genesis of Floodplain Soils. 8

2.4 Effect of annual flooding and drying on soil formation. 10

2.5 Utility of floodplain soils. 12

2.6 Soil classification.



3.0 Location of the study area. 15

3.1 Climate and Vegetation. 15

3.2 Geology and soil 16

3.3 Field work. 18

3.3.1 Field reconnaissance. 19

3.3.2 Materials.

3.3.3       Method. 19

3.4 Laboratory Analyses. 20

3.4.0 Physical Properties. 20 Particle size analysis. . 20 Moisture content 20 Saturated Hydraulic Conductivity (Ks). 20 Dispersion Rates (DR). 20 Infiltration Rates (IR). 21

3.4.1 Chemical Properties. 21 pH.. 21 Exchangeable acidity. 21 Total nitrogen. 21 Soil organic carbon. 21 Available phosphorus: 21 Exchangeable bases. 21 Cation exchange capacity. 22 Trace elements. 22 Base saturation. 22 Exchangeable sodium percentage. 22

Carbon/Nitrogen Ratio (C/N). 22

3.5 Statistical Analysis. 23

3.6 Soil classification. 23



4.1 Morphological Properties. 24

4.2 Soil morphology. 39

4.3 Physical Properties.

4.4 Colour. 43

4.5 Physical properties. 44

4.6 Chemical Properties. 61

Soil pH.. 61

Available phosphorus. 61

Organic Matter. 61

Exchangeable Bases. 62

4.7 Clay minerals. 62

4.8 Heavy Metals or Trace Elements. 63

4.9 Soil Genesis. 64

4.10 Soil Classification. 65

4.11 Management Suggestions. 66



5.1 Suggestions for further research. 68



The soils of Api-River flood plain in Opi, South-eastern Nigeria were studied to investigate the morphological characteristics and determine the pedogenic processes that are contemporaneous and to propose management systems for the sustainable cultivation of the land. 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.


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. Soil morphology provides a long term record of hydric period and soil aeration and is widely used to identify wetlands. Many wetlands experience only short periods of saturation and some are never flooded. Delineating these drier areas through direct observations of saturation or flooding is inconvenient and expensive (Megonigal et al., 1993). As a result, soil profile and plant community characteristics are heavily relied on for indirect evidence of flooding regime. Hydric soils are commonly identified by the presence of one or more field indicators including a low chroma matrix or a surface horizon high in organic matter. Chroma is the relative purity of the particular spectral colour or the degree of vividness in contrast to greyness (Ibanga, 2006). The matrix chroma of a mineral horizon in the top 30cm must be less than 1 when mottles are absent or less than 2 when mottles are present to satisfy hydric soil criteria. The use of field indicators to determine moisture regime assumes that strong correlations exist between redox potential, oxygen content, water table depth, and physical features such as chroma. These relationships, however, will break down if microbial activity is limited by pH, temperature, or low organic matter (Megonigal et al., 1993). It is important to verify that hydromorphic features are quantitatively related to redox processes and soil saturation, given their widespread use for wetland identification. Soil colors have been found to be related to the level of water saturation during the year. Fletcher and Veneman, (2005) found out that, soils without excess water during the year are usually aerated. The effect of soil moisture regime is recognized in soil genesis and classification and also in plant nutrition. Akamigbo (1981) observed that several complex factors including soil erosion and flooding contribute to the decline in the use of soils. Flooding most often keeps the soil more or less permanently waterlogged, thus limiting their potential use and the level of development in areas so affected. Flood plain soils are of special interest to many earth scientists. According to Gerrard (1992), flood plains occupy a significant proportion of the earth’s surface, approximately 2% of Africa. Although alluvial soils are generally associated with river-flood plains but they are difficult to define satisfactorily. This is because they may have developed on fluvial, lacustrine or marine deposits. Thus alluvial soils occur on coastal plains, deltas, rivers terraces and alluvial fans as well as river flood plains. Soils on river terraces are often called alluvial but many river terraces are comparatively old and soils formed on them are often well developed and completely different from soils on recent fluvial sediments. Gerrard (1992) also stated that the geomorphological development of flood plains has a tremendous effect on soil development. The temporal development of soil types follows a chronology imposed by the deposition of flood plain sediments, while such soils are strongly affected by a variety of landforms, relief, texture and moisture status of flood plains. A well-executed study of pedogenesis in this respect will provide information on the properties and nature of the soils of the area and how these properties influence or are influenced by flooding. It will also make available information on the land resource characteristics of the area, based on which conclusion can be drawn on the most appropriate land use to ensure sustained productivity of the soil as well as the appropriate control measures to adopt. Lack of detailed information of soil and land characteristics had been one of the major factors limiting agricultural development in the tropics (Okusami et al., 1987). This is particularly true of soils formed in alluvial sediments in Api River flood plain of Eastern Nigeria where agricultural activities are very intensive. Not much work has been done about the Api River flood plain soils. The production of vegetables like Telferia occidentalis and other crops like cocoyam (Colocasia esculenta) etc is very high at Api river flood plain soils. The farmers there also grow other crops like cassava (Manihot esculenta) and yam (Dioscorea spp.) depending on the characteristics of the soil type. Research Objectives The major objective of the study was to study the morphology and characteristics of the Api River flood plain soils in order to infer the pedogenic processes that are contemporaneous in the soils and to propose different management systems for the sustainable cultivation of the lands. The specific objectives of the study were to: a. study and characterize the different profiles representing the physiographic mapping units of the flood plain; b. and infer the cotemporary pedogenic processes; c. classify the pedons according to USDA and FAO/WRB classification system; and; d. recommend management practices.


Morphology of flood plain soils Morphology deals with spatial distribution pattern of the soil characteristics. Morphological characteristics are used to distinguish between different soils and they are used in classification of soils (Soil Survey Staff, 1998). Goemorphological studies have a beneficial impact on the accurate mapping and classification of soils by developing an appreciation for regional soils landscape relationships. Geomorphological studies reveal the sequence of geomorphologic events that affect the age and parent material factors of soil formation, (Parsons and Herriman, 1976). Standard soil morphological descriptions have been quantified and combined in a soil profile development index for evaluating soil development (Gobin, et al., 2000). They also observed that morphological variables like texture, iron stone, and soil color account for most of the definite variations of the soils and provide an efficient means of characterizing tropical soils derived from sedimentary parent materials. Farmers often describe soils in combinations of single morphological characteristics e.g. (red sand or stone) and often relate their decision making on land use and management to these soil descriptions. Every soil has its specific inherent natural properties. The highest groundwater levels and water table fluctuations are routinely estimated by soil scientists from a soil’s morphology and the consistence of the soil. Gray colours are associated with saturated and chemically reducing soil environments, while yellowish brown colours are related to generally aerobic and chemically oxidizing conditions. Soils without any excess water during the year usually are aerated and yellowish brown coloured soils with high water tables during some part of the growing season exhibit gray colouration at the depth of the high water mark and below (Fletcher and Veneman, 2005). 2.1 Processes of soil development. Soil is a product of interaction between climate, parent material, relief and organism over a period of time. Its formation involves complex pedogenic processes ( Boul et al., 1997) such as addition, losses, translocation, and transformation. While climate and organism actively influence soil formation, topography indirectly affects rates of pedogenesis and distribution of soil nutrients (Onweremadu and Mbah, 2009). A large number of processes are responsible for formation of soils (Pidway, 2006). The pedogenic processes, which represent collectively the physical, chemical and biological processes in soil, determine the characteristics of the resulting soil. According to Anderson (1997), pedogenesis is concerned with the process that determines the morphologically significant properties, such as horizons of clays or sesquioxide enrichment and leached horizons. It also influences the functional properties of soil, such as the ability to retain and recycle nutrients, the environment for soil micro flora, and the medium presented to a developing root. Boul et al. (1997) considered soils to be formed by basic processes of addition, removal, transformation and transfer after an initial step of parent material deposition. For a particular soil, the relative importance of these processes varies and the result is the variety of profiles seen in any landscape. Most pedologists have recognized the influence of topography on soil properties (Moorman, 1981; Akamigbo and Asadu, 1986). Different results have been obtained from toposequence studies of different areas. Topography may bring about the difference in soil properties of some related soils. This sequence is referred to as a toposequence (Brady, 1974) which has been defined by Juo and Moormann (1981) as a succession of soils from crest to valley bottom which contains a range of soil profiles that are representative of the landscape and soils. Toposequences have been used by many pedologists to characterize soils (Akamigbo and Asadu, 1986). According to Akamigbo and Asadu (1986), in the work they did at Opanda, Eha-Amufu, and Nkpologu, topography in combination with other soil forming factors affect the depth or thickness of soil solum, particle size distribution, organic matter content, cation exchange capacity, total exchangeable bases and exchangeable acidity.