ABSTRACT

Characterization, classification and evaluation of soils in Osisioma Ngwa, South Eastern Nigeria was carried out. A preliminary reconnaissance survey delineated the study area into three (3) mapping units based on toposequence namely, floodplains, gentle slopes and crests. Flexible grid method was adopted to identify different physiographic units of the area. Nine profile pits: three at floodplains, four at gentle slopes and two at crest were dug; described and examined to represent the study area. Soil samples were collected from genetic horizons. Soil map was produced in a GIS environment, using morpho-physical and soil chemical properties. The results indicated a moist top soil colour of greyish brown (7.5YR 5/2) to brownish grey (5YR 5/1) epipedons over greyish brown (5YR 6/2) endopedons that had dark reddish brown (5YR 5/6) to yellow orange (7.5 YR 7/8) redoximorphic features (mottlling) for floodplain soils. The gentle slope mapping units had dark reddish brown (5YR 3/2) to brown (10YR 4/6) epipedons over yellowish brown (10YR 5/6) endopedons. Crest mapping units had dark reddish brown (5YR 3/3) to dull reddish brown (2.5YR 4/4) epipedons over reddish brown (2.5YR 4/6) to bright brown (2.5YR 5/8) endopedon. Physically, floodplain units had an almost equal proportion of sand (140-550gkg-1), silt (140-570gkg-1) and clay (190-460gkg-1). Sand particles were more dominant in the surface soils of gentle slopes and crest units (580-880gkg-1). Chemically, the soils of floodplain unit were moderately acid (pH 5.3 – 6.4). The gentle slope and crest physiographic units had strongly acid reactions (pH 4.7 – 5.5). At floodplains basic cations were medium (1.4 – 2.6 cmolkg-1) for Ca, low (0.4 – 2.63 cmolkg-1) at gentle slope and crest, high for Mg, moderate for K and low for Na in all mapping unit. Cation Exchange Capacity in the study area was low to moderate (5.1 – 9.8 cmolkg-1) at floodplain and crest (5.4 – 10.7 cmolkg-1), but moderate to high (5.5 – 16.2 cmolkg-1) at the gentle slopes. Total Nitrogen was high (0.5-5.4 gkg-1) at the floodplain, but low at the gentle slope (0.1-0.9gkg-1) and crest (0.1- 0.8gkg-1).  Available phosphorus was low to medium. Floodplain soils were characterized by adequate micro-nutrients (Cu, Fe, Mn, Zn). At the gentle slopes and crest micro-nutrients were marginal to adequate. The fertility capability classification of soils in the study area indicated that floodplain soils had loamy top soils having less than 35% clay sub soils and evidence of gleization. Gentle slopes and crest had Sandy (S) top soils with fertility problems. Land Capability classification placed the floodplains under capability class III and capability subclass IIIw with limitations in poor drainage (wetness). Gentle slopes were placed capability class IV and capability sub-class IVf, while crest as capability class IV and capability sub class IVft due to limitations of fertility and slope. The soils are fit for crop cultivation under good management. Major pedogenic processes in: floodplains include leaching, gleization.  Gentle slope and crest units include erosion, illuviation, lessivage, braunification, and leaching. The floodplain soils were classified as Fluvaquentic Eutrudept (USDA) and Fluvisol (FAO-UNESCO). Gentle slopes and crests as Arenic Kanhapludults  (USDA) or Acrisol (FAO-UNESCO).

TABLE OF CONTENT

Title page                                                                                                                                i

Declaration                                                                                                                             ii

Acknowledgements                                                                                                                iii

Dedication                                                                                                                               iv

Table of content                                                                                                                      v

List of figures                                                                                                                         vii

List of tables                                                                                                                           viii

CHAPTER 1: INTRODUCTION

1.1       Objectives of the Study                                                                                              4

CHAPTER 2: LITERATURE REVIEW

2.1       The Pedogenic Concept                                                                                              5

2.2       Physiography and Soil Formation                                                                              9

2.3       Properties, Formation and Development of Alluvial Soils                                        12

2.4       Properties of Coastal Plain Soils                                                                                13

2.5       Agricultural Potentials of Coastal Plain Soils and Alluvial Soils.                                     14

2.5.1    Key environmental problems of coastal plain soils and alluvial soils                 15

2.5.2    Managing coastal plain soils in southeastern nigeria                                                 16

2.6       Land Evaluation                                                                                                         16

2.6.1    Land capability classification (LCC)                                                                         17

2.6.2    Fertility capability classification (FCC)                                                                     21

2.7       Micronutrients in Soils                                                                                               24

2.8       Soil Classification                                                                                                      26

CHAPTER 3: MATERIALS AND METHODS

3.1       Study Area                                                                                                                  26

3.1.1    Geology and parent material                                                                                      28

3.1.2    Climate                                                                                                                       28

3.1.3    Vegetation and land use                                                                                             28

3.2       Sampling Technique/Design                                                                                      29

3.3       Laboratory Analysis and Procedures                                                                          31       

3.3.1    Physical analysis                                                                                                         31

3.3.2    Chemical analysis                                                                                                       31

3.4       Soil Classification                                                                                                      32

3.5       Land Evaluation                                                                                                         33

3.5.1    Land capability evaluation                                                                                         33

3.5.2    Fertility capability classification (FCC)                                                                     35

3.5       Statistical Analysis                                                                                                     35

CHAPTER 4: RESULTS AND DISCUSSION

4.1       Morphological Characteristics                                                                                   36

4.2       Physical Characteristics                                                                                             40

4.3       Chemical Characteristics                                                                                            45

4.4       Land Evaluation                                                                                                         51

4.4.1    Fertility capability classification                                                                                51

4.4.2   Land capability classification                                                                                      56

4.4   Classification of Soils in the Study Area.                                                                       60

CHAPTER 5: CONCLUSION AND RECOMMENDATION

5.1       Conclusion                                                                                                                  62

5.2       Recommendation                                                                                                       63

REFERENCE

APPENDICES

LIST FIGURES

1. Map of study area showing sampling locations.                                                    28

2. Fertility capability classification map of  Osisoma Ngwa L.G.A. Abia State    53

3. Land capability classification map of Osisioma Ngwa L.G.A. Abia State.   58

LIST OF TABLES

3.1: Coordinates of Selected Sampling Locations in the Study Area.                                    31

3.2: Simplified Conversion Table of USDA Land Capability Classification Different

       for Tropical Soils                                                                                                             35

4.1: Morphological Characteristics of Soils in Different Physiography in Osisioma Ngwa,

       South Eastern Nigeria                                                                                                      38

 4.2: Physical Properties of Soils in the Study Area                                                               42

4.3: Chemical Characteristics of Soils on Different Physiographic Unit in the Study Area            47

 4.5: Checklist showing Type, Substrata Type and Modifiers                                               51

4.6: Fertility Capability Classification (FCC) of Identified Physiographic Units of

       Osisioma, South Eastern Nigeria.                                                                                    54

Table 4.7: Land Capability Classification of Osisioma Ngwa                                               55

LIST OF PLATES

 1.        Soil profile pit                                                                                                 84

CHAPTER 1

INTRODUCTION

Soil characterization provides information on land evaluation based on its potential and limitations to guide policy formulation on use and management of land resources for various competing uses. According to Esu (2004) and Egbuchua (2011) soil characterization for agricultural purposes does not only establish relationship between soil properties and land form, but also gives initial information on the nutrient status, limitations and ensure sound judgment on how soils respond to specific use. Onyekwere (2017) remarked that characterization of soils is helpful in the appraisal of soil productivity.

Terrain attributes are widely used for digital soil mapping because relief is an important factor in soil formation. According to Wilson (2012) and Zhang et al. (2012) common terrain characteristics involve elevation, topography, wetness, aspect, profile curvature, and slope index. Terrain characteristic are normally used to describe the landscape morphology and predict its effect on environmental processes. Nsor and Akamigbo (2014) posited that slope steepness is among most important factors that cause variation in soil characteristics. They further remarked that soils of valley bottom were averagely better than those of middle slope and crest in important fertility indices. The type of soil formed in a particular place is related to relief or toposequence of the area (Nsor, 2017). Akpan-Idiok et al. (2013) noted that deposition of fine and coarse sediments is in the floodplains due to floodwater deposit. Hossain et al. (2011) observed that soils formed on floodplains are different in their morphological, physical and chemical attributes from adjacent locations, which may be because of its sedimentation age, drainage, mineralogy and topography.

The estimation of land potential for alternative uses is known as land evaluation. Evaluation of natural resource is important for maximum use of land and to stop degradation. A reasonable land use plan is obtained through a precise and confident land evaluation method. There are several methods of land evaluation such as parametric methods, maximum limitation method and fuzzy sets method (Sharififar et al., 2016). The result of land evaluation is a document that should provide a technical basis for decision-making on optimal land use, whether private or public. Fuzzy sets methodology gives a more realistic output in comparison with the Boolean approach (Nisar-Ahmed et al., 2000).

The physical evaluation reveals the nature of limitations and hazards, which is useful information to the land manager. However, the economic evaluation reveals the expected economic benefits, which in general drive the decision-making process, or at least are a sina qua non for successful land use (Chang and Ko, 2014).

The essence of land evaluation is to predict inherent capacity of land unit to support a specific or general purpose land use for a long period without deterioration (De Ia and Van, 2002). Evaluation of land resource, their management and planning, therefore, has become an important component of sustainability throughout the world. Land evaluation may enhance soil productivity and overall sustainability. In developing countries, land evaluation systems in agriculture are based on qualitative interpretation, though this may rest with the user. The final decision as to which alternative use land is to be put rests with the user.

Land capability is degree of appropriateness for general use. Thus, they help in answering questions for managing a transition towards a more environmentally efficient and sustainable

land use and evolve better information on world scale that impacts land use decisions (Foley et al., 2005).

Fertility capability classification is land evaluation based on categorizing of soils according to the type of limitations they present (Akamigbo, 2010). Sanchez et al. (2003) remarked that fertility capability classification focuses attention on surface soil properties most directly related to management of field crops and is best used as an interpretative classification with more inclusive soil classification. It seeks to evaluate important physical, chemical and morphological soil properties that are important towards soil fertility management. This system of land evaluation group soils base on type of limitations they provide for agronomic management of its physical and chemical properties (Boonme, 2005). Fertility capability evaluation of soils is intended to highlight the potentials of these soils in terms of texture of the top and sub soils as well as its limitations (modifiers) specific to crop production.

Agricultural productivity has been on the decline in recent time. This might be due to inadequate soil information on soil characteristics, continuous nutrient mining through crop uptake, wrong land use policy and poor soil management. This study however seeks to provide soil information on the soil characteristics and to evaluate the capabilities of the soils on diverse physiographic terrains in the study area. This will facilitate proper land use and overall agricultural productivity of the area. This underscores the need for this study with the following objectives.