CHARACTERIZATION AND EVALUATION OF FOUR TOPOSEQUENCES IN EHA-ALUMONA, EASTERN NIGERIA

ABSTRACT

Inadequate information on the influence of landscape on soil properties is a major factor limiting agricultural production in Nigeria. In order to characterize and evaluate four toposequences at Eha-alumona, Eastern Nigeria, soil properties were studied. On each toposequence, three profiles were sited one the on crest, mid slope and valley bottom. Standard routine analysis was carried out on the samples collected.  The result showed that soil pH was consistently the least variable along the toposequence and at all depths. Highly variable properties on the upper slope (crest) include: CEC, base saturation, exchangeable H₂; on the middle slope (hill slope) they were exchangeable K, CEC, base saturation and exchangeable H₂; and on the toe slope (valley bottom ) they were available P. CEC, base saturation and exchangeable H₂. The moderately variable properties on the middle slope were Ca, Mg, ECEC and N. For the physical properties, clay, silt and total sand were highly variable on the upper slope. Notable differences were found to exist among the various properties evaluated. Variations in soil properties exist and were due to topographic positions and horizon depths. The study also show that the midslope suffers surfacial erosion while the foot slope and the summit do not, instead, they gain organic and inorganic matter enrichment.  Most properties were highly to moderately variable, thus, uniform soil management practices along the toposequence should be avoided.  The soils of toposequence one were classified under USDA sub-order as Lithic Haplustults (crest), Arenic Fragiustults (mid-slope) and Aquic Kandiustults (toe slope). The soils of the toposequence 2,were classified as Arenic Kandiustults (crest), Arenic Kandiustults (mid-slope) and Arenic Kandiustults (toe slope). For toposequence 3, they were classified as Arenic Haplustults (crest), Arenic Kandiaquults (mid-slope) and Grossarenic Kandiaquults (toe slope). At the upper slope of toposequence 4, the soils were classified as Petroferric Haplustults, mid slope as Typic Kandiustults and the foot slope as Aquic Kandiustults The above soils correlate with Acrisols under FAO-UNESCO Soil Classification.  Toposequence one and four were moderately suitable, while toposequence two and three were marginally suitable for arable crop production.

TABLE OF CONTENTS

Title page               –           –           –           –           –           –           –           i

Acknowledgement         –           –           –           –           –           –           ii

Certification    –       –           –           –           –           –           –           –           iii

Dedication      –            –           –           –           –           –           –           iv

Abstract       –           –           –           –           –           –           –           v

Table of Contents   –           –           –           –           –           –           –           vii

List of Tables            –           –           –           –           –           –           –           ix

CHAPTER ONE: INTRODUCTION               –           –           –           –           1

CHAPTER TWO: LITERATURE REVIEW      –             –           –           4

2.1 Toposequence.         –           –           –           –           –           –           –           4

2.2 Effects of Topography on Soil Properties and Soil Formation     –           5

2.3 Effects of Parent Material on Soil Properties and Soil Formation           6

2.4 Soil Classification –           –           –           –           –           –           –           –           7

2.5 Soil Classification Systems              –           –           –           –           8

2.6 The United States Soil Taxonomy              –           –           –           –           9

2.7 FAO/UNESCO System    –         –           –           –           –           –           10   

2.8 Soil Evaluation      –                 –           –           –           –           –           –           18

CHAPTER THREE: MATERIALS AND METHOD    –           –           –           20

3.1 Location    –           –           –       –           –           –           –           –           20

3.2 Geomorphology    –                    –           –           –           –           –           22

3.3 Climate      –           –            –           –           –           –           –           –           22

3.4 Vegetation            –         –           –           –           –           –           –           23

3.5 Agriculture                 –           –           –           –           –           –           –           24

3.6 Soil Samples          –    –           –           –           –           –           –           –           24

3.7  Particle Size Distribution –       –           –           –           –           –           –           24

3.8 Bulk Density         –                  –           –           –           –           –           –           24

3.9 Erodibility Index  –           –           –           –           –           –           –           25

3.10   pH Determination          –           –           –           –           –           –           25

3.11  Organic Carbon  –             –           –           –           –           –           –           25

3.12 Total Nitrogen     –           –    –           –           –           –           –           –           25

3.13 Available Phosphorous   –       –           –           –           –           –           25

3.14 Exchangeable Bases           –           –           –           –           –           25

3.15 Exchangeable Acidity     –          –           –           –           –           –           25

3.16 Cation Exchange Capacity (CEC)  –           –           –           –           –           26

3.17 Base Saturation   –               –           –           –           –           –           –           26

3.18   Co-efficient of Variation (CV) –          –           –           –           –           26

 3.19 Limitation Method         –     –           –           –           –           –           27

CHAPTER FOUR: RESULTS AND DISCUSSION              –           –           28

Summary and Conclusion       –           –    –           –           –           –           –           59

REFERENCES        –           –           –            –           –           –           –           61

APPENDIX   –           –           –           –           –           –           –           –           65

LIST OF TABLES

Table 1: Morphological properties of the toposequences        -29

Table 2: Soil erodibility- assessed by clay ratio (sand + silt)/clay ratio -33

Table 3: Land quality and characteristics       –           –           –           –      34

Table 4: Physical Properties    –           –           –           –           –               –           36

Table 5 Bulk density and total porosity values              –           –           –           39

Table 6: Chemical Characteristics Of Representative Profiles           –           42

Table7: Classification of the pedons studied  –           –           –           –           –  44

Table 9: Variability in Physical Properties along the Toposequence One (Isi-enu) — – 46

Table 10: Variability in Chemical Properties along the Toposequence One 47

Table 11:  Variability in Physical Properties along the Toposequence Two (Akwari-enu) –           –           –           –           –           –           –           –           49

Table 12: Variability in Chemical Properties along the Toposequence Two 50

Table 13: Variability in Physical Properties along the Toposequence Three (Akwari-ani)  –           –           –           –           –           –           –           –           52

Table 14: Variability in Chemical Properties along the Toposequence Three            –           –           –           –           –           –           –           53

Table 15: Variability in Physical Properties along the Toposequence Four (Eha-ndiagu)   –           –           –           –           –           –           55

Table 16: Variability in chemical properties along the toposequence Four 56

Table 17: Overall Variability in Chemical Properties along the four Toposequences            –           –           –           –           –           –           –           57

CHAPTER ONE

INTRODUCTION

            Characterization of soil provides a useful means for understanding soil distribution and variability. The modern soil survey is a fundamental basis for land use planning because it contains both qualitative and quantitative data which enable predictions of many kinds to be made. It aids in correlating and predicting the adaptability of   various crops, grasses, and trees, to soils and their behaviour and productivity under different management. Field studies that depict the variability and distribution of soil are panacea for total utilization of a given tract of land. Such understanding enables useful prediction to be made wherever such soils occur making it possible for soils of different parts of the world occurring under similar and different climatic condition to be compared (Buol et al 1980). Soil characterization goes beyond soil testing, it is an integration of both physical and chemical nature of soil. It analysis the inherent characteristics and properties of a given soil with the aim of characterizing them into similar soil units and capability land use units.

            Soil suitability evaluation involves characterizing the soil in a given area for specific land use type. The information collected in soil survey helps in the development of land-use plans and to evaluate and predict the effects of the land use on the environment. The suitability of a given piece of land is its natural ability to support a specific land use type. Suitability may be a major kind of land use, such as rain fed agriculture, livestock production, forestry, etc.  

            As these qualities derived from the land characteristics,  such as slope angle and length, and soil texture which are measurable or estimable, it is advantageous to use these latter values to study the suitability. For assessing the suitability of soils for crop production, soil requirements of crops must be known. Also, these requirements must be understood within the context of limitations imposed by land form and other features which do not form a part of the soil but may have a significant influence on use that can be made of the soil (FAO,1976).

            Soil classification on the other hand helps to organize our knowledge and facilitate the transfer of experience and technology from one place to another and to compare soil properties. It provides a link between soil characterization and soil survey. According to Lark and Wheeler (2000), variation in soil properties has long been known and had been the subject of much research. It was in recognition of this that Sir Ronald-fisher, and then at Rothamsted, developed a formidable array of statistical methods.

            Accordingly, horizons may differ in organic matter content, structure, texture, pH, base saturation, cation exchange capacity as well as many other soil physicals and chemical properties. According to Mullar and Mc Bratney (2001), variability in soil properties at the series level is often caused by small changes in topography that affect the transport and storage of water across and within the soil profile. Hunter et al (1982) and Yost et al (1982) reported that soil-forming factors affect different properties differently at different depths. Variability of soil pH, for e.g. increases with depth (Ogunkunle and Ataga, 1985). Ogunkunle (1993) working on Alfisols of southwestern Nigeria, observed that soil pH was the least variable (low variability) property, irrespective of depth. The variability of properties like organic matter, available phosphorus, total nitrogen and CEC, increases with depth. Properties, such as soil pH and porosity are among the least variable, while those pertaining to water or solute transport are among the most variable. Percentage sand ranges from low to moderate variability. Organic matter and % clay range from moderate to high variability. Available phosphorus and potassium were observed to be highly variable (Jury, 1986 et al, Beven et al, 1993, Wollenhaupt et al, 1997).  In general the more variable these properties, the more variable the crop growth and yield. Thus, understanding soil variability is essential in applying location specific (precision-agriculture) management strategies. Therefore, the general objective of this study was to assess the degree of variability of some soil physical and chemical properties along four toposequences

 for assessing their agricultural potentials.

The specific objectives were to: (i) characterize and classify the soils of  four toposequences.  (ii) assess the effects of slope characteristics on physico-chemical properties.

(iii) evaluate the agricultural potentials of the four toposequences.

CHAPTER TWO

LITERATURE REVIEW

            Spatial variability of various soil properties is inherent in nature due to soil forming factors: relief, parent material climate, organisms and time. These factors give soil profiles their distinctive characteristics.  Due to these usual processes, soil physical properties vary from one point to another across landscapes. Despite the deviation, spatial variation is not random but tends to follow a certain pattern in which the variability decreases with decrease in distance between points along the landscapes. Two samples close to each other are more likely to have small differences and those far apart do have big differences, while those much further apart are likely to be independent of each other (Lucian, 2008). However sampling at wider sample spacing may be sufficient for relatively homogenous landscape while sampling at short intervals may be needed if the soils are quite heterogeneous.    

2.1 Toposequence.

 Toposequence is a sequence of related soils from the hill top to the valley floor. Farmers often cultivate the entire toposequence. Some however, restrict their cultivation to only a section of it. In spite of these reported variability in soil properties and crop yield along the toposequence, recommendation for agronomic practices are often made to farmers without due consideration for specific topographic locations that might influence the management options such as fertiliser rate and types, tillage operations and herbicides application (Oluwatosin et al, 2001). This brings about sharp variations in crop yield. It is a known fact that an understanding of the basic soil properties is essential for developing soil management practices that will maintain the productive potential of a soil. Appropriate and proper use of an area of land depends upon the characteristics of such land. Soil topography plays a major role as one of the factors that influence pedogenesis and in the process that dictates the distribution and use of soils on the landscape.  Esu et al 2008). Topography or local relief controls much of the distribution of soils in the landscape to such an extent that soils of markedly contrasting morphologies and properties can merge laterally with one another and yet be in equilibrium under existing local conditions.  Many of the differences in soils with variable topography are due to some combination of microclimate, pedogenesis, and geologic surfacial processes.  The soils differ as a result of erosion, transportation, and deposition of surficial material as well as leaching, translocation and deposition of chemical and particulate constituents in the soil.  These processes result in morpho-logical changes, associated with soil color (grayness) and horizonation as a result of changes in hydrology related to topographic position (Hall, 1983). 

2.2 Effects of Topography on Soil Properties and Soil Formation

            Three main components of topography have been recognized by Gerrard (1981) to affect soil movement processes. These are the slop e steepness, slope angle and slope length.

Gerrard (1981) reports that generalized relation between slope angle and soil properties reveals that for acidic soils, pH decreases with increasing slope gradient. According to him an inverse relation exists for all soils (acidic and calcareous) between slope angle, and percentage nitrogen and carbon. He further observes that percentage silt and clay decline with increasing slope angle.

Jenny (1980) specifically reports highly significant correlation between percentage nitrogen and slope length. Gerrard (1981) concludes that good statistical relationships exist between many soil properties and slope and position but points out that the relationships are not sufficiently well established to enable efficient models to be constructed.

Local soil variations in texture, colour, mottling soil wetness etc. are often associated with topographic changes, although there is not always a one-to-one correspondence these changes he argues may be associated with geological erosion and the associated deposition on hill side, the exposure of different parent materials and variation in site drainage.

Gerrard (1981) asserts that difference in drainage is responsible for the gradual colour changes that are frequently seen in catenae. In support of his assertion he refers to many West Africa catenas where the colour of the upland, well drained soil is usually reddish brown-the colour showing the presence of non-hydrated iron oxide in the soil. The colour as he observes changes from reddish brown to orange brown on the midslope then to yellowish brown and sometimes yellow on the lower slopes. On the lowest slope the soils are usually bluish grey, greenish-grey in colour.

According to Pregitzer et al (1983) soil nutrient status varies along with soil development and is strongly related to topographic positions.

2.3 Effects of Parent Material on Soil Properties and Soil Formation

            Parent material is the material that soil develops from and may be rock that has decomposed in place, or material that has been deposited by wind, water or ice. The character and chemical composition of the parent material plays an important role in determining soil properties especially during the early the stages of development. Parent material composition has a direct impact on soil chemistry and fertility. Those rich in soluble ions-calcium, magnesium, potassium and sodium are easily dissolved in water and made available to plant.

                        Soil erodibility which is known to relate to the degree of soil development can be assessed by the use of clay ratio (Bouyoucos 1935). He defined the clay ratio as (sand + silt) /clay and emphasizes that it correlates with soil erodibility. From his studies, soils with low clay ratios (ratios less than 11.2) are considered non-erosive hence stable or well developed while soils with high values (ratios greater than 11.2) are considered very erosive.

            According to Buol et al (1980) bulk density can be used to determine the degree of weathering and alteration of C horizons as the bulk density drops from values near 2.0gm/Cm³ with increasing weathering and associated development of voids furthermore, it can be used to evaluate volume changes during soil genesis as either gains or losses from specific horizon.

2.4 Soil Classification

             Soil classification deals with the systematic categorisation of soils based on distinguishing characteristics as well as criteria that dictate choices in use. The purpose of any classification is to organize our knowledge, so that the properties of objects may be remembered and their relationships may be understood most easily for a specific objective.

One of the primary aims of soil classification systems as proposed or employed by Russian pedologists since the time of Dukuchaev’s first soil classification is to group the soil according to their productivity and utilization problems, and to determine, compare, and explain their fertility differences.  We classify soil in order to: organise knowledge (economy of thought), show relationship, remember facts better, and establish groups for practical purposes Iniobong (2003). One of the major problems facing pedologists is the choice of soil properties on which to base the separation of classes. Many soil properties can only be described quantitatively, such as colour, structure, consistence, degree of drainage, while others are very difficult and very expensive to measure. The choice of which properties for use, therefore, depends on the objective of the classification, which can be special or general. Fitzpatrick (1980) attributes the present confusion and non-international agreement on soil nomenclature and classification to the complex nature of soils, lack of adequate knowledge of many soils and the aims of soil classification which are often not clear. One of such great difficulties in soil classification is that soils rarely exist as discrete individuals with clear boundaries.    

            The most useful soil classification is a general one that can be interpreted accurately for a wide variety of uses. These include interpretations in terms of plant adaptability and sustained yields under alternative sets of practices and in terms of the suitability of the soils.

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