Micromorphological and Mineralogical Evaluation of Ultisols Developed over Different Parent Materials in Northern Guinea Savannah, Nigeria

Micromorphological and Mineralogical Evaluation of Ultisols Developed over Different Parent Materials in Northern Guinea Savannah, Nigeria.

ABSTRACT

Micromorphological and mineralogical properties can provide insights and aid interpretation of soil classification. Field and laboratory studies were conducted on soil formed in two different parent materials in Plateau State.

With a view to characterize physical, chemical and morphological properties of selected soils, investigating the micromorphological and mineralogical properties of Ultisols derived from basalts and granite-gneisses, and determining if differences in properties could be used in the classification of Ultisols at the lower levels of Soil Taxonomy and World Reference Base (WRB).

Based on the geological map sheet used to identify different parent materials, eight (8) profiles were dung and described. Results obtained revealed that micromorphology of surface horizon in basaltic derived soils shows a porous (compound packing) and crumb microstructure.

The groundmass consists mainly of fine iron hydroxides in crystallitic micromass. In the subsoil horizons, the microstructure varied between vughs and channels with subangular shapes.

Compound coatings of radial distributed and isotropic (“amorphous”) iron hydroxides line the pores. In many cases, several coatings of isotropic iron hydroxides, differing in colour intensity, fill the pores. In granitic soils, surface horizon was mainly crumb with vughs and channels microstructure.

Complete infillings coating clay, orthic typic nodules and subhedral crystals, red and yellow mineral colour indicate finely dispersed hematite/some amorphous Fe gels and goethite respectively. The subsurface horizons were mainly vughy microstructure.

Anhedral to euhedral crystal mineral grains with interference colour, strongly impregnated groundmass iron hydroxides nodules (anorthic and orthic) with black dotted micromass.

On the whole, granitic derived parent material compares in terms of pedofeatures characteristics, speckled groundmass and vughy microstructures.

Micromophologically, old parent materials have porphyric c/f related distribution pattern, low c/f 2u ratios, poor sorting and common infilling and coatings of voids as compared to enaulic c/f related distribution, high c/f 2u ratio in young parent materials.

Similarly, self-mulching as a pedofeatures was observed in basaltic soils as opposed to granite parent material. The micromorphological properties of all soils are affected by their parent materials and genesis. The coarser textured soils have compact grain structure while the finer-textured soils have an apedal microstructure.

Mineralogical composition of the soils were similar (kaolinite, micavermiculite, chlorite, rutile, quartz, goethite, hematite and gibbsite) between parent materials but different in proportions, except for gibbsite and chlorite which was absent in granitic derived soils and quartz, rutile and halloysite were absent in basaltic soils.

According to the USDA system of classification, profiles BST01 and BST02 (basaltic PM) and GNT03 and GNT04 (granite PM) were classified as Typic Haplustults while GNT02 was Typic Plinthaquults.

The evidence of pedofeatures such as porphyric c/f and typic orthic nodules confirms highly weathered soils. Profiles BST03 and BST04 are classified as Andic Haplustepts and GNT01 as Oxic Haplustepts.

In the FAO/WRB system, profiles BST01 and BST02 are classified as Ferralic Acrisols, BST03 and BST04 as Andic Cambisols. While profiles GNT02, GNT03 and GNT04 are classified as Haplic Acrisols, GNT01 as Arenic Cambisols.

Therefore, the distinct differences in micromorphological features among these soils might be employed as diagnostic horizons to differentiate soils while the quantifiable micromorphological features might potentially be selected as diagnostic indices for soil taxonomic classification.

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TABLE OF CONTENTS

COVER PAGE……………. i

TITLE PAGE………………. ii

DECLARATION…………….. iii

CERTIFICATION…………………………… iv

ACKNOWLEDGEMENT……………………………………. v

ABSTRACT……………… vii

TABLE OF CONTENT………………. ix

LIST OF TABLES…………………………….. xiii

LIST OF FIGURES………………….. xiv

LIST OF PLATES……………… xv

CHAPTER ONE INTRODUCTION

1.1. Background Information……… 1

1.2. Justification………………………………………… 2

1.3. Objectives of the Study………………………… 3

CHAPTER TWO LITERATURE REVIEW

2.1. Importance of Micromorphological to Soil Genesis and Classification…………… 4

2.2. Influence of Parent Material on soil Macro and Micromorphological Properties….5

2.3. Influence of Parent Material on soil Physical Properties……………………………7

2.4. Influence of Parent Material on Chemical Properties………………………………8

2.5. Influence of Pedogenesis on Micromorphological Properties………………………10

2.6. Influence of Pedogenesis on Physical Properties……………………………………15

2.7. Influence of Pedogenesis on Chemical Properties……………………. …………….15

2.8. Influence of Parent Material on Soil Mineralogical Properties……………………. 17

2.9. Soil Classification………… 19

CHAPTER THREE MATERIALS AND METHODS

3.1. Physical setting of Study area………………………….21

3.1.1. Location……………………..21

3.1.2. Climate………………21

3.1.3. Vegetation and landuse……………24

3.1.4. Geology and geomorphology…………..24

3.2. Field Studies…………………26

3.2.1. Soil profile citing……..26

3.2.2. Morphological description…………26

3.2.3. Soil sampling……………26

3.3. Laboratory Studies………………..27

3.3.1. Sample preparation…………..27

3.3.2. Particle size distribution analysis…….. 27

3.3.3. Bulk density and porosity…………………. 27

3.3.4. Soil pH………. 28

3.3.5. Exchangeable bases, CEC and exchangeable acidity …………………………. 28

3.3.6. Cation exchangeable capacity (CEC) of the clay fraction………………………. 28

3.3.7. Effective CEC…………………………………….. 28

3.3.8. Bases saturation…………………. 29

3.3.9. Organic carbon (OC)…………. 29

3.4. Micromorphological Studies………………. 29

3.4.1. Preparation of thin section……. 29

3.4.2. Mineral identification………….. 31

3.4.3. Micromorphological terminologies………… 31

3.5. Clay Mineralogy……………………. 31

3.6. Data Analysis…………. 32

3.7. Soil Classification…… 32

CHAPTER FOUR RESULT AND DISCUSSIONS

4.1. Morphological Properties………….. 33

4.1.1. Soil depth…………………. 33

4.1.2. Soil colour……………………….. 33

4.1.3. Soil structure……………. 41

4.1.4. Soil consistence……………………………………….. 41

4.1.5. Miscellaneous……………………………… 43

4.2. Physical Properties……… 44

4.2.1. Particle size distribution…………. 44

4.2.2. Bulk density and porosity………………… 47

4.3. Chemical Properties…………………….. 49

4.3.1 Exchangeable bases…………………….. 52

4.3.2. Exchangeable acidity (EA)……………………………… 53

4.3.3. Cation exchange capacity (CEC)……………………… 54

4.3.4. Base saturation (BS)………………………………… 55

4.3.5. Soil pH……………………. 55

4.3.6. Soil organic carbon………………… 55

4.4. Micromorphological Properties……………………. 58

4.4.1. S-matrix (groundmass)…………………… 59

4.4.2. Microstructure……………………. 64

4.4.3. Related distribution patterns (C/F)…………………… 66

4.4.4. Pedofeatures……………………. 70

4.4.5. Miscellaneous……………………………………………………….. 72

4.5. Mineralogy Distribution of the soil Profiles…………………………. 76

4.5.1. Clay mineralogy…………………………………………………………. 76

4.6. Soil Classification………………………………………………………………… 95

4.6.1. Criteria for classification……………………………………………………… 95

4.6.2. Classification…………………………………………………………………… 96

Chapter Five Summary And Conclusions

REFERENCES…………………………………………………………………… 104

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INTRODUCTION

1.1 Background Information

Ultisols are highly weathered soils which occupy about 9% of the pedosphere (Brady and Weil 1999).

In Nigeria, particularly in the Guinea Savannahs, Ultisols, Inceptisols, Entisols, Alfisols and Vertisols constitute the bulk of the soils, while Ultisols take greater percentage (Harpstead, 1973; Hill and Rackham, 1974; Ojanuga, 1979; Kparmwang 1993; Olowolafe 1995).

The processes active in the formation of Ultisols include dissolution of clay and siltsized quartz, accumulation of aluminium and ferric iron, translocation of clay and clay sized minerals, neoformation of clay, and segregation of aluminium and iron increasing into plinthite and concretions (Brady and Weil, 1999).

Ultisols have been reported to develop under moist condition in warm tropical climates on old land surfaces, under different vegetation (Brady and Weil, 1999). As such, Ultisols are more highly weathered and acidic than Alfisols but less acid than Spodosols and less weathered than Oxisols.

Ultisols pose principal soil constraints which may be grouped into four broad categories namely: nutrient availability and retention, nutrient toxicities, water availability and physical degradation due to erosion.

Despite the above constraints, Ultisols possesses good micro-aggregate stability, good workability etc. In comparison, with the Alfisols, which has high cation exchange capacity and aluminium toxicity is not a problem.

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REFERENCES

Abayneh, E., Zauyah, S., Hanafi, M.M. and Rosenani, A.B. (2007). Genesis and classification of sesquioxidic soils from volcanic rocks in sub-humid tropical highlands of Ethiopia. Geoderma 136: 682–695.
Adepetu AA. (1986). Agricultural practices and adjustment in the region. JPERDP final report, p. 342–55. Chapter 20. Department of Geography, University of Durham,.
Ahn, P.M. (1970). West African Soils. Oxford University Press, Fly House, London. 332p.
Ahn, P.M. (1993). Tropical soils and fertilizer use. Longman U.K. 264p
Allen, B.L. and Hajek, B.F. (1989). Mineral occurrence in soil environments. p. 199– In: J.B. Dixon and S.B. Weed (Editors), Minerals in Soil Environments. 2nd (ed.) Soil Science Society of America, Madison, WI.
Akamigbo, F.O.R. and Asadu, C.L.A. (1983). Influence of parent material on the soils of Southeastern Nigeria. East African Agricultural and Forestry Journal.48:81- 91.