Soil Characterization,

Classification and Survey

Soil Characterization,

Classification and Survey

Ivara Ejemot Esu

HEBN Publishers Plc

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© Ivara Ejemot Esu 2010First Published 2010

ISBN 978 978 081 373 4

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v

To my beloved late father; a man of high integrity,

resourcefulness and uncommon vision

Pa Jonathan Ejemot Esu

(1905 – 1976)

Dedication

vi

Soil Characterization, Classification and Survey is a revised version

of Fundamentals of Pedology which was published by Stirling-Horden

Publishers (Nig) Ltd, Ibadan in 1999. The change in title of the book is

for greater clarity among its target audience as to its content.

The book covers required lecture notes in courses such as Principles

of Soil Science, Introductory Pedology, Soil Taxonomy and Conservation,

Soil Characterization and Classification and Soil Survey and Land Use

Planning offered in Faculties of Agriculture, Forestry and Environmental

Sciences in most Universities, Polytechnics and Colleges of Education

in Nigeria and many African countries.

The book is based on my personal experiences of teaching most of

these courses to undergraduates and graduate students at the Kaduna

Polytechnic and the National Water Resources Institute, Kaduna (1975

– 1984), Ahmadu Bello University, Zaria (1984 – 1994), University of

Uyo (2007-2008), University of Calabar (1994 – date); all in northern

and southern Nigeria and at the University of Ghana, Legon (2006-2007).

For those who were familiar with the earlier edition “Fundamentals of

Pedology”, this revised edition has effected the corrections and has

expanded the contents of most of the chapters in light of the ever

changing concepts in Pedology. A completely new chapter has also been

included to deal with Laboratory Data Used in Pedological Studies and

their interpretation. The chapter is meant to assist final year and

postgraduate students with the interpretation of the data often generated

from soil analysis and indeed the current and appropriate methods to be

used in soil characterization in the laboratory.

The chapter on Principles of Soil Classification has also been

tremendously expanded to include diagnostic criteria used in soil

classification. A pictorial description of each of the twelve soil orders

of Soil Taxonomy has been included as Appendix 1. Most recent revisions

in the criteria used in FAO/UNESCO Soil Classification system, namely,

the World Reference Base for Classification (WRB) is also dealt with

extensively, among others. A detailed glossary of most of the terms

used in the book has been included in Appendix 2 as well for a much

Preface

vii

easier referencing.

The book will be must useful to students of Agriculture, Geography,

Environmental Protection Management and Agricultural Education in

Colleges of Education, Polytechnics and Universities in Nigeria and other

African countries.

Ivara Ejemot Esu, OFR

B.Sc (Ife) M.Sc (Minnesota) Ph.D (ABU)

Professor of Soil Science

University of Calabar, Nigeria.

viii

Contents Page

Dedication .................................................................................................................. v

Preface ...................................................................................................................... vi

List of Figures. ......................................................................................... xiv

List of Plates...................................................................................xv.

List of Tables...................................................................................xvi

1. Introduction ................................................................................ 1

Pedology as a Discipline of Soil Science ................................................. 1

What is Soil? .................................................................................................. 1

Why Study Soil? ........................................................................................... 2

Careers in Soil Science ............................................................................... 3

Revision Questions ...................................................................................... 5

References ..................................................................................................... 5

2. Soil Description Terms .............................................................. 6

Introduction .................................................................................................. 6

Soil Profile .................................................................................................... 6

Soil Horizon ................................................................................................. 9

Soil Solum .................................................................................................. 13

The Pedon ................................................................................................. 13

Polypedon/Soil Individual/Soil Body .................................................. 13

Sequum/Bisequal/Buried Soil ................................................................ 14

Topsoil and Subsoil .................................................................................. 14

Mineral and Organic Soils ....................................................................... 14

Revision Questions ................................................................................... 15

References .................................................................................................. 15

3. Components of Soil ................................................................. 17

Introduction ............................................................................................... 17

Mineral Matter ........................................................................................... 18

Organic Matter .......................................................................................... 19

Soil Water ................................................................................................... 20

Soil Air ........................................................................................................ 21

Revision Questions ................................................................................... 22

References .................................................................................................. 22

4. Soil Forming Rocks and Minerals ........................................... 23

Introduction ............................................................................................... 23

Soil Forming Rocks ................................................................................. 23

Igneous Rocks ........................................................................................... 23

Sedimentary Rocks ................................................................................... 24

ix

Metamorphic Rocks ................................................................................. 25

Rock Forming Minerals ........................................................................... 26

Silicate Minerals ......................................................................................... 26

Iron Oxide Group ................................................................................... 28

Carbonate Group..................................................................................... 28

Phosphate Group ..................................................................................... 28

Sulphate Group ........................................................................................ 29

Other Minerals .......................................................................................... 29

Weathering of Rocks and Minerals ....................................................... 29

Why Study Weathering? ........................................................................... 30

Physical Processes of Weathering .......................................................... 30

Chemical Processes of Weathering ........................................................ 32

Factors Governing the Stability of Minerals to Weathering .............. 35

Weathering products of Common Soil Minerals in Rocks ............. 38

Igneous Rocks ........................................................................................... 38

Sedimentary Rocks ................................................................................... 38

Metamorphic Rocks ................................................................................. 38

Revision Questions ................................................................................... 39

References .................................................................................................. 40

5. Factors of Soil Formation........................................................ 41

Introduction ............................................................................................... 41

Parent Material .......................................................................................... 42

Types of Parent Material ......................................................................... 43

Climate ....................................................................................................... 45

Variables of Climate ................................................................................ 45

Organisms .................................................................................................. 46

Role of Plants ........................................................................................... 47

Role of Animals ....................................................................................... 47

Role of Microorganisms ......................................................................... 48

Relief ........................................................................................................... 48

Altitude ....................................................................................................... 48

Shape of Landscapes ............................................................................... 48

Aspect of Slope ........................................................................................ 51

Time ............................................................................................................ 51

Concept of “Time Zero”....................................................................... 52

Relative Stages of Soil Development ................................................... 52

Relative Rate of Soil Development ....................................................... 53

Revision Questions ................................................................................... 53

References .................................................................................................. 54

x

6. Soil Forming Processes ............................................................ 56

Introduction ............................................................................................... 56

Eluviation – Illuviation ............................................................................ 57

Leaching amd Enrichment ...................................................................... 61

Decalcification and Calcification ............................................................ 61

Dealkalization and Alkalization ............................................................. 62

Allitization and Deallitization ................................................................. 63

Salinization and Desalinization ................................................................ 64

Podzolisation ............................................................................................. 64

Lateritization .............................................................................................. 65

Gleization ................................................................................................... 66

Ferrolysis ..................................................................................................... 68

Pedoturbation ........................................................................................... 70

Revision Questions ................................................................................... 70

References .................................................................................................. 71

7. Soil Morphological Properties ................................................. 73

Introduction ............................................................................................... 73

General Site Information ........................................................................ 74

Description of Individual Soil Horizons .............................................. 75

Horizon Designation ................................................................................ 75

Soil Colour ................................................................................................ 80

Determination of soil colour ................................................................. 80

Mottling ...................................................................................................... 82

Soil Texture ................................................................................................ 83

Definition of Soil Textural classes ......................................................... 84

Soil Structure ............................................................................................. 87

Soil Consistence ........................................................................................ 91

Cutans ......................................................................................................... 92

Soil Pores .................................................................................................... 92

Roots .......................................................................................................... 92

Included Materials .................................................................................... 93

Horizon Boundary Characteristics ......................................................... 94

Example of Soil Profile Description .................................................... 94

Revision Questions ................................................................................... 98

References .................................................................................................. 98

8. Laboratory Data Used in Pedological Studies ...................... 100

Introduction ............................................................................................. 100

Pedon Characterization Data ................................................................ 100

Physical Properties .................................................................................. 100

Chemical Properties ............................................................................... 102

xi

Mineralogical Properties ....................................................................... 104

Thin Sections for Soil Micromorphology .......................................... 104

Handling and Preparation of Samples in the Laboratory ............... 104

Pedological Inferences from Laboratory Data ................................. 105

Particle Size Analysis ............................................................................... 105

Bulk Density ............................................................................................ 105

Coefficient of Linear Extensibility (COLE) ...................................... 106

Soil Moisture Parameters ...................................................................... 106

Soil pH ..................................................................................................... 107

Organic Carbon/Total Nitrogen ......................................................... 109

Electrical Conductivity (EC) ................................................................. 110

Extractable (Free) Iron .......................................................................... 110

Cation Exchange Capacity (CEC) ....................................................... 111

Percentage Base Saturation (PBS) ........................................................ 113

Extractable P and Phosphate Retention ............................................. 113

Mineralogical Properties ........................................................................ 113

Soil Micromorphology.......................................................................... 114

Revision Questions ................................................................................. 115

References ................................................................................................ 115

9. Principles of Soil Classification .............................................. 118

General Concepts of Classification ..................................................... 118

Definition of Soil Classification ........................................................... 119

Purposes of Soil Classification ............................................................. 119

Steps Involved in Soil Classification ................................................... 120

Kinds of Soil Classification .................................................................. 120

USDA Soil Taxonomy System ............................................................. 121

Diagnostic Surface Horizons or Epipedons ...................................... 123

Diagnostic Subsurface Horizons or Endopedons ............................ 124

Diagnostic Characteristics for Organic Soils ...................................... 128

Other Diagnostic Soil Characteristics or Diagnostic Features ....... 129

Soil Moisture Regimes ........................................................................... 131

Soil Temperature Regimes .................................................................... 132

Categories of the USDA Soil Taxonomy .......................................... 133

Soil Order ................................................................................................ 133

Suborder .................................................................................................. 136

Great Group ........................................................................................... 137

Subgroup ................................................................................................. 141

Family ....................................................................................................... 141

Series ......................................................................................................... 143

xii

FAO-UNESCO Soil Classification System/

World Reference Base for Soil Resources (WRB)............................. 143

Soil References Groups ......................................................................... 144

Correlation between the USDA and WRB Systems of

Classification ............................................................................................ 153

Revision Questions ................................................................................. 155

References ................................................................................................ 155

10. Principles of Soil Survey .........................................................157

Concept of Soil Survey ......................................................................... 157

Types of Soil Survey .............................................................................. 158

Schematic Soil Surveys .......................................................................... 158

Exploratory Soil Surveys ...................................................................... 158

Reconnaissance Soil Surveys ................................................................. 159

Semi-Detailed Soil Surveys ................................................................... 159

Detailed Soil Surveys ............................................................................. 160

Very Detailed Soil Surveys .................................................................... 160

Map Scales and Mapping Units ........................................................... 160

Basic Soil Survey Procedures................................................................ 162

Rigid Grid Procedure ............................................................................ 162

Free Survey .............................................................................................. 163

Soil Survey Methods Involving Remote Sensing Data .................... 164

Phasing of Soil Survey Operations ..................................................... 165

Office Work ............................................................................................ 165

Field Reconnaissance Visit ..................................................................... 166

Field Work ............................................................................................... 166

Laboratory Analysis of Soil Samples .................................................. 168

Cartographic Production of the Soil Map ........................................ 168

The Soil Survey Report ......................................................................... 169

Revision Questions ................................................................................. 170

References ................................................................................................ 170

11. Principles of Land Classification ........................................... 172

Concept of Land Classification ........................................................... 172

Land Capability Classification System................................................. 173

Land Capability Classes ......................................................................... 173

Land Capability Subclasses ................................................................... 174

Land Capability Units ............................................................................ 176

Land Suitability Classification Systems ................................................ 176

Concept of Land Suitability Classification ......................................... 176

Land Suitability Classification Involving Rainfed Agriculture ......... 177

Land Suitability Classification Involving Irrigated Agriculture ........ 182

References .............................................................................................. 199

xiii

Appendices

Appendix 1: Pictorial Representation of Modal Profiles of the Twelve

Soil Orders of Soil Taxonomy. .............................................. 201

Appendix 2: Glossary of Pedological Terms ............................................. 206

Index:..........................................................................................................................255

xiv

List of Figures

Figure 2.1: Processes which promote the development of horizons in soils ................ 11

Figure 2.2: A pedon of a soil body within a landscape .......................................... 12

Figure 3.1: Volume composition of a silt loam surface soil in optimum condition for

plant growth ...................................................................................... 18

Figure 4.1: Stability to weathering of some common soil-forming minerals (After Goldich,

1938 and Jackson et al, 1984) ..........................................................37

Figure 5.1: Sedentary, colluvial and alluvial parent materials if soils along

a typical taposequence Western Nigeria (Adopted from Symth and

Mantgomary,1962) ............................................................................ 50

Figure 6.1: Decalcification and Calcification Processes along a Hill slope .......................... 62

Figure 7.1: Hypothetical mineral soil profile showing the major horizons that may be

present ........................................................................................................... 77

Figure 7.2: Soil colour names for several combinations of value and chroma and hue

10YR. ........................................................................................................... 81

Figure 7.3: Standard USDA Soil Textural Triangle ...................................................... 86

Figure 7.4: Soil Description Sheet Used in the Field .............................................. 95

Figure 7.5: “Long - hand” Profile Description of Kukum Daji series (KD) ........... 97

Figure 9.1: Multiple category and Hierarchical system of the USDA soil

Taxonomy .......................................................................................... 122

Figure 10.1: Base map showing baseline, traverses, auger - points and soil boundry

lines in a rigid procedure of soil survey .............................................. 163

Figure 10.2: Soil map of Alhaji Jibrilu’s farm at Kuyello, Northern Nigeria.

(The map has been produced from the rigid grid Base map in

Figure 10.1) ..................................................................................... 169

Figure 11.1: Land capability classification map derived from the soil map in

Figure 10.2 ...................................................................................... 175

xv

List of Plates

Plate 1: A vertical cross-section made on a landscape to expose soil along a road-cut

(soil profile) in Imo State, Nigeria .............................................................. 7

Plate 2: A deep soil profile on coastal plain sands with the parent material

exposed only at great depth at Owerri, Nigeria .......................................... 7

Plate 3: A deep soil profile with the underlying bedrock several materes below the soil

surface at Aboada, River State, Nigeria .......................................... 8

Plate 4: A shallow soil profile in a road-cut exposing an underlying granitic bedrock at

about 50cm depth along Ogoja-Odajie Mbube road in Cross River State,

Nigeria...............................................................................................................8

Plate 5: A freshly dug profile pit with marked horizons for description ................. 74

xvi

List of Tables

Table 4.1: A simplified classification of common igneous rocks according

to the size of mineral grains in the rock and reaction ............................... 24

Table 4.2:Selected common primary and secondary minerals in soils ......................... 27

Table 5.1:Agents, mode of deposition and name of deposit of transported parent

materials ................................................................................................. 43

Table 6.1: Some processes of soil formation that are complexes of subprocesses and reactions

(Adapted from Buol et al 1973)..........................................................................58

Table 7.1: Size limits of soil separates in the USDA and ISSS schemes ................ 84

Table 7.2:Classification of soil textural classes (USDA system) .............................. 87

Table 7.3:Diagrammatic Definition and location of various types of soil structure .. 89

Table 7.4:Types and classes of soil structure ............................................................ 90

Table 9.1:Names of the soil orders in the USDA soil taxonomy with their

derivation, formative elemnts, pronounciation, and major

characteristics ........................................................................................ 133

Table 9.2:Soil orders and their suborders in soil taxonomy .................................... 138

Table 9.3:Formative elements in names of suborders in soil taxonomy .................... 139

Table 9.4:Formative elements for names of great groups and their

connotation ............................................................................................ 140

Table 9.5:Some commonly used particle-size, mineralogy, cation exchange

activity, and temperature classes used to differentiate soil families

(Source: Brady and Weil, 1999) ........................................................... 142

Table 9.6:The Ten Sets of the Reference Soil Groups of the WRB ....................... 144

Table 9.7:Diagnostic horizons, properties and materials used in the identification

of reference soil groups of the WRB (Source: ISSS-ISRIC-FAO,

1998) .................................................................................................... 145

Table 9.8:Key to the reference soil groups of the World Reference Base (WRB)

[Source: ISSS-ISRIC-FAO, 1998] ..................................................... 147

Table 9.9:Approximate correlation between the soil orders of the USDA soil

taxonomy and the reference soil groups ................................................... 154

Table10.1:Cheaklist of field material/equipment required for soil survey ............... 167

xvii

Table11.1:Structure of the FAO land suitability classification (Adapted from

FAO Soils Bull. 52, 1984 ................................................................. 178

Table11.2:Definitions of land suitability orders and classes(Adapted from

FAO Soils Bull, 52, 1984) ................................................................. 179

Table11.3:Suggested letter suffixes for indicating land suitability subclasses

(Adapted from FAO Soils Bull, 52, 1984). .......................................... 181

Table 11.4: Example of modified USBR land suitability Classes ......................... 184

Table 11.5 Modified USBR land classification specification used in Laos and

Thailand (Source: FAO, 1979) ........................................................... 185

Table 11.6:Example of modified USBR land suitability class specifications for

gravity irrigation used by a local consultancy group with only

physical parameters involved (Source: Esu, 1988) ................................ 190

Table 11.7: Soil index rating for major soil units in the Kaduna area of Nigeria

(Source: Esu, 1982) .......................................................................... 195

Table 11.8:Physico-chemical properties of Hadeija floodplain soils .......................... 197