ABSTRACT
Soil erosion is the physical removal of topsoil by water flowing over and through the soil profile. Erodibility of soil is a major consideration in helping the government to identify potential risk areas and in developing sound management practices for land uses. This study assesses the erodibility status of soils formed from three geological formations of southeastern Nigeria. Three geological formations, upper coal measures (Okigwe), Coastal Plain Sand (Umuahia) and Bende-Ameki (Bende) were identified and selected for the study. Six profile pits were examined and sampled according to FAO guideline for soil description. Undisturbed core samples were collected from each pedogenic horizon and at 0-30cm (topsoil), 30-60cm (subsoil) depths for determination of hydraulic conductivity, bulk density and pore size distribution, using Darcy’s equation method. Soil samples were also collected at various pedogenic horizons for determination of texture, aggregate stability and organic matter, Erodibilityindex (K), dispersion ratio (DR), clay dispersion index (CDI) and clay ratio (CR) were calculated from the results of laboratory analysis and were used for assessment of erodibility status of soils of the study area. Pearson correlation analysis method was used to determine the relationship between erodibility index (K) with certain soil properties like organic matter (OM), CR, DR and CDI, while statistical method of mean and percentages were used to analyze the questionnaires for land use in the study area. The result showed that the mean clay content for the topsoils of Okigwe, Umuahia, and Bende are 21.33 %, 24.67 % and 25.00 % respectively. The corresponding values for the subsoils are 22 %, 19 % and 22 % respectively. Bende topsoil with the highest total sand value of 71 % was followed by topsoils of Okigwe and Umuahia which have 69.67% each, the subsoils showed total sand values of 68.33 %, 73.65 % and 73.00 % for Okigwe, Umuahia and Bende soils respectively.Topsoils and subsoils of Okigwe, Umuahia and Bende Soils have percent aggregate stability values of 44.28 % and 45.00 %, 34.48 % and 43.40 % and, 43.80 % and 45.50 % respectively. The mean OM content for Okigwe soil is 1.49 %, each at both topsoil and subsoil, those of Umuahia and Bende are 1.97 % and 1.22 %, and, 1.84 % and 0.53 % respectively. DR, CR, and CDI showed positive significant relationships with the erodibility index (K) of soils of the study area. There is also positive relationship between sand, silt, organic matter and erodibility index (K) and a negative relationship between clay and erodibility index. More than 50 % of the households in the study area plant economic trees, while arable farming and free range livestock farming are very popular. There is apparently lack of good erosion control measures in the study areas specially in Umuahia where 40 % of the households do not attempt any form of erosion control measures. The erodibility status of soils of the study areas ranked according to their level of erodibility is as follows, Bende>Okigwe>Umuahia. Revegetation and use of organic manure to supply the organic matter content needed to bind soil aggregates are recommended.
TABLE OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of content vi
Abstract xii
CHAPTER 1: INTRODUCTION
CHAPTER: 2 LITERATURE REVIEW
2.1
Soil Erosion 6
2.2
Factor of Soil Erosion 8
2.3
Erosion and Soil
Properties 11
2.4
Land Use 14
2.5
Effect of Land Use on
Soil Properties 15
2.6
Land Use and Soil Erosion 16
2.7
Land use Systems 18
2.7.1 Forest 18
2.7.2 Pastures 20
2.8
Farm Practices and
Operations Determining the Extent of Erosion Hazards 21
2.8.1 Bush
clearing 21
2.8.2 Weeding 22
2.8.3 Cropping
systems 22
2.9
Soil Erosion Control
Measures 23
2.9.1 Agronomic
technique and erosion control 25
2.9.2 Conservational
tillage (mechanical practices) 29
2.9.2.1
Mulch farming 30
2.9.2.2
No-tillage farming 30
2.9.2.3
Minimum tillage 31
2.9.2.4
Contour ridging 31
2.9.2.5
Tie ridges or basin
tillage 31
2.9.3
Soil conditioners 32
2.9.4
Roadside erosion 32
2.9.5
Gully erosion control 32
CHAPTER 3: MATERIALS AND
METHODS
3.1
Physical Environment and Geographical
Location of the Study Areas 34
3.1.1
General 34
3.1.2
Specific site information 35
3.1.2.1 Okigwe 35
3.1.2.2 Umuahia 37
3.1.2.3 Bende 39
3.2
Site Selection 41
3.3
Field Methods 41
3.4
Profile Description 45
3.5
Laboratory Determination 48
3.5.1
Physical parameters 48
3.5.1.1 Saturated
hydraulic conductivity 48
3.5.1.2 Particle
size Aanalysis 49
3.5.1.3 Water
dispersible clay 49
3.5.1.4 Bulk
density, porosity and pore-size distribution 49
3.5.1.5 Aggregate
stability 49
3.5.2
Chemical parameters 49
3.5.2.1 pH
determination 50
3.5.2.2 Organic
carbon 50
3.5.2.3 Total
nitrogen 50
3.5.2.4 Exchangeable
bases (Na, K, Ca, and Mg) 51
3.5.2.5 Exchangeable
acidity 51
3.5.2.6 Cation
exchange capacity 51
3.5.2.7 Available
Phosphorus 52
3.6
Assessment of Erosion
Status 52
3.7
The Soil Classification 53
3.8
Determination of
Approximate Clay Mineral in the Soil 54
3.9
Data Analysis 55
CHAPTER
4: RESULTS AND DISCUSSION
4.1 Site
Information, General Soil Information and Morphological Characteristics
of the Soil Study 56
4.2 Physical Properties of Soils of the Study
Areas 78
4.2.1 Sand,
silt and clay 78
4.2.2 Bulk density and porosity 79
4.2.3 Aggregate stability and hydraulic conductivity
79
4.3
Chemical Properties of Soils
of the Study Area 90
4.3.1 Soil
pH, nitrogen and organic matter 90
4.3.2 Sodium,
potassium, calcium and magnesium 91
4.3.3 Cation
exchange capacity, base saturation and phosphorous 92
4.4 Some Physical and Chemical Ratios of
Soils of the Study Area 101
4.4.1 Dispersion
ratio,clay ratio, clay dispersion index and erodibility Index 101
4.4.2 Ca:
Mg, exchangeable soidum percentage and soiudm adsorption ratio 102
4.5 Relationship Between Erodibility Index and
Soil Properties 107
4.6 Summary
of Land Use and Field Observations/Questionnaires 112
4.6.1 Land
use type based on the result of the questionnaire 112
4.6.2 Land
Preparation methods based on the result of the questionnaire 115
4.6.3 Erosion
control measures based on the result of the questionnaire 117
CHAPTER 5: CONCLUSION AND RECOMMENDATION
5.1 Conclusion 120
5.2 Recommendation 122
5.3 Suggestion for Further Research 123
References
Appendix
LIST OF TABLES
3.1 The
co-ordinates of the sampling points 43
4.1a Morphological
characteristics of Okigwe soil 62
4.1b Morphological
characteristics of Umuahia soil. 69
4.1c Morphological
characteristics of Bende soil 76
4.1.1
Results of the
classification of the soils 77
4.2.1 Physical
properties of Okigwe soil 81
4.2.2 Physical
properties of Umuahia soil 82
4.2.3 Physical properties of Bende
soil 83
4.2.4 Physical
properties of topsoil (0-30cm) of the study area 84
4.2.5 Physical
properties of the subsoil (30-60cm) of
the study areas 85
4.3.1 Chemical properties of topsoils
(0-30cm) of the study areas 94
4.3.2 Chemical properties of subsoil
(30-60cm) 95
4.3.3 Appropriate clay minerals in the soils 96
4.3.4
Chemical Properties of topsoils (0-30cm)of the study areas 97
4.3.5 Chemical Properties of subsoil
(30-60cm) of the study area 98
4.3.6 Approximate clay mineral in the soil 99
4.4.1 Some chemical erodibility indices
for Okigwe soil 103
4.4.2 Some chemical and erodibility indices
for Umuahia soil 104
4.4.3 Some chemical and erodibulity indices for Bende soil 105
4.4.4 Mean values of some chemical and
erodibility indices for the study area 106
4.5.1 Correlation result of the physical and
chemical properties of Okigwe Soil with
The erodibility index (K) 109
4.5.2 Correlation result of the physical and
chemical properties of Umuahia Soil with
The erodibility index (K) 110
4.5.3 Correlation result of thr physical and
chemical properties of Bende Soil with
The erodibility index (K) 111
4.6.1 Land use type based on the result of
the questionnaire 114
LIST
OF FIGURES
1: Soil map of Southeastern
Nigeria 44
2: Location map of the study areas. 45
3: Geological map of the study
areas 46
4: Potential erosion map of
Nigeria 47
6: Thickness of eluvial
horizons of the location 92
7: Thickness of Illuvial
horizons of the locations 93
8: Mean clay content of
eluvial horizons of the location 93
9: Mean clay content of
illuvil horizons of the locations 94
10: Mean clay content of A+B
horizons (estimated original clay) of the
locations 94
11: Mean blulk densities of eluvial
horizons of the locations 95
12: Mean bulk densities of
illuvial horizons of the locations 95
LIST
OF PLATES
1: Profile OK/UU/P1 – Okigwe,
Umuka Soil 58
2: Profile OK/AO/P2 – Okigwe,
Alaokwa Soil 61
3: Profile UM/UA/P1 –
UmuahiaUmuakam Soil 65
4: Profile UM/UB/P2 – Umuahia,
Ubakala Soil 68
5: Profile B/AO/P1 – Bende,
Amoba Soil 72
6: Profile B/IE/P2 – Bende,
Isiegbu Soil 75
CHAPTER 1
INTRODUCTION
Generally,
soil erosion implies the physical removal of topsoil by various agents
including falling raindrops, water flowing over and through the soil profile,
wind velocity and gravitational pull (Pitmentel, 1997).
It
is feared that some 5.7 million hectares of cultivated land now is completely
lost for agricultural production every year through soil erosion. The United
Nations Environmental program estimated that 1.5 billion hectares of land that
were once biologically productive have gone out of production due to soil
erosion (UNEP, 1986; and Pitmentel, 2006).
Plaster
(1992), observed that over the past 40 years a stream of technological
improvements, including fertilizers and improved crop varieties, has masked the
effect of erosion on productivity. He further stressed that when the soil
becomes thin enough, these technologies will not save yields.
Therefore,
studies on erodibility status of soils formed from some geological formations
of southeastern Nigerian will lead to increased awareness on soil and crop management
practices needed to save growers from losses due to soil erosion.
Lal
(1990) reported that the factors of erosion are those natural or artificial
parameters that determine the magnitude of perturbation of land - vegetation -
climate equilibrium. Hence, confirming the studies of Barber (1983) which
showed that soil erosion is a function of the land use and it's interaction
with climate, and that adopting an appropriate land use reduces erosion risks
and sustains productivity.
Lal
(1990) also stated that soil erosion is caused by land misuse and this can be
controlled only by proper land use and appropriate soil and crop management
practices.
Morgan
(2005) observed that the factors controlling the working of the erosion system
are the erosivity of the eroding agent, the erodibility of the soil, the slope
of the land and the nature of the plant cover. He further stated that, in order
to understand when and how much erosion is likely to occur, these factors must
be examined in detail and the relevant aspects of them identified more
precisely.
Soil
erosion is influenced by many physical and chemical properties of the soil and
their interaction with climate and management systems (Ofomata et al, 2001).
Since
soil susceptibility to erosion is influenced always by changing properties,
soil erodibility is dynamic, with continuous intensive cultivation and with
ever increasing emphasis on urban development, soil vulnerability to erosion is
likely to increase. Therefore, the land use system and soil management
practices recommended should be able to check possible increase in erosion risk
with time (Lal, 1990). One of the aims of good soil management is to avoid
structural breakdown, therefore restricting cultivation to those times when the
soils resistance to the shear or cutting forces is greatest would be valuable
control strategy (Szymanski et al,
2011).
The
incident of soil erosion in southeastern Nigeria is not new as it has formed a
subject for serious consideration since 1920. Soil erosion occurs all over southeastern
part of Nigeria and as a matter of fact, it is the most striking feature on the
land surface of that part of the country.
The awareness of the existence and
perhaps, danger of soil erosion was highlighted by Daddley stamp in 1938.
Stamps reviews werefollowed by the special study of the phenomenon by Grove
(1951) in parts of eastern Nigeria.
Jungerus (1969) studied the soils of southeastern
Nigeria and classified them into five groups namely; “Lithosols,” young soils
derived from recently deposited materials, “ferruginous tropical soils,” “Ferrallitic
soils” and “hydromorphic soils.”
Processes governing the erodibility of
soils formed from different geological formations in southeastern part of
Nigeria are not well understood, so more research is required to understand the
principles influencing it and also evaluates their erosion status based on the
underlying parent materials which will ultimately enable erosion control
agencies and the government to identify potential risk areas. This
identification of erosion risk areas require detailed studies and evaluation of
the soil properties that potentially confer susceptibility of soils of the
study area to erosion and the effect of land use system.
Nigeria has been battling with erosion
since the 1920s, yet it remains a major problem (Grove, 1952 and Ofomata, 2001).
As soil erosion is now becoming a national problem the first stage in solving
the problem is identification of potential risk areas through careful evaluation
of the physical and chemical properties of the soils formed from different
geological formations and the effect of land use in relation to soil erosion in
the study area. Information from such studies will form a benchmark for
national soil conservation and land use policy. Though this research will
emphasize on agricultural land use, for this is the dominant land use pattern
in the study areas, mention could be made of urban/industrial land use insofar
as it affects soil properties.
Morgan (2005) reported that much of the
understanding about erosion research stems from empirical studies in which a
wide range of data on soil loss and presumed controlling variables, like
relief, rainfall, surface materials (Lithology), population density, vegetation
etc, is collected and the best relationships are sought using statistical
methods particularly correlation and regression analysis. He also emphasized
that since this analytical approach is adopted by numerous researchers working
in many different areas of the world, it is not too surprising that the result
is a multiplicity of variables being recognized as important, but none of them
has been isolated as the most significant. This state of affairs has given rise
to the use of some texture - based indices to present and precisely evaluate
potential susceptibility of soil to erosion.
At present there is paucity of basic
information delineating certain soil characteristics and land use management practices
that determine erodibility status of soils formed from some geological
formations of southeastern Nigeria. It is therefore, against this backdrop that
this research work is being carried out.
The general objective of this work was to
characterize the soils and identify the major soil properties influencing the
soil erosion in the study area and evaluate the extent of erosion and
susceptibility based on the underlying geology of the study areas.The specific
objective were to;
1)
Characterize the soils of
the three geological formations (Upper coal measures “Okigwe”, Coastal Plain
Sands, “Umuahia” and Bende-Ameki formation, “Bende”
2)
identify the erodibility
potentials of the soils of the study area.
3)
relate the erodibility
status to erodibilty indices and soil properties
4)
identify land management
practices and erosion control measures in the selected study sites
Login To Comment