ABSTRACT
Erodibility potentials of soils of different parent materials under different land uses in Abia State, South Eastern Nigeria were studied. Soil samples were collected from four different land uses which are oil palm plantation, forest, arable crop land and fallow land, located at Umudike, Bende, Ameke and Owerrinta respectively. The experiment was a 4 x 4 x 3 factorial experiment in a Randomized Complete Block Design with five replications. The factors include the four locations (Umudike, Bende, Owerrinta and Ameke), the four land uses (oil palm plantation, forest, arable crop land and fallow) and three depths (0-15, 15-30 and 30-45cm). The soil samples were analysed for their physical, chemical and mineralogical properties. The data obtained were subjected to Analysis of Variance, regression and correlation analysis. The erodibility factors (k) of the soils were 0.186, 0.157, 0.124 and 0.114 for sandstone, shale, alluvium and coastal plain sands, respectively. The erodibility factors of the land uses were 0.272, 0.155, 0.099 and 0.044 for arable farm, fallow, oil palm and forest respectively. The arable farm had the highest k value while the lowest was observed in the forest land. Regarding Gerald’s erodibility indices, the soils of shale, alluvium, and coastal plain sands were in group II which were well drained soils in sandy grade free material. The soil of sandstone (0.186) was in group III which was graded loams and silt loam. The erodibility of forest land (0.044) and oil palm (0.099) were in group I which indicated moderate erodibility. The erodibility of the soils under fallow (0.155) fell in group II and the soils of the arable crop (0.272) were in group III. There were significant differences (p≤ 0.05) in estimated soil loss among the soils. The estimated soil losses of the soils were 382.01, 340.32, 337.89 and 267.97 tons/ha/yr for shale, sandstone, alluvium and coastal plain sands respectively. The estimated annual soil losses were 562.95, 340.33, 250.42 and 147.57 tons/ha/yr for arable farm, fallow, oil palm and forest, respectively. The minerals identified include quartz, hematite, magnetite, kaolinite, microcline, albite, iroxide, and montmorrilonite. Most of the minerals were primary minerals especially fieldspars. The soils also contained some oxides of iron. The soils were dominated by quartz and kaolinite. The soils from alluvium parent material had montemorrillonite in reasonable quanitity. The presence of quartz and kaolinites showed that the soils were highly weathered and leached. The high erodibility observed from the study may be due to unsustainable land use which destroyed vegetative cover, reduced soil structural stability and organic matter content thereby making the soil very susceptible to erosive forces.
TABLE
OF CONTENTS
Title page i
Declaration ii
Certification
iii
Dedication iv
Acknowledgment v
Table of contents vi
List
of tables ix
List of figure xi
Abstract xii
CHAPTER 1
Introduction 1
CHAPTER 2
Review of Related Literatures 4
2.1 Soil
Erosion 4
2.2 Soil
Erosion in South Eastern Nigeria 5
2.3 Soil Erodibility 6
2.3.1 Land
use types and erodibility 8
2.3.2 Soil texture and soil erodibility 10
2.3.3 Soil structure and erodibility 12
2.3.4
Soil erodibility and aggregate
stability 13
2.3.5
Soil organic matter and soil
erodibility 14
2.3.6 Soil minerology and erodibility 16
2.3.7 Infiltration rate and permeability of soils 16
2.3.8 Saturated hydraulic conductivity and soil erodibility 18
2.3.9 Bulk density and soil erodibility 19
2.4
Soil Chemical Properties 20
2.5 Soil
Porosity 21
2.6 Factors Affecting Soil Erosion 21
2.7 Erosion Prediction 24
2.7.1 Universal soil loss equation 24
2.7.2 Water erosion prediction project (WEPP) 25
2.8
Soil Water 26
CHAPTER
3
Materials and Methods 28
3.1 Description of the Study Area 28
3.2 Experimental Design 30
3.3 Soil
Sampling and Preparation
30
3.4 Laboratory
Studies 31
3.4.1 Texture 31
3.4.2
Microaggregate stability 31
3.4.3 Mean
weight diameter (MWD) and water stable aggregates (WSA) 32 31
3.4.4 Saturated
hydraulic conductivity (Ksat) 32
3.4.5 Bulk
density (BD) 32
3.4.6 Soil chemical properties 34
3.4.7 Mineral identification using x-ray
diffraction method 34
3.5 Soil
Erodibility Determination 35
3.6 Estimation of Mean
Annual Soil Losses 36
3.7 Data
Analysis 37
CHAPTER 4
Results and
Discussion
4.1 Some
physical Characteristics of the Soils 38
4.2 Bulk Density of the Soils Studied 40
4.3 Organic Matter Content of the Soils
Studied 41
4.4 Saturated
Hydraulic Conductivity (Ksat) 44
4.5. Mean Weight Diameter of the Soils 46
4.6 Clay
Flocculation Index of the Soils 48
4.7 Dispersion
Ratio and Clay Dispersion Index 50
4.8 Aggregated
Silt+ Clay (ASC) of the Soils 53
4.9 Soil Moisture Retention Characteristics 55
4.10 The
Chemical Characteristics of the Soils 61
4.10.1 Soil pH, nitrogen, phosphorus and potassium 64
4.10.2 Soil Ca, Mg, BS and ECEC 70
4.11 Erodibility
(k)of the soils 77
4.12
Estimated annual soil losses (tons/ha/yr) of the soil
studied 80
4.13
Correlation analysis of some physical properties of the
soil with
erodibility
factor ( k) 82
4.14
Correlation analysis of some physical
properties and water retention
characteristics
on the erodibility of the soils 84
4.15 Correlation
analysis of some chemical properties and the erodibility
of
the soils 87
4.16 Soil minerology
of the soils studied 89
Fig
12: X-Ray defractogram of mineral fraction of soils of 0-15cm
depth under different land uses in Owerrinta
|
4.16.1 Soil minerology and the land use types 94
4.16.2 Mean percentage
of the different minerals within soil depths 95
4.17 Correlation of soil
minerals with erodiblity 97
CHAPTER 5
Conclusion and
Recommendations 100
References 103
Appendices
LIST OF TABLES
3.1:
Structural class indices of soils 35
3.2: Permeability
class indices of soils 36
4.1: Some physical properties of soils under
study 39
4.2: Bulk
density of the soils studied 41
4.3: Organic
matter content of the soils studied 43
4.4: Saturated
hydraulic conductivity Ksat (cm/hr) 45
4.5: Mean
weight diameter of the soils 47
4.6:
Clay flocculation index of the soils 49
4.7: Dispersion
ratio of the soils (%) 51
4.8: Clay
dispersion index (%) 52
4.9:
Aggregated silt+ clay (ASC) of the
soils 54
4.10: Available
water content (%) 57
4.11: Field
capacity (%) 58
4.12:
Gravimetric moisture content (g/cm3) 59
4.13: Permanent
wilting point (%) 60
4.14: The
chemical characteristics of the soils 62
4.15:
pH of the soil studied 66
4.16: Nitrogen
(%) of the soil studied 67
4.17:
Phosphorus (mg/kg) of the soils studied 68
4.18:
Potassium (cmol/kg)of the soils 69
4.19: Calcium
(cmol/kg) content of the soils 73
4.20:
Magnesium (cmol/kg) contents of the
soils 74
4.21:
Effective cation exchange capacity
(cmol/kg) of the soils 75
4.22:
Base saturation (%) of the soils 76
4.23: Erodibility
factor (k) of the soils studied 78
4.24: Standard
erodibility indices 79
4.25:
Estimated soil losses of soils studied 81
4.26:
Correlation of some soil parameter with
erodibility 83
4.27: Correlation
analysis of soil structural properties, water retention
characteristics
and erodibility of the study soil 86
4.28: Correlation analysis of some chemical
properties and the
erodibility
of the soils 88
4.29: Description of the soil mineral in the soils
studied 91
4.30a: Percentage intensity
of the mineral in the different locations 92
4.30b: Percentage
intensity of the mineral in the different locations 93
4.31: Table of percentage intensity of the mineral for different
land uses 95
4.32: Soil minerals
and their intensity with depth 96
4.33:
Correlation of soil minerals with
erodibility 98
LIST OF FIGURE
1: X-ray defractogram of mineral fraction of
soils of 30-45 cm depth
under
different land uses in Umudike 99
CHAPTER 1
INTRODUCTION
Soil erosion is an ecological issue
of great concern in the Southeastern part of Nigeria in general and Abia State
in particular. Erosion problems arise mainly from natural causes but their
extent and severity are increasingly being attributed to man’s ignorance and
unsustainable land uses (Enabor and Sagua, 1988). According to Ofomata (2009),
soil erosion is simply a systematic removal of soil, including plant nutrients,
from the land surface by various agents of denudation. It occurs in several
parts of Nigeria under different geological, climatic and soil conditions.
In Southeastern
Nigeria, the soils are naturally prone to erosion due to their fragile nature
and ease of leaching, being mainly utisols and alfisol (Oguike and Mbagwu,
2009). The situation is further aggravated due to practices like bush burning
and indiscriminate excavation (Igwe and Ejiofor, 2005). Since 1991, Abia state
has witnessed increased economic and infrastructural activities with obvious
consequences on soil exposure and its attendant soil degradation.
Soil erodibility is the degree of
susceptibility of the soil to erosion. It is an estimate of the ability of
soils to resist or succumb to erosion, based on their physical and chemical
characteristics (Ojo and Johnson, 2010). It depends on soil structure, texture
and composition. There is a mutual relationship between soil erosion and parent
materials based on land use types (Ozdemir and Ashkin, 2003). Soils developed
from different parent materials are different and soil characteristics depend
on parent rock characteristics (Pellek, 1986). This in turn affects its
erodibility depending on the land use type. Human activities like tillage,
grazing, lumbering and deforestation affect the degree of soil exposure to
erosive forces. There are different types
of parent materials in Abia state, they include coastal plain sands, shale,
alluvium, sandstone etc. The coastal plain sands also known as Benin formation
is the largest geological formation in eastern Nigeria (Chikezie et al., 2009). It can be found in
Osisoma, Amakama and Umudike in Abia State. Alluvium are parent materials
transported by flowing rivers and stream. They can be found in Ukwa West, Ukwa
East and Owerrinta. Shale parent materials are predominant in Bende, Ibeku, and
Arochukwu while sand stones are found in Amake, and Isuikwuato. Generally, soil
erosion occurs where there is lack of adequate soil cover. Soil cover either by
plants leave or mulch help to reduce the direct impact of rain or wind on soil
thereby reducing erosion. Soil mineralogy is one
of the most important factors to consider in studying soil erodibility because
of its impact on aggregate stability, soil seal formation, water absorption and
resistance to erosive forces (Wischmeier and Smith, 1978). Soils dominated by
quartz and kaolinite are more resistant to erosive forces than soil dominated
by illite and montemorrilonite (Igwe et
al., 1999). Soils high in oxides of iron and aluminum, as well as
kaolinitic clay, are more aggregated compared to soils dominated by
montmorillonite and illite clay minerals (Troeh, 2000). This implies that soils
high in oxide of iron and aluminium are more resistant to erosion compared to
soil dominated by montemorrillonite and illite.
Soil
is taken to be the world’s most valued resource (Willet, 2004). The loss of
this resource, through land degradation processes such as soil erosion, soil
salinization, acidification, is one of the most serious environmental problems
we are faced with, as it destroys the means of producing food (Willet, 2004). In
recent years, much of the natural vegetation (forest, and pasture) within Abia
State has been converted to different land uses. These changes in land use over
time, have affected soil properties related to soil erodibility. Soil erosion
is a major environmental problem in Southeastern Nigeria especially Abia state
(Chikwendu and Uchenna,2019).
This work studied the erodibility of soils in
relation to their uses and mineralogy in Abia State. An indepth study of the
erodibility potentials of soils formed from different parent materials under
different land uses will help in adopting good soil management system. Findings
from this research will boost the bank of information that will foster
sustainable agricultural land uses. This will also help to curb the menace of
soil degradation and erosion in Abia state.
The general
objective of this study was to determine the erodibility of some soils of Abia
state formed on different parent materials under different land uses. The specific objectives of the study were to:
i.
determine the physical
and chemical properties of soils in Abia state and their influence on the erodibility
of the soils
ii.
determine the erodibility
potentials of some soils formed on different parent materials in Abia state
iii.
predict the soil losses
using the rainfall erosivity factor ( R) and the soil erodibility factor (k)
iv.
evaluate the effect of
land uses on the erodibility of some soils of Abia state;
v.
determine the mineralogy
of the soils in relation to erodibility
of the soils.
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