ABSTRACT
This study was carried out in Imo State, Southeastern Nigerian to investigate the effect of clay minerals from selected parent materials (Coastal plain sand, Alluvium, Imo Clay Shale, False Bedded Sandstone and Upper Coal Measure) at different soil depths (0-20, 20 - 40 and 40 – 60cm) on soil potassium dynamics including forms, adsorption properties, and kinetics. Soil sampling was carried out with soil auger in three replicates from each parent material giving a total of forty-five composite samples. The experimental design was a 5 x 3 factorial in Randomized Complete Block Design (RCBD). Statistical analysis revealed significant (P<0.05) variation in soil physical and chemical properties with parent material and soil depth except Magnesium, Available Phosphorus, Total Exchangeable Acidity and Effective Cation Exchange Capacity that were not significant. However, interactions between parent materials and soil depth were not significant in influencing all the physical and chemical properties of the soils studied. With the exception of available phosphorus, soil of Imo clay formation was most superior in soil fertility variables, while the least values of these properties were found in soil of coastal plain sand formation. With respect to depth, top layers had significant greater amount of these fertility indices. The mineralogy of the clay-sized fraction of the soils showed the dominance of kaolinite and quartz with some amounts of Smectites and Montmorillonite at lower soil horizons especially soils formed on Imo clay Shale and upper coal measure. Haematite and goethite were the predominant pedogenic iron oxides and gibbsite which is an aluminum oxide was also identified. While the concentrations of quartz and kaolinite decreased with depth, the occurrence of smectites, goethite and hematite in mostly soils of Imo clay Shale and upper coal measure formations increased with soil depth. The potassium forms varied significantly (P<0.05) with parent material, soil depth and their interactions. Irrespective of parent material and depth, solution potassium (mean of 0.067 cmol/kg) had the least values, while the highest amounts of K were observed in the structural K fraction (mean of 11.786 cmol/kg). Most of the minerals except quartz correlated negatively with solution K and positively with structural K. Freundlich and Langmuir models sufficiently described potassium adsorption properties of soils. Irrespective of the adsorption model used, the K adsorption capacity was in the increasing order of Coastal Plain Sand > alluvium > False Bedded Sandstone > upper coal measure > Imo clay shale. Apart from quartz, other minerals especially hematite, goethite, gibbsite, kaolinite and smectite related positively with K sorption capacity and energy coefficient. Both parent material and soil depth as lone factors significantly influenced the kinetic rate constant (Ki), but their interactive effects were not significant. The means Ki values occurred in the following order: Coastal Plain Sand (21 x 10-3 m-1) < alluvium (22 10-3 m-1) < False Bedded Sandstone (38 10-3 m-1) < upper coal measure (38 10-3 m-1) < and Imo clay shale (49 10-3 m-1). The rate constant (Ki) generally increased with soil depth. In the same vein, goethite, haematite, smectite and kaolinite correlated positively with Ki, while the correlation between Ki and quartz was negative. In view of the above, K nutrition may be a constraint to crop productivity in these soils due to high K adsorption capacity and adsorption rate, unless there is high K fertilization and reduction of adsorption through liming and organic matter addition. Freundlich and Langmuir equations are recommended for description of sorption data, while First Order Reaction model is suitable for predicting the rate of soil K adsorption in soils of Imo State, Southeastern Nigeria.
TABLE OF CONTENT
Title
Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Tables
of Contents vii
List
of Tables xii
List
of Figures xiii
Abstract xv
CHAPTER 1: INTRODUCTION 1
1.1 Background to the Study 1
CHAPTER 2: LITERATURE REVIEW 7
2.1 Clay Minerals Group 10
2.1.1 2: 1 Clay Minerals Group 12
2.2 Physical Characteristics of Clay 15
2.2.1 Kaolinite Group 19
2.2.2 Montmorillonite / Smectite Group 21
2.2.3 Illite (Clay – Mica) Group 24
2.2.4 Chlorite Group 27
2.3 Isomorphous Substitution 27
2.3.1 Adsorption and Ion Exchange 28
2.3.2 Surface Charge Properties 32
2.4 Clay Mineralogy of Selected Soil 32
2.4.1 Mineralogical Characterization of Clay
Fraction 33
2.4.2 Mineralogical Composition of Clay Fraction 34
2.4.3 Physical Properties of Clay Soil 35
2.4.4 Soil Moisture Retention 37
2.5 Role of Clay Minerals in the Supply and
Availability of Plant Nutrient 39
2.5.1 Role of Clay Mineral on Potassium
Availability 40
2.5.2 Influence of Clay Mineral on Soil Physical
Properties 41
2.5.3 Influence of Clay minerals on Soil
Acidification 42
2.6 Potassium Fertility in Soils 43
2.6.1 Forms of Potassium as a Function of Clay
Mineralogy 47
2.6.2 Clay Mineralogy and its relationship with
Potassium Forms 59
2.6.3 Potassium Forms and Physicochemical
Properties 51
2.6.4 Soils of Imo State 53
2.6.5 Characteristics of Soils of Imo State 54
2.6.6 Land Use Changes as it Affects Soil
Properties and Clay Mineralogy 54
CHAPTER 3: MATERIALS AND METHODS 56
3.1 Study Area 56
3.1.1 Soil of the Area 56
3.1.2 Site Characteristics 57
3.1.3 Soil Sampling 59
3.1.4 Sample Preparation 64
3.2 Determination of Physicochemical
Characteristics of Soil 64
3.2.1 Particles Size 64
3.2.2 pH 64
3.2.3 Exchangeable Bases 64
3.2.4 Cation Exchange Capacity 65
3.2.5 Organic Carbon 65
3.2.6 Available Phosphorus 65
3.2.7 Total Nitrogen 66
3.2.8 Exchangeable Acidity 66
3.2.9 Exchangeable Basic Cation 66
3.2.10 Effective Cation Exchange Capacity (ECEC) 66
3.2.11 Base Saturation 66
3.3 Forms of Potassium 66
3.3.1 Total Potassium 66
3.3.2 Water – Soluble K 67
3.3.3 Exchangeable Potassium 67
3.3.4 Non-Exchangeable of Fixed Potassium 68
3.3.5 Available Potassium 67
3.3.6 Mineral or structural Potassium 67
3.4 Potassium Adsorption Experiment 67
3.4.1 Langmuir Equation 69
3.4.2 Freundlich Sorption Isotherm 69
3.5 Kinetics of Potassium Adsorption 70
3.5.1 Potassium Sorption Kinetic Modeling 71
3.6 Mineralogical Analysis 71
3.7 Statistical
Analysis 74
CHAPTER 4: RESULTS AND DISCUSSION 75
4.1 Physical and Chemical Characteristics of
the Soils Studied 75
4.2 Mineralogical Composition of the Soils of
Studied Area 80
4.2.1 Mineralogical Composition of Soils Formed on Alluvium at
Different Soil Depths 100
4.2.2 Mineralogical Composition of Soils Formed on Coastal Plain
Sand at Different Soil Depths 100
4.2.3 Mineralogical Composition of Soils Formed on False Bedded
Sandstone at Different Soil Depths 101
4.2.4 Mineralogical Composition of Soils of Imo Clay Shale at
Different
Soil Depths 102
4.2.5 Mineralogical Composition of Soils Formed on Upper Coal
Measure at Different Soil Depths 104
4.2.6 Correlation between Clay Minerals and Some
Selected Soil Properties 104
4.3 Forms and Distribution of Potassium in
the Soils 107
4.3.1 Water –Soluble K 107
4.3.2 Exchangeable Potassium 109
4.3.3 Non – Exchangeable Potassium 111
4.3.4 Available Potassium 111
4.3.5 Structural / Mineral K 112
4.3.6 Total Potassium 113
4.4.1 Correlation Coefficient between the Potassium Forms and Some
Physical and Chemical Properties of
the Soils 114
4.4.2 Relationship between Forms of Potassium and Clay Minerals 117
4.5 Potassium
Sorption Characteristics of the Soils 120
4.5.1 Potassium Sorption Characteristics of the Soils 120
4.5.2 Langmuir Adsorption Isotherm 126
4.5.3 Langmuir Bonding Energy Constant 127
4.5.4 Langmuir Adsorption Maximum 130
4.5.5 Freundlich Adsorption Isotherm 136
4.5.6 Freundlich Adsorption Energy 136
4.5.7 Freundlich Adsorption Capacity 137
4.5.8 Comparism between Freundlich and Langmuir Adsorption Indices 144
4.5.9 Clay Minerals and K- adsorption Indices 145
4.6 Potassium
Sorption Kinetics of the Soils 147
4.6.1 Relationship between Clay Minerals and Potassium Kinetics
Indices 158
CHAPTER 5: CONCLUSION AND RECOMMENDATION 160
5.1 Conclusion 160
5.2 Recommendations 162
References
Appendices
LIST OF TABLES
2.1 Occurrence
of Soil Clay Minerals in relation to weathering Process Principal Mechanism and Soil Types from Pedro,
1982 9
2.2 Charge
Characteristics and Cation Exchange Capacities of Clay
Minerals from Bohn et al.1985,
McBride 1994 18
3.1 Soil
Parent Materials and Sample locations 60
3.2 Sample
Locations, Sample Codes and Coordinates Points at in situ 61
4.1 Some
Physical and Chemical Properties of the Soils used Study 79
4.2 Mineralogical
Properties of the Soil 99
4.3 Correlation
Coefficient between Clay Minerals and Some
Selected Soil Properties 106
4.4 Form
and Distribution of Potassium in the Soils 110
4.5 Correlation
Coefficient between the Potassium Forms and Physical and Chemical Properties of the Soils 115
4.6 Correlation
Coefficient between Clay Minerals and the Different Forms of Potassium 119
4.7 Potassium
Sorption Characteristics of the Soil Samples Using Langmuir and Freundlich Equations at Different Soil Depth
and Parent Materials 128
4.8 Correlation
Coefficient between Clay Mineral and K- Adsorption indices 147
4.9 Variables
used in Modeling K sorption Kinetics with a Pseudo First-Order Model.
Parameters include the Rate Constant and Sorption Capacity 157
4.10 Correlation Coefficient between Clay Mineral and K-adsorption
Indices 159
LIST OF FIGURES
2.1 Structural arrangement of 1:1 Clays minerals 11
2.2 1:1 Structure arrangement of 2:1 Clays
minerals 13
2.3 2:1 Structure arrangement of 1:1 and 2:1 Clays minerals 17
2.4 Adsorption
and Ion Exchange in 1:1 clay minerals 30
2.5
Adsorption and Ion Exchange in 2:1
clay minerals 30
3.1 Geologic Map of Studied Areas in Imo
State 63
4.1 X- Ray Diffractogram of Soil Minerals 82
4.2: Potassium Sorption Isotherm for Soils from
Isieke 122
4.3: Potassium Sorption Isotherm for Soils from
Umuele 123
4.4: Potassium Sorption Isotherm for Soils from
Umuinem 124
4.5: Potassium Sorption Isotherm for Soils from
Ubana 125
4.6: Potassium Sorption Isotherm for Soils from
Umuopia 126
4.7: Langmuir adsorption of k for soil of Akwu 131
4.8: Langmuir adsorption of k for soil of Umuachishi
1/c (mg-1 L) 132
4.9: Langmuir adsorption of k for soil of Ubahu 133
4.10: Langmuir adsorption of k for soil of Umuokwa 134
4.11: Langmuir adsorption of k for soil of Amaikpa 135
4.12: Freuendlich K adsorption for soil of Umuopia 140
4.13: Freuendlich K adsorption isotherm for soil of
Umuezukwe 141
4.14: Freuendlich K adsorption isotherm for soil of
Okpala 142
4.15: Freuendlich K adsorption isotherm for soil of Umuayata 143
4.16: Freuendlich K adsorption isotherm for soil of
Umuopia 144
4.17. K sorbed against Equilibrium Time at different
Depths for Soil of Isieke 148
4.18: K
sorbed against equilibrium time at different depths for soil of Umuokwa 148
4.19: K
sorbed against Equilibrium Time at different Depths for Soil of Umuezukwe 149
4.20: K
sorbed against Equilibrium Time at different Depths for Soil of Okpala 149
4.21. K
sorbed against Equilibrium Time at different Depths for Soil of Umuele 150
4.22: K
sorbed against Equilibrium Time at different Depths for Soil of Amaikpa 150
4.23: K
sorbed against Equilibrium Time at different Depths for Soil of Umuopia151
4.24: K
sorbed against Equilibrium Time at different Depths for Soil of Umuezeaga 151
4.25: K
sorbed against Equilibrium Time at different Depths for Soil of Akwu 152
4.26: K
sorbed against Equilibrium Time at different Depths for Soil of Ubana 152
4.27. K sorbed against Equilibrium Time at
different Depths for Soil of Umuachishi 153
4.28: K sorbed against Equilibrium Time at
different Depths for Soil of Umuayata153
4.29: K
sorbed against Equilibrium Time at different Depths for Soil of Ubahu 154
4.30: K
sorbed against Equilibrium Time at different Depths for Soil of Umuinem154
4.31: K
sorbed against Equilibrium Time at different Depths for Soil of Umuzegem 155
CHAPTER
1
INTRODUCTION
1.1 BACKGROUND TO THE STUDY
Minerals
are natural inorganic compounds with definite physical, chemical and
crystalline properties. They can be classified into primary (chemically
unaltered) or secondary (chemically altered) minerals, silicates and non-
silicates, crystalline and non-crystalline minerals (Brady and Weil, 2008).
Soil minerals play an important function in determining the soil's adaptability
and behavior for different land uses (Hinsinger et al. 2009).
The
primary mineral part of the soil is inherited from the parent material, and are
usually found in the sand and silt fraction of soils but may be modified under
the influence of different factors and processes while secondary minerals are
mainly found in the clay and silt fractions because the particle size of
primary minerals usually decrease during weathering. The mineralogical
constitution of soil is complex. The Earth's crust includes almost 100
elements, yet just eight of them (O2, Si, Al, Fe, Ca, Na, K, and Mg)
make up 98.5 percent of the crust and constitute the soil body's foundation.
The silicates and alumino-silicates are the most dominant minerals in most soil
types, accounting for 60% of all extant minerals. They may be found in both
main and secondary minerals. The primary minerals formed as a consequence of
the weathering of igneous, sedimentary, and metamorphic rocks, whereas the
secondary minerals formed as a result of the primary minerals' chemical weathering
(Brady and Weil, 2008).
As
in other parts of the tropics, rain-fed agriculture featuring different types
of crops mainly for subsistence has continued to be plagued with plethora of
problems which result in soil fertility decline. Brown et al. (2004) identified geographical variables, particularly
weather and human operations as major antecedents to soil nutrient loss in the
tropics. In addition, the increasing populations of people on fragile
landscapes coupled with intensive soil tillage during agricultural production
are other factors leading to severe soil degradation in tropical environments
(Fungo et al. 2011, Lufafa, et al. 2003).
Clay
minerals are natural, earthy, fine-grained material which develops plasticity
when mixed with limited amount of water. Among these materials are hydrated aluminum
silicates which are very stable during catalytic
treatment processes. They have surface endowed with weakly acidic and basic
sites. Clay mineral analysis has been widely used to
characterize soil parent material and to relate it to the bedrock (Bronger et al. 1994) as well as to associated
mineralogical transformations that occur with changes in climate and weathering
intensity (Bini and Mondini, 1992). Phyllosilicates (clay minerals) dominate
the portion (0.002mm or 2 microns) of many soils, according to Kostic (2000),
which affects the soil's physico-chemical characteristics (especially in terms
of its plasticity, stickiness, swelling, shrinkage, cohesion and the soil
structure and moisture retention). The silicate structure is the most important
in the study of clay mineralogy is the layer - minerals which have there
structure referred to as phyllosilicates. Clay minerals are determined by their
chemical composition, layered structure and size. Kaolinite, smectite
(montmorillonite, saponite), mica (illite), and chlorite are the four divisions
of clay minerals (Shichi and Takagi, 2000; Nayak and Singh, 2007; Burhan and
Ciftci, 2010). The clay mineral characteristics of a given soil type influence
largely the capacity of the soil to supply nutrient to plants and the kinetics
of its ability to replenish the soil solution after the depletion of the
rhizosphere (Hinsinger, 2009). Different types of clay mineral hold and retain
differing kind and quantity of nutrients. Therefore, characterizing the clay
minerals availability in a particular soil can be an important index in
understanding and possibly predicting the degree to which the soil can retain
and supply nutrients to plants, since mineral surfaces serve as potential sites
for nutrient adsorption and storage. The chemistry of minerals of parent
material has an impact on clay mineralogy of soil. As weathering proceeds, the
clay content increases as a result of physical and chemical alteration of
primary minerals (Mehdi et al. 2007).
The amount of mineralogical constitution affects soil water holding based on
the amount and percentage of clay minerals found in a soil type. One of the
most vital variables influencing soil chemical and physical characteristics is
the mineralogical composition of the clay component. Their types and amounts
are influenced by several factors such as climate, topography, vegetation and
bedrock type (Libo et al. 2015).
Clay, minerals particularly certain common clay minerals like kaolinite,
montmorillonite, and illite, are good tracers of bedrock weathering activities
(Tang et al. 2002). Furthermore, the
kinds and amounts of clay minerals are thought to be a significant restriction
on soil's physical and chemical characteristics.
Potassium
being an imperative plant nutrient plays several roles in plants such as enzyme
activation, protein synthesis, ion absorption and transport, photosynthesis and
respiration (Mengel, 2007). Among the major plant nutrients in soil, potassium
is the most abundant. Its amount in the soils varies depending on parent
material, degree of weathering, gains through fertilizers and losses through
crop removal, erosion and leaching. Total K content in soils ranges between 0.5
– 2.5 % with lower values in coarse-textured soils formed from sand stones or
quartzite and higher content in soils developed from parent material rich in K-
bearing minerals (Havlin et al.
2005).
Soil
potassium is found in four diverse forms viz soil solution K, exchangeable,
non-exchangeable and mineral potassium. Soil solution K form is most mobile and
prone to leaching in soils. Exchangeable and solution K are frequently regarded
as easily accessible forms to plant, while non-exchangeable and mineral K are
slowly available forms. Potassium that is only accessible gradually, which is
fixed and non-exchangeable, is the form trapped between the layers or sheets of
certain clay minerals; plants can use only very little of it during a single
growing season (Spark 1987). The major sources of non-exchangeable K in soils
are K-rich 2:1 clay minerals such as micas (illite) clays which also fix K
between their layers when they become dry, but do not release all of the fixed
K when wet. However, the distributions of different forms of K in soil
characteristics are linked to soils. such as soil minerals, particle size
distribution, cation exchange capacity (CEC), and soil salinity. The
relationship between K forms and soil properties can be used to predict K
availability in soil, K cycling and K supplying power of soils (Sharpley, 1989;
Najafi Ghiri et al.
2011).
It
has been revealed that under multiple cropping systems, the potassium status of
soil is depleting rapidly and various potassium pools in soil is essential for
sustainable crop production (Fareeha Habib et
al. 2014). The potassium release rates from soil under long term cropping,
fertilizer application and manuring helps to predict the fate of added K in
soil as well as nature of K supply from soil to plant (Samra and Swarup, 2001).
Potassium as a macronutrient is often taken up in large quantities by crops
under intensive cropping and its uptake is in many crops almost equal to
nitrogen (Marschner, 1995).
Based
on the weathering phase of these minerals, potassium discharge from the
interlayer is extremely slow (Rehm and Schmitt, 2002). Particle size and
chemical content affect the discharge of K from clay minerals (Huang, 2005). K
that is easily accessible is either dissolved (water soluble) or retained on
the top of clay particles (exchangeable K). Fixed or non-exchangeable forms of
potassium, according to Bhonsel et al.
(1992), may be the primary source of potassium for plants. Clay content and
clay mineralogy of soil, as well as the crops cultivated, control a dynamic
equilibrium that occurs between various forms of potassium in soils and the
destiny of applied K in soil. Vermiculite and beidellite have a greater K
fixation capability than montmorillonite among expanding 2:1 layer silicates
(Ross and Cline 1984). Depending on how much weathering has occurred and other
variables, soil micas or illites have three capacities to fix or release K.
(Tributh et al. 1987).
In
addition, minerals’ K release to soluble and exchangeable forms and its
adsorption by exchange sites depends on the equilibrium between different
phases of soils K (McLean and Watson 1985) which may be affected by such
factors as root uptake, fertilizer K applied, soil moisture, soil pH and soil
temperature (Sparks 1987). Several investigations have shown a link with clay
mineralogy composition and potassium forms (Sharpley 1989; Bohnsle et al. 1992; Liu et al. 1997; Ghosh and Singh 2001; Surapaneni et al. 2002; Srinivasarao et
al. 2006). Understanding the nutritional condition and nutrient-supplying
capacity of soils requires a thorough understanding of clay mineralogy. The
mineralogy of soils may have a significant impact on the dynamics of K.
(Surapaneni et al. 2002). In most
tropical and sub-tropical regions, information concerning K distribution in
particle size fractions of soils was also very scanty. The connections among
clay mineralogy and potassium forms, on the other hand, may be utilized to
assess prospective soil K richness, forecast potassium cycles, and predict
plant absorption (Sharpley, 1989). In Imo State, Southeastern Nigeria, there is
little research / knowledge on the clay mineralogy and potassium condition of
land utilized for various agricultural uses. This study was therefore designed
to generate information relating to the mineralogical properties of soils of
contrasting parent materials as they affect the potassium status, adsorption
and kinetics in Imo State.
The
specific objectives are:
i.
to identify and
characterize the clay minerals of some soils formed from contrasting parent
materials in Imo State.
ii.
to determine the
different forms of K and their relationships with the clay minerals in these
soils.
iii.
to determine the K
fixation capacity and the kinetics of K adsorption in these soils.
iv.
to determine the
relationship between the clay minerals and the K-sorption characteristics of
these soils.
v.
to determine the
relationship between the clay minerals and K kinetics.
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