Soil Dispersion and Hydraulic Conductivity in Relation to Clay Content, Exchangeable Sodium Percentage and Electrolyte Concentration in Soils of Southeastern Nigeria.
ABSTRACT
The objective of the study was to investigate the influence of some soil properties on dispersion and hydraulic conductivity of soils. Twenty soil samples collected from a depth of 0-20 cm were analyzed for their physical and chemical properties.
The total clay fraction (clay) of the particle size distribution ranged from 80 to 380 g/kg with a mean of 203 g/kg and a coefficient of variation (CV %) of 47.5%. Total silt was between 20 and 400 g/kg with a mean of 129g/kg and a CV of 86.9%.
Water-dispersible clay (WDC) varied from 60 to 160 g/kg, with an average WDC value of 95.5g/kg and a CV of 30.1%. The values of water- dispersible silt (WDSi) ranged between 10 and 380 g/kg with a mean value of 101g/kg and a coefficient of variation of 109.7%.
The electrical conductivity of the soils ranged from 16 to 22 μS/cm with a mean of 17.95 μS/cm and a coefficient of variation (CV %) of 9.30%. The exchangeable sodium percentage (ESP) of the soils varied from 0.43 to 2.76% with a mean of 1.1% and CV of 46.36%.
The soil organic carbon content of the soils ranged from 0.8g/kg to 27.2g/kg. Total nitrogen content of the soils ranged from 1.0 to 3.4g/kg with a mean of 2.4g/kg and a coefficient of variation (CV %) of 20.83%.
The clay dispersion ratio (CDR) of the soils varied between 0.16 and 0.92 with an average CDR of 0.58 and 46.6% coefficient of variation (CV).
The total clay content (clay) had highly significant negative correlations with dispersion ratio (DR), clay dispersion ratio (CDR) and clay dispersion index (CDI) ‘r’ = – 0.84**, – 0.91** and – 0.91** respectively, but positively, it had highly significant correlations with clay flocculation index (CFI) and aggregated silt and clay (ASC) ‘r’ = 0.91** and 0.96** respectively.
The total clay content correlated negatively and significantly with exchangeable sodium percentage (ESP) ‘r’ = – 0.49*.
Exchangeable sodium percentage had significant and positive correlations with exchangeable sodium (Na+), electrical conductivity (EC) and bulk density (BD) (r = 0.52*, 0.48* and 0.46* respectively). Soil organic carbon (SOC) correlated positively and significantly with hydraulic conductivity (Ksat) ‘r’ = 0.54*.
Dispersion ratio (DR) positively and highly significantly correlated with CDR and CDI (r = 0.86** and 0.87**) respectively but negatively and highly significantly, it correlated with CFI and ASC (r = -0.87** and -0.93**).
Clay dispersion ratio (CDR) had a positive and highly significant correlation with CDI (r = 0.99**). Water- dispersible clay (WDC) had a negative and significant correlation with BD (r = -0.53*).
Water-dispersible silt (WDSi) also had a negative and significant correlation with BD (r = -0.54*). Dispersion ratio (DR) had positive and significant correlations with pH both in water and in KCl (r = 0.46* and 0.56*) respectively.
The clay contents had positive and highly significant correlations with the levels of dispersion in all the soils. As the amount of 0.1N NaOH used for dispersion increased, the amount of dispersed clay increased while hydraulic conductivity of the soils decreased correspondingly.
TABLE OF CONTENTS
Title page…………i
Certification…..…ii
Dedication……..iii
Acknowledgement…………iv
Table of contents…..v-ix
List of tables …….. x-xi
Abstract. xii
CHAPTER ONE: INTRODUCTION
CHAPTER TWO: LITERATURE REVIEW
2.1 Nature of soil…….5
2.2 Functions of soil –Soil health….5
2.3 Soil clays…………6
2.4 Mineralogy of clays……7
2.5 Oxide minerals…………….8
2.6 Exchangeable sodium percentage (ESP) as a measure of soil sodicity……9
2.7 Soil electrolyte concentration (C)….11
2.8 Electrical conductivity (EC)…12
2.9 Salinity effects on soils………….13
2.10 Surface crusting……..15
2.11 Soil organic matter and soil organic carbon……17
2.12 Soil structural stability……………..18
2.13 Bulk density – Soil porosity…….18
2.14 Soil hydraulic properties…………19
2.15 Soil strength………..19
2.16 Aggregate stability of soils….…..20
2.17 Effects of electrolyte concentration and exchangeable sodium percentage on dispersion
and hydraulic conductivity of soils …20
2.18 Relationship between salinity and sodicity and soil physical properties (EC/SAR)……21
2.19 Consequences of soil dispersion in southeastern Nigeria…23
CHAPTER THREE: MATERIALS AND METHODS
3.1 Site description….25
3.2 Field study……………..27
3.3 Laboratory study and methods……….27
3.3.1 Oxide minerals determination…………………27
3.3.1.1 Process of digestion and silica determination…….28
3.3.1.2 Aluminium oxide determination………28
3.3.1.3 Other oxide minerals determination…………………..29
3.3.2 Soil bulk density determination………29
3.3.3 Saturated hydraulic conductivity…………30
3.3.4 Saturation percentage……………30
3.3.5 Total porosity…….30
3.3.6 Organic carbon and organic matter determination…31
3.3.7 Total nitrogen determination…….31
3.3.8 pH determination……….….31
3.3.9 Exchangeable acidity…..31
3.3.10 Available phosphorus…………31
3.3.11 Exchangeable bases and CEC………31
3.3.12 Exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR)…… 32
3.3.13 Electrical conductivity determination….32
3.3.14 Separation of water-stable aggregates…….32
3.3.15 Aggregate stability….33
3.3.16 State of aggregation………..33
3.3.17 Particle size distribution……33
3.3.18 Dispersion ratio………….34
3.3.19 Clay dispersion ratio……….34
3.3.20 Clay flocculation index…….34
3.3.21 Clay dispersion index………………34
3.3.22 Aggregated silt and clay…..34
3.3.23 Influence of sodium hydroxide saturation on dispersion and hydraulic conductivity at different levels of concentration………35
3.4 Data analysis….35
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Results……….36
4.1.1 Exchangeable bases, exchangeable acidity, CEC, available P, total nitrogen and soil organic carbon…36
4.1.2` Total clay, Total silt, sand, bulk density (BD), hydraulic conductivity (Ksat), total porosity and saturation percentage………38
4.1.3 Water-dispersible clay, water-dispersible silt, Dispersion ratio, Clay Dispersion Ratio,
Clay dispersion index, Clay Flocculation Index, and aggregated silt and clay………………40
4.1.4 Variability in the clay and silt contents of the studied soils…………………………….42
4.1.5 pH, electrical conductivity (EC), exchangeable sodium percentage (ESP) and sodium
adsorption ratio (SAR)…42
4.1.6 Water stable aggregates (WSA), mean weight diameter (MWD), Aggregate stability
(AS), and state of aggregation…………..…44
4.1.7 Oxide minerals contents of the soils……………46
4.1.8 Particle size distribution after dispersion with different levels of sodium hydroxide…..48
4.1.9 Hydraulic conductivity (Ksat) for the treated samples…………….50
4.1.10 Correlation coefficients for the linear relationships among water-dispersible fraction indices 52
4.1.11 Correlation coefficient matrix of water-dispersible clay (WDC) factors and some soil properties……..54
4.1.12 Correlation coefficients for the linear relationships between the oxide minerals, soil dispersion indices and other soil properties….56
4.1.13 Correlation coefficients between ESP, Exchangeable Cations, SAR, EC, Clay, CEC,BD, SOC, %Sat, WDC, and Ksat……58
4.1.14 Correlation coefficients for the linear relationships between different levels of dispersion and clay, silt and sand contents…60
4.1.15 Statistical relationships between different levels of dispersion and conductivity of water through the samples………62
4.2 Discussion….64
4.2.1 Roles of clay content, exchangeable sodium percentage and electrical conductivity on clay dispersion and hydraulic conductivity of soils….64
4.2.2 Relationships between iron and aluminium oxides, magnesium oxide, sodium oxide, potassium oxide, zinc oxide, cupper (II) oxide, silicon (IV) oxide, calcium oxide, manganese (II) oxide, dispersion indices and some soil properties………..…65
4.2.3 Relationships between organic carbon, CEC and soil dispersion indices………………66
4.2.4 The effects of different levels of dispersion on clay, silt, sand contents and hydraulic conductivity….67
4.2.5 The role of pH and bulk density on dispersion and hydraulic conductivity……………67
4.2.6 Electrolytic and sodicity effect on water-dispersible clay………………………….…..68
4.2.7 Implications of the results to land use and soil management………….……………..…68
CHAPTER FIVE: CONCLUSION
REFERENCES…………72-80
INTRODUCTION
Clay dispersion leads to soil erosion which is a major environmental problem in several parts of southeastern Nigeria. Soil erosion has been directly linked to the rate and volume of water- dispersible clay in a soil.
Potential soil erosion in areas of high rainfall has been estimated using water-dispersible clay and its indices (Amezketa et al., 1996; Igwe 2001; 2003; 2005; Igwe and Agbatah 2008; Calero et al., 2008).
Soil dispersion hardens soil and blocks water infiltration, making it difficult for plants to establish and grow. The major implications associated with decreased infiltration due to sodium-induced dispersion include; reduced plant available water and increased runoff and soil erosion (Warrence et al., 2003).
Dispersion causes a reduction in macro porosity and therefore, lowers infiltration rates and hydraulic conductivities as well as an increase in soil strength and other undesirable soil physical properties.
Exchangeable sodium percentage (ESP) is the amount of sodium adsorbed to soil particles and it is a measure of soil sodicity.
Sodic soils contain a large amount of exchangeable sodium and low levels of soluble salts. Gopali et al., 2007 stated that sodic soils are associated with structural changes that principally affect permeability of soils and that ESP is the major influence in the dispersibility of soils.
It is generally recognized that high levels of exchangeable sodium (Na+) lead to soil structural deterioration, which is accompanied by a reduction in water movement through the soil profile.
According to Hiebert et al., (2010), elevated levels of sodium in soil can result in deleterious sodic effects in soil. These effects include swelling and dispersion of clay, which can lead to decreased infiltration capacity and lower hydraulic conductivity, producing poorly drained soils.
REFERENCES
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Amezketa, E., Aragues R., and Gazol, R. (2004). Infiltration of water in disturbed soil columns as affected by clay dispersion and aggregate slaking. Spanish Journal of Agricultural Research 2(3), 459-471.
Amusan, A.A., Shitu A.K., Makinde W.O., and Orewole O. (2006). Assessment of changes in selected soil properties under different land use in Obafemi Awolowo University Community, Ile- Ife, Nigeria. Electron. J. Environ. Agric. Food Chem., 5(1): 1178-1184.
Anikwe, M.A.N. (2010). Carbon Storage in Soils of South Eastern Nigeria under Different Management Practices. Carbon Balance and Management 2010, 5: 5 doi: 10.1186/1750- 0680-5
Association of Official and Analytical Chemists (2003). Official Methods of Analysis of the Association of Official Analytical Chemists. 12th edition. Washington DC.
Bajracharya, R.M., Elliot, W.J., and Lal, R. (1992). Inter rill erodibility of some Ohio soils based on field rainfall simulations. Soil Science Society of America Journal, 56: 267 – 272.
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