ABSTRACT
The effect of sesquioxides and carbon content on soil structural stability was carried out on soil samples collected from four plantation land use systems (cocoa, coconut, oil palm and rubber plantation) at three depths (0-20cm, 20-40cm, 40-60cm) in Edo state. The study also assessed the physicochemical properties of the study soils as well as the relationship between sesquioxides, organic carbon and heavy metals content with depth. Spatial variability of selected properties was assessed with the help of geostatistical map tool and a 4x3 factorial analysis in RCBD was carried on the laboratory data, while FLSD at 5% was used for separation of statistically significant means. The relationships between selected soil properties were assessed by simple linear correlation and multiple linear regression. The result shows that the soils were generally sandy loam, there were no significant differences on percent water stable aggregate (WSA) or mean weight diameter of aggregate for the different land use systems studied. The oil palm land use recorded the highest mean weight diameter of aggregate stability followed by cocoa and rubber while the lowest value was observed in coconut land use but the highest percent water stable aggregate was observed in rubber land use, (85.49%) followed by coconut, (77.41%) oil palm, (76.48%) while the lowest value was observed in cocoa, (74.68%) land use. Both aggregate stability index showed increase with increased soil depth in the different land uses. Soil pH in H2O and KCl were highly acidic, the value for pH in H2O ranged from 4.75-5.22 while in KCl it ranged from 4.22-4.77, and both were significantly different at p<0.05. Organic carbon was low and differed significantly at p<0.05 in the different land uses, rubber plantation soil recorded the highest mean values of 1.76%, while coconut plantation recorded the lowest mean values of 0.88%. Micronutrients (Fe, Cu, Zn, Mn, and B) differed significantly at p<0.05 in the different land uses and also with depth. Oxides of Al and Fe varied from 2.92%- 363% and 4.25%-9.75% at 0-20cm soil depth for Al and Fe respectively. However, Al2O3 increased with increased soil depth, while Fe2O3 decreased with increased soil depth except in oil palm land use at 40-60cm soil depth. The Al2O3 and Fe2O3 had a positive significant correlation at p<0.05 with Mg, copper and zinc, while other parameters were not significantly different. The study showed that sesquioxides and organic carbon had a positive relationship with aggregate stability with coefficient of determination R2=0.35 in cocoa land use, while for coconut, oil palm and rubber plantation, Fe2O3 and organic carbon had a positive relationship with aggregate stability with coefficient of determination R2=0.27, R2=0.44 and R2=0.52 respectively in the different land uses. This shows that organic carbon and oxides of Fe contributed more to aggregate stability than oxides of Al. The Al2O3 and Fe2O3 affected the heavy metal content of the soil as indicated by a high Al2O3 coefficient of determination (R2=0.73) for coconut, R2=0.72 for oil palm and R2=0.64 for rubber on the heavy metal while in cocoa land use, with low coefficient of determination (R2=0.37). The Fe2O3 coefficient of determination was R2=0.80 for cocoa, R2=0.95 for coconut, R2=0.88 for oil palm and R2=0.69 for rubber land use. The result on spatial variability as shown by the Arc- map indicated that, the physicochemical properties vary highly in the different direction, in the different land uses. Therefore, there is a need for precision agriculture in these land uses in Edo State in order to reduce cost of input such as organic and inorganic fertilizer to achieved maximum output.
TABLE
OF CONTENTS
Title Page i
Declaration
ii
Certification iii
Dedication
iv
Acknowledgement v
Table of Contents
vi
List of Tables
ix
List of Figures x
Abstract xi
CHAPTER
1: INTRODUCTION 1
1.1 Objectives
of the study 4
CHAPTER 2: REVIEW OF RELATED LITERATURE 5
2.1 Plantation
crops and their Characteristics 5
2.2 Soil
and climate requirement of selected tree crops 8
2.3 Effect of land use system on plantation
crops 11
2.4 Agronomic practices for plantation crops 12
2.5 Spatial variation of physical and
chemical properties in soils 14
2.6 Effects of bulk density on soil properties 15
2.7 Effects of porosity on structural stability 17
2.8 Effects of hydraulic conductivity on soil
structure 18
2.9 Soil water 19
2.10 Effects of macro elements in plantation
soils 20
2.11 Effects of Aluminum and Hydrogen to
Plantation Crops 28
2.12 Importance
of micro elements to plantation crops 29
2.13 Effects of sesquioxides on soil structural
stability 38
2.14 Effect
of soil organic carbon on soil structural stability 42
CHAPTER
3:
MATERIALS AND METHODS 47
3.1 Description of study area 47
3.2 Soil Sampling 49
3.3 Laboratory analysis 49
3.3.1 Particle size determination
49
3.3.2 Bulk density
50
3.3.3 Soil
moisture content 51
3.3.4 Saturated hydraulic conductivity
51
3.3.5 Aggregate
size determination by wet sieve method 52
3.3.6 Organic carbon
53
3.3.7 Determination of soil pH
54
3.3.8 Determination of available phosphorus 55
3.3.9 Determination of exchangeable cations 56
3.3.10 Percentage base saturation (%BS) 57
3.3.11 Exchangeable
acidity 57
3.3.12 Determination of nitrogen 58
3.3.13 Extraction of micro nutrients 59
3.3.14 Determination of sesquioxides 59
3.3.15 Determination of boron 60
3.4 Statistical
analysis 59
CHAPTER
4: RESULTS AND DISCUSSION
4.1 Characteristics
of soil physical and chemical properties of the
study area 60
4.2 Effect of pH on Different Plantation Land 62
4.3 Percent organic matter and organic carbon
content in the different
plantation land uses 63
4.4 Nutrients
content in the different plantation land uses 64
4.5 Effective
cation exchange capacity contents in the different
plantation land uses 67
4.6 Percent
base saturation concentration in the different plantation
land
uses 68
4.7 Oxides of aluminum
content in the different plantation land uses 69
4.8 Oxides of iron content in the different
plantation land uses 70
4.9 Micro nutrients content
in the different plantation land uses 71
4.10 Physical
properties of the different land uses 75
4.11 Depth
variation of chemical properties of the plantation land uses 82
4.12 Relationship
between aggregate stability, sesquioxides and organic
carbon content in the different land uses 98
4.13 Relationship
between oxides of aluminum and heavy metals in the
different plantation land uses 107
4.14 Relationship
between oxides of iron and heavy metals in the
different plantation land uses 115
4 .15 Chemical
properties of arc map distribution in the different
land uses 123
4.16 Physical
properties of arc map distribution in the different
land uses 142
CHAPTER 5: CONCLUSION
AND RECOMMENDATIONS 158
5.1 Conclusion 148
5.2 Recommendations 149 References 150
Appendices 176
LIST OF TABLES
4.1: Chemical properties of the plantation
soils studied 61
4.2: Physical propertied of the different land
uses plantation 75
4.3: Depth variation of chemical properties of
the plantation land use
systems
studied 81
4.4: Range values of physical properties of soils 88
4.5: Correlation coefficient
between some chemical properties of the
different land uses 95
LISTS
OF FIGURES
3.1: Map
Showing the Study Area 48
4.4: Relationship
between aggregate stability sesquioxides and organic
carbon in plantation land
use 100
4.20: Relationship
between oxides of aluminium with heavy metals in
Plantation land uses 102
4.36: Relationship
between oxides of Iron with heavy metals in plantation
land uses 104
4.49: Arc
map showing soil pH in H2O distribution in the different land uses 125
4.50: Arc map
showing organic carbon concentration in the different land uses 127
4.51: Arc map
showing the nitrogen concentration in the different land uses 129
4.52: Arc map
showing the phosphorus concentration in the different land uses 131
4.53: Arc map
showing the potassium concentration in the different land uses 133
4.57: Arc map
showing Al2O3 concentration in the different land uses 141
4.58: Arc map
showing Fe2O3concentration in the different land uses 143
4.59: Arc map
showing zinc concentration in the different land uses 145
4.60: Arc map
showing copper concentration in the different land uses 147
4.63: Arc
map showing bulk density level in the different land uses 150
4.64: Arc
map showing total porosity level in the different land uses 152
4.65: Arc map
showing hydraulic conductivity level in the different land uses 154
CHAPTER 1
INTRODUCTION
Sesquioxides
refer to the oxides and hydroxides of iron, aluminium, titanium, manganese and
silicon in the soil (Ojo-Atere and Ajunwon, 1985 and Essoka and Esu, 2000).
They are crystalline and amorphous in nature, although a small fraction may be
present as organic complexes and together they influence several soils physicochemical
properties (Hassan et al., 2005).
They play significant roles in swelling and aggregate formation, cation
exchange capacity, anion adsorption, surface charge, Pspecific surface area,
nutrient transformation and pollutant retention in soils (Aghimien et al., 1988; Essoka and Esu, 2000 and
Hassan et al., 2005)
Sesquioxides,
also known as inorganic agent, particularly the amorphous forms are regarded as
a main mechanism for stabilizing aggregates (Six et al., 2004 and Kogel–Knabner et
al., 2008). They can stabilize organic matter and reduce SOM turnover due
to a large specific surface area (Eusterhues et al., 2003 and Wagai and Mayer, 2007). Saidy et al. (2012) reported, the chemical adsorption of SOM onto sesquioxides
surface by addition of artificial hydrous oxides. Barthes et al. (2008) reported that Al containing sesquioxides has a more
important aggregating role than soil organic matter in tropical soils. The role
of sesquioxides in the stabilization of SOM through the organomineral complexes
has been also reported (Vanlutzow et al.,
2006 and Kogel –Knaber et al., 2008).
In Ultisols and oxisoils however, large macro aggregates can be stabilized
solely by sesquioxides (Zhang and Horn, 2001and Barthes et al., 2008). Sesquioxides are very important, dense and resistant
to soil mechanical stress but are not stable under hydraulic stress (Zhou et al., 2012).
Elliot
(1986) reported that carbon concentration increase with increasing aggregate
size because large aggregate sizes are composed of micro aggregates and organic
binding agents. Hence, soil organic carbon (SOC) associated with aggregate is
an important element produced from mineralization because it is less subjected
to physical, microbial and enzymatic degradation (Trujilo et al., 1997). Polyvalent Al3+ and Fe3+ cations
improve soil structure through cationic bridging and formation of
organo-metallic compounds and gels (Amezketa, 1999). In acidic soils with low
clay and soil organic carbon contents such as oxisols both the Al3+
and Fe3+ control aggregation (Oades and Waters, 1991). The
interaction of Al and Fe oxides with Kaolinite can contribute with soil organic
carbon to improve the structural stability of soils (Six et al., 2000). The role of soil organic carbon as an aggregating
agent is very much dependent on the soil type and also, when Al and Fe oxides
are high, they reduce the effect of soil organic carbon as aggregating agent
(Oades, 1984 and Igwe et al., 1995)
Aggregate
stability of a soil define the resistant of soil structure against mechanical
or physio-chemical destructive force (Duniway et al., 2009). Aggregate stability strongly influences soil
structure and has relevant implication on soil organic carbon protection. Chenu
(2000) indicated the importance of soil organic carbon and humic compounds in
aggregate stabilization in two different mechanisms, first by increasing soil
hydrophobility and then reducing its breakdown by slaking. Secondly, organic
carbon increases the aggregate under particle cohesion. Soil organic carbon
affects porosity and indirectly aggregate stability (Luqato et al., 2009 and Papadopoulos, 2009). A
good soil structure is important in sustaining long term crop production on
agricultural soils because it influences water status, workability, resistant
to erosion, soil nutrients availability, crop growth and development (Piccolo
and Mbagwu, 1999 and Eneje et al.,
2005).
Land
use changes, mostly cultivation of natural lands in tropical areas have led to
negative effects on soil organic matter components (Fallahazade and Hajabbasi,
2011). With continuous growing of crop, physical properties and productivity of
soils commonly decline due to decrease in organic matter contents and soil pH (Oguike
and Mbagwu, 2009). Intensive cropping syetem has also been recorded to lead to
disaggregation in surface soil due to decrease in organic matter
The
sesquioxides and soil organic carbon in tropical and subtropical soils (eg
Ultisols and Oxisols) are widely regarded as the main inorganic and organic binding
agents of soil structural stability respectively (Six et al., 2004 and Bronick and Lal, 2005). The two binding agents
involve in soil aggregation have been investigated intensively by (Denef et al., 2012; Kogel-knabner et al., 2008 and Pronk et al., 2012). However, their
co-existence in the soils makes assessment of their contribution to structural
stability difficult. Therefore, this study was designed to assess the effect of
the sesquioxides and soil organic matter contents of different plantation land
use types on soil structure and fertility status of these soils.
1.1 OBJECTIVES OF THE STUDY
The
specific objectives include:
i.
To determine the soil
physico-chemical properties of four plantation land use system (Oil palm,
Rubber, Coco-nut and Cocoa) in Edo state.
ii.
To evaluate the
relationship between sesquioxides, organic carbon and soil aggregate stability
with depth.
iii.
To evaluate the
relationship between heavy metals and sesquioxides with depth.
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