ABSTRACT
The research was on the impact of Agricultural ecosystem on available carbon stock and soil water storage for irrigation management and climate change mitigation. A free survey method approach was used in the selection of sampling sites which covered six different land uses. These includes; virgin forest (VF), that is untilled forest, Afforestation Forest (AF), Grassland (GL), continuous cultivated land (CCL), cattle transient (CT) and Uncultivated land (UCL). The sampling sites were geo-referenced with the aid of Global Positioning System (GPS) technology to obtain the study co-ordinates. Disturbed soil samples at 0-30 cm, 30-60 cm and 60-90 cm depths were collected in both rainy and dry seasons from each of the six different ecosystems for laboratory analysis. Data collected includes particle size distribution, Soil bulk density, soil porosity, organic carbon, Net Carbon flux, soil moisture retention, Aggregate stability and structural stability index. Modeling and optimization of net carbon flux and organic carbon stock variation with seasons and soil moisture retention Agricultural practices were conducted using response surface method. Data collected were analyzed using ANOVA, correlation coefficient. The result obtained from the ANOVA suggested that for all the ecosystems, there was significant variations in soil moisture content at 0.01% for the depths considered. The highest values were recorded at 0-30 cm depth in rainy season and 60-90 cm depth in dry season. Agricultural practices significantly (P ≤ 0.05) influenced the organic carbon (OC) and total nitrogen (TN) content of the soils which were higher under natural undisturbed forestation land (VF) when compared with other agricultural practices in both seasons. Least values of OC and TN status of the site studies were obtained under continuously-cropped land (CCL) in raining season (2.50 gkg-1 for OC and 0.31 gkg-1 for TN) and dry season (3.57 gkg-1 for OC and 0.39 gkg-1 for TN). Also, in both seasons, no significant (P ≤ 0.05) difference was recorded between CT and GRL effect on OC whereas reverse was the case for TN. The lowest carbon stocks in the study sites were found in soils under CCL, CT and GRL which were 31.31, 34.98 and 33.39 Mgm-3 for raining season and 38.28, 43.32 and 45.22 Mgm-3 for dry season, respectively. Highest values of CO2 were recorded in CCL (4.96 % for rainy season and 7.77% for dry season) which was difference form those recorded in NUEFL by 78.02 % and AF by 69.56 % under raining season. Whereas, under dry season CCL recorded higher value of CO2 than those obtained for VF (74.26 %) and AF by 72. 20 %. Values of Net C flux were consistently negative and significantly lower in soils under CCL (-22.35 and -23.31) for rainy season. This shows that natural undisturbed forestation land (NUFL) and afforestation plantation (AFP) practices enhanced vegetation cover which improves sequestration of carbon flux as well as other soil properties and place soils of the study areas at a lower risk of degradation and climate change effect.
TABLE OF CONTENTS
Title Page i
Declaration page ii
Certificate page iii
Dedication iv
Acknowledgment v
Table of Contents vi
List of Tables ix
List of Figures x
Abstract xii
CHAPTER
1: INTRODUCTION
1.1
Background of the Study 1
1.2
Problem Statement 3
1.3
Aim/Objective of the
Study 4
1.4
Justification of the
Study 5
1.5
Scope of Study 6
CHAPTER
2: REVIEW OF RELATED LITERATURE
2.1 Effect
of agricultural practice on soil water 7
2.1.1 Soil
moisture retention 7
2.1.2 Soil
total porosity 8
2.2 Effect
of Agriculture Practices on Soil Stability 8
2.2.1 Soil
bulk density 8
2.2.2 Soil
structural stability 9
2.2.3 Soil
aggregate stability 11
2.3 Effect
of Agricultural Practice on Carbon Sequestration 14
2.3.1 Soil
organic carbon stock 14
2.3.2 Soil
carbon stock 17
2.3.3 Soil
carbon emission 20
CHAPTER
3: MATERIALS AND METHODS
3.1 Study
Site 23
3.2 Field
Work 23
3.3 Laboratory
Analysis 27
3.3.1 Particle size distribution 27
3.3.2 Soil bulk density 27
3.3.3 Soil porosity 27
3.3.4 Organic carbon 28
3.3.5 Net carbon flux 28
3.3.6 Soil moisture retention 28
3.3.7 Aggregate stability 29
3.3.8 Structural stability index (SI) 29
3.3.9 Statistical analysis and
optimization 30
CHAPTER
4: RESULTS
4.1 Soil
Water Characteristics as influenced by Agricultural Practices 34
4.1.1 Soil
moisture retention 34
4.1.1.1
Optimization of the soil moisture content of the study area 57
4.2 Effect
of Agricultural Practices and Soil Depth on Soil Stability 59
4.2.1 Soil
water stable aggregates
59
4.3 Effect
of Agricultural Practices and Soil Depth on Carbon Stock 64
4.3.1 Organic carbon storage in large and small
macro aggregates 64
4.3.2 Soil organic carbon stock and carbon emission 80
4.3.2.1 Optimization of the soil organic carbon
stocks 91
4.3.3 Net C
flux 93
4.3.4 Soil properties Interactions with seasons 104
CHAPTER 5: CONCLUSION AND
RECOMMENDATION
5.1 Conclusion 108
5.2 Recommendation 109
5.3 Contributions
to Knowledge 111
References 112
LIST
OF TABLES
3.1
Study sites and agricultural practice history of the 6 sites used for the study 26
3.2
Experimental range and the levels of the variables 31
3.3
Multilevel general factorial design for the three independent variables 32
4.1:
Relationships between agricultural practices, soil depth, moisture
content and total
porosity 44
4.2: ANOVA model fitting of the soil moisture
content in the study area 46
4.3: Fit Statistics for soil moisture
content 48
4.5: ANOVA
model fitting of the total porosity in the study area 52
4.6: Fit Statistics for soil total
porosity 54
4.7:
Effect of agricultural practices and soil depth on water stable aggregates 61
4.8:
Effect of agricultural practices and soil sampling depth on organic
carbon (gkg-1) sequestration in large and small
macro aggregates 66
4.9:
Effect of agricultural practices and soil sampling depth on organic carbon,
total nitrogen, and C/N ration in both seasons
69
4.10: ANOVA
model fitting of carbon to nitrogen ratio in the study area 77
4.11: Fit statistics for carbon to nitrogen ratio 79
4.12:
Effect of agricultural practices and soil depth on carbon stock and
carbon emission 83
4.13: Fit statistics for soil
organic carbon stock 88
4.14: ANOVA for the quadratic model
fitting to the soil organic carbon
stock of the study area 89
4.15:
Fit Statistics for net C flux 97
4.16: ANOVA for the model fitting to the net C flux
data 98
4.17: Simple correlation coefficient
(r) among selected soil properties under
raining and dry seasons 106
LIST
OF FIGURES
Pages
3.1: Sampling sites 24
4.1: Average values of soil moisture retention for all
the agricultural practices
at different soil
sampling depths for the rainy season 36
4.2: Average values of soil moisture retention for all
the agricultural practices
at different soil
sampling depths for the dry season 37
4.3: Effect of agricultural practices on soil moisture
retention (m3m-3)
during the rainy
season 39
4.4:
Interaction of agricultural practices and soil depth on total porosity
in raining season 41
4.5:
Interaction of agricultural practices and soil depth on total porosity
in dry season 42
4.6:
Surface bar chart plots for moisture content of the study area 50
4.7: Plots for the overall porosity of the research area
with seasons 56
4.8 Optimization curve of the soil moisture content 58
4.9: Interaction of agricultural
practices and soil depth on MWD 63
4.10: Interaction of agricultural practices and soil
depth on organic carbon
in raining season 72
4.11:
Interaction of agricultural practices and soil depth on organic carbon
in dry season 73
4.12: Interaction of agricultural practices and soil
depth on total nitrogen
in raining season 74
4.13:
Interaction of agricultural practices and soil depth on total nitrogen
in dry season 75
4.14: Factor plot representing the individual
variable effect on soil
carbon stock 85
4.15: Surface bar char plot of soil
organic carbon stock 86
4.16:
Organic carbon stocks in the soil's optimization curve 92
4.17:
Interaction of agricultural practices and soil depth on carbon stock
in both season 95
4.18:
Surface bar chart plots for net C flux 101
4.19:
Factor plot representing the individual variable effect on net C flux 103
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF
THE STUDY
Soil
is an important natural resource for any country's agricultural and industrial
development. Its numerous applications include providing anchorage for growing
plants and supplying nutrients and water to crops. Soil quality for
agricultural production is determined by the soil's sustainable supply of plant
nutrients, air, and water (Omeke, 2016), as well as its carbon status.
Unfortunately, most soils have degraded due to a variety of anthropogenic and
natural factors, resulting in a reduction in water retention capacity and
carbon storage. This has an impact on soil water conservation, irrigation water
requirements, and management strategies. Water management in irrigation
promotes the application of water in an amount sufficient to meet the needs of
the growing plant while preventing the plant from drying up or the soil being
saturated. Water and energy can be saved by reducing unnecessary applications
and increasing application precision. Farmers' various agricultural practices,
as well as the nature of the agricultural ecosystem before the agricultural
practice is implemented, influence soil water conservation and the density of
carbon stock available in the soil, which influences soil water retention and
crop irrigation schedules (Omeke, 2017).
Soil,
in general, plays an important role in the global water and carbon (C) cycles
because it contains approximately three times more carbon than the atmosphere
and approximately 3.8 times more carbon than the biotic pool (Zomer et al., 2002). As a result, soil serves
as both a source and a sink for atmospheric carbon and global water reservoir
depending upon land use and management practices (Lal, 2003 and Swift, 2001).
Soils are composed in part of decomposed plant matter and water (Sanderman et al., 2017). This means they contain a
lot of carbon and water from the atmosphere that those plants absorbed while
alive. Soils, particularly in agricultural zones where decomposition is slow,
can store or "sequester" this carbon or soil water for an extended
period. Without soil, this carbon or soil water would have completely returned
to the atmosphere as carbon dioxide (CO2), the primary greenhouse
gas responsible for climate change. Converting natural ecosystems such as
forests and grasslands to farmland, on the other hand, disturbs soil structure,
releasing much of the stored carbon and water, thus contributing to climate
change. According to research, the expansion of farmland over the last 12,000
years has released approximately 110 billion metric tons of carbon from the top
layer of soil, roughly equivalent to 80 years of current-day US consumption
(Sanderman et al., 2017). Management
practice with less soil disturbance increases soil water retention capacity and
carbon stock, whereas intensive cultivation, decreased moisture content and
carbon storage in soil ecosystems. Additionally, land intensifications and land
use changes from the native ecosystem, to the cultivated arable ecosystem
result in carbon loss, soil water loss, and decreased soil productivity (Nasrin
et al., 2016). As a result,
understanding the potential differential effects of agricultural practices on
soil water and carbon stock would improve agricultural sustainability, reduce
carbon discharge into the atmosphere, and aid in the management of irrigation
water needs in particular agricultural zones. Agricultural practices that
reduce water and carbon losses can result in net carbon accumulation in
agricultural soils by sequestering or storing atmospheric carbon dioxide (CO2)
in the soil, improving agricultural productivity and preventing climate damage.
The ability of agricultural practices to optimally sequester or store carbon
and soil water by rehabilitating utisols is significant (FAO, 2010). Practices
that sequester carbon in arable soils with minimal soil water loss tends to
improve resilience in the face of climate variability, which has increased
global temperature, resulting in increased soil moisture loss. As a result,
such practices are likely to improve long-term soil adaptation to changing
climates (FAO, 2010 and Giri et al.,
2007). As a result, managing soil organic carbon to keep the soil healthy and
with optimal water retention capacity is a major concern and a difficult task
in plant irrigation water management. A strategy for increasing and maintaining
high-productivity crop yields must include integrated approaches to soil carbon
and water management that recognize soil as the foundation and storehouse of
most plant nutrients and water that are essential for plant growth (Odunze et al., 2017). As a result,
understanding the dynamics of the soil carbon stock and water conservation
characteristics of the soil should be part of the considerations when planning
any irrigation management practices in any agricultural zone based on a
particular tillage practice implemented. These two parameters are influenced by
the physical and engineering properties of the soil. Optimizing the effects of
soil physical properties on these two important parameters will aid in
determining the optimal water and carbon stock requirement for crop growth, as
well as assisting in the selection of the best tillage and irrigation practices
that will aid crop growth and balance the carbon and water storage capacity in
the ecosystem. As a result, environmental degradation caused by excess carbon
transfer from the soil to the atmosphere is also avoided.
1.2 PROBLEM STATEMENT
Several
agricultural practices studied have revealed significant potential for managing
irrigation water by mitigating water and carbon stock in soils through the use
of recommended agricultural practices (Anil and Balkrishna, 2017). They also
discovered that certain agricultural practices and technologies could reduce
water losses or conserve water during irrigation, and aid in mitigating the
negative impact of agricultural practices on crop productivity and climate change.
However, a review of the literature revealed that there was insufficient
information on the effect of agricultural soil condition on soil water storage
capacity and carbon stock in Nigeria's South Eastern Agroecology. Furthermore,
there is insufficient information on the impact of soil physical property
manipulation from agricultural practices on soil carbon stock and water storage
capacity. Soil structure improves air and water permeability, which improves
soil's ability to absorb and hold water and carbon. A 1% increase in soil
organic carbon is reported to increase field capacity by 2.2%, permanent
wilting point by 1%, and available water capacity by 1.5%. (Hudson, 2006; Brady
and Weil, 2002). Soil tillage practices, therefore, improve soil organic matter
status and soil water retention (Kumar et
al., 2014). Thus, improving soil water retention capacity through soil
carbon content accumulation holds the key to soil productivity and
sustainability. However, there is a scarcity of data on the influence of water
storage capacity and carbon stock on various agricultural practices and soil
physical properties.
1.3
AIM/OBJECTIVE OF THE STUDY
1.3.1 Aim of the study
The
aim of the study is the assessment of the impact of agricultural ecosystem on
available carbon stock and soil water storage for irrigation management and
climate change mitigation
1.3.2 Specific objectives
of the study are;
i.
To determine the effect
of selected agricultural practices on variations soil physical properties.
ii.
To determine the effect
of selected agricultural practices on soil carbon stock and water storage
capacity.
iii.
To determine the optimum
soil water storage capacity and carbon stock for different agricultural
practices and seasons for irrigation management using the response surface
method.
1.4
THE JUSTIFICATION OF THE STUDY
Organic
soil Carbon has a significant impact on soil properties and is required for
crop production, environmental quality, nutrient cycling, and soil moisture
conservation. Carbon storage aids in mitigating global warming, reducing soil
degradation, and ensuring long-term agricultural production (Swift, 2001).
Changes in agricultural management practices will contribute to soil
degradation and change the amount and quality of soil organic carbon. This will
have an impact on the dynamics of carbon emissions to the atmosphere and water
storage capacity (Ogle et al., 2005).
Agricultural management practices that promote optimal ground cover reduced
soil disturbance, and water loss, on the other hands may contribute to carbon
storage and soil water enhancement. As a result, it would promote the long-term
productivity of soil ecology. Soil over-exploitation has resulted in the
exhaustion of intensive agricultural production systems, steadily declining
productivity (Reginald et al., 2007),
degraded soil quality, over-exposure of the soil profile, and high carbon
emissions into the atmosphere, environmental degradation, increased rate of
soil water loss, and excessive soil water demand for irrigation due to the high
rate of water loss. As a result, understanding the interactions of soil
physical properties and agricultural practices (farm conditions) with water
storage capacity and carbon stock will assist farmers in modifying their
agricultural practices while also conserving soil water and carbon to achieve
optimum soil performance to enhance productivity and balance the ecosystem.
This will reduce irrigation water demand in the face of global water scarcity
caused by global warming. It will also lower the cost of irrigation while
lowering the cost of farm input, lowering the overall cost of crop production
and increasing farmer profit at a higher margin. Thus, the current study is
justified.
1.5
SCOPE OF THE STUDY
The
research will be limited to evaluating the physical properties, carbon stock,
and water flux of the selected farm conditions using management models
influenced by different agricultural ecosystems. The agricultural ecosystem
(farm conditions) to be studied will consist of undeforested (virgin forest),
deforested, grassland, tilled land, cattle route, and uncultivated land. While
tilled land is the primary focus, other farm conditions were used as the
controls.
Login To Comment