ABSTRACT
During agricultural operations such as bush clearing, soil preparation, planting, and crop harvesting the soil is subjected to high compaction stresses. However, the magnitude of stress-induced on the soil by agricultural machines is seldom studied, especially in the humid tropics. This study examines the response of Zea mays and Phaseolus vulgaris on loamy clay soil and loamy sand soil compacted at different levels. The soils were compacted at the following levels: 0 blow (control), 5 blows, 10 blows and 15 blows. Numerical simulation was performed using PLAXIS 2D to ascertain the stress distribution in the soil due to vehicular load. Results show that the coefficient of permeability of the soil was affected by compaction with more than a 70 % reduction in the loamy clay. The compaction of the soil led to a reduction in the plant height, biomass, and root density. There was a significant difference between the root weight based on the different compaction levels and soil type with p-values < 0.001. Generally, on both the loamy clay and loamy sand soils there were apparent signs of compaction stresses on the leaves of the Zea mays and Phaseolus vulgaris, making the plant leaves pale in colour and pancake-like. The from the numerical simulation show that stress distribution in the soil due to vehicular loads increase in the void ratio and increase in depth directly below the axles but increases with depth between the axles. There was a higher concentration of the effective stress at the midpoint (i.e., directly under the wheel) of the tyres compared to the stresses in between the axles; with a maximum of 107.53kPa, 101.67kPa, 87.49kPa, 79.19kPa, 72.31kPa for 0.1, 0.3, 0.5, 0.7 and 0.9 soil void ratios, respectively for the front axle. Rear tyres transmit more stress to the soil compared to the front tyres. It is concluded that soil compaction changes soil structure by increasing bulk density and penetration resistance and decreasing the total porosity of the soil, with negative consequences to crop growth and development.
TABLE OF CONTENTS
Cover
page i
Title
page ii
Approval
page iii
Certification iv
Dedication v
Acknowledgment vi
Table
of contents vii
Abstract vi
CHAPTER
1
INTRODUCTION 1
1.1
Background of the study 1
1.2
Statement of the problem 4
1.3
Aim and objectives 5
1.4
Justification of study 6
1.5
Scope of study 6
CHAPTER
2
LITERATURE REVIEW 7
2.1
Food security and agricultural mechanization 7
2.2
Soil compaction 10
2.3
Causes of soil compaction 12
2.4
Factors affecting soil compaction 14
2.5
Measurement of soil compaction 16
2.6
Benefit of soil compaction 18
2.7
Effect of soil compaction on soil properties 18
2.7.1
Soil porosity 22
2.7.2
Soil strength 22
2.7.3
Water infiltration rate 23
2.7.4
Reduction of aeration 23
2.8
Effect of soil compaction on agricultural productivity 23
2.8.1
Effect of soil compaction on crop growth and development 24
2.8.2
Plant Height - 25
2.8.3
Crop vegetative growth 25
2.8.4
Crop root systems and growth 26
2.8.5
Crop lodging 28
2.8.6
Plant nutrient uptake 28
2.8.7
Plant water uptake 29
2.8.8
Effect of soil compaction on biomass and crop yield and economics 30
2.8.9
Effect of Soil Compaction on Draft Force Requirement and Fuel
Use 31
CHAPTER
3
MATERIAL AND METHOD 33
3.1 Study Area 32
3.2
Materials 34
3.3
Experimentation 34
3.4Sampling 34
3.5Soil
test 35
3.5.1
Particle size distribution 35
3.5.2
Natural moisture content 35
3.5.3
Permeability Test 36
3.5.4 Oedometer Test 37
3.5.5 Direct Shear Test 39
3.6
Compaction Treatment of the Soil 40
3.7
Planting 40
3.8
Measurement of the Plant Traits 41
3.9 Finite Element Model 41
3.9.1 Mesh and Model Geometry 41
3.9.2
Stress-strain constitutive relationship 42
3.10
Statistical Analysis 43
CHAPTER 4
RESULTS AND DISCUSSION 44
4.1 Soil Characterization 44
4.2 Effect of compaction on bulk
density 45
4.3 Effect of compaction on the
permeability of the soil 47
4.4 Effect of compaction on plant growth 48
4.4.1 Plant height 48
4.4.2 Plant root 50
4.5 Stress distribution in the soil
due to compaction 54
4.5.1 Soil model and properties 54
4.5.2 Vehicle model and tyre configuration 51
4.5.3 Finite element simulation 56
4.5.4 Vertical stress propagation 58
4.5.5
Effective stress between the axle 60
CHAPTER 5
CONCLUSION
AND RECOMMENDATION 63
5.1 Conclusions 63
5.2 Recommendation 64
REFERENCES 62
APPENDIX 77
LIST
OF FIGURES
Figure 2.1: Soil compacted due to machinery traffic causing soil damage,
increased
waterlogging, and reduced water
infiltration. 8
Figure 2.2 Effect of soil compaction on the properties of soil and its
productivity 10
Figure 2.3 Degradation of soil due to soil compaction in different
continents 12
Figure 2.4: Estimated area of field trafficking for three typical tillage
system
experiment in Champaign County 20
Figure 2.5: Effect of soil compaction due to combining harvester traffic on
penetrometer resistance ploughed silty
loam soil. 21
Figure 2.6: Soil compaction due to machinery traffic in a soybean crop
field 23
Figure 2.7: Effect of soil compaction on corn growth and development 25
Figure 2.8: Rooting length of cereals 7 days after planting
under-uncompacted
and compacted soil. 27
Figure. 3.1 Map of the study location 33
Figure 3.2 Oedometer test machine 38
Figure 4.1: Particle size distribution of the loamy sand (LS) and loamy
clay (LC)
used for the study 39
Figure 4.2: Plot of bulk density against compaction level 40
Figure 4.3: Plot of coefficient of permeability of soil against the
different compaction
level 42
Figure 4.4a: Plot of plant height (cm) against the plant age (days) for zea
maize (corn) 42
Figure 4.4b: Plot of plant height (cm) against the plant age (days) for
Phaseolus vulgaris 44
Figure 4.5: Plot of the number of roots versus the soil depth (cm) 47
Figure 4.6: Boxplot of the biomass 49
Figure 4.7: Calibration of the Oedometer test parameters 50
Figure 4.8: Model domain showing the boundary conditions, soil and wheel
loads 53
Figure 4.9: Effective vertical stress distribution in the soil with depth
for the various
void ratios 54
Figure 4.10: Effective vertical stress distribution between the axles in the
soil with
depth for the various void ratios 56
Figure 4.11: Stress bulb of the soil induced by tractor loads 58
LIST OF TABLES
Table 4.1: Summary of the properties of the soil used for the study 40
Table 4.2: Plant roots as affected by soil compaction. 46
Table 4.3: Calibration of the soil parameters obtained from the oedometer
test 50
Table 4.4: Configuration of the
vehicle and tyre properties used in the PLAXIS 2D model 52
CHAPTER 1
INTRODUCTION
1.1
Background
of the Study
The
performance of agricultural soils plays an important role in food production
necessary for the survival of man (Hillel, 2009). Soil is a non-renewable
resource, which has the potential for a high rate of degradation but has slow
regeneration and formation processes (Van-Camp et al., 2004). Hence, the sustainable use of soil is essential to
curb the menace of food insecurity, water inadequacy, biodiversity, and climate
change (Lal, 2009).
Soil
degradation causes a substantial reduction in agricultural productivity and has
always been a great distress to farmers (Duran and Rodriguez, 2008). The rapid
increase in global population has led to excessive land exploitation, resulting
from the mechanization of forests and farms in almost all developed countries
as well as developing countries. Hence,
soil degradation will remain an important global issue in the twenty-first
century (Yang et al., 2016).
Soil
compaction is one of the physical forms of soil degradation which leads to
changes in soil structure and influences soil productivity (Hamza and Anderson,
2003). Again, a plant’s ability to obtain mineral nutrients and water from the
soil is dependent on its capacity to develop extensive root systems. Soil
compaction, which refers to the densification of soil layers (Arora, 2007), may
restrict deep root growth. This will adversely affect plant access to subsoil
water, especially during periods of sparse rainfall and high
evapotranspiration; this is typical within the middle to late growing season
(Chen and Weil, 2010). The resulting increased drought stress may limit plant
growth and yield (Bouwman and Arts, 2000).
Hence, the compaction of agricultural soils has been a major problem for
agricultural practice globally including in Nigeria, leading to a reduction in
crop yield (Adekalu and Osunbitan, 2000).
Unlike
other forms of soil degradation (e.g., water logging, salinity, or soil
erosion), which can be identified from the surface of the soil, compaction of
soils causes hidden destruction of the soil structure (Hamza and Anderson,
2003). Hence, it is difficult to locate and rationalize. According to Cavalieri
et al. (2008), changes in soil water
content because of soil compaction modify soil moisture tension and diffusion
of gases, resistance to penetration, hydraulic conductivity, air permeability
and other soil physical properties. Soil
compaction causes a reduction in soil porosity with a concomitant increase in
soil bulk density and a decrease in air permeability and hydraulic conductivity
(Arora, 2007). It is also coupled with the decline in hydraulic conductivity of
soil and the development of hard crust below the tilled layer and smeared layer
(Arora, 2007). While some crops require moderate compaction, others are very
sensitive to compaction (Adekalu and Osunbitan, 2000).
Currently,
heavier, and stronger Machines/tractors have been used on farmland aimed at
reducing human labour (Mari et al.,
2006). The vast majority of soil compaction and shearing in modern agriculture
is due to vehicular traffic, which is an integral part of the soil management
system. The increasing size of agricultural implements is a significant cause
of induced soil compaction and deterioration of soil structure. In addition,
many agronomic practices must be performed frequently in a very short time and
when soil is wet and conducive to compaction. This results in deeper stress
penetration and subsoil compaction.
To
alleviate the effect of soil compaction deep ripping has been used (Schmidt et al., 1994), but the benefits of deep
tillage may be short-living (Calonego and Rosolem, 2010) and costly in terms of
energy and time. The use of deep tillage to alleviate compaction also disrupts
the surface mulch that develops after years of no-till management, increasing
the soil’s susceptibility to erosion and sealing (Wiermann et al., 2000).
Reduction
in crop yield due to soil compaction may be minimized if we can develop a
better understanding of soil behaviour under various stresses. This will entail
the development of compaction characteristic curves and predictive equations
which will provide a guide for farmers in choosing the best condition for
carrying out farming operations (Adekalu and Osunbitan, 2000). Again, this is
particularly important in Nigeria where there is no standardization of
machinery for agricultural production (Adekalu and Osunbitan, 2000). The effect
of compaction on the stress distribution with depth in agricultural soils in
Nigeria is rarely studied. Since soil type can affect the rate of soil compaction,it
is pertinent to study the effects of compaction on the productivity of
different varieties of crops in Nigeria. Hence, this present study intends to
ascertain the effects of different capacityloads on soil physical properties
relevant to root proliferation and crop yield using maize (Zea mays) and
beans (Phaseolus vulgaris) as a case study.
Maize (Zea mays) and beans (Phaseolus
vulgaris) are one of the major food grains of the tropics, “grown in the
rain forest and derived savannah zones of Nigeria” (Olaniyi and Adewale, 2012).
Its economic value has increased tremendously over the years. According to Iken
and Amusa, (2004), because many agro-based industries depend on maize as raw
material, maize farming (cultivation) has transited from subsistence-level to
commercial level. Apart from sorghum, maize is the most important cereal crop
in Nigeria (FAO, 2013). The Central Bank
of Nigeria in 2014, estimated a 1.2% growth in maize crop production (CBN,
2014). Abba (2017) noted that Nigeria as the largest producer of maize in
Africa, producing about 8.0 million tons per annum; most of these productions
are mechanized. It is well known that compaction could affect plant growth, but
this effect has been rarely quantified. In this regard, the results from the
study will be important in quantifying the effects of compaction on maize
productivity. This study performed a numerical simulation to understand the elastoplastic
stress-strain response of the soil to due induced stress from tractors.
1.2
Statement
of the Problem
Soil degradation is a global menace, leading to
ecological challenges such as soil erosion, landslides, and poor performance of
plants. The physicochemical properties of soil are altered due to soil
degradation (Yang et al., 2016),
which invariably affects the agricultural potential of the soil. Hence,
altering biodiversity and ecosystem succession (Kumar et al., 2013), reduces seedling's development and growth (Juying et al., 2009; Shrivastva and Kumar,
2015). This, therefore, affects food security. Soil degradation is caused by
natural (Singh and Kumar 2018) or anthropogenic activities (Kumar et al. 2016).
Soil compaction is the physical form of soil degradation resulting sometimes
from farming practices.
The growing human population has necessitated the need
for increased food production to cater for the teeming population. Hence, the
use of heavy machines/tractors for farming activities has become a norm.
According to Muhammed et al. (2015), this increased use of power machines with
high wheel loads leads to the compaction of the subsoil layers in agricultural
fields or lands.
Soil compaction occurs mostly from the passage of
tractor wheels during cultivation practice. Studies have shown that compaction
alters the soil's chemical and physical properties such as bulk density,
hydraulic conductivity, water infiltration, soil air permeability etc. (Lipec
and Hatano, 2003; Sakai et al.,
2008). The compaction of soil is responsible for the degradation of soil across
the globe (Flowers and Lal, 1998; Hamza and Anderson, 2003). This affects plant
root proliferation and invariably food security. To curb this menace, it will
be necessary to ascertain the optimum level of compaction required for
different classes and types of plant root systems. Again, if the soil
compaction is carried out in steep slopes, this can result in increased runoff
and ultimately increase soil erosion and sediment transport which could be a
serious problem for the landscape as well as crop survival.
1.3
Aim
and Objectives
The general objective of this study is to ascertain
the effect of compaction of two different agricultural soils on the performance
of maize (Zea mays) and Cowpea (Phaseolus vulgaris) and to model
the stress distribution in soil due to tractor loads.
1.3.1 Specific Objectives
The specific objectives of the study are to:
(i)
Ascertain the response of
the above and below-ground traits of maize and cowpea due to varying levels of
compaction.
(ii)
Study the relationship
between soil type, soil hydraulic conductivity of the soil and compaction
levels.
(iii)
Compare the performance
of the maize and cowpea on soil compacted at different levels.
(iv)
Carry out a numerical
simulation of the stress regime in the soil due to applied machinery loads.
1.4
Justification
of Study
Compaction has been shown to affect nutrient uptake
and may induce nutrient deficiencies (Batey, 2009). Reduced aeration in wheel
tracks has been shown to increase the potential for denitrification, which
could cause nitrogen deficiency if enough nitrogen is lost. Knowing that maize
is one of the important cereals consumed in Nigeria (Abba, 2017), it will be important
to ascertain the impact of compaction on its productivity and performance. The
result of the study will serve as a guide to farmers and decision-makers in
choosing the best type of equipment to be used for farming activities. This
study will also contribute to more understanding of the effect of compaction on
the physical properties of different types of soil. It will also quantify the
effect of compaction on soil physical properties due to soil type or
classification.
1.5
Scope
of Study
The performance of Zea mays and Phaseolus
vulgarisin soils compacted at different levels was evaluated. Several
laboratory experiments such as permeability, bulk density and infiltration test
etc. were carried out using standard laboratory techniques to ascertain the
physical properties of the soil compacted with varying loads. Again, the study
ascertained the above-ground and below-ground traits of the Zea mays and
Phaseolus vulgarisplants as they grow. A numerical model was carried out
to determine the stress distribution in the soil due to typical loads coming
from tractors.
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