CHAPTER ONE
BACKGROUND TO THE STUDY
1.1 INTRODUCTION
Soil is defined as the upper most layer
of the earth crust which supports plant growth. Soil is a living entity
on which all terrestrial habitats dwell on. Soil over the years has been
degraded by environmental degradation. Environmental degradation is a
worldwide environmental issue which affects not only the soil but also
the natural environment (Diaz and Telleria, 2014). Soil degradation
according to Davies, et al., (2010) is the decline in soil
quality that can be a result of many factors, especially continuous crop
production. Diaz and Telleria (2014), added that soils hold the
majority of the world’s biodiversity, and healthy soils are essential
for food production and an adequate water supply. Soil degradation also
has huge impact on biological degradation, which affects the microbial
community of the soil and can alter nutrient cycling pest and disease
control, and chemical transformation properties of the soil (Davies,
2009).
The environmental impact of soil
degradation on agriculture especially on arable crop production as
pointed out by Evans (2016) varies based on the wide variety of
agricultural practices employed around the world. Ultimately, the
environmental impact depends on the types of crop production and the
various types of farm/agricultural practices (such as shifting
cultivation, mixed cropping, plantation, bush fallowing etc). It also
depends on the system used by farmers. The connection between emissions
into the environment and the farming system is indirect, as it also
depends on other climate variables such as rainfall and temperature
(Evans, 2016). According to him, there are two types of indicators of
environmental impact of soil degradation on arable crop production
“means based”, which is based on the farm’s production methods, and
“effect based” which is the impact that farming methods have on the
farming system or on missions to the environmental.
Environmental degradation and loss of
ecosystem services will directly affect pests (weeds, insects and
pathogens), soil degradation and nutrient depletion, growing conditions
through climate and weather, as well as available water for irrigation
through impacts on rainfall and ground and surface water (Evans, 2016).
These are factors that individually could account for over 50% in loss
of crop yield in a given year. The interactions among these variables
(soil, land, water, vegetation, forest, etc), compounded by management
systems and society, are highly complex. A changing climate will affect
evapo-transpiration, rainfall, river flow, resilience to grazing,
insects, pathogens and risk of invasions, to mention a few (Diaz and
Telleria, 2014). The impact of soil degradation is intensified on all
sloping land, where with each degree of slope more of the surface soil
is carried away as the water moves downhill into valleys and streams.
The degradation of the natural soil
through various human activities such as farm practices causes severe
ecological problems and leads to damages of buildings, infrastructures,
land degradation and production of sediment (Ndakara and Abotutu, 2010).
Indeed soil erosion cause severe ecological degradation and leads to
damage of buildings, infrastructures, land degradation and production of
sediments (Ndakara and Efe, 2010). This process of soil erosion could
be slow and continues unnoticed, or it may occur at an alarming rate
causing serious loss of top soil.
Recent studies (such as Myers,
2013; Diaz and Telleria, 2014; Stockings, 2016; Evans, 2016) have shown
that the natural ecosystems suffer degradation losses. This is
especially evident along stream banks, where degradation occurs
naturally due to the powerful action of the adjacent moving water.
Increased soil losses occur on steep surfaces when a stream cuts through
adjacent land. Even on relatively flat land, stream banks are eroded
during heavy rains and flooding (Stocking, 2016). Although soil
degradation has been taking place very slowly in natural ecosystems
throughout geologic time, its cumulative impacts on soil quality over
billions of years have been significant.
Approximately 50% of the
earth’s land area is devoted to agriculture: About one-third is planted
to crops and two-thirds is grazing land (Myers, 2013). Forests occupy
about 20% of the world’s land area. Of these three areas, cropland is
most susceptible to degradation because of the frequent cultivation of
soils and that vegetation is often removed before the crops are planted
which exposes the soil to wind and rainfall energy. In addition,
cropland is often left without vegetative cover between planting which
intensifies degradation on agricultural lands, degradation rates that
are estimated to be 75 times greater than degradation in natural forest
areas (Myers, 2013).
Nutrient depletion as a form
of soil degradation has a severe economic impact at the global scale,
especially in Africa. Stoorvogel, et al. (1993) estimated
nutrient balances for 38 countries in Africa. Annual depletion rates of
soil fertility were estimated at 22 kg nitrogen (N), 3 kg phosphorus
(P), and 15 kg potassium (K) per ha. In Nigeria, soil degradation alone
results in an annual loss of Nitrogen and Phosphorus totalling US$1.5
billion. In South Asia, the annual economic loss is estimated at US$600
million for nutrient loss by erosion, and US$1,200 million from soil
fertility depletion (Stocking, 2016; UNEP, 2014).
In developing countries, soil
degradation is particularly severe on small farms that are often located
on marginal lands where the soil quality is poor and the topography is
frequently steep. In addition, poor farmers tend to raise raw crops such
as corn and beans; raw crops are highly susceptible to degradation
because the crop vegetation does not cover the entire tilled soil
surface (Stockings, 2016). The prime causes for exposed soil are
overgrazing and the removal of crop residues for cooking fuel but even
by the 1990s researchers realized that these causes are so intertwined
with the effects of rainfall variability and the occurrence of drought
on the vegetation that it can be difficult to determine how much erosion
is due to human activity (Boardman, 2010). During the degradation
process organic matter and essential plant nutrients are removed from
the soil and soil depth is reduced. These changes not only inhibit
vegetative growth but reduce the presence of valuable biota and the
overall biodiversity of the soil (Evans, 2016). These factors interact,
making it almost impossible to separate the specific impacts of one
factor from another (Boardman, 2010). During soil degradation by
rainfall, water runoff significantly increases with less water entering
the soil and less water available to support the growing vegetation.
Degraded soil carries away vital plant nutrients such as nitrogen,
phosphorus, potassium, and calcium. Typically, the degraded soil
contains about three times more nutrients per unit weight than are left
in the remaining soil.
Once the organic matter layer
is depleted, the productivity of the ecosystem, as measured by plant
biomass, declines both because of the degraded soil structure and the
depletion of nutrients that were contained in the organic matter. In
addition to low yields, the total biomass of the biota and overall
biodiversity of these ecosystems is substantially reduced (Boardman,
2010). He observed that soil degradation has indirect effects on
ecosystems that may be nearly as damaging as the direct effects in
reducing plant biomass productivity. Beyond the damage to rain fed
agricultural and forestry ecosystems, the effects of soil degradation
reach far into surrounding environments (Chambers, et al., 2012).
The environmental impact of soil
degradation on agriculture, especially on arable crop production
involves a variety of factors from the soil, to water, the air, animal
and soil diversity, people, plants and the food itself. Some of the
environmental issues that are related to agriculture are climate change,
deforestation, genetic engineering, irrigation problems, pollutions,
soil degradation, and waste (UN, 2007). Generally, soil degradation and
erosion removes soil at approximately the same rate that soil is formed
(Boardman, 2010). This result to the low crop yield of agricultural
production. However, increased soil degradation at a much faster rate
than it is formed is a recent problem and due to mankind’s action which
leave the land unprotected and vulnerable coupled with naturally
occurring erosive rainfall or wind storms makes soil degradation huge
environmental issues. This occurs in both agricultural/farming areas as
well as the natural environment (Diaz and Telleria, 2014). It is against
this background that this study is carried out to examine the effects
of soil degradation on crop production: an assessment of total nitrogen
and available phosphorus in the rainforest of Obiaruku, Delta State.
1.2 STATEMENT OF RESEARCH PROBLEM
The major problems associated
with soil degradation include loss of farmlands, poor agricultural
productivity, loss of live stock breeding, erosional problems, soil
infertility, among others. The problems could be stated and discussed
below;
Loss of organic matter:
Soils may be susceptible to erosion, loss of organic matter leading to
poor structure, and pollution by pesticides and heavy metals. Soil
erosion has effects external to the farm, through siltation of water
courses and transport of pesticides and nutrients. The latter can also
be conducted to water via leaching and sub-surface flow. Cultivation
systems are among the most important factors influencing soil properties
(Boardman, 2010). Both ground and surface waters can be influenced by
nutrient and pesticide pollution from arable land. This results in
reduction in the quality of drinking water and necessitates expensive
treatment. It also has ecological consequences for aquatic life
(Stockings, 2016).
Loss of soil nutrients:
Another major problem associated with soil degradation is that
intensification of farming systems, encouraged by government has
exacerbated the problems of soil degradation. Nutrients, especially
phosphates cause eutrophication of water, which upsets the ecological
balance and can result in undesirable effects such as fish death and
algal blooms. Problems are greatest where farming is not intensive and
lower in Southern Nigeria. Nitrates are particularly prone to leaching,
and concerns over nitrates in water supplies have led to legislation in
the form of the Nitrates (Evans, 2016).
Loss of ecosystem:
Environmental degradation and loss of ecosystem services will directly
affect pests (Weeds, insects and pathogens), soil degradation and
nutrient depletion, growing conditions through climate and weather, as
well as available water for irrigation through impacts on rainfall and
ground and surface water. A changing climate will affect
evapo-transpiration, rainfall, river flow, resilience to grazing,
insects, pathogens and risk of invasions, to mention a few (UNEP, 2008).
Unsustainable practices in irrigation and production may lead to
increases salinization of soil, nutrient depletion and erosion. Nutrient
depletion as a form of land degradation has a severe economic impact at
the global scale, especially in Sub-Sahara Africa. Stoorvogel, et al.
(2013) estimated nutrient balances for 38 countries in Sub-Sahara
Africa. It was discovered that there is an annual depletion of soil
fertility, annual economic loss, nutrient loss all caused by soil
degradation and erosion (UNEP, 2014; Stocking, 2016).
Loss of farmland: Soil
degradation has posed a serious threat to human existence most
especially farmers. Environmental hazards such as soil degradation and
erosion among others has given rise to lopsided concentration of
vehicles in some of the road thus making the road a place of great
conflict between man and the environment (Cohen, 2007). Obiaruku and its
environs are facing the problem of soil degradation. Thus, during the
rainy season, some areas become inhabitable and uncomfortable for human
dwelling. Also farmlands are flooded leading to premature harvest of
farm produce and was away of the topsoil thereby resulting to low crop
yield o agricultural productivity.
Reduction in soil fertility:
Soil degradation has severely caused damage to the soil by greatly
reducing the fertility of the soil and cause the development of
monstrous soil gullies in the land. Even though there is no specific
data on statistics on the extent of soil degradation and fertility in
degradation of Obiaruku region, there is evidence to show that majority
of the topsoil is increasingly depleted by soil erosion. This is
depicted by outdated and unscientific practices. The impact of
urbanization and mechanized farming has utter-aggravated the problem.
Today, soil degradation is now
synonymous with disaster, dangers, despair, destruction, death and
damage to economic properties as well as environmental problems caused
by flooding, removal of the natural vegetative cover exposes the soil to
the action of wind running water. Some of the natural factors which
tends to increase soil degradation in Obiaruku region includes, soil
type and soil has much impact on farmlands and arable crop production
effects of organic matter on soil properties, soil is also lost when it
is down slope, road network, commercial places, farmlands which is as a
result of mechanization and urbanization, and other life and properties
are not well of the range of soil degradation. It has been observed that
due to its topography and heavy rainfall, the entire land of Obiaruku
or rather most part of the region has been plague and subjected to soil
degradation which has heavily contributed to a menace to her
inhabitants. A lot of studies have been carried out by scholars on the
causes of soil degradation. This study will therefore focus on the
effects of soil degradation on agricultural crop production in the
rainforest region of Obiaruku using total nitrogen and available
phosphorus as a case study. This study will also address the identified
problems and proffer solution accordingly.
1.3 AIM AND OBJECTIVES
The aim of this study is to examine the
effects of soil degradation on crop production: an assessment of total
nitrogen and available phosphorus in the rainforest of Obiaruku, Delta
State. However, the specific objectives of the study are to:
- examine the causes of soil degradation and their effects;
- examine the concentrations of total nitrogen in degraded and rainforest control sites;
iii. examine the concentrations of available phosphorus in degraded and rainforest control sites;
- postulate management approaches to conserve the rainforest soils and manage the degraded ecosystem.
1.4 RESEARCH HYPOTHESES
The following null research hypotheses formulated were tested in this study:
- There is no significance difference in the concentration of total
nitrogen in the soil between the degraded and control sites at 0.05
level of confidence.
- There is no significance difference in the concentration of
available phosphorus in the soil between the degraded and control sites
at 0.05 level of confidence.
1.5 SIGNIFICANCE OF THE STUDY
This research work will cover the entire
of Obiaruku region which falls under the rainforest environment and
it’s to look intensively at the effects of soil degradation on crop
production: an assessment of total nitrogen and available phosphorus in
the rainforest of Obiaruku, Delta State. It would offer suggestion(s) on
the problems of soil degradation and environmental degradation at large
and its adverse effect on agricultural crop production.
Therefore, the study will help
in help to unfold the deterioration effects of soil degradation on
agricultural crop production as well as causes of soil degradation in
the rainforest region and other related land use in Obiaruku region, and
the level of total nitrogen and available phosphorus nutrient in
degraded soil and also to look at the concentrations of total nitrogen
and available phosphorus in degraded and rainforest control sites, and
also to look at or proffer lasting solution(s) to combat the soil
degradation problem(s) on agricultural crop production in the study
area.
1.6 SCOPE AND LIMITATION OF THE STUDY
The scope of this study was strictly
based on the effects of soil degradation on crop production: an
assessment of total nitrogen and available phosphorus in the rainforest
of Obiaruku, Delta State and to offer suggestion(s) on the causes and
effects of soil degradation in the study area.
The scope of the study was
initially designated to cover all the communities that make Obiaruku.
However, because of time and financial constraints, the scope was sealed
down. In this regard the only selected major areas were covered in this
study. The time was also short to carry out the research work coupled
with academic work. These limitations notwithstanding, the
data/information generated from this study and research finding will be
of invaluable assistance of the management of soil degradation and its
control.
1.7 THE STUDY AREA
1.7.1 Location and Boundary
Obiaruku covers about 158 square kilometers (61 square mile). It is located on latitude 050 401 and 050 451 North of the equator, and longitudes 060 051 and 060 251 East
of the Greenwich meridian. On the north, it is bounded by Urhonigbe in
Edo State, on the East and South, it is bounded by Ukwuani and Ika
South Local Government Areas of Delta State respectively. On the west,
it is bounded by Abraka in Ethiope East Local Government Area of Delta
State. Obiaruku region consist of various settlements and its made up of
various quarters namely: Umuebu, Obinomba, Odaku, Isumpe, Umusume,
Odafe, Ogbeje, and Obiaruku main town.