The atmosphere of the Earth may be divided into several distinct layers, as the following figure indicates.
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| Layers of the Earth's atmosphere |
Friday, 6 December 2013
Thursday, 5 December 2013
atmospheric pressure
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In aviation and television weather reports, pressure is given in inches of mercury ("Hg), while meteorologists use millibars (mb), the unit of pressure found on weather maps. |
As an example, consider a "unit area" of 1 square inch. At sea level, the weight of the air above this unit area would (on average) weigh 14.7 pounds! That means pressure applied by this air on the unit area would be 14.7 pounds per square inch. Meteorologists use a metric unit for pressure called a millibar and the average pressure at sea level is 1013.25 millibars.
Wednesday, 4 December 2013
The atmosphere
The atmosphere of Earth is a layer of gasessurrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperatureextremes between day and night (the diurnal temperature variation).
The common name given to the atmospheric gases used in breathing and photosynthesis isair. By volume, dry air contains 78.09% nitrogen, 20.95% oxygen,[1] 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%. Although air content andatmospheric pressure vary at different layers, air suitable for the survival of terrestrial plants andterrestrial animals currently is only known to be found in Earth's troposphere and artificial atmospheres.
The atmosphere has a mass of about 5×1018 kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The Kármán line, at 100 km (62 mi), or 1.57% of the Earth's radius, is often used as the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reenty of spacecraft at an altitude of around 120 km (75 mi). Several layerscan be distinguished in the atmosphere, based on characteristics such as temperature and composition
Composition
Air is mainly composed of nitrogen, oxygen, andargon, which together constitute the major gases of the atmosphere. Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration of water vapor (a greenhouse gas) varies significantly from around 10 ppmv in the coldest portions of the atmosphere to as much as 5% by volume in hot, humid air masses, and concentrations of other atmospheric gases are typically provided for dry air without any water vapor.[3] The remaining gases are often referred to as trace gases,[4] among which are thegreenhouse gases such as carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds. Many substances of natural origin may be present in locally and seasonally variable small amounts as aerosols in an unfiltered air sample, including dust of mineral and organic composition, pollen and spores, sea spray, andvolcanic ash. Various industrial pollutants also may be present as gases or aerosols, such aschlorine (elemental or in compounds), fluorinecompounds and elemental mercury vapor. Sulfur compounds such as hydrogen sulfide and sulfur dioxide (SO2) may be derived from natural sources or from industrial air pollution.
Tuesday, 3 December 2013
MORSE CODES
Morse Code
| .- | A | Alpha |
|---|---|---|
| -... | B | Bravo |
| -.-. | C | Charlie |
| -.. | D | Delta |
| . | E | Echo |
| ..-. | F | Foxtrot |
| --. | G | Golf |
| .... | H | Hotel |
| .. | I | India |
| .--- | J | Juliet |
| -.- | K | Kilo |
| .-.. | L | Lima |
| -- | M | Mike |
| -. | N | November |
| --- | O | Oscar |
| .--. | P | Papa |
| --.- | Q | Quebec |
| .-. | R | Romeo |
| ... | S | Sierra |
| - | T | Tango |
| ..- | U | Uniform |
| ...- | V | Victor |
| .-- | W | Whiskey |
| -..- | X | X-Ray |
| -.-- | Y | Yankee |
| --.. | Z | Zulu |
| .---- | 1 | Wun |
| ..--- | 2 | Too |
| ...-- | 3 | Tree |
| ....- | 4 | Fow-er |
| ..... | 5 | Fife |
| -.... | 6 | Six |
| --... | 7 | Seven |
| ---.. | 8 | Ait |
| ----. | 9 | Nin-er |
| ----- | 0 | Ze-ro |
Thursday, 7 November 2013
THE SOIL
Soil is a
natural body of decomposed mineral and organic matter, layered upon the earth´s
surface, which is capable of supporting plants life. i.e. soil as a natural
entity evolved from an underlying basement material (rocks) forming horizons,
which is in direct respond to certain factors and processes which are present
upon the surface of the earth, and that
it has the ability to support plant growth.
As firmly
established, V.V Dokuchaev (1846-1903), the father of Pedology; a Russian
Scientist who was a geologist by training, advanced that soil develops because
of the interplay of parent material, climate, organisms, topography, and time.
All processes of soil formation, including those of weathering and
re-distribution of the products of weathering, results from the combine
operation of the soil forming processes. More so, the properties and character
of the soil is also in direct relationship with the factors and processes of
soil formation. i.e. how a soil behaves or react to certain biogenic and
anthropogenic influences, is a product of the factors and processes that has
given rise to its formation. For example, soil properties such as, texture,
structure, chemical composition, mineralogy, PH (degree of alkalinity or
acidity), etc are all in direct relationship to the type of parent material,
prevailing climate pattern, organism type, and the dominant soil forming
processes in operations. This informs the wide variations of soil type and
properties present on the earth surface.
Soil is the most basic of all resources, considering
the role it plays in the provision of food, ecosystem sustainability, and
shelter of the world population of several billions. It is unfortunately non-renewable nature of
resource is further compound by the fact that once place under continuous use,
it tends to undergo some depreciation in quality, unless adequate measures are taken to minimized or prevent
such. When soil undergoes negative changes, thereby regressing from a state of
high production to low usefulness which normally result in reduced yield due to
lack or insufficiency of nutrient and water availability for plant growth or
higher costs and decrease efficiency of added nutrient, it is said to have
undergone degradation.(Young,1976).
Many ancient civilizations thrived on good soil and
decline as soil becomes degraded through misuses. E.g Riparion and Harappan
Kalibargan culture in the Indus Valley. The problem of soil degradation has
increased drastically since the 18th century and this is due to
improper land use and poor land management techniques.
Based on the judgment of over 250 experts around the
world, Global Assessment of Human induced Soil Degradation (GLASOD) estimated
that nearly 2 billion hectares of land (15% of total global land area of 13
billion hectares, or 23% of the 8.7 billion hectares used by humans for crops,
pasture, and forest and woodlands) had been degraded as a result of human
activities since world war ΙΙ. Out of this, about 749 million hectares had been
lightly degraded, indicating that productivity had been reduced somewhat but
could be restored through modifications in farm management: 910 million
hectares had been moderately degraded, indicating greater losses in productivity
that would require costlier improvement to reverse: 305 million hectares were
strongly or extremely degraded, implying losses in productivity that is virtually
irreversible (Older et. al., 1991).
GLASOD estimated that 38 percent of the world’s cropland
has been degraded to some extent since 1945. Degradation had affected 65
percent of cropland in Africa, 51 percent of cropland in Latin America, 38
percent of cropland in Asia, 25 percent of cropland in North America, Europe
and Oceania. GLASOD identified erosion (primarily due to water) as the
principal cause of cropland degradation, affecting 1.6 million hectares (mostly
in Asia and Africa).
Soil degradation is one of the guidelines and
indicator used in ascertaining the manifestation of land degradation; hence it
is one of the building block components of land degradation which has
interlocks with many other components of land degradation. It is also
conceptually rather wide and difficult to accommodate in a few simple measures.
(Micheal and Nurnagham, 2000) (See fig1.1.)
According to Lindert (2000), soil degradation is
define as any chemical, physical or biological change in the soil’s condition
that lowers it agricultural productivity. Defined as its contribution to the
economic value of yields per unit of land area, holding other agricultural
inputs same.
Soil degradation occurs under a wide variety of
conditions and circumstances. Nevertheless, some environments are more at risk
of soil degradation. These risks of degradation affects how people manage their
biophysical environment, but also how their environment affects them. Depending
on the type of condition and the prevailing circumstances that results in the
various forms of soil degradation, some of these forms of soil degradation are
reversible, while others are not. Whether a particular form of degradation is
reversible or irreversible depends on whether or not there exists an
economically feasible substitute for the degraded soil property. Soil nutrient
depletion, for example, is largely reversible because organic or inorganic
fertilizers can substitute for nutrient taken up in harvested crops or lost
through other processes. Soil erosion on the hand, is ineffectively
irreversible because there is no economically feasible substitute for such
properties as soil depth or water holding capacity-although the productivity
impact of soil erosion will depend critically on initial topsoil.
Some environments are naturally more at risk to land
degradation than others. Factors such as steep slopes, high rainfall intensity
and soil organic matter influence the likelihood of the occurrence of
degradation. Identification of these factors allows land users to implement
techniques that safeguard against loss of productivity. Measures taken to
prevent, control, counteract soil degradation is referred to as soil
conservation or management and or copping strategies.
Management practices also exert a significant
influence on the susceptibility of a landscape to degradation. Extensive and
poorly manage land use system are more likely to degrade than intensive,
intricately-manage plots. Milder forms of land degradation can be reversed by
changes in land management techniques, but more serious forms of degradation
may be extremely expensive to reserve (such as salinity) or may be, for
practical purposes irreversible. The aim of conservation is to ensure a
sustainable high yield of crops over time and over a given area. Various
techniques are employed for sustainable agriculture. Just as soil degradation
varied in wide variety of forms, so also the techniques for cropping with it varied
remarkably. These include a commitment to proper soil management: in some
cases, conventional high analysis fertilizers may be most effective tool to
use, while in some, techniques such as terracing, mulching, windbreak cropping
etc is more effective. However, an important step towards ensuring effective
soil conservation is to get information through state extensive publications on
condition of the soil.
According to
expert-based GLASOD Survey referred to earlier on, about 15% of soil on the
earth surface is degraded (Oldman et. al., 1990). The highest proportions were
reported in Europe (25%), Asia (18%) and African (16%): the least is North
America (5%). As a proportion of the degraded area, soil erosion is the most
extensive, causing more than 83% of the area degraded world wide (ranging from
99% in North America 61% in Europe): nutrient depletion causes a little over
4%, but 28% in South America; salinity less than 4% world wide but 7% in Asia;
contamination about 1% globally but 8% in Europe: soil physical problems 4%
world wide but 16% in Europe (Oldman et. al.,1990).
1.2. Statement
of the Research problem
Soil
degradation has the potential for inflicting serious damages to food security,
Ecosystem balance, organism existence, wildlife preservation, water supply and
quality, and the general wellbeing of the earth’s biosphere if left
unchecked and managed. The damaging
effects potentially represent in soil degradation is inherit in the fact that
it is associated with lots of processes and mechanisms which are biophysical in
nature that has the potential of causing severe implications for the
environment wherever and whenever they are in operation; problems of
sedimentation, carbon emissions affecting climate change, reduced watershed
function, and changes in natural habitants leading to loss of genetics stock
and biodiversity are some of the problems associated with soil degradation.
Within the context of food security, rural livelihood
and world population growth, soil degradation forms a crux of interest for
study, vise-versa it’s developments, effect and required management techniques
for sustainable development. The population is projected to attain 8 billion in
2020, 35% higher than the 1995 world population figure (UN 1996). 70-75%of the
projected population is said to be within the rural areas, 60% of the
population are in the developing countries population employed by agriculture
and Agro-allied sectors of the economy (UN 2000). Consequently, the demand for
food, shelter, clothing and water supply will rise, as income grows diet
diversify, and urban growth accelerated. The growth of world population has
made various government authorities across the world to organized conferences
and workshops targeted at global food security, which there is the advocacy of
increase in food production by 70%, to enable every human being has access to
adequate food. This increase will have to come about mainly through investment
in the agricultural sector by at least 60% over current levels. Greater
priority has to be given to agricultural research, development and productivity
(FAO, 2009). More so, The International Food Policy Research Institute (IFPRI)
estimates that if current level of agricultural research and investments in
agriculture and social welfare continues developing countries food grain
production will increase by only 1.5% per year during 1995-2020, and livestock
production will grow by 2.7% per year, rates much lower than in previous decade
(Pinstrop-Anderson, Pandya-lorch, and Rose grant, 1997). However, due to the
lack of comprehensive date linking soil quality to agricultural productivity
among other factors, the models on which 2020 projections of future production
growth are based do not include soil quality as a component of productivity,
nor the building of soil capital and other land-improving investment as
component of agricultural investment. Thus there is growing concern in some
quarters that inter-temporal degradation of agricultural soil resources-that
is, a decline in long-term productivity potential-is already seriously limiting
production in the developing world (Lal 1990; UNEP 1982: UNCED 1992).
International
bodies such as FAO, IFPRI, World Bank and UNEP had developed or proposed
programs aimed at responding to these growing concerns of the productivity
potential of the agricultural sector with respect to the degradation of agricultural
soil resources works are being done to monitor soil degradation more
systematically. International agricultural research institute have expanded
their work to understand and improve tropical soil management and
rehabilitation (FAO 1992; IFAD 1992; WOORLD RANK; Fortin and Engelberg 1997;
Dumenski et al, 1991; ISRIC 1998; Nelson et al, 1997).
Several land degradation studies have been carried out
in Nigeria, on the effect of land use on soil. Landuse changes from tropical
rainforest to intensive cropping have effects on fertility and stability of
soils present in the South Western Nigeria (Lal, 1976). The depletion of major
soil elements such as silicon(si) calcium(ca) magnesium(mg) potassium(k) and
sodium(Na) and the relative accumulation of iron (Fe) and Aluminum (Al) oxides
and hydroxides in the deeply weathered soil is associated with the soils in the
above named region of Nigeria. The Cation Exchange Capacity (CEC) and PH
(degree of alkalinity or acidity) values are also generally low, as is the
content of soil organic matter while soil texture is dominated by sand and
clay, with only minor amount of silt. Similarly, observation was made also by
Jones (1997) and Yakubu (2004) concerning soils present in zaria region (a
region found in the Northern plain of Nigeria), that a decrease in carbon
content is associated with soils present in samara area of zaria after 20 years
of cultivation without the application of any form of fertilizer. That the mean
values of soil texture, soil moisture, water soluble aggregate, organic matter,
nitrogen, phosphorus, CEC, Aluminum, PH, and base saturates were in most cases
significantly higher over the natural vegetation than on arable land, home
garden plot, fallow land, rangeland and orchard. Land clearance and conversion
from native vegetation to pinus and eucalyptus plantation has a range of mostly
negative effects on soil quality, as reported by Jaiyeoba (1996) concerning
Afaka Forest Reserve near Kaduna in Kaduna state.
As in most places in Nigeria, factors such as high
population growth, rapid change in landuse, urbanization, landscape alteration,
pollution, the impact of high rainfall intensity resulting to flooding in
combination with continuous crop cultivation which has lead to serious land
degradation, is also associated with the Evbohighae community of Edo state
(south western Nigeria located in the rainforest of eco-climate zone of
Nigeria). One of the distinctive characteristics of the Nigerian eco-climatic
zone is abundant rainfall which usually measures over 2000mm annually. Although
the area is forested, but such forest is been depleted over time, exposing the
soil surface to direct rainfall impact and subsequently generating huge amount
of over-land flow or surface run-off. This run-off causes soil erosion and
consequently the depletion of soil fertility.
Soil fertility is a major challenge facing the
Nigerian farmers, such that various conservative methods have been developed by
them to combat its effects. These conservative methods vary from one area to
the other, depending on several factors. To effectively tackle soil degradation
in this region (Evobhighae community of Edo state), adequate and continuous
information is required on the nature and extent of soil degradation and the
ways farmers manage the problem.
While some information on the causes, processes and
pattern of soil degradation is available for some areas, and the rate of
generating of such information rapidly increasing, there is generally lack of
quantitative information in many areas, and none for the Evbohighae community
of Edo State, Nigeria. The need for such information is what constitutes the
problem of interest, over which this study seeks to advance an understanding.
The result question that the study seeks to address includes;
·
What are the different forms and extent of soil degradation
processes over Evbohighae community of Edo State, Nigeria?
·
What is the severity of the problem?
·
What are farmers’ concerns and how do they perceive it?
·
What are farmers’ responses to the problem in term of copping
strategies?
1.3 Aim and
Objectives
The aim of this study is to assess the extent and
severity of soil degradation in the Evbohighae community of Edo State Nigeria,
through rapid quantification of soil loss rate and the evident in the field of
what farmers have said they see, and copping strategies of the farmers in the
area. This aim is to be achieved through the following specific objectives.
i.
Examine the form of soil degradation in the area.
ii.
Assess the severity of various forms of soil degradation in
the area.
iii.
Identify the indicators farmers use in assessing soil
degradation in the area.
iv.
Examine the ways the farmers and the community cope with the
problem of soil degradation in the area.
1.4 Research
Hypothesis.
Arising from the aim and objectives of the study are
the following hypothesis;
i.
Soil degradation in the area is severe.
ii.
Farmers’ in the area have evolved a variety of methods in
copping with soil degradation.
1.5 Scope of
the study
Figure 1.4 and
1.5, shows the location of Evbohighae community and the study area. The study
is confined to Evbohighae community area located on the plain of Orhionmwon
local government area of Edo state. The area demarcated for the study is rather
arbitrary and is some 20km radius around Evbohighae community. The area
compasses settlements with varying degree of accessibility. While some are
relatively accessible by road along the major road axis around the community,
some are in remote location, accessible only through footpath. Irrespective of the smallness of the area,
there is also some degree of heterogeneity in the physiographic condition of
the area. The area encompasses upland plains and flood plains which together
with the diversity on settlement pattern is expected to result in some
variations of soil pattern and therefore landuse, and consequently variation in
soil degradation.
In terms of the focus of the subject matter, the scope
is confined to assessable on field. The interview with the farmers on the other
hand will aim at collecting information on the practical ways they assess soil
degradation and how they are copping with the challenge.
1.6
Justification of the Study
The ability of the Global Food and Agricultural System
to meet future demand for food, feed and fiber is severely threatened by a
number of risk factors and challenges, among which is land degradation. One
billion people on the earth surface today are at present chronically
undernourished and many more suffers from various forms of malnutrition, which
signal a failure of global governance in the food and agriculture domain
(FOA-OECD Outlook, 2009).
The recent world food crises of 2007-2008 provide a
clear reminder that the global food and agricultural systems including current
natural agricultural trade policies and world trade roles, is highly
vulnerable. Such that, unless deliberate actions are taken to address that risk,
the focus in the long-term adequacy and sustainability of food supplies
projected by global Authorities (United Nation, World Bank, FAO and UNEP) to
assist the almost 1billion people who are undernourished to day and to prevent
the death of thousands of young children who die every day from disease which
they would mostly likely survive under conditions of better nutrition, would
seriously be jeopardized (FAO 2008). Hence, the series of world food summits
that had been held between the early 80s to recent (2010) calls for the
intensification of food production and food supplies through mechanized
agriculture and the use of hybridized agricultural seeds and roots for
sustainable food production.
This intensification programmed has the potential for
increasing food production for increasing production and supply, while
simultaneously strengthening the regional and national economies. However, it
is the land users in the marginal areas who are most seriously affected by land
degradation. The opportunity for intensification on their land is low. This
often leaves the users and owners of the more marginal land with no prospect of
developing their limited land resources, and therefore frequently dependent on
government subsidies.(Dregne, 1997). Hitherto, this call for intensification of
agricultural food production as seen in the light of achieving 70% increase in
food production, increase in agric-agro allied investment over current levels,
and greater priority given to agricultural research, development and extension
services in order to achieve the yield and productivity gains that are needed
to feed the world in 2020, plays down to the bearing capability of the hand
resources to march up with these desired goals. More often than not, the land
resource had not been able to march up with these humanitarian targets due to
land resources misuse and mismanagement, inadequate and lack of quantitative as
well as qualitative information about the causes, processes and patterns of
land degradation. Hence, this challenge of land degradation poses to the
desired sustainable food production and increase in the socio-economic system
(United Nations 1997).
Soil resource is essentially non-renewable. Hence, it
is necessary to adapt a positive approach to sustainable management of this
finite resource. The challenge of African agriculture is not only enhancing
production to meet the increase food demand of the expanding population, but
also the judicious use of soils so that their productivity is sustained in the
foreseeable future. Perhaps the starting point for meeting the land degradation
challenge in the 21 century is producing accurate and relevant information on
the farm, extent and severity and the farmers perspective of the soil
degradation problem in the various ecological zone of the country (Nigeria).
However, levels of soil degradation and conservation for various localities are
necessary for proper comparison and for future planning. Although, a lot may be
known about soil degradation and conservation in other parts of Nigeria, very
little or none is known of such with respect to the Evobhighae community of Edo
state.
It is in the light of this: sustainable food
production to meet the ever growing demandful population; rehabilitation of
degraded land in both qualitative and quantitative comprehensive manner; the
provision of adequate and relevant quantitative as well as qualitative
information about it causes, processes and patterns of land degradation;
Availability of land degradation data for proper comparison with other areas
and for future planning, is this study justified.
1.7 Literature
review
1.7.1 Definition of soil degradation
Soil, like the human body have a self regulating
ability, as well as capacity self restoration through soil formation. The self
restoration ability however, is at extremely slow rate. It is also the case
that soil misuse and extreme of condition can upset the self regulating ability
of the soil and causes it to regress from high to low state of usefulness and
or diminishes its productivity (Deji 1970; FAO 1997; PHY 1979; Kowal and Kassam
1978). Soil degradation phenomena may take place without man’s influence, but
it is often accelerated when man’s activities directly or indirectly set in
motion the disappearance of the protective cover of the natural vegetation
(Jaiyeoba and Leow, 1983).
Given the numerous activities of man that had great
impact on soil, cultivation is the most prevalent. Thus, a condition of decline
of soil quality and ability to be multipurpose resource is describes as soil
degradation (IFAD 1992). Similarly, Lindert (2000) defines soil degradation
more specifically as “any chemical, physical, or biological changes in the
soil’s condition that lowers it agricultural productivity, defined as its contribution
to the economic value of yields per unit of land area, holding other
agricultural inputs same”. Another definition describes it on the emphasis of
land i.e. land degradation generally signifies the temporary or permanent
decline in the productive capacity of the land i.e. the aggregate diminution of
the productive potential of the land, including its major uses (rain-fed,
arable, irrigated, rangeland, forest), its farming systems (e.g. smallholder subsistence)
and its value as an economic resource (UN/FAO, 2000). This link between
degradation (which is often caused by land users’ practices) and its effects on
land use is central to nearly all published definition of land degradation. The
emphasis on land rather than soil broadens the focus to include natural
resources such as climate, water, landforms and vegetation. The productivity of
grassland and forest resource, in addition to that of cropland, is embodied in
this definition. Other definitions differentiate between reversible and
irreversible land degradation. While the terms are used here, the degree of
reversibility is not of a particularly useful measure-given sufficient time all
degradation can be reversed. So, reversibility depends upon whose perspective
is being assessed and what time scale is envisaged. Whilst soil degradation is recognized as a major aspect of
land degradation (as illustrated in fig 1.1), other processes which affects
productive capacity of cropland, rangeland and forests such as lowering of the
water table and deforestation are captured by the concept of land degradation.
Hitherto, a degraded soil is not simply one that is poor;
it is a soil in which the productive capacity has substantially lowered as
compared with the one under natural condition or ecologically stable
agriculture.
1.7.2 Forms of
soil degradation
Depending on the dominant processes, land degradation
displays different forms and affects on the land’s productivity. All forms of
land degradation will ultimate lead to a reduction the soils’ fertility and
productivity (Blum, 1998). The forms of soil degradation result from both natural
and human induced processes, such as agricultural productivity. Some forms of
soil degradation are reversible; others are not. Wither a particular form of
degradation is reversible or irreversible depends on whether or not there exist
on economically feasible substitute for the degraded soil property. Soil
nutrient depletion, for example, is largely reversible because organic or
inorganic fertilizers can substitute for nutrients taken up in harvested crops
or lost through other processes. Soil erosion, on the other hand, is
effectively irreversible because there is no economically feasible substitute
for such properties as soil depth or water-holding capacity although the
productive impact of soil erosion will depend critically on initial top soil
dept. (Michael and Niamh, 2008)
1.7.2.1. Soil
erosion
Soil erosion is the most widely recognized and the
most common form of land degradation and therefore a major cause of falling
productivity. However, since the effect of soil loss varies depending on the
underlying soil type, soil loss by itself is not an appropriate proxy measure
for productivity decline. For example, a loss from 1mm from a soil in which the
nutrients are concentrated close to the surface will show a greater impact on
productivity than the same level of soil loss from a soil which the nutrient
are more widely distributed (e.g. a luvisol for the first case, and a vertisol
for the second case – see appendix for details).
Again, there is considerable linkage between erosion
and other type of degradation. For example; nutrients through taking more
nutrients away in the harvested crops than are returned, is less visible but is
common cause of soil fertility decline. Soil erosion by water often accompanies
such depletion of nutrients. An eroded soil will almost have less organic
matter (biological soil degradation), increased bulk density` (physical soil
degradation) and other problems such as water logging, salinity and sodicity.
a.
Soil erosion by water.
This type of erosion is referring to the removal of
soil particles by the action water’ this is usually seen:
Ø Sheet erosion by fluid
mechanism.
A more or less uniform removal of a thin layer of topsoil
by the action of fluid, (water). The soils are transported by rainwater surface
flow to the river and stream systems. Sheet erosion is characterized by a
lowering of the soil level, leaving raised pedestals where the root mass of the
vegetation protects it
Ø Rill erosion.
This type of erosion occurs in small channels in the
field, usually as a result of the action of water.
Ø Gully erosion.
This type of erosion occurs in large channels, similar
to incised rivers. This type of erosion can be triggered by the less or
vegetation in areas where the micro topography results in concentrated stream
flow during the rains. They can also be triggered by erosion along livestock
tracks, footpaths and road edges. This process can start with rills’ and end up
with gullies that are tens of meters deep. One important feature of soil
erosion by water is the selective removal of the finer and more fertile
fraction of the soil.
(b). Soil
erosion by wind.
This refer to
the removal of soil particles by wind action usually this is sheet erosion,
where soil is removed in thin layers, but sometimes the effect of the wind can
curved and hollow and other features, such as dunes, barchans, losse, etc
depending on whether it is constructive or destructive in action.
1.7.2.2 Soil
Fertility Decline.
This form of soil degradation refers to the
degradation of soil physical, biological and chemical properties caused by;
(a). Reduction in soil organic matter, with associated
decline in soil biological activities.
(b). Degradation of soil physical properties as a
result of reduced organic matter (structure, aeration, and water-holding
capacity) caused by reduced organic matter (Om).
(c). Adverse changes in soil nutrient content leading
to deficiencies, or toxic levels, of nutrient essential for healthy plant
growth.
(d). Buildup of nutrient toxicities (by heavy metals,
xenobiotics, and acidification) through the incorrect application of
fertilizers.
1.7.2.3
Waterlogging.
This is a form of degradation which is caused by a
rise in around water close to the soil surface or inadequate drainage of
surface water, often resulting from poor irrigation management. As a result of
water loggings, water saturates the root zone leading to oxygen deficiency.
1.6.2.4
Salinity. This is increased in salt in the soil water
solutions or sodication on increase of sodium cations (Na†) on the soil
particles. Salination often occurs in conjunction with poor irrigation
management. Mostly, sodication tends to occur naturally. Areas where the water
table fluctuates may be prone to sodication. In humid regions, salt affected
soils occur only when subjected to sea water intrusion in river deltas and
other low lying land near the sea (ESCAP, 1990).
1.7.2.5
Sedimentation or ‘Soil burial’
This form may occur through flooding, where fertile
soil is buried under less fertile sediments; or wind blows, where sand
inundates grazing lands’ or catastrophic events such as volcanic eruptions.
In addition to
these principal forms of soil degradation, other common forms of soil degradation
includes;
(a). Lowering
of the water table.
This usually occurs where extraction of groundwater
has exceeded the natural recharge capacity of the water table for urban and
industrial uses also causes this form of land degradation.
(b). Loss of vegetation
cover.
Vegetation is
important in many ways, it protects the soil from erosion by wind and water and
it provides organic material to maintain levels of nutrients essential for
healthy plant growth. Plant roots helps to maintain soil structure and
facilitate water infiltration.
(c). Increased stoniness and rock cover of
the land.
This
will usually be associated with extreme levels of soil erosion causing
exhumation stones and rocks.
(d). contamination by hazardous waste.
Hazardous waste
is being produced in growing amount as a necessary or wasteful by-product in
the production of many products and chemicals. As treatment and safe dumping is
often a very costly affair, it is attractive to get rid of it cheaply and more
quickly. This results in careless storage in basins, dumping in careless mixed
with normal garbage, and dumping in water course and open field.
Although the
foregoing list neatly breaks down the components and forms of soil degradation
by cause, vary often these agents of degradation acts together. For example,
strong winds often occur at the form of a storm, thus wind erosion and water
erosion may result from the same event. Additionally, a soil that has suffered
some form of degradation may be more likely to be further respect except for
the level of degradation (Micheal and Niamb, 2000; ESCAP, 1990).
1.7.3 Causes
of Soil Degradation.
Soil degradation is a biophysical process; its
underlying causes are firmly rooted in the socio-economic, political and
cultural environment in which land users operate. For example, for some land users’
poverty may be a key factor that leads to land degradation. since poor land user
may become stuck in a cycle if degradation, where there poverty preludes
investment in the land, lack of investment lead to further land degradation,
and degradation to more poverty.
Similarly, according to UNEP, (1986), land degradation
is a symptom of under-development in the developing countries. It results from a
combination of social and economic factors, such as poverty and inequitable
distribution of land resources, inappropriate land use systems and farming
methods. In the dry land or areas, these factors are exacerbated by climate and
fragility of the ecosystem. This position was further justified by Lal,(1998),
that “Subsistence agriculture, poverty and illiteracy are important causes of
land and environmental degradation. Because, people most be healthy,
politically and economically motivated to care for the land”. This is why a
comprehensive and detailed land degradation study does not only includes the
physical aspect of the degradation, but also the socio-economic and cultural
status of the land users is also surveyed and analyzed, in order to fully
understand the intricate relationship that exist between the physical
environment factors and the socio-economic status of land users in the form and
extent of the prevailing land degradation process in operation.
The causes of soil degradation, is viewed under these
three broad headings;
i.
Physical (environmental and climatic) causes of land
degradation
ii.
Socio-economic causes of land degradation
iii.
Cultural (practices) causes of land degradation
i Physical
(environmental and climate) causes of soil degradation
It is obvious that physical
environmental factors especially climate, plays a fundamental role in
triggering soil degradation. This is more particularly important in the areas
that receive high rainfall amounts and intensities, as it usually results to
soil erosion. While some environments are naturally more at risk to land
degradation, others are not factors such as steep slopes, high intensity
rainfall, and soil organic matter influences the likelihood of the occurrence
of degradation. Although degradation processes do occur without interference by
man, these are broadly at a rate which balances with the rate of natural
reliabilitation. So, for example, water erosion under natural forested
corresponds with the subsoil formation rate. Accelerated land degradation is
most common caused as a result of human intervention are determined by the
natural landscape (Hudson, 1981; Micheal and Niamh, 2000)
Topography
is another important physical aspect encouraging soil degradation. Generally, the
steeper and longer the slope the greater the ratio of erosion. Nevertheless,
very considerable erosion takes place in many areas of sub-Sahara Africa where
slopes are less than 10 from the horizontal (Hudson, 1981). Thus,
the most frequently recognized main causes of land degradation include:
a.
Overgrazing of rangeland
b.
Over cultivation of cropland
c.
Water logging and salinization of irrigated land
d.
Deforestation
e.
Pollution and industrial causes.
ii Socio-economic factors of soil degradation
Soil degradation may be a
biophysical process, but it is driven by socioeconomic and political causes.
High population density is not necessarily related to land degradation.
However, what the population does to itself and to the land goes a long way in determine
the extent and severity of land degradation. People can be a major asset in
reversing the degradation trend. However, subsistence agriculture, poverty and
illiteracy are important causes of land and environmental degradation. People
must be healthy and politically and economically motivated to care for the land
(Lal, 1998). The above position had earlier been justified by UNEP, (1986) as
to the causative factor of the socioeconomic factors such as poverty and
inequitable distribution of the land resources, inappropriate land use systems
and farming methods.
Other
socioeconomic factors of soil degradation include:
a.
Land tenure system.
Security of land tenure
affects farmers’ willingness to invest resources in land improvement and
protection against degradation insecurity of land tenure shortens the
time-frame used by farmers for decision making, making it less likely tha
measures which protect against land degradation will achieve return in the
planning horizon of the land user. Where the occupier of land is ensure of the
future, extraction ( or “soil mining”) will occur to ensure that these
resources are not lost to the individual.
b.
Pressure on the land
A growing population, for
example puts greater demands on the land.
Farms are split into ever-smaller units as land is shared amongst family
members. Land shortage acts as incentives for land users to push the boundaries
of cultivation into marginal areas, less suited to continuous use. Increasing
numbers of people required more food, more water, more fuel wood and more
construction materials, all of which must be sourced from the environment,
thereby increasing the rate potential for the land to be degraded.
c.
Poverty
Poverty affects how land
users manage their land. It reduces the options available, rolling not some
conservative practices because they required too much investment on land, labor
or capital. Similarly, poverty tends to encourage farmers to focus on immediate
needs rather than on those whose benefits may materialize only in the long term
as associated with most modern conservative practice.
d.
Economic incentives
There are number of ways in
which the markets may affect a land user’s decision about degrading or
conserving farming practices. Price structures for agricultural produce often
favor the urban purchaser over the rural vendor. As a result it may not be
possible for a land user to recover the costs of more expensive non-depredating
production methods in the selling price achieved for produce.
e.
Off-sets versus on-site cost
Costs and benefits encored
on-site ( the farmer’s field, for instance) are private or personal to that
land user. Costs incurred, says, as a result of sedimentation into dams and
rivers off-site are a consideration for society. Few land user will be prepared
to invest private resources solely for the benefit of society, unless society
supports such activities through subsides. Where the land user does not bear
the all costs of land degradation, the incentives to take action to reduce land
degradation, may be insufficient for the land user to change practices or adapt
new technologies.
iii. Cultural (practices) causes of land degradation
Many cultural practices employed
by most land users exert a significant influence on the susceptibility of a
landscape to degradation. Extensive and poorly managed land use systems are
more likely to degrade than intensive, intricately managed plots. Thus, the
human factor acts as a catalyst to degradational processes. This is often
failed by the demand for firewood and clearance for cultivation, as well as
grazing and browsing by livestock (Peter, 1970; Micheal and Niamh, 2000)
The reduction in the
fertility of soil is brought about by exploitative cropping with shorter fallow
periods and inadequate return of nutrients to the soil. This practice often
makes the soil more vulnerable to erosion. Once eroded soil becomes
increasingly less fertile and less able to support vegetation, the result is
the inability of the reduced vegetation cover to act against erosive mechanism.
Hence, creating a vicious circles between degradational activities and
continuous cropping with shorter fallow periods (IFAD, 1992)
Various studies carried out on the Zaria and
its region shows that the practice of tillage is common among the various land users
who are engaged in various cropping activities. Although land tillage is
devised to control the structure of the soil, because it helps to reduce the
fractional resistance of the soil to both wind and water, increase porosity,
infiltration and decreasing over-land flow and helps in wood control. However,
as observed by Jaiyeoba and Leow, (19830), soil tillage was discovered be a
factor that triggered the complete breakdown of soil aggregate, making the soil
more susceptible to erosional activities. More so, studies conducted by Aina,
(1979) on the sail to direct impact of high kinetic energy of rainfall, which
triggers soil erosion, and subsequently results in loss of soil nutrients.
Bush burning is also a
serious cultural practice that has varied severe implication to the land
surface. It constitute a vary factor of soil degradation. This is mostly
practiced by rural subsistence farmers, where it is however to note that bush
burning in its immediate effects does not constitute a degradation problem,
except where it now aid to accelerate erosional activities (IFAD 1992)
1.7.4 Impacts of Soil Degradation.
Humans’ uses about 8.7
billion hectares of land worldwide. About 3.2 hectares are potentially arable.
Of which a little less than half is used to grow crops. The remaining
1.7billion hectares of potentially arable land, along with non arable land,
functions as postures, forest, and wood land. Recent global studies estimate
the soil quality on the three-quarters (3/4) of the world’s agricultural land
has been relatively stable since the middle of the 20th century
(scherrr1999). However, based on the findings of over 250 exports around the
world, Global Assessment of human induced soil degradation (GLASOD) estimated
that nearly 2 billions of land (12% of total global land area of about 13 billion
hectares, or 23% of the 8.7billion hectares used by humans for crops, pasture
and forest, and wood lands) had been degraded as a result of human activity
since world war ii. Out of this, about 749million hectares had been lightly
degraded, indicating that productivity had been reduced somewhat, but could be restarted
through modifications in form management practices. 910 million hectares had
been had been moderately degraded, indicating greater losses in productivity
that would required costlier improvement practices to reverse: 305 million hectares
were strongly or extremely degraded, implying losses in productivity that is
virtually irreversible (Oldman et al, 1991). Regionally, GLASOD estimated that
38% of the world’s cropland had been degraded to some extent since 1945.
Degradation had affected 65% of croplands in Africa, 51% of cropland in Latin
America, 38% of croplands in Asia, and 25% of cropland in North America,
Europe, and Oceania. GLASOD identified erosion (primary due to water) as the
principal cause of cropland degradation, affecting 1.6 billion hectares (mostly
in Asia and Africa).
The economic importance of
this observed degradation has been a matter of debate in major world summits on
food security and desertification. A review of literature had suggest the economic
effect may be of much greater importance than previously thought. A global
agricultural model suggest a slight increase in degradation relative to
baseline trends could results in 10-70% higher world prices for key food commodities
(such as rice, millet, wheat, sugar, maize, and tubers) in 2020, and increased
child malnutrition. Such that though food imports will increase, one out of
every four children under six years of age in developing countries will still
be malnourished in 2020 (Pinstrop- Anderson, Pandya-Lorch, and Roseqrent 1997).
Besides affection the
economy of food supply, soil degradation is also diminishes agricultural income
and economic growth. In southwestern and Southeast Asia, estimates for total
annual economic loss from degradation range from under one-seven percent (1-7%)
of Agricultural Gross Domestic Product (AGDP). Given that more than half of all
land in this region is not affected by degradation, the economic effects in the
degradation areas would appear to be quite serious. Estimates for eight African
countries shows annual economic loss ranging from 1% of AGDP (Agricultural
Gross Domestic Product) in Madagascar to
9% in Zimbabwe. Country models simulating the effects of soil
degradation in Ghana and Nicaragua find annual economic growth to be reduced by
nearly a percentage point. Because the poor are particularly dependent on
agriculture, on annual crops (which generally degrade soils more than perennial
crop), and on common property lands (which generally suffers greater
degradation than privately managed land), and because they often look the
capacity to make land improving investments, the poor tends to suffer more than
the rich from soil degradation.
Consequently, the
seriousness of erosion in the conversion of tropical forest to cropland susceptible
to erosion amount to 1.33x106 ha for close forest and 2.35x106ha
of woodland, potential moist forest land of 3.62x106km has been
reduced by 51 times (Brown et al, 1985). Similarly, since 1950, the loss of
croplands in Nigeria has increased to over 20.5 times, such that it has
experienced the reduction in maize yield by 52% and that of cowpea by 38%.
Hence, a global projection of less of cropland to degradation is estimated to
rise to 150 to 360 million hectares of land by 2020 of the rate of land loss
continue at this alarming rate of 25% annually (Okigbo, 1985).
1.7.5 Assessment of Soil Degradation
Soil degradation occurs at
widely varying rates, and to varying degrees, over the landscape, hillside, and
between fields. It encompasses a vast array of biophysical and socio-economic processes,
which make its assessment difficult to encapsulate in a few simple measures. It
occurs over a variety of timescales- from a single storm to many decades. It happens
over many spatial scales- from the site of impact of a single raindrop through
a whole fields and catchments. Without extreme care, measurements undertaken at
one set of scares cannot be compared with measurements at another. The
perception of the scale and seriousness of land degradation is usually
influenced by the timing of any investigation. Many forms of soil loss are
mostly easily seen during or shortly after crops become established in fields.
Nutrient deficiencies and other factors that affect crop production is best
observed when crops are in field and relative growth rates can be assessed.
Actives production is best assessed at harvest times when output can either be
weight, or the standard number of units (sacks/bundles) counted. Repeated
measurements, gives a more complete picture of the effects of the processed
leading to land degradation (Micheal and Niamh, 2000)
Assessment of land degradation
is viewed under the four (4) broad approaches;
(i)
The adoption of farmers’ perception is assessing soil
degradation and the focuses on the concern of land-users in assessing soil
degradation.
(ii)
The concentrates on relatively simple field indicators in
assessing soil degradation.
(iii)
The use of triangulation assessment.
(iv)
Use of semi-quantitative assessment.
i.
The Adaption of Farmers
Perspective in Assessing Soil Degradation
One major factor about soil degradation is
that while it manifests itself in very many ways, the local people often see
these in entirely different ways compared to the trained scientist. The concern
of farmers is in its effect on production. Hence, most responses from them in
soil quality are tied to some aspect of agricultural production: reduced yield;
greater difficulty in maintaining yields, more weed; stones on the surface
making plouging difficult. The farmers’ perspective is, therefore, most often
articulated through how production is changing and the way is which plants
soil, water supplies and natural vegetation have deteriorated, making
production more problematic. The farmers’ perceptive will usually be different
from, and the ascribing of cause and effect wide unrelated to, the scientific
explanation. Erosion-induced loss in soil productivity or example may occur
through a variety of processes, describing in partially scientific term. These processes
present a complicated interactive and cumulative picture of how land
production, but only some of these individual processes may be recognized by
formers.
Difference in thinking and
explanation between the farmers’ and the trained scientist are not always as
stark, but can be every bit as powerful. Thus, there are three main advantages
of adopting a farmer’s perspective approach to land degradation assessment.
First, measurements area formers realistic of actual field level processes.
Secondly, assessment utilizes the integrated
view of the ultimate client for the work, the farmer. Thirdly, results provide
a far more practical view of the type of interventions that might be accepted
by land users. The above three main advantages is ownable to the fact that
farmers are the primary source of information. They decide on the appropriate
indicators of production and they chose the levels of seriousness of land
degradation. They are able to put current production into context in turns of both
historical trends and changes in production methods.
The Focuses on the Concern of Land-users Approach in
assessing Soil degradation.
This approach is very
similar to the farmers’ perspective approach reviewed above within the context
of the farmer as the primary land user. However, other land users such as the
Authorities (responsible for dealing with the impacts of land degradation). Government
(policies legislature), civic bodies (organizations), scientist and
professionals; their concern to certain level and effects of land degradation
have also contributes to the gathering of documented notes and works on
assessing land degradation. For example, the concern of the authority in charge
of power supply towards the interruptions or supply of electricity due to
damaged hydroelectric installations or sediment waterways by degradational
processes such as the erosion-induced siltation of dam provides a
socio-economic assessment implication into land degradations. Relatively, these
type of assessment approach provides a secondary information on the extent and
severity of land degradation when compared to the primary land users.
(ii)
The concentration on
relative simple field indicators in assessing soil degradation.
Soil degradation indicators
are information containing evidences about the extent, severity and type of
degradational activities in a locality as presented by the observed type of
degradation on the field. Degradation indicators generally provide information
about the type of degradation occurring in a place and its extent of impact.
They are used to ascertain the certainty and occurrence of soil, the
development of degradation indicators is such that it applies to different time
scales and different spatial scales. And armour layer, for example, often forms
after one or two heavy storms in the early growing season, while tree mounds
may take soon more years to form. Also, a soil pedestal may be only 3mm across,
whereas a gully can in exceptional cases be 5km long. The farmer apply to the
timescale inherent soil degradation indicators, while the later explains the
spatial scales associated with soil degradation indicator.
Single
indicators gives singular items of evidence for soil degradation or its impact.
They are susceptible to error, misinterpretation and chance. Especially in the
case of field assessment where many of the measurements can only be described
as rough reading, the use of only one indicator- say a tree mound-to conclude
definitively that land degradation has occurred as questionable and
problematic. Hence, a combination of various indicators for further
understanding as to whether or not land degradation is occurring.
Three
particular areas of combining indicators are highlighted as;
·
Combinations to show both the process and likely cause of
land degradation through time.
·
Combinations to provide corroborating evidence and a
consistent view of land degradation
·
Methods to bring individual indicators together for comparative
and overall assessment, including how to search for a suite of indicators and
how to develops a semi-quantitative procedure for getting an overall picture.
(iii)
The use of triangulation in
soil degradation assessment.
This method of assessment
provides the gaining of a consensus view of overall trend from different types
of assessment. This is done by the following procedures:
a.
Map out the field slope as a sketch, noting the position of
any obvious features such as gulling, rills, tree mounds, boundary walls.
b.
Obtain the history of land use. When the plot of land started
to be used, one grown, any change in land use, subdivisions of the land, and
similar important events that could have had a bearing on the land.
c.
Determine any significant events. Landslides, exceptionally
heavy storms and soil wash, dates when trees were cut down.
d.
Mote any particular farming techniques that may have
implications for soil degradation (ridging practice across/ down the slope;
land cultivation down slope);
e.
Then, with the map in 1. Above and preferably accompanied by
the farmer, go through the indicators of the processes of land degradation.
f.
Then, with the former (most importantly this time), determine
the indicators of the impact of land degradation.
g.
Compile a comprehensive table of indicators and results,
looking for trends consistency and areas where there is broad agreement on the
scale of degradation.
h.
Return to the farmer with your account of the comprehensive
picture, and get his/her evaluation of your diagnosis.
(iv)
Use of Semi-quantitative
Assessment.
The above assessment had
listed the combination of indicators which has attempted to use absolute
(scale) levels of land degradation, such as tones soil per hectares. With the
approximate nature of the techniques of assessment, this can be misleading on
loss careful precautions (health warming’s) are taken. To say that exactly 126 t/ha/yr
of soil loss has occurred is folly, implying that it was more than 125 and less
than 127. This degree of exactitude is unjustified. The developed stage of
assessment to correct for this is called a semi-quantitative assessment. This
does not give an actual measure of land degradation, but a prediction of potential
land degradation according to the environmental factors that encourage it.
“Erosion Hazard Ratings”-HER is one example. The factors of erosion-slope, soil
type, vegetation cover, and rainfall- are rated on a numeric scale, usually one
to five in severity of likelihood to cause erosion then these individual factor
ratings are combined either through a scoring system or through a simple model,
to give an overall hazard rating.
1.7.6 Soil Conservation
The task of soil conservation is not a recent
development. Since soil was identified as degradation, the task of its
conservation has identified for several years. Measures such as shifting
cultivation and application of fertilizer are being used with a view to
correction the processes of soil degradation in many parts of the world and
evidence for this abound. For instance, since the early 1930’s when Prof. Bemelt
had to persuade the United Nation (US) government to aid farmers to farm their
land in such a way that the land does not deteriorate with use. Also, during
the early 1966, there exist the soil conservation movements in America, whose
prime objective was the possible restoration or soil productive power, raising
food produce, and reducing the level of soil depletion.
Similarly, several high
profile initiatives aimed at improving the use and conservation of the world
natural resource base and preserving a healthy environment, including
addressing land management issues have been held during the last decade. The
three United Nation (UN) conventions within the said period, aimed at combating
desertification slowing climate change, preserving the bio-diversity,
attention, was said to be the most serious factors contributing to
environmental degradation.
According to FAD, (1975),
Soil conservation is the management measures or attempts applied to soil to
have control or prevent its deterioration and or degradation. These measures
can either be preventive or remedial in nature. Preventive practices minimize
the chances of soil degradation occurring or the magnitude or severity of the
damages when degradation manifest. Practices such as food farming practices,
efficient soil managed, rational land use, as well as effective crop and
livestock management was identified as management method for soil conservation
(FADM, 1976).
In Nigeria, soil
conservation practices varied from one geographical location to the other, as
influenced by climate type, crop type, soil type. Cultural farming systems,practising
land tenures and socio-economic relatives. Practices such as (i) Manuring and Mulching
(ii) planted fallows and cover crops (iii) sustainable farming system (iv)
adequate rotation, (v) home gardens or compound farming (vi) alley cropping and
related agro forestry system, and (vii) chemical and organic fertilizer
applications, are employed mainly as remedial measures for soil life. The
Zonkwa people of Kaduna State, Nigieria practice the system of ridges and
furrow especially on slope with angles of more than 310, the ridges
arranged across the slope serve to reduce the impact of runoff, while the
furrow trap the rain water and encourages soil infiltration (Kastina, 1990).
Similarly, the practice of stepped-level benched stone terraces and rectangular
ridges are practiced in Jos plateau, and the use of stone-lines practice in
Niger State, Nigeria (FAD, 1986).
Summarily, fig 1.1, 1.2, 1.3
and 1.4 illustrates the various types of soil degradation processes and their
causative agents, soil degradation is one of the building blocks of land
degradation, the intrinsic relationship that exist between soil degradational
processes, types and forms, the socio-economic status of the land user, and the
two extreme view in assessing soil degradation between the land user (farmer)
and the trained scientist.
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