Agro-ecosystems are biological and natural resource systems managed by humans for the primary purpose of producing food as well as other socially valuable nonfood goods and environmental services. These are contained within larger landscapes, which include uncultivated land, drainage networks, rural communities, and wildlife. Agro-ecosystems cover more than one-quarter of the global land area, but almost three-quarters of the land has poor soil fertility, and about one-half has steep terrain, constraining production. A further limitation is the growing competition from other forms of land use such as urban, industrial
Introduction
Agro-ecosystems
are biological and natural resource systems managed by humans for the primary
purpose of producing food as well as other socially valuable nonfood goods and
environmental services. These are contained within larger landscapes, which
include uncultivated land, drainage networks, rural communities, and wildlife. Agro-ecosystems cover more than one-quarter of the
global land area, but almost three-quarters of the land has poor soil
fertility, and about one-half has steep terrain, constraining production. A
further limitation is the growing competition from other forms of land use such
as urban, industrial, commercial, or residential. While the global expansion of
agricultural area has been modest in recent decades due to various reasons,
intensification has been rapid; as irrigated area increased, fallow time has
decreased and the use of new inputs with modern technologies has grown and is
producing more output per ha than ever. At a time when the
world's human population is expanding rapidly and its need for more land to
produce food, fiber and fuelwood is also escalating, valuable land is being
degraded through erosion and other means at an alarming rate. According to the Pilot Analysis of Global Ecosystems
(PAGE) study, about two-thirds of agricultural land has been degraded in the
past 50 years by soil erosion, salinization, compaction, nutrient depletion and
pollution. Globally, about 40 percent of agricultural land has been strongly
degraded, and about 65 percent of agricultural land has experienced some amount
of soil degradation. This chapter presents the goods and services
produced by world agro-ecosystems including human nutrition, and describes its
extent, growth, alteration, present state, constraints, and the challenges
(e.g. soil erosion, degradation etc.). This chapter also examines agricultural
situation in Bangladesh
with a focus on land degradation, desertification in the Northern region,
technological issues and the environment. The chapter then briefly discusses
the issues of land use changes (conversion) including management options. It
may be pointed out that there are several issues related to land degradation
that intersect with other concerns. The most important of these have been addressed
in other chapters of this book. For example soil pollution is addressed in
Chapter 11, and floods and droughts are discussed in Chapter 16 under natural
disasters. The biodiversity chapter addresses issues of shrinking wetland in
the dry season.
A: Agro-ecosystems
Economic Importance
Goods and Services: Agricultural
ecosystems or “Agro-ecosystems” cover 28 percent of the world’s land surface
(excluding Antarctica and Greenland). In 1997,
global agriculture accounted for US$1.3 trillion in output of food, feed and
fiber, and for 99 percent of the calories human consumed. Of the economic
activities, agriculture is most important to developing countries, accounting
for 31 percent of their GDP, and more than 50 percent in many parts of
Sub-Saharan Africa. In middle-income countries, agriculture account for 12
percent of GDP. But in the industrialized countries of Western Europe and North America, the contribution of agriculture to GDP is
less than 3 percent, although the value of the agricultural output in these
countries represents 79 percent of the total market value of world agricultural
products. Beyond the economic value of the agricultural products,
agro-ecosystems provide employment for millions. In 1996, out of 3.1 billion
people living in rural areas, 2.5 billion- 44 percent of the world
population-were estimated to be living in households dependent on agriculture.
The labour force directly engaged in agriculture is estimated to be 1.3
billion- about 46 percent of the world’s labour force. From a regional
perspective, East, South and South East Asia as well as in Sub-Saharan Africa,
agricultural labour accounts for 56-65 percent of the total labour force, as
oppose to only 2.4 percent in North America.
Human Nutrition: Globally,
agro-ecosystems have been very successful in keeping pace with the demand for
food, feed and fiber in response to population growth. Since 1970, crop outputs
have doubled and livestock products have tripled. On average, per capita food
supplies were 24 percent higher in 1997 than in 1961, and real food prices were
40 percent lower. In fact, global agro-ecosystems produce sufficient food to
provide every person on the planet with 2,757 kcal a day, which is enough to
maintain a productive and healthy life (minimum human requirement for
nutrition). However, the irony is, many people do not have adequate access to
the food they need, and an estimated 790 million people (1999) are ill fed or
chronically undernourished in the midst of ample food supply. The highest
incidence of undernourished people is in Sub-Saharan Africa (33 percent)
followed by the Caribbean (31 percent), and South Asia
(23 percent). Further, global demand for food has been increasing since 1980,
driven by population growth, urbanization and income induced changes in
lifestyles. One of the most remarkable changes in such demand is the dramatic
increase in meat consumption, particularly in the developing world- commonly
labelled by as “Livestock Revolution”. Between 1982 and 1994, global meet
consumption grew by 2.9 percent on an annual basis, but it grew five times
faster in developing countries than in developed countries, where meat
consumption is already saturated. Between 1995 and 2020, global population is
expected grow by one-third, totalling 7.5 billion people. Global demand for
cereals is projected to rise by 40 percent with 85 percent of the increase in
demand coming from developing countries. Meet demand is projected to increase
by 58 percent with roughly 85 of the increase coming from developing countries-
an indication of additional feed requirement. Demand for roots and tuber crops
is expected to grow 37 percent, with 97 percent of this increase is coming from
the developing world. If income level of the poor goes up or significant
progress is made in poverty alleviation during this period, there will be a
further increase in demand for food. This is simply because the poor and
malnourished are more likely to use their increased income to buy food from the
ample supply (market) as they previously could not afford to do so.
State of the
Agro-ecosystems
An
agro-ecosystem may be defined as a dynamic association of crops, pastures,
livestock, other flora and fauna, soils, water, and the atmosphere. It is the
basic unit of study for an agro-ecologist, and is somewhat arbitrarily defined
as a spatially and functionally coherent unit of agricultural activity, and
includes the living and nonliving components involved in that unit as well as
their interactions. It can be viewed as a subset of a conventional ecosystem.
At the core of an agro-ecosystem, lies the human activity of well managed agriculture
(Figure 5.1). However, an agro-ecosystem is not restricted to the immediate
site of agricultural activity (e.g. the farm), but rather includes the region
that is impacted by this activity, usually by changes to the complexity of
species assemblages and energy flows, as well as to the net nutrient balance.
Figure
5.1: A Typical Agricultural Field; Source: Google image
Extent and Growth: Agriculture is one of the most common and major land
uses on the planet Earth. Naturally, agro-ecosystems in the world are quite
extensive and determining their extent is not an easy task; it depends on how
they are defined and utilized. The Pilot Analysis of Global Ecosystems (PAGE)
study, mostly making use of satellite imagery, defined agricultural areas as
those where at least 30 percent of the land is used for cropland or highly
managed pasture. With respect to this definition, agro-ecosystems cover
approximately 28 percent of total land area (excluding Greenland and Antarctica). Since this measure allows some overlaps with
forest and grassland ecosystems, the Food and Agricultural Organization of the
United Nations (FAO), reports (2000) an even greater percentage (37) of land
under agriculture. The difference between PAGE and FAO figures lies in the fact
that FAO’s figures are derived from national production statistics rather than
from remote sensing data, and include all permanent pasture. The actual area of
agro-ecosystems probably falls some where between these two estimates. According to FAO estimates, the total area
under global agriculture expanded slowly between 1966 and 1996, from 4.55 Bha
to 4.92 Bha- about an 8 percent increase. Despite this growth, agricultural
area has actually decreased in many industrialized countries. The United States, Western Europe, and Oceania
(mainly Australia)
have progressively been taking land out of agriculture for the last 30 years
(Figure 5.2). These regions have removed a total of 49 Mha from agricultural
production. Agricultural land has also decreased in Eastern
Europe, mainly because of liberalization of trade policies and
poor economic conditions. South Asia’s total
agricultural area has remained stable for more than 20 years at roughly 223
Mha. However, slow expansion of agricultural area is still observed in some
regions such as in China and
Brazil
(by 0.8 percent per year) between 1986 and1996.
Figure 5.2: Area of
Agro-ecosystem; Source: World Resources Institute 2000
Physical Constraints: Many of the world’s agricultural land, offers less
than optimal conditions for normal agricultural practices. Poor soil conditions
limit production on a significant portion of global agricultural land.
Constraints of soil fertility include high acidity, low potassium reserves,
high sodium concentrations, low moisture-holding capacity, limited depth or
steep slopes. Approximately, 36 percent of world agricultural land is
characterized by significant soil constraints including slopes of 8 percent or
more (inclination). On a regional distribution, areas with both steep slopes
and significant soil constraints make up 30 percent of temperate, 45 percent of
subtropical and, 39 percent of tropical agricultural land. In these regions,
average agricultural yields are generally lower and degradation risks are
generally higher than in more ecologically favoured environments. Anyway, these
marginal lands represent a significant share of global agriculture and support
approximately one-third of the world’s population.
The Challenges
Intensification of agriculture: As population has grown and good agricultural land has become scarcer,
inputs such as water for irrigation, modern seed (HYV), chemical fertilizer,
pesticide, herbicide and labour have been applied more intensively to increase
crop output. Although the net global expansion of agricultural area has been
modest in the past three decades, intensification of agriculture has been quite
rapid. Irrigated area, for instance, grew from153 Mha in 1966 to 271 Mha in
1998- a significant expansion. Although global irrigated land accounts for only
5.5 percent of total agricultural land- 17.5 percent of cropland- in some
regions irrigation is much more extensive. For example, where Sub-Saharan
Africa and Oceania (mainly Australia)
together represent only 3 percent of the global irrigated land, China and India contain 41 percent of the
world’s irrigated area. In the later group (Asian countries), where population
pressures are greatest, virtually all of the cropland is harvested each year,
some times two to three times a year, as the use of new technology has replaced
traditional practices of leaving land fallow to restore fertility. Even
marginal lands in Africa are in continuous use
to meet demands for food. Many agro-ecosystems are vulnerable to the stresses
imposed on them by intensification of agriculture. There is much local evidence
of soil salinization and waterlooging due to poorly managed irrigation (see
Chapter 11); loss in soil fertility caused by over-cultivation and compaction
by tractors or livestock, and lowering of water tables through over pumping for
irrigation.
Extent of Soil Degradation: The condition of soil is a good measure of the long-term productive capacity
of an agro-ecosystem.
We generally consider the land degraded
when the soil is impoverished or eroded, water runs off or is contaminated more
than is normal, vegetation is diminished, biomass production is decreased, or
biodiversity diminishes. Degradation of the land resource means to a great
extent a degraded agro-ecosystem on which depends the livelihood of the rural
mass. Today, agriculture provides the majority of crops, feed and livestock on
which human nutrition depends. On farmlands the degradation results in low crop
yields; on ranchlands it means fewer livestock can be supported per unit area;
on nature reserves it means fewer species. Land degradation is of great concern
because soil reformation is extremely a slow process. Although, topsoil is classified as a potentially renewable resource (as because it
is continuously regenerated by natural processes), in tropical and temperate
regions of the world, however, it takes roughly 200-1,000 years (depending on
climate and soil type) for 1 inch (2.54 centimeters) of new topsoil to form.
Figure 5.3: An Image
of Typical Soil Degradation
Figure 5.4: An Image
of Typical Land Degradation
The International
Soil Reference and Information Centre in the Netherlands estimates that every
year roughly 3 million ha (7.4 million ac) of cropland are ruined by soil
erosion, 4 million ha are turned into deserts, and 8 million ha are converted
to nonagricultural uses such as homes, highways, shopping centres, factories,
water reservoirs etc. Worldwide, some 1.9 billion ha of agricultural land have
been degraded to some extent; about 300 million ha of this land is strongly
degraded, while 910 million ha- about the size of China- are moderately degraded.
Nearly 9 million ha of former croplands are degraded to such an extent that
they no longer support any crop growth at all. The 1990 Global Assessment of Soil Degradation (GLASOD) provides a more
comprehensive global scale estimates of soil degradation. The GLASOD study
suggested that between the mid 1940s and 1990 some 1.97 Bha of land had been
degraded representing 15 percent of terrestrial area (excluding Greenland and Antarctica). Although different types of soil degradation
are associated with different kinds of agricultural land use, in cumulative
terms, about two-thirds of agricultural land has been degraded in the past 50
years by erosion, salinization, waterlogging, compaction, nutrient depletion,
and pollution (Figure 5.5) . About 40 percent of global agricultural land has
been strongly degraded. South and Southeast Asia,
for example, where agricultural production systems are among the most intensive
in the world, have soils that are among the most degraded. In these regions,
soil slopes are significantly steeper, more subject to erosion, and more likely
to be salinized, acidic, depleted of potassium, and saturated with aluminium
than the soils of most other regions.
The cumulative productivity loss from soil degradation
over the past 50 years (as has been roughly estimated by PAGE researchers,
using GLASOD figures), are to be about 13 percent for cropland and 4 percent
for pasturelands. The economic and social impact of soil degradation has been
even far greater in developing countries than in industrialized countries,
particularly on the issue of food supply. Agricultural productivity is
estimated to have declined significantly on approximately 16 percent on
agricultural land, especially on cropland in Africa and Central
America. Sub-regional studies have documented significant
aggregate declines in crop yields due to soil degradation in many parts of
Africa, China, South Asia,
and Central America. Crop yield losses in Africa from 1970 to 1990 due to water erosion alone are
estimated to be 8 percent. Total annual economic loss from soil degradation in
South and Southeast Asia is estimated to be 7
percent of the region’s agricultural GDP. Agriculture faces an enormous challenge to
meet the food need of growing population. If proper preventive measures are not
taken, the situation will worsen and national food security will be seriously
hampered.
Figure 5.5: Areas of Concern for Soil degradation; Source Google image
Extent of Topsoil
Erosion: The movement of
surface litter and topsoil from one place to another is called topsoil
erosion. Due to overgrazing by cattle or other human activities, the
cover of vegetation almost gets removed from the land; the soil becomes exposed
and gets eroded by the action of strong wind, rainfall etc. Since the
grassroots are very good binders of soil, when removed the soil becomes loose
and susceptible to the action of wind and water. The rates of erosion vary from
region to region because of topography, rainfall, wind speed, and the type of
agricultural practices used. In China
for example, the average annual soil loss reported to be about 40 metric tons
per ha (18 tons per acre), whereas the U.S. average is 18 metric tons per
ha (16 tons per acre). The two main natural agents of erosion are flowing water
and wind. However, some anthropogenic activities such as farming, logging
construction, overgrazing by livestock, deliberate burning of vegetation and
other actions that destroy plant cover leave soil vulnerable to erosion (Figure
5.6). Today, topsoil is eroding lot faster than it forms, causing an estimated
85 percent of the world's land degradation. A study (1992) by the World
Resources Institute and the UN Environment Programme found that soil on more
than 12 million square KM of land- an area the size of China and India
combined- had been seriously eroded since 1945. The study also found that about
89,000 square KM (34,000 square miles) of land scattered across the globe was
eroded to such an extent that crop growth is no longer feasible because of a
combination of overgrazing (35 percent), deforestation (28 percent), and
unsustainable farming (28 percent). Two-thirds of the seriously degraded lands
are held in Asia and Africa. Each decade, the
world is losing about 7 percent of its topsoil from actual or potential
cropland. The situation is worsening as many farmers in LDCs plow up marginal
lands to survive. If topsoil erodes faster than it forms on a piece of land,
the soil there becomes a non-renewable resource. According to an estimate, annual
erosion rates for farmlands throughout the world are 7-100 times the natural
renewal rate. Cropland aside, construction sites usually have the highest
erosion rates by far.
Nutrient
Depletion:
Besides reduced soil depth, soil erosion leads to reduce
crop productivity because of loss of water, organic matter and soil nutrients.
When soil erodes, vital plant nutrients such as nitrogen, phosphorous,
potassium, and calcium are also lost. Losing topsoil makes soil less fertile;
less able to hold water and as such low productivity. Chemical fertilizers do
not have humas content that reduces the soil’s ability to hold water, and as a
result of their application the soil is more likely to become compacted- less
suitable for crop growth. Further, the resulting sediment clogs irrigation
ditches, boat channels, reservoirs, and lakes. The sediment-laden water is
cloudy, and tastes bad, fish die, and flood risk increases. Soil erosion is one
of the world’s critical problems; if not slowed, it will seriously reduce agricultural
production and degrade the quality of agro-ecosystem. With U.S. annual cropland erosion rates
of about 18 metric tons per ha, an estimated $18 billion of plant nutrients are
lost annually.
Figure 5.6: Soil Erosion; Source:
Google image
Changes in Yield Growth: Soil erosion can lead to poor crop growth and yield reductions
through loss of soil fertility and plant nutrient depletion. Moreover, soil
structure, texture and stability can be affected by such losses. Global agriculture
today faces an enormous challenge to meet the food need of an additional 1.7
billion people- the projected population increase by 2020. Rapid yield growth
in major food crops (mostly cereals) has been instrumental in meeting the food
need of growing populations, particularly in the second half o the past
Century. Recently, however, the growth of yield in cereal crops has been
slowing, raising concerns that future production may not be able to keep pace
with demand. Moreover, there are local evidences that maintaining the growth
yields, or even holding yields at current levels, requires proportionately
greater amounts of fertilizer input, implying that the quality of the
underlying soil resource may be deteriorating (see Chapter 11- Land Degradation
for detail).
Management: Soil
Conservation Practices
The
art of soil conservation is concerned with keeping the soil intact and
maintaining the soil nutrients at a certain desired level following certain
basic principles. Soil conservation involves reducing soil erosion and preventing
and storing soil fertility. With careful husbandry, soil can be replenished and
renewed indefinitely. Among the most important considerations in a soil
conservation program are topography, ground cover, climate, soil types and
tillage systems. Water runs downhill. The faster it runs, the more soil it
carries off the lands. Water runoff can be reduced by leaving grass stripes in
waterways and by strip- farming- the
planting of different kinds of crops in alternating stripes along the land
contours. The stripes of cover crop trap soil that erodes from the row crop,
and catch and reduce water runoff. Terracing can be used to reduce
soil erosion on steep slopes, each of which is converted into a series of
broad, nearly level terraces that run across the land contour (Figure 5.7). The
edges of the terrace are planted with soil anchoring plant species. Terracing
retains water for crops at each level and reduces soil erosion by controlling
runoff. In mountainous areas such as Himalaya, and the Andes,
farmers have traditionally built elaborate systems of terraces. Soil erosion
can be reduced by 30- 50 percent on gently sloping land by means of contour farming- plowing and
planting crops in rows across, rather than up and down, the sloped contour of
the land. Each row planted along the contour of the land acts as a small dam to
help hold soil and slow the runoff of water.
Soil erosion can also be reduced by alley
cropping or agro-forestry- it is a form of intercropping in which several crops are
planted together in stripes or alleys between trees and shrubs that can provide
fruit or fuel wood. The trees provide shade and help to retain and slowly
release soil moisture. Sloping bare land on which water runoff quickly creates
gullies can be restored by gully reclamation.
Small gullies can be seeded with quick-growing plants such as wheat,
oats, and barley for the first season, whereas deeper gullies can be dammed to
collect silt and gradually fill in the channels. Fast-growing shrubs, vines and
trees can also be planted to stabilize the soil. Regarding ground cover, the easiest way to
provide cover that protects soil from erosion is to leave crop residues on the
land after harvest. Mulch is a general term for protective ground cover that
can include manure, wood chips, straw, seaweed, leaves, and other natural
products. In conventional-tillage farming, the land is plowed and then the soil
is broken up and smoothed to make a planting surface, thus leaving it
vulnerable to erosion. However, as oppose to this method, many U.S.
farmers are trying conservation-tillage farming. The
idea is not to disturb the soil while planting crops. With minimum tillage
farming, special tillers break up and loosen the subsurface soil without
turning over the topsoil, previous residues and cover vegetation. In no-till
farming, special planting machines inject seeds, fertilizers, and weed killers
into slits made in the unplowed soils. Conservation tillage is used on about
one-third of U.S.
croplands. The U.S. Department of Agriculture (USDA) estimates that using
conservation tillage on 80 percent of U.S. cropland would reduce soil
erosion by at least half.
Figure 5.7: Strip
Farming in Bali, Indonesia; Source: Google Image
nd egradas
chapters have beeionsed in chjImplications for Bangladesh
Importance
of Agricultural Sector
Bangladesh is predominantly a
rural-agrarian country. The great uniformity
of landmass, the fertile alluvial soil, and the tropical monsoon climate
provide excellent conditions for agricultural production. Land is the most precious
of all natural resources in Bangladesh.
Degradation
of the land resource means to a great extent, a degraded agro-ecosystem on
which depends the livelihood of the rural mass (Figure 5.8). The role of
agriculture in the growth and stability of the economy of Bangladesh
can hardly be estimated. Agriculture accounts for nearly one-fourth of GDP
(contribution includes its sub-sectors of crops, livestock, forestry and
fisheries), and about two-thirds of employment. Although the share of
agriculture to GDP has been declining since her Independence in 1971, it will remain the
largest single contributor to the economy in the years to come. This sector
will not only play a vital role in achieving self-sufficiency in food
production, but will also continue to be an important source of export earning,
particularly in the areas of diversification. The crop sub-sector, which was 79
percent of the total agricultural output in 1990/91, dominates the agricultural
scenario in Bangladesh.
Food crops alone account for about three-quarters of the total agricultural
output. Rice is the principal food crop that covers about 75 percent of the
total cropped area, accounts for 70 percent of the value (added) of total crop
output, and constitutes 92 percent of the total foodgrains produced annually in
the country. Being the staple food of Bangladeshi people, rice
provides about 75 percent of the calories and 55 percent of the protein in the
average daily diet, and ensures political stability for the country. Since the
stable supply of rice has great implications for food security, many views food
security as synonymous to achieve self-sufficiency in rice production. The dominance
of rice in the crop sub-sector virtually assures stability in the structure of
production. Major shifts in crop diversification will be limited as long as
rice is important to the diet of the nation as the chief source of calorie and
protein. Wheat, potato, pulses, and oil seeds are the other principal food
crops. If proper preventive measures are not taken, the
situation will worsen and food security will be seriously hampered. This section deals with causes of land
degradation in Bangladesh
both in terms of deterioration of soil quality and loss of land.
Figure 5.8: A
Typical Agro-ecosystem in Bangladesh
Agricultural Intensification and Performance
Population growth
and scarcity of cultivable land in Bangladesh have led to more
intensive agriculture and cultivation of HYV of crops to meet the growing need
for more food. In fact, Bangladesh
has made steady progress in food production in the post-Independence period.
Advances in rice science and technology have enabled Bangladesh to meet the food needs
of fast growing population. Rice production increased substantially over the
years following the introduction of HYV seeds, and application of modern
agricultural inputs i.e. use of chemical fertilizers along with pesticides, and
irrigation. The total land irrigated in the country in 1999-2000 was 4.51
million ha, which has increased to 5.26 million ha in 2005-06 or 66 percent of
the net sown area. The use of chemical fertilizers and pesticides in crop
cultivation in Bangladesh
has also increased tremendously. On the average, about 160,000 tons of chemical
fertilizers and 3000 tons of pesticides were used in 1990. Since 1980s, the use
of chemical fertilizer in Bangladesh
has been consistently increasing. The total quantity of chemical fertilizer used
in 2005/2006 was about 3.7 million mt, a four-fold increase over its use in
1980/81. In recent years, use of
pesticides has also increased at an alarming rate; in 1997 it was 11,367 mt and
by 1999 it had increased to 14,340 mt. In terms of output, between 1971/72 and
2004/05 rice production has more than doubled- increased from 9.8 million mt to
25.2 million mt. This impressive growth in rice production over the last three
decades or so has generated a sense of complacency regarding Bangladesh's ability to meet the
future demand for rice.
Impacts of Technology
on the Environment
Acceleration in
production has resulted in an increase in per capita rice availability, and led
to self-sufficiency in output by the early 1990s. Intensive rice cultivation,
however, has been under some strains since then. There are many studies
reporting that recent trend in the growth in rice production raises serious
concern regarding the sustainability of the past achievements. Despite
increases in input application, yields per acre have declined or stayed the
same on about two-thirds of the area planted with HYVs in the 1990s. Changes in rice productivity under modern
inputs although reveal some interesting points regarding self-sufficiency it
has failed to achieve the goal of sustainable production in real terms.
Maintaining the growth in yield or even holding yields at current levels
requires greater amounts of fertilizer input, implying that the quality of the
underlying soil resource base may be deteriorating. According an estimate,
about 1.8 million ha of land in Bangladesh
are either on the threshold level or acute stage of zinc deficiency. Out of 27
agro-ecological zones in Bangladesh,
18 fall in the nutrient grades of poor to very poor in 1998.
Fertilizer and pesticides over-dozes have
already been depleting soil fertility in Bangladesh. Chemical fertilizers do
not have humas to the soil, and thus its ability to hold water will decrease,
and the soil will soon become compacted and less suitable for crop growth. By
decreasing the soil’s porosity, inorganic fertilizers also lower the oxygen
content of soil. Although pesticides are
used at low dozes still they are a cause of soil contamination (sprayed over
standing crops ultimately contaminate the surrounding soil). The pesticides not
only destroy harmful insects, but also destroy beneficial top soil microbes-
resulted in reduction of the biological nutrient replenishment of the soil and
reducing its fertility. Although irrigated land can produce crop yields that
are two to three times greater than those from rain-fed systems, irrigation has
downside. As a result of irrigation, the land remains inundated in most of the
seasons, which creates an adverse effects on soils because of continued oxygen
deprivation in the sub-soils. Further, irrigation may destroy soil fertility
through salinization (Chapter
6), the accumulation of which stunts crop growth, lower yields, and eventually
kills crop plants, and ruins the land. According to an estimate severe
salinization to date has reduced yields on 10 percent of the world’s irrigated
cropland, and another 30 percent has been moderately salinized. Further,
continuous waterlogging
(Chapter 6) will mean absence of oxygen in the soil. Prolonged submersion in
water will leach out micronutrients and organic matters in the soil, resulting
in the loss of soil fertility. Waterlogged soil environment is the breeding
ground for different types of pests and disease causing microbes and animals.
Overall,
the impression of intensive rice cultivation is that the resource base for
agriculture is shrinking. If the present cultivation systems continue, then by
2020 land degradation may pose a serious threat to food production. Bangladesh
will face enormous challenge by 2020 in trying to achieve food self-reliance
and to ensure food security for all in the country. Demand for rice will
increase with the increase in population. According to an estimate, the
population of Bangladesh
will be 169 million by the year 2025. As a result, land-person ratio will
decline gradually. To feed the extra million, Bangladesh will be in need to
produce about 27.8 million mt of clean rice by the year 2025, which is roughly
21 percent higher than the production level of 2000. The demand has to be met
from our limited and shrinking land and water resource bases. Therefore, a core
concern of all of us is how to sustain rice productivity while protecting and
enhancing the environment.
Management
Continued
agricultural intensification need not lead to excessive environmental
degradation. Farming communities in all parts of the world have responded to
soil degradation, particularly when it affect their livelihoods, with measures
such as planting trees to control erosion, regulating cultivation around local
water sources, utilizing organic fertilizers, salt tolerant species of
vegetation, drought resistant crop varieties, restricting over extraction of
groundwater, pesticides, controlling pests by using different biological and
physical methods (integrated pest management such as frog farming in crop land
is ecologically sound- kills insects) and other pollutants, designing good
drainage networks, rehabilitating degraded soils, and adopting new technologies
for efficient use of irrigation waters. The development of biotechnology suitable
for land scarce conditions is a very important consideration in this regard.
Development of ecologically sound technologies such as integrated pest
management, and restoration of soil fertility through better management of soil
organic matter (bio-fertilizers) is recommended. The introduction of legumes
and green manure into the cropping pattern and minimum tillage in combination
with crop residues can contribute to higher level of production and also
improve soil fertility. Farmers should be encouraged to adopt farming practices
that are ecologically sound for their areas including organic farming.
Indigenous farming systems often contain a wealth of environmental knowledge,
which needs to be assessed and adapted with the changing circumstances. More
funds have to be allotted to smallholder needs and more incentives given to
scientists.
B: Land Resources
Land is a finite
and valuable natural resource. We depend on land for our food, fibre, fuel wood
and the other basic amenities of life. Soil, specially the top soil, is
classified as a potentially renewable resource because it is being continuously
regenerated by natural process, although at a slow rate. However, when rate of
erosion is faster than rate of renewal, then the soil becomes a non-renewable
resource. Experts believe that the average global soil erosion rate per annum
is 20-100 times faster than the renewal rate. Moreover, with rapid population
growth, the demand for land is also increasing. Hence, there is more and more
pressure on the limited land resource base, which is getting degraded due to
overuses. Land degradation is a real problem because soil formation is an
extremely slow process. According to an estimate, about 200-1000 years are
needed for the formation of one inch (2.5 cm) soil, depending on the soil type
and climatic factors.
Land Degradation
Land
degradation is a process which leads to decline in the fertility or future
productive capacity of soil as a result of human activity. In other words, it
is commonly referred to the
unfavourable alteration of our land resources largely because of anthropogenic
activities. That means loss in the capacity of a given land to support growth
of useful plants on a sustained basis. Land degradation is one of major
ecological issues of the world which may be defined as an overall lowering of
land qualities because of adverse physical and chemical changes brought in by
human activities in to such an extent that these changes adversely affect all
biological communities in general and human society in particular. Top soil erosion, nutrient depletion,
loss of organic matter, accumulation of pollutants in the soil due to
industrial effluents, uses of agro-chemicals such as fertilizers and
pesticides, acid deposition, irrigation related problems such as slinization
and waterlogging of soils, and lowering of water tables are some of the
pressing land degradation issues of our time. These are results of many factors
and/ or combination activities which damage the soil and restrict their use or
production capacity. Considering its impacts on food security and environment,
it is being important in many parts of the world. The productivity of some
lands has declined by 50 percent due to soil degradation and desertification.
Large-scale degradation of land resources has been reported from many parts of
the world. From Table 6.1 it appears that about 70 percent of the total land of
the world is under degradation.. The economic impact of land degradation is
extremely severe in densely populated regions of South
Asia and Sub-Sahran Africa. In the case of Bangladesh, there is no exception.
The main causes of land degradation in Bangladesh are rapid population
growth accompanied by poverty, improper land use, lack of policy, ineffective
implementation of existing laws and guidelines. Unsustainable agricultural
practices, soil erosion, soil nutrient mining, loss of organic matter, soil
compaction, contamination, land transformation such as encroachment of
agriculture and settlements on forest lands also create pressure on limited
land base. Further, growing demands for urbanization and rural infrastructure
are also aggravating the situation; construction of roads, embankments,
polders, earth excavation, mining and quarrying all lead to land degradation.
Table 6.1: World’s
Degraded Lands by Regions (in million km sq.).
Continent Total
Area Degraded
Area % Degraded
Africa 14.326 10.548 73
Asia 18.814 13.417 71
Australia & the Pacific 7.012 3.759 54
Europe 1.456 0.943 65
North America 5.782 4.286 74
South America 4.207 3.058 73
Total 51.597 35.922 70
Source:
Dregne and Chou, 1994.
Soil
pollution
is a form of land degradation. When the action of external factors leads to a
deterioration of the soil quality by the removal of its useful chemical
components- nutrients or by accumulation of toxic substances that are harmful
to the flora and fauna using it, then it may be said that the soil is polluted.
It is mainly the consequences of urbanization and industrialization, but modern
day agricultural practices are also responsible for it. Soil is polluted when
large quantities of wastes from different sources (urban industrial- chemical
and metallic, municipal solid, radioactive etc.) are dumped on it or mix with
the soil. In a natural state, soil inhibit distinctive flora and fauna such as
bacteria, fungi, algae, protozoa, earth worms, several other pests and insects
which make the biological system of soil complex. As such, soil has been a potential carrier of
microbial growth and pathogens that endanger human health. While some
microorganisms help in maintaining the soil fertility, others act as chronic
pollutants.
Since
the economy of Bangladesh
is agro-based and land is a scarce resource in the country, is being degraded
in different ways including pollution. But comprehensive studies are lacking on
the issues of land degradation in Bangladesh. Table 5.1 presents the
main factors that are causing land degradation in Bangladesh. Among the major types of land degradation
that occurs in Bangladesh
shifting cultivation, top soil erosion, nutrient depletion, salinization and
waterlogging are important from the perspective of agro-ecosystems. However,
the level of land degradation is not uniform in Bangladesh; its extent vary
seasonally and by regions (i.e. The Chittagong Hill-Tracts, Modhupur forest,
Barind Tract, coastal belt, and the flood plains) as well as the pressures are
not always the same either.
Table
5.1: Factors Causing Land Degradation in Bangladesh
Soil degradation may be caused by a number of
factors: (i) Physical- e.g. loss of top soil due to water or wind erosion; (ii)
chemical- e.g. depletion of nutrients or toxicity due to acidity or alkalinity
or water logging; and (iii) bio-chemical- which affects the micro-flora and
reduce the microbial activity of soil. Some other factors such as
deforestation, extensive cultivation of marginal land, improper agricultural
practices like cropping intensity, soil compactness, monocropping, poor
manuring, misuse of fertilizers, excessive irrigation, and mining may
accelerate the process of land degradation. The following is the list of some
driving forces of land degradation in Bangladesh and their impacts.
TABLE #
Driving Forces State
and Impacts
Population growth Poverty; depletion of natural
resources
Intensification of agriculture Soil erosion and nutrient
loss; yield reduction; siltation
Bio-technology Misuse
of chemical fertilizers and pesticides; soil pollution
Irrigation problems Salanization and waterlogging; soil
degradation
Urbanization Increased
land conversion and unplanned uses
Industrialization Open discharge of industrial
chemicals to land; loss of quality
Rural settlement Conversion and seizing
of productive agricultural land
Brick making and kiln Loss of topsoil; destruction of
productive land
Quarrying and mining Degradation of land; Loss of soil quality
Construction of polders, embankments Loss of productive agricultural land
Construction of rural roads Loss of fertile agricultural
land
Riverbank erosion Loss of land; degradation of quality
Land sub-divisions Fragmentation of holdings and
degradation of quality
Shifting Cultivation
Improper cultivation in hill slopes,
terraces and piedmont alluvial plains are major contributors to land
degradation in Bangladesh.
Shifting cultivation on hills, locally known as “Jhum” cultivation is a common
practice (see Chapter 6 for details) among the tribal communities in the
greater Chittagong Hill-Tracts CHT). This is the traditional community-based
agricultural method practiced by indigenous people of CHT, is one of the major
causes of land degradation- soil erosion. An evaluation of the
Sanghu-Matamuhuri reserve forest indicated that shifting cultivation, which was
practically non-existent in 1961, accounted for 17,135 ha in 1984. (about 23
percent of the total area). In recent years, this traditional agricultural
practice is considered as the most inefficient way of using the virgin forest
lands. The soils of hilly area are the most susceptible to water erosion in
which sheet, rill and gully erosion occurs frequently. About 75 percent of the
hilly areas in Bangladesh
have very high susceptibility to erosion. Losing top soil make soil less
fertile, less able to hold water. This often leads to low crop productivity
because of loss of water, organic matter and soil nutrients such as nitrogen,
phosphorous, potassium, and calcium.
Deforestation
Deposition of sandy materials on
agricultural land is a consequence of deforestation in the hills of the upper
catchment areas, particularly in the lower part of the piedmont areas of
greater Mymensingh and valleys of Sylhet and the CHT. During the monsoon
season, when heavy rainfall occurs in the upland areas, it causes flash floods
in the low lands. The runoff carries sandy materials that spread over
agricultural lands. Near foothills, such deposits are quite high that compels
farmers to abandon the affected areas from agricultural production. According
to a study, erosion of topsoil in CHT has increased, and 17 percent of the soil
resources have deteriorated between 1964 and 1985. A study on top soil erosion
in Khagrachari, Rangamati and Bandarban Districts reveals that top soil erosion
ranges from 100 to 120 tons per ha annually. The resulting sediment clogs
irrigation ditches, boat channels, reservoirs, and lakes. The sediment-laden
water is cloudy, tastes bad, fish die and flood risk increases. Due to increase in the number population in
the CHT region there is a high demand on agricultural production, which is also
creating stresses on scarce forest lands. As a consequence, the normal
regeneration time of forest is not being allowed, and the soil is loosing its
fertility.
Human
Settlements
The population pressure and scarcity of
cultivable land has caused a heavy influx of settlers from the plain land to
the unprotected forestlands of Madhupur and Barind tracts. The Madhupur forest
area has almost been denuded due mainly to deforestation, and has further been
aggravated by many other factors such as its closeness to the capital city- Dhaka, improvement to road communication, urbanization
and industrialization. In the Barind
tract, land degradation is caused mainly due to over exploitation of biomass
from agricultural lands and unscientific agricultural practices- mostly
cultivation of HYV rice through groundwater irrigation. The process has been
aggravated not only by irregular rainfall, but also by reduced water flow in
the adjacent rivers that normally play a vital role in replenishing soil
fertility and researching aquifer. Clearing of forest land for settlements and
unwise land management for agricultural use accelerate erosion of the top soil
(Figure 5.9). As a result, the infertile
compact clay is exposed to the surface.
Figure 9: An Image of Typical Land-Use
Changes
Land Conversion
Construction of Road: Mileage of
inter-District highways and network of rural roads have increased tremendously
over the past few years. Most of these roads and highways traverse through the
floodplain. These have to be constructed on raised ground as a protection
against the annual flooding. Land is degraded in two ways: i) there is a huge
loss of fertile agricultural land in a land hungry country. ii) Unplanned
construction of rural roads may result in drainage congestion- ultimately
causing flood. Urbanization:
Urbanization is necessary for socio-economic development of a country, but the
present process in Bangladesh
invariable reduces the amount of good agricultural land. As urbanization
proceeds, the requirement for space increases. Land development takes place in
the urban fringe for the construction of residential, commercial and industrial
buildings. Unplanned Industrial Development: As the urban area spreads outward,
more and more fertile agricultural land is lost permanently. Unplanned
industrial expansion is of great concern because it encroaches on fertile land,
and industrial effluents deteriorate the quality of soils and affect fisheries.
The
rivers of Sitalakhya, Buriganga, Karnaphuli and Passur and their banks are a
few of many good examples. Brickfields:
Brickfields located on the outskirts of all the urban areas in Bangladesh
are another source of land degradation. The brickfields are set up on marginal
agricultural land; owners take lease of the land from farmers. Thus, each year
the topsoil on thousands of acres of land is lost to brick making; the
subsequent harvest is poor; regaining the strengths of the land is a time
consuming process. Management: Proper land use planning and
zoning would be appropriate measures to combat this type of land degradation..
Any necessary earth excavating activity should be balanced through replacement
and preserving the topsoil.
Quarrying and Mining
In Bangladesh,
quarrying for boulders, stones and gravel has become a threat to the environment.
In Chokoria, Lama and Alikadam of Chittagong, boulders and stones and gravel
are collected by cutting into hillsides and digging at their bases. The hills
are laid bare as much of their natural rock formation is destroyed.
Consequently, with the advent of the rainy season huge landslides and flash
floods wash away villages in these areas. Large tracts of agricultural land are
covered by sands and become unsuitable for cultivation. Mining
for coal also degrades the land where this is practiced. The topsoil is removed
and trenches are cut to reach the coal seams. The deeper layer of soil becomes
devoid of nutrients that comes to the surface after the mining operation.
Beside this, coal wastes left on the land makes it acidic so that nothing can
grow on it. Management: Measures should be taken to stop rampant excavation of hills, and also
earth excavation for the preservation of the topsoil.
Flood Protection Embankments and Polders
Bangladesh is a country of river networks.
Embankments built along the riverbanks to protect the life and property of the
people living on the floodplain may serve this purpose during moderate floods,
but these have adverse environmental impacts on the land they are suppose to
protect. Embankments intercept the natural flow of floodwater over the land and
disrupt the natural delta building process. Flood brings sediment- a beneficial
process whereby the fertility of vast tracts of land in the floodplain is
renewed and ecological balance is maintained. This process is interrupted as
embankments hamper accretion by stopping the sediment from spreading over the
land. It also means a loss in soil fertility. Polders
in the coastal areas: Agricultural lands in the coastal area are prone to
incursion by saline water during the diurnal tide. Polders are built to protect
such lands. Polders are built to protect such lands from saline intrusion of
tidal water to increase agricultural productivity. However, there are problems.
There was initial increase in crop production; later the polder areas have
become waterlogged. Due to lack of proper maintenance, the connecting canals
have silted up and the polder areas are at lower level than the channels. The
brackish water entering the polder area during high tide cannot recede or
cannot be drained out. Thousands of has of land have now become water logged
and the soil salinity has increased, rendering these unsuitable for growing
crops. Without immediate rehabilitation, vast areas of land will be permanently
degraded. Beel Dakatia in the Khulna
region had suffered a similar fate. Management: Construction of flood protection
infrastructures such as embankments and polders should be undertaken in
conjunction with the Environmental Impact Assessment (EIA). Since Bangladesh
is pat of an active delta, the processes of delta formation should not be
obstructed. Flood warning systems should be improved; homesteads should be
built on raised grounds to protect human lives, property and livestock. Crops
that are water tolerant or have a shorter growing season should be planted in
flood prone areas.
Desertification
Desertification is a serious form of land degradation, a problem growing
in many parts of the world. It is a process whereby fertile land is reduced to
a desert-like condition, the transformation of which may take place in several
stages. The barrenness of land is mostly human induced. It is the consequence
of mismanaged use of land. Natural event like drought may only be partly
responsible for this condition. In fact, drought may also be the outcome of the
loss of vegetative cover. According to an estimate, moderate desertification
may be linked to a 10-25 percent drop in crop productivity; severe
desertification is 25-50 percent drop; and very severe desertification is a
drop of more than 50 percent productivity.
Every year, a significant portion of the land area of the earth is under
the threat of desertification and 200,000 sq KM of its land is becoming a
desert. The regions most adversely affected by desertification are areas
located in arid and semi arid climates i.e. sub-Saharan Africa, the Middle
East, Western Asia, parts of Central and South America, the western half of the
United States, and Australia.
In Bangladesh,
the Northern region shows clear signs of desertification. The southwest region
is also under a similar threat, although the factors responsible for it are
somewhat different. According to an UN estimate, 8.1 million square KM (3.1
million square miles)- an area the size of Brazil
and 12 times the size of Texas- have become desertified during the past 50
years. On a global scale, about 60
percent of rain-fed croplands, and 30 percent of irrigated croplands are
threatened by desertification. The total area of this threatened land is 33
million square KM (13 million square miles)- about the size of North and South America combined. The cumulative effect of
desertification threatens the livelihood of at least 900 million people in 100
countries. In the case of Bangladesh,
the Northern region shows clear signs of desertification. The southwest region
is also under a similar threat, although the factors responsible for it are
somewhat different. If current trends continue, desertification could threaten the
livelihoods of more than 1.2 billion people by 2010.
Figure 5.10: An
Image of Land Degradation; Source: Google image
Figure 5.11:
Desertification
Figure 5.12:
Desertification
Figure 5.13: Land
Degradation and Desertification
Figure 5.14: Land
Degradation and Desertification
Causes and Consequences
In general, the barrenness of land is mostly human induced. It is the
consequence of mismanaged use of land. Practices that make topsoil vulnerable
to desertification include over cultivation, overgrazing on fragile rangelands;
deforestation, mining, faulty irrigation techniques leading to increased soil
erosion, fall of water table, soil compaction by farm machinery, salt buildup
and waterlogging. Over cultivation of land results in exhaustion
of nutrients presents in the topsoil. The depleted soil eventually becomes
unsuitable for crop cultivation. Left fellow, it is soon eroded by wind and
rain. For Bangladesh, the
most important cause of desertification in its Northern and Southwestern region
is withdrawal of water by India
in upstream of the Rivers Ganges and Teesta. In Bangladesh, land that is
intensively cultivated is showing a downward trend in productivity. To improve
the yield of the cropped area, excessive chemical fertilizers are being used
which, in turn, is destroying the natural fertility of the soil. Overgrazing
on land, which has sparse vegetation, may lead to its total destruction. As the
soil is striped bare, the topsoil is blown away by the wind or washed away by
rain. Because of high population pressure and intensive agricultural practices,
there is hardly any land for grazing animals in Bangladesh. Deforestation
is a major problem faced by Bangladesh.
Each year trees are cut down beyond the natural regeneration capacity of the
forest ecosystem. Forests provide protective tree covers that keep the soil
moist. The humus content of the soil being high, the water retention capacity
is also high. When trees are felled indiscriminately, large areas of forestland
become treeless. Exposed to the sun’s rays directly, the soil soon becomes dry
as the rate of evaporation increases. It is than at the mercy of the wind and
rain. The topsoil is soon lost and the land becomes barren. Drought:
Natural event such as drought may only be partly responsible for this
condition. In fact, drought may also be the outcome of the loss of vegetative
cover. Every year, a significant portion
of the land area of the earth goes under the threat of desertification. The
consequences of desertification include worsening drought, famine, threat to
biodiversity, declining living standards, and a growing numbers of
environmental refugees. Frequent drought, however, is an indication of severe
desertification.
Desertification
in Bangladesh
As already mentioned above, the main causes of desertification are soil
erosion resulting from over cultivation, overgrazing, deforestation, increase
in soil salinity due to different reasons and fall in the underground water
table. For Bangladesh,
however, the most important cause of desertification in its Northern and Southwestern
region is withdrawal of water by India in upstream of the Rivers
Ganges and Teesta. Withdrawal of water in the upstream of the Ganges and other
rivers flowing through India
has led to drastic reduction in the availability of surface water in Bangladesh.
The whole Northern region becomes dry. As there is no enough water to recharge
the underground aquifers, the water table falls drastically. Further, the
withdrawal of underground water for irrigation purposes, surpasses the rate of
research of the underground aquifers. The fall in the water table makes it
impossible for crops to grow in many areas. Water Withdrawal in the upstream of the Ganges and other rivers
flowing through India has
led to drastic reduction in the availability of surface water in Bangladesh.
The whole Northern region becomes dry. As there is no enough water to recharge
the underground aquifers, the water table falls drastically. Further, the
withdrawal of underground water for irrigation purposes, surpasses the rate of
research of the underground aquifers. The fall in the water table makes it
impossible for crops to grow in many areas. These factors, accompanied by rapid
population growth, povery and poor land management are aggravating the problem. The Ganges-Kobadak
Project: In the southwest, dry season crop cultivation is
dependent on irrigation. The Ganges-Kobadak Barrage project was supposed to
provide adequate water of 400,000 acres of cropland. However, the project was
adversely affected by the construction of the Farakka barrage in India.
Due to shortage of water, large areas of land may undergo desertification if
the project cannot be implemented and utilized fully. Drought: Although drought may seem to be a natural
phenomenon, human activities leading to deforestation may reduce rainfall in an
area and enhance drought like condition. Bangladesh often experiences
moderate to severe droughts between October to May. Droughts are severe in the
northwest and southwest regions of the country. These areas experience less
rainfall during the year compared to other areas of the country and these are
the areas undergoing desertification. Vast tract of land in the northwest known
as Barind, are the worst affected areas. The summer months are hot and dry.
Maximum temperature may soar to 43 degree C. Once green areas are denuded of
trees, vegetation becomes sparse. To make matter worse, rivers are rapidly
being filled up by sediments as the flow has decreased due to building of
barrages in the upstream. Fields are flooded during the monsoon. However, as the flood recedes,
crop fields are covered by coarse sands instead of the fertile alluvium that
was previously deposited. Thus, many croplands are turning into vast tracts of
sand-covered fields that cannot be productively cultivated. Further, in many
countries of the world including Bangladesh, productivity of land is
adversely affected by salinization. If irrigation of the crop is not managed
properly it may lead to salinization of the soil (see Chapter 11).
Management
The most effective way to deal
with desertification is to drastically reduce overgrazing, deforestation, and
the destructive forms of planting, irrigation and mining that are to blame.
More over, reforestation programs may be under taken which will anchor soil and
hold water while slowing desertification and reduce the threat of global
warming. Some beneficial effects of agro-forestry are as follows:
- Reduction of
loss of soil as well as nutrients through reduction of run-off;
- Addition of
carbon and its transformation through leaf, twig, bark fall etc.;
- Nitrogen
enrichment by fixation of nitrogen by appropriate trees, shrubs etc.;
- Improvement
of physical conditions of soil i.e. water holding capacity, permeability,
drainage etc.;
- Release and
recycling of nutrients of by affecting biochemical nutrient cycling;
- More microbial associations and addition
of more root biomass;
- Moderately
affect on extreme conditions of soil acidity and alkalinity;
- Create more
favourable microclimate by windbreak and shelterbelt effect;
- Lowering effect
on the water-table in areas where the water table is high;
- Increase soil
cover by litter and pruning;
- Increase soil
resistence to ersosion by maintenance of organic matter;
- Stablize
earth structures by root systems; and
- Make
productive uses of the land occupied by conservation works.
