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Lecture -10:
Effects of Agriculture on the
environment
ENV 107: Introduction to Environmental Science
Dr. A.K.M. Saiful Islam
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
How agriculture changes the
environment
† Agriculture has both primary and
secondary effects.
† Primary effect, also called an on-site
effect, is an effect on the area where the
agriculture takes place.
† A secondary effect, or off-site effect, is
an effect on an environment away from
the agricultural site, typically downstream
and downwind.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Agriculture driven major
environmental problems
† Major environmental problems the result
from agriculture include
„ deforestation,
„ desertification,
„ soil erosion,
„ overgrazing,
„ degradation of water resources,
„ salinization,
„ accumulation of toxic organic compounds,
and
„ Water pollution including eutrophication *
* Increase of chemical element in pond is called eutrophication
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
The effects of agriculture on the
environment
† The effects of agriculture on the environment
can be divided into three groups: (1) local, (2)
regional, and (3) global
† 1.
„
„
„
Local effects are those effects include
erosion,
loss of soils, and
increases in sedimentation downstream in
local rivers.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
The effects of agriculture on the
environment
† 2. Regional effects are those that generally
result from the combined effects of farming
practices in the same large region. Regional
effects include
„ the creation of deserts,
„ large scale pollution,
„ Increases in sedimentation in major rivers
and in the estuaries at the mouths of the
rivers, and
„ Changes in the chemical fertility of soils over
large areas.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Soil Erosion
(a) Gully soil erosion on
Cleared and plowed farmland
(b) Agricultural runoff carrying
Heavy sediment load
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Making Soils Sustainable
† One way to counter soil erosion is to promote new
soil formation.
† Another way to counter erosion from plowing is
contour plowing. In contour plowing the land is
plowing along the contours, perpendicular to the
slope and as much as horizontal plane as possible.
† An even more efficient technique to slow erosion is
to avoid plowing altogether. No-till agriculture is
farming practice that includes not plowing the
land.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Contour Plowing
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
No-till Agriculture (soybean crop
planted in wheat stubble)
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Carrying capacity of Grazing lands
† The carrying capacity of land for cattle varies with
the rainfall and the fertility of the soil.
† When carrying capacity is exceeded, the land is
overgrazed.
† Overgrazing reduces the diversity of plant
species, leads to reduction in the growth of
vegetation and dominance of plant species that
relatively undesirable to the cattle, increases the
loss of soil by erosion as plant cover is reduced
and results in damage from the cattle tampering on
the land.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Overgrazing
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Desertification: A regional effect
† Desertification is the deterioration of land in arid,
semi-arid and dry sub humid areas due to changes in
climate and human activities.
† The leading cause of desertification are bad farming
practice such as:
„ failure to contour plowing or
„ simply too much farming,
„ overgrazing,
„ the conversion of rangelands to croplands in marginal
areas where rainfall is not sufficient.
„ poor forestry practices including cutting all the trees
in an area marginal for tree growth.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
3. Global effects of agriculture
1. First agriculture changes land cover, resulting in
changes in reflection of light by the land
surface; the evaporation of water ; the
roughness of the surface; and the rate of
change of chemically compounds.
2. Second, modern agriculture increase CO2.
3. Agriculture also affect climate though fire
associated with clearing land for it.
4. Artificial production of nitrogen compound for
use in fertilizer which may be leading to
significant change in the biogeochemical cycle.
5. Finally, agriculture affects species diversity.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
DDT
† The real revolution in chemical pesticides – the
development of more sophisticated pesticides – began
with the end of World War II and discovery of DDT
and other chlorinated hydrocarbons, including aldrin
and dieldrin.
† At first DDT was thought to be the long-sought magic
bullet: It appear to have no short-term effect on
people and seems like kill animal.
† DDT was not very soluble in water and therefore did
not appear to pose an environmental hazard
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Adverse effects of DDT
† Initially, DDT was used very widely until three things
were discovered:
„ 1. It has long-term effects on other, desirable
organisms, including the ability of birds to produce
eggs and a possible increased incidence of cancer in
other organisms,
„ 2. It is stored in oils and fats and is concentrated as
it is passed up food chains, so that the higher an
organism is on a food chain the higher the
concentration of DDT it contains, a process known as
food chain concentration or, biomagnification ,
„ 3. the storage of DDT in fats and oils allows the
chemical to be transferred biologically even though it
is not very soluble in water.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Integrated Pest Management (IPM)
† Modern approaches to pest control involves IPM, an
ecosystem approach to pest management that integrates
a variety of techniques include:
„ The use of natural enemies of pests, including
parasites, diseases, and predators.
„ The planting of greater diversity of crops to reduce
the chance that pests will find a host plant.
„ No-till or low-till agriculture, which helps natural
enemies of some pests to build up in the soil, and
„ The application of a set of highly specific chemicals,
used much more sparingly than in earlier approach.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Biological Control
† A part of IPM, Biological Control is a set of methods
to control pests organisms by using natural ecological
interactions including predation, parasitism, and
competitions.
† For example, ladybugs are common predators of
many plant-eating pests.
† It is possible to buy of quantities of ladybugs for
release in home gardens or farms. The hope is that
these ladybugs will feed on pests and reduce their
abundance.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Biological Pest Control