Transcript Soil Erosion and its Control

Land Degradation &
Soil Erosion
Introduction
 Land degradation
 Soil Erosion
 Water Erosion
 Wind Erosion
 Soil Conservation

Land Degradation
This is the reduction of the productive potential of
lands for human use.
Land degradation is caused by such phenomena as:
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Overgrazing by animals
Deforestation
Inappropriate agric practices
Soil erosion
Two main components of land degradation are;
1.
2.
Damage to plant communities
Soil degradation
Soil Erosion
Soil Erosion - the detachment and movement and
redeposition of soil.
Two main types of erosion are:
1.
Natural Erosion - normal geological soil movement by wind,
water, ice, or gravity.
2.
Accelerated Erosion - erosion more rapid than natural erosion,
primarily as a result of action by humans or other animals.
On-Site Effects of Accelerated
Erosion
Erosion results in the loss of soil itself
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The surface horizons which usually contain much
of the soil nutrients are eroded.
The subsoil horizons which are less useful remain
The quality of remaining topsoil may also be
impaired.
1.
2.
3.
Organic matter is removed
Water holding capacity and cation exchange capacity is
lower
Essential nutrients are removed
Off-Site Effects of Accelerated
Erosion
Erosion moves sediments and nutrients off the land
to rivers and lakes
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The nutrients impact water quality through the process
of eutrophication
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Caused by excess nitrogen and phosphorus
Runoff water may also carry toxic metals and
organic compounds, e.g., pesticides
Sediment Problems
Sediments are major water pollutants and could
cause a wide range of environmental damage.
Smother crops and other vegetation
Fill roadside drainage ditches and destroy structures
Problems of turbidity of streams
1.
2.
3.
4.
Prevents sunlight from penetrating water
Reduced photosynthesis
Death of submerged aquatic vegetation
Upsetting aquatic food chain
Sediment Problems (contd.)
Health Hazard
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The finest particles blow the farthest and present
major human health hazards
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lung problems
Soil Loss Tolerance
Although every soil loss is detrimental, some loss
can be tolerated.
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Different soils have soil-loss tolerance limits
Tentative soil-loss tolerance limits have been
developed for soils
Soil moved annually by erosion in the U.S. equals
approximately 5 billion metric tons (2/3 by water,
1/3 by wind).
Average annual cropland soil loss in the US is
calculated to be 11 Mg ha-1 y -1
Models for Predicting Extent
of Soil Loss
Universal Soil Loss Equation (USLE)
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Simple model that relates soil erosion to easily
observed factors
The main point of this model is the fact that
water induced erosion is a result of the
interaction of rain and soil
A = RKLSCP
A, predicted soil loss, is the product of
R
=
rainfall erosivity
K
=
soil erodibility
L
=
slope length
S
=
slope gradient or steepness
C
=
cover and management
P
=
erosion control practices
The equation has been modified a bit (RUSLE) to better define
the factors and computerize the model
Mechanics of Water erosion
1.
Detachment of soil particles from the soil mass
Influence of raindrops (detachment, granulation and
movement of soil particles)
2.
Transportation of the detached particles downhill
Floating, rolling, dragging and splashing
3.
Deposition of the transported particles at some
place lower in elevation.
Eroded materials can easily travel long distances.
Types of Water Erosion
1.
Sheet Erosion
Uniform removal of soil from the land surface
2.
Rill Erosion
Sheet flows begin to concentrate on tiny channels
(termed rills) that become dominant –bare lands
3.
Gully Erosion
Volume of runoff may concentrate more and cut
deeper into soil. Rill become larger channels –gullies.
Water Erosion Control
Conservation tillage
Form of tillage that protects the soil from ravages of
erosion.
Herbicides (kill weeds chemically rather than
mechanically)
Minimum tillage (planting seeds without removing the
plant residues.
Wind Erosion
Wind erosion is most common in arid and semiarid
areas.
It occurs when strong winds blow across soils with
relatively dry surface layers.
Finer soil particles can travel very long distances
and can cause all kinds of health problems in
humans
Wind Erosion
Like water erosion, wind erosion involves three
processes
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Detachment, transportation, and deposition.
Transportation of particles could be by:
Saltation -movement by series of short bounces
Soil creep –movement of large aggregate along surface
Suspension – movement of dust particles parallel to the
ground surface and upwards into the atmosphere.
Factors Affecting Wind Erosion
Wind velocity
Wind turbulence
Surface roughness
Soil properties
Vegetation.
Predicting Wind Erosion
 Wind
I =
C=
K=
L=
V=
erosion prediction equation (WEQ)
E = f(ICKLV)
soil erodibility factor
climate factor
soil-ridge roughness factor
width of field factor
vegetative cover factor.