LAST LECTURE
Soil nutrient management
THIS LECTURE
Soil erosion and its control
Soil Erosion Lethbridge Coulees North of University of Lethbridge, 14 Sept 2007
Only 2 mm rain the previous day
SOIL EROSION
Transport of unconsolidated Earth material from one
place to another place
Modes of Transport (denudational agents):
• Water
Dust storm Lethbridge Coulees North of University of Lethbridge, 19 Aug 2008
Maximum gusts 78 km/hr (wind force 9)
SOIL EROSION
• Soil erosion is a natural process
• Sediment & other soil material are translocated within or
transported out of the system all the time…at different time
scales
• Rate of natural soil erosion is very slow
• Ice
• Processes can cause large amounts of sediment to move
(e.g. concentrated erosion) or more gradually through time
(e.g. soil creep)
• Gravity
• Relative importance depends on environments
• Wind
• People
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EFFECTS OF SOIL EROSION
Two primary divisions:
1) On-site effects (local)
- Simple loss of the soil itself (mostly A-horizon)
- Vital part of the soil system.
- Removal of A-horizon leaves behind the B and C.
2) Off-site effects (regional).
- Sediment transported out of the immediate soil system
- Can create water pollution problems
- Important factor in leaching of chemicals/nutrients from soil
- Excess sediment can smother plants, damage infrastructure,
destroys fish habitat, fill ditches
- Wind blown dust removes large amount of top soil over large areas
SOIL LOSS TOLERANCE
Much more erosion if
natural vegetation is
destroyed by plowing
EROSION BY WATER
Soil aggregates destroyed at surface by rainsplashes,
encouraging sheet and interill erosion
Detachment:
Rain drops falling on bare ground and/or sheets of water flowing over soil
surface can dislodge soil particles
Transportation:
Detached particles move downhill by floating, rolling, dragging, and
splashing
Deposition:
Particles eventually accumulate somewhere, either permanently or
temporarily
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Water concentrates
in small channels
Common on bare fields
Relatively uniform erosion
over entire soil surface
Tillage can erase/fill in
rills but cannot replace
lost soil
Any remaining soil
protected by pebbles
Lack of channels
TYPES OF SOIL EROSION BY WATER
Channelized erosion
Appears catastrophic,
but more soil is lost
through sheet or
rill erosion
All types of soil erosion - sheet, rill and gully – can occur
at the same time
Development depends on the intensity of the rainfall and
the soil surface conditions
Deep channels
cannot be erased
by cultivation
SOIL EROSION BY WIND
Eolian erosion = deflation + abrasion
3
ABRASION
=
SANDBLASTING
VENTIFACTS
rocks with faces abraded/polished by prevailing winds
Dreikanter Vierkanter
3-sider
4-sider
Wind-abraded tree trunks
Pakowki Lake, S Alberta
EOLIAN TRANSPORTATION
Pakowki Lake dunes, S. Alberta
NET TRANSPORT
80% saltation
20% creep
DESERTIFICATION
SOIL EROSION MODELS
Several types of soil erosion models, ranging from complicated process
models to simple empirical models.
Common in soil management is the Universal Soil Loss Equation (USLE).
USLE was developed and tested for a given range of conditions.
USLE uses a simple multiplication of factors to predict soil loss (A) :
A=RxKxLxSxCxP
Where:
A is the predicted soil loss.
R = Rainfall erosivity (based on rainfall intensity: how long and how hard)
K = Soil erodibility
L = Slope Length
S = Slope Gradient
C = Cover and Management
P = Erosion Control Practices (e.g. Cropping sequence, surface residue, surface
roughness, canopy cover
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USLE SOIL EROSION MODEL
SOIL EROSION MANAGEMENT AND MITIGATION
A=RxKxLxSxCxP
• Plug in the values for each factor from existing tables
• Can change the values for the equation and see what
effect management practices will have
• Easily implemented in a GIS
• USLE is simple, but often not suited to specific situations
(e.g. no wind erosion factor, so useless for the Palliser Triangle)
Soil management in Indian Himalayas (Himachal Pradesh), June 2006
In contour-strip farming, the ridges must be high enough
to hold back water from heavy rainfall events
Grassed waterways to
prevent gully erosion,
Kentucky, USA
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Terraced farming, SW China
Terraced agriculture in
the Indian Himalayas
June 2006
Disk chisel tillage
WIND EROSION MANAGEMENT
Disk chisel
Moldboard plowing
(a)
(b)
(c)
No-till farming
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Shelterbelts
SHELTERBELTS
•
You have to know your
prevailing wind direction
•
Even for regulating soil
moisture by creating or
preventing snow drifts
shelterbelts can be of use
Just North of Lethbridge
18 Dec 2007
READING FOR TUESDAY
Chapter 18: Soil chemical pollution
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