Unit 13: Soil Erosion
Chapter 11
Objectives
How soil erosion affects your life
 Magnitude of the soil erosion problem
 Causes & methods of soil erosion
 Controlling erosion
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Introduction
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North America’s most devastating
environmental disaster
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Geologic Soil Erosion – natural wearing
away of land surface by water, wind, or ice
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Much topsoil lost resulting in greatly decreased
production capability
Plugs channels & raises riverbeds, increasing
flood risks
Not addressed here
We’ll address erosion related to human
activity
The Soil Erosion Problem

Erosion problem two-fold
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Exposed B horizons, much less productive
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Lost productivity
Sediment pollution
9-18% corn yield reductions
17-24% SB yield reductions
Al toxicity risks much higher
The Soil Erosion Problem
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Sediment
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Major carrier of pesticides & fertilizer that
pollutes the ecosystem where it settles
Also make lakes, rivers more shallow
Ex. Eastern Washington – in last century,
40% of topsoil has eroded
 Much focus on stream bank erosion,
erosion at construction sites (land left
unprotected for extended time)

The Soil Erosion Problem
Minimization is the goal (elimination of
erosion impossible)
 Since 1935 $30 b spent to erosion control
in U.S.
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Nature of Water Erosion
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Effects: destroys human-made
structures; fill reservoirs, lakes, rivers;
damages land
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Mud, silt, sediment
Eroded material usually the richest part of
the soil
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Highest nutritive content
Most organic matter
Nature of Water Erosion
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Causes of Water Erosion
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Peds disintegrate w/ impact of rain drops
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Soil aggregates separate
Particles can move ~5’ w/ splash erosion
Most destructive on bare soil
Rainfall then moves particles w/ water flow on
soil surface
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Scours channels in soil surface
 Each subsequent rain adds to depth/width of these
channels
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Form: gullies, rills
Nature of Water Erosion
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Causes: excessive tillage, burning crop
residue, overgrazing, clear-cutting forests
Raindrop Splash Erosion
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Not as detrimental in clay soils due to strong
adhesion forces
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More common in fine sands, silty soils
Clays more likely to crust over, decreasing
aeration, slows infiltration
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Water then must wash over soil surface
Nature of Water Erosion
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Sheet & Channelized-Flow Erosion
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Sheet erosion – water moves an entire layer of
soil
Rills – water-cut channels in the soil
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Gullies – large, deep channels caused by
excessive movement of water
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Can be erased by tillage
Can’t cross w/ equipment
Sheet & rill most common & problematic

Harder to detect
http://www.soils.umn.edu/ac
ademics/classes/soil2125/im
g/erosb3.jpg
http://topsoil.nserl.purdue.e
du/fpadmin/weppmain/overv
iew/rill.html
http://www.igsb.uiowa.edu
/Browse/gullyero/gullyero.
htm
Erosion Tolerance
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Erosion Tolerance Level (T) – maximum
rate of annual soil loss that will permit
crop productivity to be maintained
indefinitely
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Highly erodable land – reduce erosion to 5
t/ac/yr
Some soils – 1-2 t/ac/yr
Water Erosion Control
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Controlling Soil Detachment
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Cropping/vegetative practices the keep soil
surface covered as much as possible
Energy from rain drops dissipated/minimized
by hitting residue first
Leaving residue cover:
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Not plowing under stubble
Planting a cover crop
Water Erosion Control
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Controlling Soil Transport
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Slow eroding water
Reduce steepness of slopes (if possible)
Construct barriers or terraces
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Reduces slope, appropriate for areas of high-intensity
rainfall
Reduces velocity of runoff
Can be costly
Water Erosion Control
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Cultivate on the contour
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Strip crop
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Plant at right angles to natural slope
Appropriate for slopes 2-8%
Plant on contour
Alternate row crops w/ close-growing crops
Not only slows erosion, but can filter what is eroded
Filter strips
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Plant on low end of field to prevent
chemicals/fertilizer from entering adjacent
ditches/streams
 IA study – 10’ filter strip reduced sediment load 70%,
30’ strip 85%
http://www.peisland.com/agrtour/xslope.html
Water Erosion Control
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Cover Crops – grown during off-season
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Legumes, cool-season grasses
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Good cover crops should:
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Hairy vetch, clover – can also add N to soil
Increase soil organic matter
Improve water infiltration
Reduce runoff
May harvest, or burn down w/ herbicide
In dry areas – use is limited due to risk of
depleting soil water content
Water Erosion Control
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Erosion Control for Construction Sites
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Erosion can far exceed any agricultural erosion
Greater effort needed to minimize erosion
Construction site barren soil can erode 1 t/ac
over a few storms
Methods used to control erosion
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Mulch
Soil binders
Logs
Blankets
Nature of Wind Erosion
Rates can be high on dry, bare, weak
aggregate soils
 Soil particles can be held in suspension
and blown away
 44% of erosion caused by wind
 Most of our land: wind erosion risk small
 Highest risk areas: TX, NM
 1/3 of land surface – high risk for wind
erosion
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Nature of Wind Erosion
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Arid & semiarid soils at highest risk
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Less vegetation, less cover
Less clay, less aggregation
Less soil moisture, lighter wt
Desertification – process of soil
degradation by wind erosion, resulting in
coarser soils, lessen ability to retain water
Wind-Erosion Control
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Ridge-till – decreases ability of wind to
blow away soil steadily across surface
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Reduces wind velocity
Traps soil
2-4” ridges ideal
Reduce field length
 Increase soil cover
 Use windbreaks
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Assignment