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Soil Erosion
“MAN HAS only a thin layer of soilbetween himself and
starvation.” This quote, attributed toBard of Cincinnati, clearly states theimportance of soil. The future ofmankind could depend on soil erosionand soil management practices.
Objective:
� Describe soil erosion and the soil erosion process.
Key Terms:
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The Process of Soil Erosion
Soil erosion is the process by which soil is moved by wind, water, or other natural
actions. Vegetation and other coverings help prevent soil erosion. When the soil is exposed, it is
vulnerable to erosion. Land that is eroded loses fertility and productivity. Plus, the soil that is
lost may pollute water or air. Two basic classes of erosion are natural erosion and accelerated
erosion.
Natural erosion, sometimes referred to as geologic erosion, occurs on land not disturbed
by humans. Examples are changes in the earth, such as rounding off mountains and filling in
valleys. Soil deposits from erosion can form highly fertile areas, such as the Mississippi Delta.
A simple experiment can be set up to study the influence of slope and surface materials on
soil erosion. Materials needed are: trays (such as cafeteria trays or lasagna pans), soil, annual
ryegrass seed, enough dried leaves to cover a pan of soil, watering can, bucket, and water.
Fill three trays with soil. Sow ryegrass seed in one tray, water, and place under bright light.
Cover the soil of a second tray with dried leaves so that the soil is no longer visible. Leave the
soil of the third tray bare. After the ryegrass in the first tray has grown a couple inches in height,
you are ready to conduct the erosion tests. Place each pan at about a 5 percent slope. Place
the bucket under a spot where water would be expected to run off. Using the watering can,
sprinkle the surface of each tray and collect the runoff. Inspect the runoff for the presence of
soil. Inspect the soil surfaces for evidence of erosion. Try increasing the slope.
ture influences the ease of detachment of soil particles. Soil particles of different sizes vary in
how easily they can be detached. Silt particles are the most easily detached. Soil structure influ-
ences infiltration of water. Good soil structure allows water to enter the soil, thus reducing the
amount of water runoff.
Slope
There are two components that determine slope. These are length and grade. Water runoff
velocity will increase as slope, or grade, increases. This causes an increase in the erosive energy
of the runoff water. On a long slope, a greater surface area collects water, increasing flow vol-
ume. Running water can also pick up speed as it flows down a long slope.
Surface Roughness
A rough soil surface slows the downhill flow of water. Surface roughness depends a great
deal on the tillage practice used on the land. In conventional tillage, the seedbed is left smooth
with very few ridges. Chisel plowing leaves the seedbed rough. Tillage across slopes or on the
contour acts to slow water flow.
Soil Cover
Bare soil is fully exposed to the erosive forces of raindrop impact and the scouring of run-
ning water. Soil cover reduces the energy available to cause erosion to the soil. A mulch, cover
crop, or crop residue absorbs the energy of the falling raindrop and reduces the amount of soil
detachment.
Summary:
� Soil erosion is the process by which soil is moved by wind, water, or other naturalactions. Natural erosion occurs on land not disturbed by humans. Accelerated ero-sion usually results from human activity on the land.
There are four basic causes of erosion—wind, water, glaciers, and land slippage.Wind erosion is the loss of soil due to the movement of wind over the land. Windmoves soil by suspension, saltation, and surface creep. Water erosion is the loss ofsoil due to water movement. Three types of water erosion are sheet erosion, rillerosion, and gully erosion. Glacial erosion occurs when the front edge of a glacierpushes soil, rocks, and other materials. Land slippage occurs when soil that is satu-rated with water slips down the hillside or mountain slope.
Soil erosion follows a simple, systematic progression that involves detachment,transport, and deposition.
Four factors that determine how susceptible a soil is to soil erosion are soil textureand structure, slope, surface roughness, and soil cover.
5. What are four factors that determine how susceptible a soil is to soil erosion?
Expanding Your Knowledge:
� Contact your local soil conservation district and ask a representative to speak toyour class about soil erosion. Be sure to have questions prepared in advance regard-ing the causes of erosion and the methods to reduce erosion.