SOIL
EROSION
Clip Art: Soil Quality Institute
You need to know
- The mechanics of soil erosion: detachment and transport. What forms are created?
- Why soil erosion is so bad for the environment.
- The Universal Soil Loss Equation and how each element relates to soil erosion.
- Management practices to reduce soil erosion.
Misconceptions:
- Coarser fractions eroded from a field are transported hundreds of miles.
1. The mechanics of soil erosion: detachment and transport. What forms are created?
A. Mechanics of Soil Erosion
erosion: Wearing away of the earth's surface by water, ice, or other natural agents. under natural environmental conditions of climate and vegetation.
Soil erosion is the wearing away and removal of the land surface by __ or irrigation water, wind, ice, or other natural or human agent at rates exceeding geologic erosion.
Erosion of soil sediments by water and wind results from two physical processes: detachment and .
1) Detachment: disaggregation and airborne movement of soil by the force of raindrops impacting the surface. A name for this is _________ erosion.
View an animation from Arizona State University, the animated GIF slows frames to 1/240th of a second to capture rainsplash impact of a single raindrop on dry sand.
What two soil fractions are most prone to detachment? _______________________ and _______________________.
2) Transport: once disaggregation has occurred, wind and water transport sediment.
What is the difference between material in suspension and material in solution?
B. Forms Created by Erosion
1) erosion: The removal of a relatively uniform thin layer of soil by largely or surface runoff (often called sheet flow). Instead of water moving downward into the soil profile, runoff now flows as a uniform sheet over the surface. Sheet erosion will be especially strong if pores are clogged with clays.
2) rills: of only several centimeters in depth are formed; occurs mainly on recently cultivated soils.
3) gullies: rills grow to 0.5 to 30 m in depth. Gully erosion is often defined for agricultural land in terms of channels too deep to easily remedied with ordinary farm tillage equipment.
2. Why soil erosion is so bad for the environment
A. Impacts
-
mortality
- loss of soil
-
of reservoirs
- Increases in turbidity results in at least three negative impacts
 | |
| |
|
View
an animation from NASA of Sahara dust crossing the Atlantic Ocean. | fertilizer transport resulting in |
| disease causing agents |
| heavy |
Buildup of sediment eroded from fields raises stream and river bottoms resulting in
Air pollution from dust generation
Destruction of property
View an animation
from the University of Wisconsin of bank erosion resulting in a house
collapsing into a river.
B. Human Dimensions
With the sometimes sterile definitions on the impact of soil erosion, it is easy to overlook the very real impact soil erosion has on the lives of people. Two multimedia resources will connect you with soil erosion.
from the Sun Sentinel, View a incisive, comprehensive
Flash slide show documenting how soil erosion contributes to Haiti`s status as
the Hemisphere’s poorest nation.
from
Kansas State University, listen to a 1940 interview with Mrs. Flora Robertson
talking about dust storms in Oklahoma. The MP3 audio format interview
concludes with an original poem `I came to Oklahoma before it was a state`.
3. The Universal Soil Loss Equation and how each element relates to soil erosion
The Universal Soil Loss Equation if defined as
A=R×K×L×S×C×P
where
A=erosion soil loss in tons per acre per year
R=rainfall factor
K=soil erodibility factor
L=slope length factor S=slope gradient factor (percentage steepness)
C=vegetative cover and management factor
P=practices used for erosion control (terraces, contouring)
Rainfall Factor (R)
1. The rainfall factor (R) is a product of the kinetic energy
(falling force) of a rainfall times its
View an animation
from Arizona State University, the animated GIF slows
frames to 1/240th of a second to capture rainsplash impact of a single raindrop
on dry sand.
2. Calculating the Soil Erodibility (K)
The soil erodibility factor (K) is estimated from four soil properties: , organic-matter content, soil structure, and permeability data.
a) texture: very fine sand and silt are most easily eroded
b) organic matter: helps increase soil aggregation, reduces rainsplash impact
c) soil structure: determines pore space and permeability. A strong soil structure is best for reducing soil erosion.
How does structure relate to ponding of surface waters and the initiation of runoff?
d) soil permeability: consider the characteristics and location of the least permeable horizon.
What is easier to manage, texture or structure?
3. Length-Slope Factor (LS)
Longer slopes erosion because water accumulates and increases in speed, collecting more cutting sediment and doing proportionally more damage.Doubling slope (percentage grade) usually more than doubles the erosion; on long slopes it may triple the erosion.
What is % grade and how is it indicated in the soil survey manual?
4. Cover and Management (C)
The cover and management factor (C) considers the of vegetative cover on the soil and all related management practices, such as time between operations (delay in planting after plowing, and so forth), weed control, tillage, watering, fertilization, and so on. The C factor is complicated because of the wide range of possibilities in cover material, management, and the manner in which crop residues can be left on soil.
What would be the difference between cotton and alfalfa as a crop?
The practice factor (P) recognizes the influence of contour planting, strip cropping, terracing, and combinations.
5. Management practices to reduce soil erosion
 | a cover crop diminishes impact and reduces the velocity of sheetflow. Roots bind particles together, create pores, and use moisture to encourage continued water penetration. |
a layer that simply covers the surface. But you need to ask whether the mulch a habitat for unwanted weeds, seeds, and insects?
A cover may also be considered non-living material like paper, plastics, wood chips, metal netting and rocks.
a is a slurry of mulch, seed, and fertilizer that keeps soil in place and retains soil moisture until the seed can germinate. A hydromulch often appears as a green surface cover.
|
alternating a cover and row crop. Because surface runoff emanating from the row crop is
slowed by the cover crop, a lot of sediment eroded from row crop is trapped by the
crop. |
| Contour cropping |
| Terraces--controls the direction and velocity of water flow. A step-like
surface constructed along a hill to help prevent accelerated erosion. |
|
grass placed along a natural drainage pathway traps sediment, pollutants, and
reduces sheetflow |
(Image: NRCS, http://www.nhq.nrcs.usda.gov/CCS/Buffers.html
| conventional till: tillage used in preparing a seedbed or cultivating a given crop in
which <30% cover of crop residues remaining on the surface. |
| _________
till: a procedure whereby a crop is planted directly into the soil with no
primary tillage since harvest of the previous crop; usually a special planter is
necessary. |
| minimum till:
less use of conventional tillage to meet crop production
requirements but not to be considered no till. |
| ridge tillage: A method of planting crops on ridges formed through tillage. The ridges are perpendicular to the slope. Usually only one seed row is planted on each ridge. |
