1. Factors Affecting Rate of Erosion
Rainfall (duration and intensity):
Anything that increases the amount of runoff relative to the infiltration rate will enhance erosion from rain.
Heavy, intense rains can quickly exceed the soil’s infiltration rate, adding to the erosiveness of the rainfall event. Soils that have been silted shut (crusting) reduces the infiltration rate as well.
Extend duration rains can saturate the surface soil profile reducing the infiltration rate and increase the erosion potential of the excess water.

2. Factors Affecting Rate of Erosion
Soil texture:
Influences water erosion by determining infiltration rate
Influences wind erosion by percentage of different soil separates
Slope length and percentage::
Influences water erosion by the amount of water running off a slope and the velocity of the water movement which is primarily determined by slope.

3. Factors Affecting Rate of Erosion
Cover (vegetation or residue):
Protects soil from erosion from the impact of raindrops
Slows water movement allowing more time for infiltration
Minimizes soil movement by wind (protects soil and slows wind)
Image source:
Images provided by USDA-NRCS

4. Soil Erosion
Wind Erosion: The breakdown of solid rock into smaller particles and its removal by wind.
It may occur on any soil whose surface is dry, unprotected by vegetation (to bind it at root level and shelter the surface) and consists of light particles.
The mechanisms include straightforward picking up of dust and soil particles by the airflow and the dislodging or abrasion of surface material by the impact of particles already airborne.
Types of wind erosion
Saltation
Suspension
Surface creep
Image source:

5. Soil Erosion by Wind
Saltation: The movement of fine soil particles (0.1 to 0.5 mm)
The horizontal distance traveled is 4 to 5 times the height of the “jump” of the soil particle
93% of the total soil movement by wind takes place below a height of 1 foot
65 to 90% of all wind erosion
Image source:

6. Soil Erosion by Wind
Suspension: Very fine dust particles thrown into the air by the impact of particles moving in saltation
Particles may travel long distances
3 to 10% of all wind erosion
Surface creep: The movement of large particles (0.05 to 20 mm) that are too heavy to be lifted by wind action, but are rolled or pushed along the surface by particles in saltation
7 to 25% of all wind erosion
Images provided by USDA-NRCS
Images provided by USDA-NRCS

7. TYPES OF MOVEMENT
Image source:

8. Soil Erosion by Wind
Wind erosion generally requires a wind speed of at least 10 mph at a height of 12 inches above the soil surface.
Wind Erosion Equation: E = f(I,K,C,L,V)
I = Soil Erodibility Index-related to cloddiness
K = Surface Roughness
C = Climatic Factor – wind velocity and soil moisture
L = Field Length Factor
V = Vegetative Cover Factor

9. Factors Responsible for Wind Erosion
Fall tillage, especially on soybean stubble
Dry fall and winter months followed by a windy March/April
Multiple freeze-thaw cycles that tend to break up surface aggregates into smaller fragments
Images provided by USDA-NRCS

10. Factors Affecting Wind Erosion
Soil surface roughness:
Smooth soil surfaces offer little resistance to wind
Roughness tends to break wind speed at the surface minimizing abrasion and breakdown of surface soil structure.
Excessive tillage creates small particles on a smooth soil surface, contributing to further soil structure breakdown by abrasion and increased erosion.
Climate
Speed and duration of the wind is directly related to the extent of soil erosion
Low soil moisture allows surface particles to be moved by wind
Freeze/dry cycles tend to break soil aggregates into smaller pieces creating more soil particles that can be move by wind

11. Factors Affecting Wind Erosion
Unsheltered distance:
Lack of windbreaks allows wind to move soil for greater distances. Knolls tend to be eroded the most with uninhibited winds.
Vegetative cover:
Loose, dry soil tends to be susceptible to wind erosion
Low levels of crop residue may not provide ample protection
Integrated approach using network of living windbreaks, combined with proper tillage, residue management, and crop selection.

12. Results from Wind Erosion
Injury to growing crops
“Soil blasting” can cause significant injury to a young growing crop. Loss of leaf surface area as a result of soil abrasion may weaken young seedlings, resulting in stand reductions or loss in plant productivity.
Drifting of soil in areas of a field can cause a change in soil texture.
Removal of wind-blown soil can be an expensive process
Image source: Howard’s personal collection
© GROWMARK, Inc.

13. Water Erosion
Water Erosion: The breakdown of solid rock into smaller particles and its removal by water.
It is a natural geological process
More rapid soil erosion results from poor land-use practices, leading to the loss of fertile topsoil and to the silting of dams, lakes, rivers and harbors.
Types of water erosion
Splash
Sheet
Rill
Gully
Images provided by USDA-NRCS

14. Erosion Caused by Water
Splash erosion: The action of rain drops as they impact a soil surface
Sheet erosion: Caused by continuous splash erosion and the continued movement of water on the soil surface
Rill erosion: The result of water flowing across the surface in amounts large enough to cause small surface cuts or small channels
Image source:

15. Erosion Caused by Water
Gully erosion: The result of water flowing through one channel over a long enough period of time to cause a ditch to form
The most severe type of soil erosion due to water
Fix it with heavy earth moving equipment
- What Grand Canyons are eventually made of
Image source:
Images provided by USDA-NRCS

16. Mechanical Structures to Control Water Erosion
Parallel Tile Outlet (PTOs) terraces
Other terraces
Drop boxes
Waterways
Rip rap
Sediment control basin
Tiling
Bedding
Images provided by USDA-NRCS
Images provided by USDA-NRCS
Images provided by USDA-NRCS

17. Conservation Practices & Erosion Control
Grass waterways: Used in the area of natural water flow to prevent gully erosion
Surface residue: Key element in reducing sheet erosion and splash erosion. Also key in controlling wind erosion
Cover crop: Protects soil from both water and wind erosion. Cover crops can be chemically killed and crops no-tilled into existing cover
Image source:
Top:
Middle:
Bottom:

18. Impact of Erosion on Crop Production
Crop yield potential: 20 to 40% less yield than non-eroded areas
Change in water holding capacity (WHC)
Lower infiltration rate as well as percolation rate
Indirect effect on soil structure may also lower WHC directly
Nutrient content: Most of the soil nutrients are concentrated in the upper four inches of the soil
Profile of a Mollisol typical of
some Midwest soils.
Image source:

19. Impact of Erosion on Crop Production
Organic Matter (OM) Content: Organic matter is primarily added to the surface of soils
As the surface is eroded, not only is OM lost directly but the ability to produce more OM is negatively impacted
Infiltration: When soil pores are sealed off at the surface water infiltration is reduced

20. Impact of Erosion on Crop Production
Water quality: Sedimentation of rivers, lakes and other bodies of water reduces water quality
Most pesticides and nutrients entering the surface water supply are attached to soil particles
Air quality: Air filled with dust is hard to breathe
Soil particles fill ditches and cause abrasive damage
Images provided by USDA-NRCS
Image source (top)
(bottom)
Images provided by USDA-NRCS

21. Erosion Control Practices
Contour Tillage: Follow the shape of the land to till and plant. Reduces speed and amount of runoff
Contour Strip Cropping: Alternate row/grain crops with meadow crops. Serves as frequent buffer strips to help filter out the suspended soil.

22. Erosion Control Practices
Terraces: Parallel terraces reduce point rows
Diversions: Similar to terraces but do not have standard spacing.
Grass Waterways: Wide, shallow, vegetated channels designed to carry peak runoff following severe rainstorms.
Image source: (top)
(middle)

23. Erosion Control Practices
Crop Rotation: Growing different crops in recurring succession on the same field.
Cover Crops: Protect soil surface from the impact of raindrops and wind erosion, add organic matter, and minimize loss of nutrients by leaching.
Images provided by USDA-NRCS

24. Characteristics of Effective Cover Crops
Add organic matter: Improves soil characteristics, such as texture, moisture-holding capacity, nutrient-holding capacity and tilth
Add nutrients: Legumes can fix N from the atmosphere and leave it for the following crop if timing is appropriate
Recover unused nutrients: Deep-rooted cover crops, such as rye, wheat, and barley, can recycle nutrients that remain in the soil for the following crop. They can capture unused nitrate-N and hold it in an unavailable organic form over the winter months.
Additional information:

25. Characteristics of Effective Cover Crops
Reduce weed growth: Prevents sunlight from reaching the soil surface, inhibiting the germination and/or early growth of weed species.
Buffer adverse growing conditions: Shade the soil during hot, dry conditions. Helps capture rain and snow.
Benefit wildlife: Provide wildlife with both food and habitat.

26. Erosion Control Practices
Riparian vegetative buffer strips: Strips of perennial vegetation that help reduce soil loss, improve water quality, and stabilize the banks of the drainage system.
Image source:
Additional information at:
Vegetative Filter Strips for Improved Surface Water Quality, Pm-1507
Buffer Strip Design, Establishment & Maintenance, Pm-1626b
Agricultural Pesticide Impacts on Prairie Wetlands, Pm-1520 
Source: U.S. Forestry Extension, Iowa State University,
Ames, Iowa

27. Impact on Erosion Surface residue
Protects soil surface from moving water, raindrop impact, and wind
Slows velocity of both wind and water
Row spacing
Narrow rows provide earlier vegetative cover offering protection from raindrop impact and wind
Cover crops
Protects the soil surface from moving water, raindrop impact, and wind

28. Impact on Erosion
Strip cropping: Slope length of rowed crop is reduced with broadcast crop (corn vs. alfalfa)
Contouring: Reduces water velocity so some sediment can settle out
Terraces: Reduces slope length and helps increase water infiltration
Grassed waterway: Main water channel protected from soil erosion. Sod reduces water velocity and erosion potential

29. Universal Soil Loss Equation (USLE)
Designed as a method to predict average annual soil loss caused by sheet and rill erosion.
Most widely accepted and used soil loss equations for 30 years
Estimates only long-term annual soil loss
Cannot be applied for a specific year or specific storm

30. Universal Soil Loss Equation (USLE)
A=RKLSCP
A = Average annual soil loss in tons/acre
R = Rainfall erosivity index
K = Soil erodibility factor
LS = Topographic factor
L is for slope length
S is for slope
C = Cropping factor
P = Conservation practice factor

31. Universal Soil Loss Equation (USLE)
Rainfall Erosivity Index (R): This is a statistic calculated from the annual summation of rainfall energy in every storm multiplied by its maximum 30-minute intensity. It varies geographically.
Soil Erodibility Factor (K): This factor quantifies the cohesive or bonding character of a soil type and its resistance to dislodging and transport due to raindrop impact and overland flow
Topographic Factor (LS): Steeper slopes produce higher overland flow, and longer slopes accumulate runoff from larger areas along with higher flow velocities. These two are usually reported together as a result. Both increase erosion potential but not in a linear fashion.

32. Universal Soil Loss Equation (USLE)
Crop Management Factor (C): This factor is the ratio of soil loss from land cropped under specified conditions to corresponding loss under tilled, continuous fallow conditions. Considered the most computationally complicated factor.
Conservation Practice Factor (P): Practices included are contouring, strip cropping, and terracing.

33. Components of a Conservation Plan
NRCS uses a three-phase, nine-step planning process.
Phase I - Collection and Analysis (Understanding the Problems and Opportunities)
1. Identify Problems
2. Determine Objectives
3. Inventory Resources
4. Analyze Resource Data
Phase II - Decision Support (Understanding the Solutions)
5. Formulate Alternatives
6. Evaluate Alternatives
7. Make Decisions
Phase III - Application and Evaluation (Understanding the Results)
8. Implement the Plan
9. Evaluate the Plan