Soil Erosion

© 2007 Donald G. McGahan (aka soilman) All Rights Reserved

A nation that destroys its soils, destroys itself! (F.D. Roosevelt, 1937)

Soil erosion is the most serious problem affecting the sustainable production of food and fiber. About 80% of the world's agricultural lands suffer moderate to severe erosion; an additional 10% suffer slight to moderate erosion. It is estimated that 54% of U.S. rangelands are over-grazed resulting in enhanced soil erosion and decreased productivity. Worldwide, about 12 million hectares of arable land are destroyed and abandoned annually because of non-sustainable farming practices. Total cultivated land is currently 1.5 billion hectares.

Worldwide, about 75 billion metric tons (Mg) of soil are eroded annually:

  • 2/3 eroded by water & 1/3 eroded by wind

The annual cost of erosion is estimated at about $44 billion in the U.S.; about $400 billion worldwide (1995).

Depending on soil forming factors, soils can sustain a loss of 1-10 Mg/ha/yr without losing significant productivity. A 1 mm (1/32 inch) thickness of soil over one hectare weighs approximately 12 Mg.

What is soil erosion?

Classes of Erosion

Geologic erosion
Erosion due to natural processes that are not affected by human activities (e.g., erosion of mountains, cutting of valleys). Normal rates of geologic erosion are on the order of 0.2-0.5 Mg/ha/yr.
Accelerated erosion
Increased erosion rates above geologic erosion rates due to human activities (e.g., grazing and farming practices).

Types of Erosion

  1. Water Erosion
    1. Sheet, or splash
      • Relatively uniform erosion from the entire surface. () Associated with sheet flow. ()
    2. Rill
      • Water concentrates and cuts small channels as it runs off the soil.
      • Cultivation will erase rills by filling channels.
    3. Gully
      • Cutting of deep channels that cannot be erased by normal cultivation.

Although gully erosion looks more catastrophic, far more total soil is lost by the less obvious sheet and rill erosion.

Factors affecting a soil's water erodibility:

  1. Texture of topsoil
    • silt and very fine sand are most erodible.
  2. Structure of topsoil
  3. Soil organic matter concentrations
    • increase soil structure and water infiltration.
  4. Infiltration/permeability rate
  5. Slope percent and slope length
  6. Soil cover (e.g., vegetation and crop residues)

Wind Erosion involves two processes: (1) detachment and (2) transportation.

movement of soil particles by a short series of bounces along the surface of the ground (50-80%).
movement of particles parallel to the ground surface and upward (3-38%).
Surface Creep
rolling or sliding of particles along the soil surface (7-25%).

Factors affecting a soils wind erodibility:

  1. Texture of topsoil
    • very fine sand and silt particles are most susceptible
  2. Structure of topsoil
    • Aggregating agents such as clays, oxides, hydroxides, and organic matter promote structure.
  3. Climate
    • wind velocity and soil moisture content
  4. Soil roughness
  5. Width of unprotected soil
  6. Soil cover
    • e.g., vegetation and crop residue.
Erosion due to Gravity
instantaneous movement of a mass of earth
Soil creep
slow and persistent movement of soil

Why should anyone care about soil erosion?

Soil Productivity

  • Erosion removes the best part of the soil (topsoil); results in loss of organic matter, plant nutrients and soil organisms, and decreases the soil thickness which reduces water and nutrient holding capacity.
  • Requires the use of fertilizers, pesticides and irrigation to offset productivity decrease. About 10% of energy used in U.S. agriculture is spent to offset the productivity loss due to soil erosion.


  • Air Pollution.
    • Fugitive dust.
      • PM10 & PM2.5
        • particulate matter less than 10 and 2 microns, respectively.
        • PM2.5 is believed to have the greatest human health risk.
      • Sand-blasting and death of plants.
      • Detrimental deposition
        • Fence rows.
        • Hedge rows.
  • Water pollution.
    • Sediments.
      • Nutrients.
      • Pesticides.
      • Pathogens.
    • Detrimental deposition.
      • Non-point source pollution.
      • Sediment Load behind dams decreases water storage capacity.
      • Sedimenting navigable waterways impeding commerce .

What can be done?

Soil Conservation Practices


  • Vegetation (establish permanent cover or seasonal cover).
  • Human-made structures
    • check dams, riprap, mulching.
  • Conservation tillage (minimum tillage, no-till).
  • Special practices (terraces, strip cropping, grassed waterways).


  • Mulch
  • Windbreaks
  • Conservation tillage