Definition
Soil erosion is the removal of soil by water, wind, or both. Surface horizons almost always contain more organic matter than subsurface horizons.
Measuring severity of erosion
The degree of soil erosion is judged by the amount of original surface material remaining in the upper 8 inches of soil. The three classes of soil erosion are illustrated in the figure to the right.
Soil erosion classes are determined from the plow layer (Ap), or upper 8 inches if the Ap is less than 8 inches:
1. None to slight: This layer contains more than 75% of original surface material.
2. Moderate: This layer contains 25% to 75% of original surface material.
3. Severe: This layer contains less than 25% of original surface material.
“Original surface material” means soil material that was once the A and E horizons (above B horizons). A soil that has never been plowed, such as in a woods, is considered to have slight erosion.