Soil properties (K factor)

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Soil erosion following removal and replacement for open-pit mining.

Provenance: © Copyright Bob Jenkins
Reuse: Licensed for reuse under CC BY-SA 2.0

The structure of the soil is an important property that influences how easy it is to erode. Peds are clumps that form in the soil and determine how water moves through the soil. In this example, moving the soil into piles and then back onto the fields disrupted the natural structure of the soil. This makes it more difficult for water to seep into the soil (called infiltration) and easier for the particles to detach and be carried away by surface runoff. This is an extreme example of human activity disrupting soil structure; more common activities include agricultural practices such as tillage and compaction of the soil by driving or walking on it.

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Healthy soil ped with high porosity.

Provenance: Photograph by Colette Kessler, USDA Natural Resources Conservation Service, South Dakota
Reuse: Licensed for reuse under CC BY 2.0

Human activity, however, is only one factor that influences the erodibility of soil. The texture of the soil (its clay, silt and sand content) also plays a big role. Soils that are rich in clay tend to stay put because the sticky clay helps keep the particles from detaching. Soils with a coarse texture (i.e., larger particles) also keep erosion rates low because it is easier for the water to infiltrate into the soil in the pore space created by the bigger particles. This infiltration decreases runoff and, therefore, the potential for erosion. Soils with high silt content are easiest to erode because the particles are easily detached and they tend to form a crust, which can lead to lots of runoff. As you might expect, soils with intermediate textures have intermediate potential to erode. Additionally, organic matter in the soil helps keep it in place and increases infiltration.

Putting all of these things together, we can begin to consider what could make one soil more susceptible to erosion than another given the same amount of rainfall, etc. This is called the soil erodibility factor, abbreviated with the letter "K". K values for a particular soil depend on the rate of infiltration, how easily particles detach, and the amount of runoff. As described above, soil texture, soil structure, permeability, organic matter content, and previous use affect these components of the K factor.

Resources

• Renard, K. G., Foster, G. R., Weesies, G. A., and Porter, J. P., 1991, RUSLE - Revised Universal Soil Loss Equation: Journal of Soil and Water Conservation, v. 46, no. 1, p. 30-33.
• Renard, K. G., Foster, G. R., Weesies, G. A., McCool, D. K., and Yoder, D. C., 1997, Predicting Soil Erosion by Water: A guide to conservation planning with the Revised Universal Soil Loss Equation (RUSLE), USDA Agricultural Research Service Agriculture Handbook Number 703, 384 p.
• RULSE: On-line Soil Erosion Assessment Tool