Soil Erodibility Factors

Soil erodibility factors (Kw) and (Kf) quantify soil detachment by runoff and raindrop impact. These erodibility factors are indexes used to predict the long-term average soil loss from sheet and rill erosion under crop systems and conservation techniques. Factor Kw applies to the whole soil and factor Kf applies only to the fine-earth (less than 2.0 mm) fraction. The procedure for determining the Kf factor is outlined in Agriculture Handbook 703, Predicting Soil Erosion by Water: A Guide to Conservation Planning With the Revised Universal Soil Loss Equation (RUSLE), USDA, Agricultural Research Service, 1997. The K factors for soils in Hawaii and the Pacific Basin were extrapolated from local research. The nomograph, shown in Part 618, Subpart B, Exhibits, Section 618.91, was not used to determine K factors for soils in Hawaii.

Soil erodibility factors Kw or Kf are used in the erosion prediction equations USLE and RUSLE. Soil properties that influence rainfall erosion are those that affect:

1. Infiltration rate, movement of water through the soil, and water storage capacity.
2. Dispersion, detachability, abrasion, and mobility by rainfall and runoff. Some of the most important properties are texture, organic matter content, structure size class, and the saturated hydraulic conductivity of the subsoil.

Source: U.S. Department of Agriculture, Natural Resources Conservation Service. National soil survey handbook, title 430-VI. Available online. Accessed 9/13/2012.