factor is soil erodibility factor which represents both susceptibility of
soil to erosion and the rate of runoff, as measured under the standard
unit plot condition. Soils high in clay have low K values, about 0.05 to
0.15, because they resistant to detachment. Coarse textured soils, such as
sandy soils, have low K values, about 0.05 to 0.2, because of low runoff
even though these soils are easily detached. Medium textured soils, such
as the silt loam soils, have a moderate K values, about 0.25 to 0.4,
because they are moderately susceptible to detachment and they produce
moderate runoff. Soils having a high silt content are most erodible of all
soils. They are easily detached; tend to crust and produce high rates of
runoff. Values of K for these soils tend to be greater than 0.4.
Organic matter reduces erodibility because it reduces the susceptibility
of the soil to detachment, and it increases infiltration, which reduce
runoff and thus erosion. Addition or accumulation of increased organic
matter through management such as incorporation of manure is represented
in the C factor rather than the K Factor. Extrapolation of the K factor
nomograph beyond an organic matter of 4% is not recommended or allowed in
RUSLE. In RUSLE, factor K considers the whole soil and factor Kf considers
only the fine-earth fraction, the material of <2.00mm equivalent
diameter. For most soils, Kf = K.
Soil structures affects both susceptibility to detachment and
infiltration. Permeability of the soil profile affects K because it
Although a K factor was selected to represent a soil in its natural
condition, past management or misuse of a soil by intensive cropping can
increase a soil's erodibility. The K factor may need to be increased if
the subsoil is exposed or where the organic matter has been depleted, the
soil's structure destroyed or soil compaction has reduced permeability. A
qualified soil scientist can assist in making this interpretation.
Guide to RUSLE use in Michigan, NRCS-USDA State Office of Michigan.