Even on sites where erosion has been minimal, conventional tillage has significantly reduced organic matter levels below their original level. In the dryer western Palouse, the combined effects of tillage erosion and water erosion has reduced topsoil organic matter content from the original 2 percent to the present level of 1 percent. With the low residue production in this area, increasing the organic matter level will be extremely slow. In the eastern Palouse, soils originally had a higher organic matter level, but higher soil erosion rates also prevail. The percent organic matter in the paleosol and other subsoil horizon now exposed at the surface on ridges and knobs is less than 0.5 percent.
Organic matter is important to soil productivity.
Loss of the organic matter-rich portion of the topsoil can seriously reduce production potential. The common occurrence of paleosol horizons in the Palouse soils creates a unique situation for soil erosion. The same principles that limit crop production potential with these paleosol horizons, however, also apply to other restrictive subsoil horizons within the root zone of soils throughout the Northwest. Whether the horizons are paleosols or not, clay-rich horizons and other restrictive layers can impact rooting depth, water infiltration, soil water storage capacity, soil fertility and other soil productivity factors as topsoil depth is decreased by erosion. Attempts to make productive soils from these exposed paleosol and other unproductive subsoils have generally not been successful.