Erosion is the detachment and transport of soil by water or wind. Most soil erosion in Kentucky is the result of soil movement by water, generally over sloping land without adequate surface cover. Disturbing the soil surface of sloping land by tillage or construction will increase the risk of soil erosion (Figure 1).
Amount of Soil Erosion – USDA’s Basic Description
Slope is the landscape feature that has the greatest influence over many of the other important soil properties that are considered when making land use decisions. For agricultural uses, slope is commonly reported as a percentage (%) while in engineering settings, slope is commonly reported in degrees. Basically, slope is a measure of elevation change over a uniform 100 foot distance. For example, a 3-foot rise in elevation over a distance of 100 feet would be a 3% slope. A 45-degree slope is equivalent to a 100% slope.
Slope dictates the speed and direction of surface water movement. The steeper and longer the slope, the faster water moves across the soil surface, which increases the potential for soil erosion to occur. The faster water moves across the soil surface, the less likely it is to move into the soil (infiltration) and decreases the soil’s ability to supply water to plants.
Increasing slope increases erosion exponentially
Sample of USDA Land Classes
USDA (United States Department of Agriculture) Uses a Class system to designate a soil’s most appropriate use.
USDA Soil Conservation Service has been renamed Natural Resources Conservation Service – USDA
USDA Land Class Descriptions
Slopes of USDA Land Classes
With this in mind here is Mason County’s soil classes when USDA’s published its most recent county-wide survey in 1986. On page 78, it allocates our county’s soil:
Why erosion maters
Agronomically, topsoil is the most important soil horizon and a substantial amount can be lost during the erosion process. The loss of topsoil will take many years to replace through natural processes. Class I soils have 7 inches or more topsoil present. Some soils that formed on steeply sloping ground (i.e. classes VII and VIII) may have never formed this much topsoil. Topsoil is the profile horizon where the majority of the water and nutrients are held for plant use. The loss of topsoil significantly reduces soil productivity. The amount of topsoil present in the surface 7 inches is also a good indicator of past soil erosion.
Slope versus Erosion
Evaluating Land Resource Potentials in Kentucky
Kentucky Erosion Prevention and Sediment Control Field Guide (intro most relevant)
USDA LAND-CAPABILITY CLASSIFICATION