Estimated Rate (tons/acre/year) of Water Induced. Estimated for
Nonfederal Lands Only
Background
Sheet and rill erosion is the removal of layers of soil from the land
surface by the action of rainfall and runoff. It is the first stage in water
erosion. NRI estimates of sheet and rill erosion do not include loss of soil
from concentrated sources, such as gully and streambank erosion.
NRI estimates for soil loss from sheet and rill (water) erosion on
non-federal lands are calculated using the Universal Soil Loss Equation (USLE)
model. The USLE erosion model is designed to predict the long-term average
soil losses in runoff from specific field areas in specified cropping and
management systems.
USLE estimates for sheet and rill erosion are calculated for cropland,
pastureland, and Conservation Reserve Program (CRP) land only. Estimates are
not made for rangeland, forestland or other land uses.
The equation is: A = RKLSCP where:
A = Computed soil loss per unit area
R = Rainfall and runoff factor
K = Soil erodibility factor
L = Slope-length factor
S = Slope-steepness factor
C = Cover and management factor
P = Support practice factor
The NRI calculations use location-specific data for the field in which the
NRI sample point falls or that portion of the field surrounding the point that
would be considered in conservation planning.
One goal of USDA-NRCS conservation planning efforts with private landowners
is to reduce sheet and rill erosion to a rate of annual soil loss that permits
crop productivity to be sustained economically and indefinitely on a given
soil. This maximum rate of sustainable soil loss is called the soil loss
tolerance factor (T Factor). T factors range from 1 to 5 tons per acre per
year.
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