• Cropland includes cultivated and noncultivated cropland.
About the Data
Estimates presented here are based upon the latest information from the
National Resources Inventory (NRI).
The NRI is a longitudinal sample
survey based upon scientific statistical
principles and procedures. It is conducted by the U.S. Department of Agriculture’s Natural
Resources Conservation Service (NRCS),
in cooperation with Iowa State University’s Center for Survey Statistics and Methodology.
These results are based upon the 2015 NRI, which provides nationally consistent
data for the 30-year period 1982–2015.
Current estimates cover the contiguous 48 States, Hawaii, and the Caribbean Area.
Release of NRI results is guided by NRCS policy and is in accordance with OMB
and USDA Quality of Information Guidelines developed in 2001.
NRCS is releasing NRI estimates only when they meet statistical standards and are scientifically
credible in accordance with these policies;
also, measures of statistical uncertainty are provided for all 2015 NRI estimates released to
The findings on erosion cover two types of erosion:
1. Water (sheet & rill) erosion - 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.
2. Wind erosion - the process of detachment, transport, and deposition of soil by wind.
Wind erosion is not reported for all states.
Erosion rates computed from NRI data are estimates of
average annual (or expected) rates based upon long-term climate data, inherent
soil and site characteristics, and cropping and management practices. These
estimates come from factors that are determined for the portion of a field
associated with an NRI sample site.
The factors are used in two erosion models:
1) the Universal Soil Loss Equation (USLE) and 2) the Wind Erosion Equation (WEQ).
The factors for these erosion prediction equations are determined for each NRI
sample site that is cropland, pastureland, or land enrolled in the Conservation
The NRI approach
to conducting inventories facilitates examining trends
in rural and developed land uses over time because—
- the same sample sites have been studied since 1982;
- the same data have been collected since 1982 [definitions and protocols
have remained the same];
- the inventory accounts for 100 percent of the surface area;
- quality assurance and statistical procedures are designed/developed to
ensure that trend data are scientifically legitimate and unambiguous.
Irrespective of the scale of analysis, margins of error must be considered.
Margins of error (at the 95
percent confidence level) are presented for all NRI estimates.
Note that estimates of change between two points in time will be less precise (relatively)
than estimates for a single
inventory year because the changes will be occurring on a smaller fraction of the landscape.
- Land cover/use. A term that includes categories of land cover and categories
of land use. Land cover is the vegetation or other kind of material that covers the land surface.
Land use is the purpose of human activity on the land; it is usually, but not always, related to
land cover. The NRI uses the term land cover/use to identify categories that account for all the
surface area of the United States.
- Cropland. A land cover/use category that includes areas used for the production
of adapted crops for harvest. Two subcategories of cropland are recognized: cultivated and noncultivated.
Cultivated cropland comprises land in row crops or close-grown crops and also other cultivated cropland,
for example, hayland or pastureland that is in a rotation with row or close-grown crops. Noncultivated
cropland includes permanent hayland and horticultural cropland.
- Erosion. The wearing away of the land surface by running water, waves, or moving
ice and wind, or by such processes as mass wasting and corrosion (solution and other chemical processes).
The term "geologic erosion" refers to natural erosion processes occurring over long (geologic) time spans.
"Accelerated erosion" generically refers to erosion that exceeds what is presumed or estimated to be
naturally occurring levels, and which is a direct result of human activities (e.g., cultivation and
- Sheet and rill erosion. 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.
- Revised USLE, Version 2 (RUSLE2). RUSLE2 is a model containing both empirical and
process-based science that estimates long-term, average-annual rates of rill and interrill (sheet) soil erosion caused
by rainfall and runoff.
- Universal soil loss equation (USLE). An erosion model designed to predict the
long-term average soil losses in runoff from specific field areas in specified cropping and management
systems. The equation is: A = RKLSCP where
A = Computed soil loss per unit area
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.
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
- Rainfall and runoff (R factor - USLE). The number of rainfall erosion index units,
plus a factor for runoff from snowmelt or applied water where such runoff is significant.
- Soil erodibility factor (K factor - USLE). An erodibility factor which quantifies
the susceptibility of soil particles to detachment and movement by water. This factor is used in the
universal soil loss equation (USLE) to calculate soil loss by water.
- Slope-length factor (L factor - USLE). The ratio of soil loss from the field slope
length to that from a 72.6-foot length under identical conditions.
- Slope-steepness factor (S factor - USLE). The ratio of soil loss from the field
slope gradient to that from a 9 percent slope under otherwise identical conditions. Used in universal
soil loss equation (USLE) calculations of sheet and rill erosion.
- Cover and management factor (C factor - USLE). The ratio of soil loss from an area
with specific cover and management to that from an identical area in tilled continuous fallow.
- Practice factor (P factor - USLE). The ratio of soil loss with a support practice
like contouring, stripcropping, or terracing, to soil loss with straight-row farming up and down the
- Wind erosion. The process of detachment, transport, and deposition of soil by
- Wind erosion equation (WEQ). An erosion model designed to predict long-term
average annual soil losses from a field having specific characteristics. The equation is:
E = f(IKCLV) where
E = Estimated average annual soil loss expressed in tons per acre per year
I = Soil erodibility index
K = Soil ridge roughness factor
C = Climatic factor
L = Equivalent unsheltered distance across the field along the prevailing wind erosion direction
V = Equivalent vegetative cover
- Soil erodibility index (I factor - WEQ). The potential soil loss, in tons per
acre per year, from a wide, level, unsheltered, isolated field with a bare, smooth, loose, and
noncrusted surface, under climatic conditions like those in the vicinity of Garden City, Kansas.
- Ridge roughness (K factor - WEQ). A measure of the effect of ridges made by
tillage and planting implements. It is expressed as a decimal from 0.5 to 1.0. Ridges, especially
those at right angles to the prevailing wind direction, absorb and deflect wind energy and trap
moving soil particles. See wind erosion equation (WEQ).
- Climatic factor (C factor - WEQ). Characterizes climatic erosivity, specifically
wind speed and surface soil moisture. The factor for any given locality is expressed as a percentage
of the C factor for Garden City, Kansas, which has a value of 100.
- Unsheltered distance (L factor - WEQ). The unsheltered distance along the
prevailing wind erosion direction across the field or area to be evaluated. For the NRI, the
unsheltered distance is expressed in feet, measured through the sample point, parallel to the
prevailing wind direction during the critical wind erosion period.
- Vegetative cover (V factor - WEQ). The effect of vegetative cover in the
wind erosion equation is expressed by relating the kind, amount, and orientation of vegetative
material to its equivalent in pounds per acre of small grain residue in reference condition (small
- Margins of Error. Margins of error are reported for each NRI estimate. The margin
of error is used to construct the 95 percent confidence interval for the estimate. The lower bound of
the interval is obtained by subtracting the margin of error from the estimate; the upper bound is
obtained by adding the margin of error to the estimate. Confidence intervals can be created for various
levels of significance which is a measure of how certain we are that the interval contains the true
value we are estimating. A 95 percent confidence interval means that in repeated samples from the same
population, 95 percent of the time the true underlying population parameter will be contained within the
lower and upper bounds of the interval.
For more definitions see the full
2015 NRI Glossary.
For more information about the NRI, visit
Send comments and questions to the NRI Help Desk
Citation for this website:
U.S. Department of Agriculture. 2015.
2015 National Resources Inventory.
Natural Resources Conservation Service, Washington, DC. 31 October 2018 *
*[use date the website was accessed]