2010 National Resources Inventory

The National Resources Inventory (NRI) is a statistical survey of natural resource conditions and trends on non-Federal land in the United States. Non-Federal lands include privately owned lands, tribal and trust lands, and lands controlled by state and local governments.


National Soil Erosion

 

Water (Sheet & Rill) and Wind Erosion on Cropland
with margins of error
1982 1987 1992 1997 2002 2007 2010
Annual Tons of Water Erosion in Millions 1,674.30
± 13.53
1,481.18
± 11.78
1,182.13
± 10.10
1,045.57
± 7.52
1,024.33
± 11.25
967.81
± 20.04
981.51
± 15.82
Rate of Water Erosion in Tons Per Acre Per Year 3.98
± 0.03
3.65
± 0.03
3.09
± 0.03
2.78
± 0.02
2.78
± 0.03
2.70
± 0.06
2.72
± 0.04
Annual Tons of Wind Erosion in Millions 1,379.76
± 28.47
1,300.40
± 25.22
990.77
± 23.58
851.26
± 19.03
810.46
± 26.56
781.64
± 37.59
741.22
± 34.13
Rate of Wind Erosion in Tons Per Acre Per Year 3.28
± 0.06
3.20
± 0.06
2.59
± 0.06
2.26
± 0.05
2.20
± 0.07
2.18
± 0.10
2.05
± 0.09
Erosion chart, see Water (Sheet & Rill) and Wind Erosion on Cropland table for data values

Erosion chart, see Water (Sheet & Rill) and Wind Erosion on Cropland table for data values
Notes:
• 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 2010 NRI, which provides nationally consistent data for the 28-year period 1982–2010. 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 2010 NRI estimates released to the public.

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 Reserve Program.

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.

Glossary

  • 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 logging).
    • 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.
      • 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
          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.
        • 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 slope.
    • Wind erosion. The process of detachment, transport, and deposition of soil by wind.
      • 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 grain equivalent).
  • 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 2010 NRI Glossary.

More Information

For more information about the NRI, visit http://www.nrcs.usda.gov/technical/NRI/

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Citation for this website:
U.S. Department of Agriculture. 2014.
2010 National Resources Inventory.
Natural Resources Conservation Service, Washington, DC. 1 March 2014*
<http://www.nrcs.usda.gov/Internet/NRCS_RCA/reports/nri_eros_nat.html>

*[use date the website was accessed]