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Average Annual Soil Erosion by Water on Cropland and CRP Land, 1987

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Description

This is a shaded polygon map where soil erosion by water on cropland and Conservation Reserve Program (CRP) land is displayed in five shaded classes of tons per acre per year using these ranges: Less than 1, 1 to 3, 3 to 5, 5 to 8, and 8 or more. The Universal Soil Loss Equation (USLE) is used to determine the values. The shaded polygons represent 8-digit hydrologic units. Areas where cropland and CRP land occupy less than 5% of the total area in 1987 are hatched. Areas with 95% or more Federal area are shaded gray. 96 million acres are eroding at a rate above 5 tons per acre per year due to water. The national erosion rate averages 3.6 tons per acre per year. Total water erosion equals 1,520 million tons annually.

Cautions for this Product:
Erosion by water includes sheet and rill erosion and excludes gully erosion. Since cropland and CRP land may occupy only a small percentage of the total area of some of the polygons, the map may leave a misleading impression as to the significance of higher erosion rates in some areas where there is little cropland. Data are not shown where cropland and CRP are less than 5% of the total area. Data are not collected on Federal land. Data are not available for Alaska or the Pacific Basin. Data for Puerto Rico and the U.S. Virgin Islands is shown by 6-digit hydrologic unit.



Sources

Source: National Resources Inventory, 1997
Distributor: USDA-NRCS-RIAD
Reliability:
NRI sample data are generally reliable at the 95% confidence interval for state and certain broad substate area analyses. Generally, analyses that aggregate data points by smaller geographic areas and/or more specific criteria result in fewer data points for each aggregation and therefore less reliable estimates. NRI maps reflect national patterns rather than site- specific information.


Layers

Aggregate Layer: 8 Digit Hydrologic Unit Areas with Federal Land
Other Layers Displayed: States, Rivers


Definitions

Conservation Reserve Program (CRP):
A Federal program established under the Food Security Act of 1985 to assist private landowners to convert highly erodible cropland to vegetative cover for 10 years. [NMCSP]

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. [NRI-97]

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). [NSSH-96]

Gully erosion:
The erosion process whereby water concentrates in narrow channels and, over short periods, removes the soil from this narrow area to considerable depths, ranging from 1 to 2 feet to as much as 75 to 100 feet. [NRI-97]

Sheet and rill erosion:
Removal by runoff water of a fairly uniform, usually imperceptible, thin layer of soil often accompanied by formation of many small eroding channels. Rills are only a few inches deep and do not hinder farm machinery. Tillage erases them, but they tend to recur after heavy rain during the growing season, especially where cover is limited. [SSM]

Universal soil loss equation (USLE):
This equation estimates average annual soil loss from sheet and rill erosion. Location specific data for the field in which the NRI point falls or that portion of the field surrounding the point that would be considered in conservation planning are used in the NRI calculations. The equation is: A = RKLSCP, where A is the computed soil loss per unit area, R is a rainfall factor, K is a soil erodibility factor, L is a slope length factor, S is a slope- steepness factor, C is a cover and management factor, and P is a conservation practice factor. [NAM]

Water Erosion:
The process of detachment, transport and deposition of soil in which the primary agent is water. This may include sheet, rill and gully erosion; however, for the purposes of this analysis, unless otherwise stated, water erosion refers only to sheet and rill erosion and excludes gully erosion.


Product Information

Product ID: 5056
Production Date: 12/7/00
Product Type: Map


For additional information contact the Resources Inventory and Assessment Division. Please include the Product ID you are inquiring about. nri@wdc.usda.gov or 1400 Independence Avenue SW - P.O. Box 2890 - Washington D.C. 20013. If you use our analysis products, please be aware of our disclaimer.