National Resources Inventory
2001 Annual NRI

Glossary of Key Terms

Conservation practice. A specific treatment, such as a structural or vegetative measure or management technique commonly used to meet specific needs in planning and conservation, for which standards and specifications have been developed. Conservation practices are in the NRCS Field Office Technical Guide, Section IV, which is based on the National Handbook of Conservation Practices.

• The practices recorded for NRI have been applied to the area of land in which the NRI point falls or the portion of the field that would be used in conservation planning. The point need not fall on a specific practice.

Conservation Reserve Program (CRP) land. A Land cover/use category that includes land under a CRP contract. [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.]

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.

Cultivated cropland. See Cropland.

Developed land. A combination of land cover/use categories, Large urban and built-up areas, Small built-up areas, and Rural transportation land.

Erodibility index (EI). A numerical expression of the potential of a soil to erode, considering the physical and chemical properties of the soil and climatic conditions where it is located. The higher the index, the greater the investment needed to maintain the sustainability of the soil resource base if intensively cropped. EI scores of 8 or above are equated to highly erodible land.

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).

Federal land. A land ownership category designating land that is owned by the federal government. It does not include, for example, trust lands administered by the Bureau of Indian Affairs or Tennessee Valley Authority (TVA) land. No data are collected for any year that land is in this ownership.

Forest land. A Land cover/use category that is at least 10 percent stocked by single-stemmed woody species of any size that will be at least 4 meters (13 feet) tall at maturity. Also included is land bearing evidence of natural regeneration of tree cover (cut over forest or abandoned farmland) and not currently developed for nonforest use. Ten percent stocked, when viewed from a vertical direction, equates to an areal canopy cover of leaves and branches of 25 percent or greater. The minimum area for classification as forest land is 1 acre, and the area must be at least 100 feet wide.

Highly erodible land (HEL). See erodibility index.

Irrigated land. Land that shows evidence of being irrigated during the year of the inventory or of having been irrigated during 2 or more of the last 4 years. Water is supplied to crops by ditches, pipes, or other conduits. For the purposes of the NRI, water spreading is not considered irrigation.

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.

Large urban and built-up areas. A Land cover/use category composed of developed tracts of at least 10 acres—meeting the definition of Urban and built-up areas.

Noncultivated cropland. See Cropland.

Nonfederal land. A land ownership designation that includes all land and water areas where the ownership is by private, municipal, county or parish, State, Indian tribal, individual Indian trust lands, the Tennessee Valley Authority, or areas under temporary control of a Federal, State, county or municipal agency or government for foreclosure or nonpayment of taxes.

Other rural land. A Land cover/use category that includes farmsteads and other farm structures, field windbreaks, barren land, and marshland.

Pastureland. A Land cover/use category of land managed primarily for the production of introduced forage plants for livestock grazing. Pastureland cover may consist of a single species in a pure stand, a grass mixture, or a grass-legume mixture. Management usually consists of cultural treatments: fertilization, weed control, reseeding or renovation, and control of grazing. For the NRI, includes land that has a vegetative cover of grasses, legumes, and/or forbs, regardless of whether or not it is being grazed by livestock.

Primary sample unit (PSU). An area of land, typically square to rectangular in shape, that is approximately 40, 100, 160, or 640 acres in size. Within the PSU, sample points are assigned. Certain data elements are collected for the entire PSU, while others are collected at the PSU points.

• The size of the PSU is based on the shape, size, and complexity of the resources being inventoried. In 34 states, PSU’s are often 160-acre square parcels measuring 0.5 mile on each side. In the western United States, PSU’s are often 40-acre or 640-acre square areas; the 40-acre units are used in most irrigated areas, and the larger PSU’s are used in relatively homogeneous areas containing large tracts of rangeland, forest land, or barren land. In the 13 northeastern states, PSU’s are defined to be 20 seconds of latitude by 30 seconds of longitude, ranging from 97 acres in Maine to 114 acres in southern Virginia. In Louisiana and parts of northwestern Maine, PSU’s are 0.5 kilometer squares (61.8 acres).

Prime farmland. Land that has the best combination of physical and chemical characteristics for producing food, feed, forage, fiber, and oilseed crops and is also available for these uses.

Rangeland. A Land cover/use category on which the climax or potential plant cover is composed principally of native grasses, grasslike plants, forbs or shrubs suitable for grazing and browsing, and introduced forage species that are managed like rangeland. This would include areas where introduced hardy and persistent grasses, such as crested wheatgrass, are planted and such practices as deferred grazing, burning, chaining, and rotational grazing are used, with little or no chemicals or fertilizer being applied. Grasslands, savannas, many wetlands, some deserts, and tundra are considered to be rangeland. Certain communities of low forbs and shrubs, such as mesquite, chaparral, mountain shrub, and pinyon-juniper, are also included as rangeland.

Rural transportation land. A Land cover/use category which consists of all highways, roads, railroads and associated right-of-ways outside urban and built-up areas; also includes private roads to farmsteads or ranch headquarters, logging roads, and other private roads (field lanes are not included).

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.

Small built-up areas. A Land cover/use category consisting of developed land units of 0.25 to 10 acres, which meet the definition of Urban and built-up areas.

Soil loss tolerance factor (T factor - USLE). The maximum rate of annual soil loss that will permit crop productivity to be sustained economically and indefinitely on a given soil.

T factor (USLE). See Soil loss tolerance factor.

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

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.

Urban and built-up areas. A Land cover/use category consisting of residential, industrial, commercial, and institutional land; construction sites; public administrative sites; railroad yards; cemeteries; airports; golf courses; sanitary landfills; sewage treatment plants; water control structures and spillways; other land used for such purposes; small parks (less than 10 acres) within urban and built-up areas; and highways, railroads, and other transportation facilities if they are surrounded by urban areas. Also included are tracts of less than 10 acres that do not meet the above definition but are completely surrounded by Urban and built-up land. Two size categories are recognized in the NRI: areas of 0.25 acre to 10 acres, and areas of at least 10 acres.

Water areas. A Land cover/use category comprising water bodies and streams that are permanent open water.

Wetlands. Lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. For purposes of this classification wetlands must have one or more of the following three attributes: (1) at least periodically, the land supports predominantly hydrophytes; (2) the substrate is predominantly undrained hydric soil; and (3) the substrate is nonsoil and is saturated with water or covered by shallow water at some time during the growing season of each year. (Cowardin, L. M., V. Carter, F. C. Golet, E. T. LaRoe. 1979. Classification of wetlands and deepwater habitats of the United States. FWS/OBS-79/31. U.S. Department of the Interior, Fish and Wildlife Service.)

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)