The NRI is a statistical survey based on well-established scientific principles created to provide support for Agricultural & Environmental policy development program implementation. It was designed and implemented to assess conditions and trends of soil, water, and related resources on non-Federal rural lands. Non-Federal lands include privately owned lands, tribal and trust lands, and lands controlled by State and local governments. The survey is conducted for the USDA by the NRCS in cooperation with CSSM. The NRI captures data on land cover and use, soils, soil erosion, wetlands, habitat diversity, selected conservation practices, and related resource attributes at scientifically selected sample sites. NRI reports provide updated information on the status, condition, and trends of land, soil, water, and related resources.
The results of the 1934 National Erosion Reconnaissance Survey, the first formal study of erosion in the United States, were instrumental in the passage of the Soil Conservation Act of 1935. That Act established the Soil Conservation Service (SCS), NRCS’s predecessor agency. Since its founding, SCS/NRCS has conducted periodic inventories of the Nation’s natural resources. The 1945 Soil and Water Conservation Needs Inventory (CNI), another reconnaissance study, was the foundation for the 1958 and 1967 CNIs, which represented the agency’s first efforts to collect data nationally for scientifically selected field sites. The 1975 Potential Cropland Study examined the conversion of the Nation’s best farmland to urban development and provided statistical data on the potential for converting other lands to cropland. Periodic NRIs were conducted in 1977, 1982, 1987, 1992, and 1997. Since 2000, NRI data have been gathered annually; major releases of these data, however, will continue to be reported at 5-year intervals. The NRI survey framework was also used to conduct several less intensive, special-issue inventories during the 1990s; these special studies investigated topical matters of concern (such as wetland conversions) and supplemented the periodic NRI surveys.
Numerous legislative acts have mandated that NRCS collect natural resources data. The Rural Development Act of 1972 directed the Secretary of Agriculture to implement a land inventory and monitoring program and to issue a report on the conditions and trends of soil, water, and related resources at intervals not exceeding 5 years. The Soil and Water Resources Conservation Act (RCA) of 1977 and other supporting legislation augmented the statutory mandate for periodic assessment of the Nation’s natural resources. To fulfill this requirement, the NRI program was developed to provide critical information regarding natural resources and to supplement the NRCS Soil Survey Program.
NRI data are designed to be part of the core components of the agency’s strategic planning and accountability efforts, and to help assess consequences of existing legislative mandates, such as the appraisals required by the RCA and the periodic Farm Bills.
The NRI tracks changes at state and national levels for a variety of soil, water, and other natural resources data on non-Federal lands. Included are:
- Broad land cover/use
- Cropland use by irrigated and nonirrigated acres
- Broad land cover/use by land capability class and subclass
- Prime farmland
- Erosion and erodibility
- Wetlands and deepwater habitats
The NRI is a longitudinal panel survey comprised of samples located in all counties and parishes of the 50 states and Puerto Rico, the Virgin Islands, the District of Columbia, and parts of the Pacific Basin. The sample design is a two-stage stratified area sample. The first-stage sampling unit is an area of land called a segment. Sample points located within the segment are the second-stage sampling units. Detailed data are collected for the sample points, with some area data collected for the segment.
Data were collected for about 300,000 segments and about 800,000 sample points in the 1997 NRI. In each NRI, data are collected on the same or a subset of the same segments and sample points. Data from 1982, 1987, 1992, and 1997 are included in the 1997 database, allowing analysis of trends. In 2000, the NRI began a transition to an annual survey called the Continuous NRI. About 42,000 segments, nationwide, are included as the “core” sample and these are sampled annually. Additionally, about 30,000 segments are selected from the remaining 258,000 each year to form a supplemental sample. This supplemental panel rotates through the remaining segments.
Photo-interpretation and remote sensing, with ancillary materials such as USDA field office records, information from local NRCS personnel, soil survey and wetland inventory maps and reports are used to collect data. The Soil Survey Database provides information on specific properties and characteristics of soil.
Area for the total surface, federal land, and large water bodies and large streams is determined using GIS databases, not estimated from segment or point data.
Computer-assisted survey information (CASI) collection methods, featuring direct entry into hand-held computers and a national database server at CSSM, were first developed for the 1997 NRI. Current photo-interpretation data collection features a desktop CASI.
Field studies are conducted to obtain data not easily obtainable using remote sensing techniques. Currently, a range survey in the western US is underway using a ruggedized handheld device for data collection.
Quality assurance procedures ensure that year-to-year differences reflect actual conditions.
The estimation procedure combines information from several sources to produce a final data set composed of records containing information for the years 1982, 1987, 1992, 1997, 2000, and annually thereafter. The estimation weight is attached to each record. Data were collected at the segment level and at the point level in each of the NRI years. In estimation, the areas measured for small streams and waterbodies, roads, and urban land collected at the segment level are converted to point data. Each of these points is given an initial weight based on the area in the segment and the probability that the segment is included in the sample. Imputation is used for unobserved data elements for the created points. Initial weights for created points and for observed points are adjusted during the estimation process using ratioing and small area estimation. Control totals for surface area, federal land, and large water areas, derived from GIS databases, are maintained throughout the process. Finally, the weights are adjusted using iterative proportional scaling (raking) so that areas estimated for major broad cover/uses for historical years (before 2000) in the current survey closely match those earlier estimates.