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National Resources Inventory
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Key Findings
Importance to the NationSoil erosion impacts soil quality, health, and productivity as well as the environment. The economic impact of mitigating soil erosion significantly burdens the agri-business sector and the Nation as a whole. Dust contributions to the atmosphere and delivery of sediment, nutrients, and chemicals to water resources are primary environmental concerns addressed by public policy makers and the stewards of our working lands. Understanding and managing these processes has
important long term implications for cropland sustainability, natural resource
condition and health, and environmental quality. Tabular ResultsMore InformationFor more information about the NRI, visit http://www.nrcs.usda.gov/technical/NRI/ See the 2003 Annual NRI Glossary for definitions of key terms. Send comments and questions to the NRI Help Desk. |
About the DataEstimates 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 2003 Annual NRI, which statistically updates 1997 NRI results with data collected during 2000 – 2003. The NRI was conducted on a five-year cycle during the period 1982 to 1997, but is now conducted annually. NRI data were collected every five years for 800,000 sample sites; annual NRI data collection occurs at slightly less than 25 percent of these same sample sites. NRI data release procedures are affected by implementation of an annual data collection approach, because the scale of NRI estimates is affected by these reduced sample sizes. Estimates are being released when they meet statistical standards and are scientifically credible in accordance with NRCS policy, and in accordance with OMB and USDA Quality of Information Guidelines. The 2003 Annual NRI data are suitable for national and many regional and state level analyses. Current estimates cover the contiguous 48 states. Future estimates will also cover Hawaii, Alaska, the Caribbean, and selected Pacific Basin islands. The findings presented here 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. 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 erosion equation factors are also used to determine an Erodibility Index (EI) for these NRI sample sites. This index is a numerical expression of the potential of a soil to erode, considering climatic factors and the physical and chemical properties of the soil – the higher the index, the greater is the investment needed to maintain the sustainability of the soil resource base if intensively cropped. Highly Erodible Land (HEL) is defined to have an EI of at least 8. The NRI approach to conducting inventories facilitates examination of trends in erosion over time because –
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. |
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