Percent Change in Prime Farmland Area, 1982 - 1992
This shaded polygon map shows the percent change in the amount of prime farmland area from 1982 to 1992 within each 8 digit hydrologic unit, using 1982 as a base year. The percentages are presented in four categories based on the following divisions: an increase of more than 2%, little change (less than 2% change), a decrease of 2% to 15%, and a decrease of over 15%. Areas with less than 5% prime farmland in both 1982 and 1992 are hatched. Areas with 95% or more Federal area are shown as gray. This map replaces map #2312.
Cautions for this Product:
Since prime farmland 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 rates of change in some areas where there is little prime farmland. Data are not shown where prime farmland is 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.
Source: National Resources Inventory, 1997
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.
Aggregate Layer: 8 Digit Hydrologic Unit Areas with Federal Land
Other Layers Displayed: States, Rivers
A land ownership class designating land that is owned by the Federal Government. It does not include, for example, trust lands administered by the Bureau of Indian Affairs nor Tennessee Valley Authority (TVA) land. No data are collected for any year that land is in this ownership. [NRI-97]
A hierarchical system developed by the U.S. Geological Survey that divides the United States and the Caribbean into 21 major regions, 222 subregions, 352 accounting units, and further subdivided into 2,150 cataloging units that delineate river basins having drainage areas usually greater than 700 square miles. [USGS]
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. It has the soil quality, growing season, and moisture supply needed to produce economically sustained high yields of crops when treated and managed according to acceptable farming methods, including water management. In general, prime farmlands have an adequate and dependable water supply from precipitation or irrigation, a favorable temperature and growing season, acceptable acidity or alkalinity, acceptable salt and sodium content, and few or no rocks. They are permeable to water and air. Prime farmlands are not excessively erodible or saturated with water for a long period of time, and they either do not flood frequently or are protected from flooding.[SSM, USDA Handbook No. 18, October 1993]
Product ID: 4985
Production Date: 12/13/00
Product Type: Map
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