There are about 1.5 billion acres of rural land in non federal ownerships in the United States. Of this, 413 million acres were in crop use in 1977 as measured by the National Resources Inventory (NRI).l Land shifted between crop and other uses in response to economic, technological, and institutional conditions. Th~ dynamics of land use differ throughout the United States, reflecting physical, demographic, and economic attributes of particular communities, locations, and regions.