Classification and mapping of agricultural land for national water-quality assessment - Gilliom, Robert J.; Thelin, Gail P.; National Water Quality Assessment Program (U.S.); U.S. Geological Survey (Washington : U.S. G.P.O. ; Denver, Colo. : Free on application to the U.S. Geological Survey, Information Services, 1997)
'National Water-Quality Assessment Program.'
Includes bibliographical references (p. 30).
Keywords: Agricultural mapping -- United States; Land use, Rural -- United States; Water quality -- United States