Gilliom, Robert J. <br/><br/>
Classification and mapping of agricultural land for national water-quality assessment / 
by Robert J. Gilliom and Gail P. Thelin. 
 - Washington :  Denver, Colo. :  U.S. G.P.O. ;  Free on application to the U.S. Geological Survey, Information Services,  1997. 
 - vi, 70 p. :  ill., col. maps ;  28 cm. 
 - U.S. Geological Survey circular ;  1131 .
<br/><br/> 'National Water-Quality Assessment Program.' 
<br/><br/>Includes bibliographical references (p. 30). 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Agricultural mapping--United States.<br/>Land use, Rural--United States.<br/>Water quality--United States.