United States, Annals of Association of American 
Geographers, 77(1), pp118-125. 
Searcy, N.D. and A.R. Longwell, 1964. Nebraska Atlas, 
Nebraska Atlas Publishing Co., Kearney, Nebraska. 
U.S. Department of Agriculture, 1981. Land Resource 
Regions and Major Land Resource Areas of the United 
States, Agricultural Handbook 296. 
U.S. Department of Agriculture, Soil Conservation Service, 
National Cooperative Soil Survey, 1994. State Soil Survey 
Geographic Data Base, CD-ROM digital data. 
Wikens, E., 1986. Terrestrial Ecozones of Canada, 
Environment Canada, Ecological Land Classification Series 
No.19, Ottawa, Ontaroi. 
Williams, J. H. and D. Murfield, 1977. Agricultural Atlas of 
Nebraska, University of Nebraska Press, Lincoln. 
1006 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996