Heady, E. O., Madsen, H.C., Nicol, K.J., and Hargrove, S. H.. “Agricultural Water Demands,” National Technical Information Service, Springfield, Virginia, Report No. PB 206-790, November 1971.
 Heady, Earl O., Madsen, H. C., Nicol, Kenneth J., and Hargrove, S. H.. Agricultural and Water Policies and the Environment, CARD Report No. 40T, Center for Agricultural and Rural Development, Iowa State University, June 1972.
 Heady, Earl O., Madsen, H. C., Nicol, Kenneth J., and Hargrove, S. H.. “Nation and Interregional Models of Water Demand, Land Use, and Agricultural Policies,” Water Resources Research, Volume 9, August 1973.
 “Iowa's New Conservancy Districts and Soil Loss Limit Regulations,” Iowa State University, Cooperative Extension Service, PM-536, June 1972.
 Movers, C. A. “The Effects of Various Legumes on the Yields of Com,” Tennessee Agricultural Experiment Station Bulletin No. 142, February 1930.
 Nagadevara, V.S.S.V. “A Modeling Approach to the Economic Impacts of Local Environmental Controls in Iowa and the Rest of the Country,” Ph.D. dissertation, Iowa State University, 1974, Appendix X, (Unpublished).
 Ibid., Appendix 3.
 Ibid., Appendix 7.
 Nagadevara, V.S.S.V., Heady, Earl O., and Nicol, Kenneth J., Implications of Application of Soil Conservancy and Environmental Regulations in Iowa within a National Framework, CARD Report 57, Center for Agricultural and Rural Development, Iowa State University, June 1975.
 National Academy of Sciences. Nutrient Requirements of Domestic Animals, No. 2, “Nutrient Requirements of Swine, Sixth Revised Edition,” National Academy of Sciences-National Research Service Publication 1599, 1968.
 National Academy of Sciences. Nutrient Requirements of Domestic Animals, No. 3, “Nutrient Requirements of Dairy Cattle, Fourth Revised Edition,” National Academy of Sciences-National Research Service, 1971.
 Nicol, Kenneth J., Heady, Earl O., and Madsen, Howard C.
Models of Soil Loss and Water Use, Spatial Agricultural Structure, and the Environment, CARD Report 49T, Iowa State University, Ames, Iowa, 1974, Appendix 3, p. 213.
 Shrader, W. D. “Legumes-How Much N Do They Provide?” Iowa Cooperation Extension Service, EC-810t, January 1973.
 Shrader, W. D. and Voss, R. D.. “Soybeans May Supply 50 Pounds of Nitrogen for Next Year's Corn,” Wallaces Farmer, 97, No. 18, September 23, 1972.
 Shrader, W. D., Fuller, W. A., and Cady, F. B.. “Estimation of Common Nitrogen Reponse Function for Corn (Zea mays) Different Crop Rotations,” Agronomy Journal,
 Stoecker, A. L. “A Quadratic Programming Model of U.S. Agriculture in 1980: Theory and Application,” Ph.D. dissertation, Iowa State University, 1974, (Unpublished).
 U.S. Dept. of Commerce, Bureau of Economic Analysis. “The Economic Base of Selected Geographic Areas, Histrocial and Projected-1929 to 2020,” Preliminary Report to the Water Resources Council. Washington, D.C.: U.S. Dept. of Commerce, 1968.
 U.S. Water Resources Council. “Water Resources: Regional and Subregions for the National Assessment of Water and Related Land Resources,” Washington, D.C.: Government Printing Office, July 1970.
 Vanderholm, D. A. “Area Needed for Land Disposal of Beef and Swine Wastes,” Iowa Cooperative Extension Service, PM 522, January 1973.
 Wischmeier, W. H. and Smith, D. D.. “Predicting Rainfall Erosion Losses From Cropland East of Rocky Mountain,” USDA Agricultural Handbook No. 282, May 1965.