Moving up the yield curve : advances and obstacles : proceedings of a symposium sponsored by Divisions S-4, S-8, and A-4 of the American Society of Agronomy and the Soil Science Society of America : the papers were presented during the annual meeting in Chicago, Illinois, 3-8 December 1978 / organizing committee, Lloyd Hossner, Robert Hoeft ; editorial committee, Larry S. Murphy, Eugene C. Doll, L. Fred Welch ; editor-in-chief, Matthias Stelly ; managing editor, David M. Kral ; assistant editor, Mary P. Wirtz.