Technologies for sustainable agriculture in the tropics : proceedings of two international symposia sponsored by Division A-6 of the American Society of Agronomy in San Antonio, TX, and Denver, CO, 1990 and 1991 respectively / editors, John Ragland and Rattan Lal ; organizing committee, John Ragland (1990), Augustine Uzo Mokwunye (1991) ; editorial committee, Kenneth Cassman, Charles Francis, Peter Hildebrand, Jagmohan Joshi, Anthony Juo, Rattan Lal, cochair, Uzo Mokwunye, Richard Morris, John Ragland, chair ; editor-in-chief ASA, Gary A. Peterson ; editor-in-chief CSSA, P.S. Baenziger ; editor-in-chief SSSA, Robert J. Luxmoore ; managing editor, Jon M. Bartels.