Biological nitrogen fixation and sustainability of tropical agriculture :  proceedings of the Fourth International Conference of the African Association for Biological Nitrogen Fixation (AABNF), held at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, 24-28 September 1990 / 
edited by K. Mulongoy, M. Gueye, and D.S.C. Spencer. 
 - Chichester, West Sussex, U.K. ;  New York :  J. Wiley,  1992. 
 - xiv, 488 p. :  ill. ;  26 cm.