@INBOOK {HAUSER:1992, title = {Estimation of symbiotically fixed nitrogen using extended N difference methods}, author = {Hauser, S. }, editor = {Mulongoy, K. and Gueye, M. * and Spencer, D. }, year = {1992}, type = {Biological nitrogen fixation and sustainability of tropical agriculture}, pages = {309--321}, publisher = {John Wiley & Sons; Sayce Publishing; International Institute of Tropical agriculture (IITA); AABNF}, address = {Ibadan, Nigeria}, }