@ARTICLE {SANGINGA:1996a, title = {Field measurements of nitrogen fixation in leguminous trees used in agroforestry systems: influence of 15N-labelling approaches and reference trees}, author = {Sanginga, N. and Danso, S. K. A. * and Zapata, F. }, journal = {Biology and Fertility of Soils}, year = {1996}, volume = {23}, pages = {26--32}, }