@INBOOK {MERCKX:2001, title = {Soil organic matter and soil fertility}, author = {Merckx, R. and Diels, J. and Vanlauwe, B. and Sanginga, P. and Denef, K. and Oorts, K. }, year = {2001}, type = {Sustaining soil fertility in West Arica Vol 58}, pages = {69--89}, publisher = {Madison, USA: Soil Science Society of America (SSSA); american Society of Agronomy}, }