@BOOKLET {WARREN:1992, title = {A preliminary analysis of indigenous soil classification and management systems in four ecozones of Nigeria}, author = {Warren, D. M. }, year = {1992}, address = {International Institute of Tropical Agriculture (IITA)}, howpublished = {Resource and Crop Management Division (RCMD) Discussion paper 92/1. 30p.}, note = {30p.}, }