Replenishing soil fertility in Africa [electronic resource] : proceedings of an international sysmposium cosponsored by Divisions A-6 (International Agronomy) and S-4 (Soil Fertility and Plant Nutrition), and the International Center for Research in Agroforestry, held at the 88th Annual Meetings of the American Society of Agronomy and the Soil Science Society of America, Indianapolis, Indiana, 6 November 1996 / editors, Roland J. Buresh, Pedro A. Sanchez, and Frank Calhoun ; organizing committee, Pedro A. Sanchez and Roland j. Buresh.