1. Special Panel on Impact Assessment Contributions Made by the CGIAR and its Partners to Agricultural Development in Sub Saharan Africa (Consultative Group on International Agricultural Research, 2001).
2. http://www.faostat.org
3. DeWit, C. T. in Proc. Wageningen Agricultural University Conference 66–70 (Wageningen Univ. Press, 1981).
4. Quiñones, M. A., Borlaug, N. E. & Dowswell, C. R. in Replenishing Soil Fertility in Africa Vol. 51 (eds Buresh, R. J., Sanchez, P. A. & Calhoun, F.) 81–96 (SSSA Special Publication, 1997).
5. Buresh, R. J., Sanchez, P. A. & Calhoun, F. (eds) Replenishing Soil Fertility in Africa Vol. 51 (SSSA Special Publication, 1997).