1. Baker R. M. & Robinson J. B. D. (1963). Res. Rept. Coff. Res. Stn., Lyamungu, Tanganyika, 1962, 49.
2. Piper C. S. (1950). Soil and Plant Analysis. University of Adelaide, 368.
3. Robinson J. B. D. (1968). Proc. Seminar on Intensification of Coffee Production in Kenya, Nairobi, December 1968. Appendix I.