1. Waring, S. A., and Bremner, J. M., Nature, 201, 951 (1964).
2. Bremner, J. M., in Methods of Soil Analysis (edit. by Black, C. A., et al.), 1241 (Amer. Soc. Agron., Madison, 1965).
3. Russell, E. W., Soil Conditions and Plant Growth, eighth ed., 254 (Longmans Green, London, 1950).
4. Bremner, J. M., Methods of Soil Analysis (edit. by Black, C. A., et al.), 1195 (Amer. Soc. Agron., Madison, 1965).
5. D'Hoore, Soil Map of Africa. Explanatory Monograph, Joint Proj. No. 11, Comm. Tech. Co-op. in Africa, Lagos, 103, 107 (1964).