1. Agricultural Advisory Council Report on Soil Structure and Fertility. In Modern Farming and the Soil, HMSO (1970).
2. Fryer, J. D. and Kirkland, K., Weed Res. 10, 133–58 (1970).
3. Kemper, W. D. and Chepil, W. S., in Methods of Soil Analysis, eds Black et al. Pt. 1 Ch. 29. Am. Soc. Agron. (1965).
4. Tinsley, J., Trans. 4th Intern. Cong. Soil Sci. 1, 161–165 (1950).