1. Williams, A. M., Rep. Rosewarne Exp. Hort. Sta. for 1960 (1961); ibid. (1963); ibid. (1965).
2. Toosey, R. D., and Smith, R. F. Y., Nature, 202, 924 (1964).
3. Methods of Analysis (Johnstown Castle, An Foras Taluntais, 1964).
4. Gallagher, P. A., and Bartholomew, W. V., Agron. J., 56, 179 (1964).