Gasser, J. K. R. and Mitchell, J. D. D. 1968. Effects of previous cropping and fertilizer-N applied in field experiments on soil-N available to ryegrass grown in pots . International congress of soil science. 9 (2), pp. 449-458.
Schofield, R. K. and Costa, J. V. B. 1935. The determination of the pF at permanent wilting and at the moisture equivalent by the freezing point method. International congress of soil science. 3 (1), p. 6.