This revision of N.Z. Soil Bureau Scientific Report 10C comprises a reprinting of sections C1-C5 (originally published in 1972 with M.W. Gradwell as sole author) and of sections C6-C9 (first published in 1976). In both cases some minor errors have been corrected and in the earlier sections some minor revisions have been incorporated for the sake of clarification. No substantial changes to the methods are involved.