First published 1971 by Keyline Publishing Pty. Ltd. Registered at the G.P.O. Sydney for transmission by post as a book. National Library of Australia Card Number and I.S.B.N. 0959957804 [email protected] P.A. Yeomans Pty. Limited 117 Pitt Street, Sydney, 2000, Australia. Offered here with the permission of Allan Yeomans (soilandhealth.org/)