THE DEVELOPMENT OF THE MODERN SUB-SOIL PLOW –   Allan Yeomans   The basic principles used in Keyline of increasing the fertility of soils has not changed since they were first described in my father, P.A Yeomans’ book, The Keyline Plan, published in 1954. What has changed is my designs of the cultivating equipment and the modification … Continue reading 6. The Subsoil Plow Story