Chemicals, humus, and the soil; a simple presentation of contemporary knowledge and opinions about fertilizers, manures, and soil fertility / Donald Percy Hopkins. Hopkins, Donald Percy 1909- Fertilizers. Manures. Humus. Soil fertility. S633 .H76 1948 631.8 HOC Includes Bibliographical references and index. London : Faber and Faber Limited, 1948. 1948. 1948 Text 287 p. : eng