Hopfen, Hans Joachim. Farm implements for arid and tropical regions / prepared by H. J. Hopfen. - Rev. ed. - Rome : Food and Agriculture Organization of the United Nations, 1969. - xii, 159 p. : illus. ; 23 cm. - FAO agricultural development paper ; no. 91 . Bibliography: p. [147]-150. LCCN: 73586274 Subjects--Topical Terms: Agricultural implements. Dewey Class. No.: 631.3 / HOE 1969