原文 (英语)

DRY-FARMING A SYSTEM OF AGRICULTURE FOR COUNTRIES UNDER LOW RAINFALL BY JOHN A. WIDTSOE, A.M., Ph. D PRESIDENT OF THE AGRICULTURAL COLLEGE OF UTAH NEW YORK 1920 TO LEAH THIS BOOK IS INSCRIBED JUNE 1, 1910 PREFACE Nearly six tenths of the earth's land surface receive an annual rainfall of less than twenty inches, and can be reclaimed for agricultural purposes only by irrigation and dry-farming. A perfected world-system of irrigation will convert about one tenth