48 TROPICAL AGRICULTURE 



off before harvesting, thus destroying all material which would 

 otherwise have been returned to the soil and leaving nothing 

 but the bare stems standing. This practice was adopted on 

 account of the supposed reduction which is brought about in 

 the cost of harvesting. With the exception of two or three 

 plantations no effort was made at all within recent years on 

 any of the Hawaiian plantations to conserve the humus of 

 the soil, to practice green manuring in any way or to adopt any 

 system of rotation. This deceptive and suicidal system of 

 robbing the soil finally led to so-called physiological diseases 

 and diminished yields which require serious attention. It was 

 soon found that the so-called senility of the Lahaina cane was 

 due entirely to the destruction of the humus in the soils and 

 the consequent deterioration of the physical condition of the 

 soil. By returning to the soil the natural cane trash, together 

 with legumes and other weeds which were allowed to grow in 

 the interval between harvesting and plowing, it was found 

 possible to bring the yield back to standard and to demon- 

 strate that the so-called senility was not a disease of cane 

 but merely an indication of poor soil management. In Java, 

 Louisiana, Mauritius, British India, Egypt, and certain other 

 cane-producing countries, some form of rotation is practiced. 

 No rotation system, however, has been adopted in Cuba, Ha- 

 waii, Trinidad, or Fiji, but in Hawaii the present tendency 

 to plow under the cane trash and to secure as much green 

 material as possible from a quick growing legume, such as 

 Crotalaria or Jack bean, may be said to take the place of the 

 regular system of rotation. 



According to results thus far obtained, it appears that in 

 Hawaii about 1,000 pounds of water are required for the pro- 

 duction of a pound of cane sugar. The average application 

 of irrigation water in Hawaii is about 75 inches in a dis- 

 trict where the normal rainfall is 25 inches. Outside of the 

 districts of heavy rainfall cane is irrigated in nearly all parts 

 of cane-producing countries On the lowlands near the sea- 



