THE IRRIGA 1 ION A GE. 321 



sugar grown. Instead of using sugar as the standard we may use the 

 total dry substance of the crops in its relation to the water received 

 per acre. The exact data furnished by the station's experiments 

 enable this to be done: 



WATER, USED TO PRODUCE 1 POUND OF DRY SUBSTANCE. 



By "dry substance produced per a jre" is meant the total amounts of water-free cane and 

 leaves produced by 1 acre of ground. During the crop period 1897-98 some rainfall water was lost 

 by percolation through the subsoil, but how much was not ascertained. During the growth of the 

 crop of 1898-99 no water was lost. Two hundred and twelve pounds of water were used, therefore 

 to produce a pound of dry substance. 



The most fertile plantation upon the Hawaiian Islands last year 

 yielded 20,500 pounds of sugar per acre, and according to the esti- 

 mate of the manager, consumed a little over 5,000,000 gallons of 

 water per acre. On this plantation a less volume of water propuced 

 double the quantity of sugar that was obtained at Spreckelsville and 

 Hamakuapoko; consequently the waste of water at those places must 

 have been great. Upon this fertile plantation, however, there are 

 ample evidences of past excessive irrigation and waste. The volume 

 of water used per acre was double that used at the experiment station- 

 to produce less sugar per acre. 



A small crop of say 30 tons of cane or 4 tons of sugar per acre can 

 not in its growth consume the volume of water demanded by a crop 

 of 80 tons of cane or 10 tons of sugar per acre. Lt can consume only 

 a fixed portion of that volume. The same principle applies in the 

 demands made upon the soil for plant food. The large crop absorbs 

 more of the soil constituents to compose its substance and promote its 

 growth. Water is only one of the essential factors which control the 

 size of the cane or other crop. The depth and fertility of the soil, 

 the fertilizing elements supplied, and the extent of cultivation are all 

 potent factors affecting production. It has already been shown in a 

 previous paragraph that the growth of the cane and the amount of 

 water used during increased growth, as indicated by the increased 

 transpiration of water by the cane, are very noticeably influenced by 

 the action of nitrogenous fertilizers. 



DISTRIBUTION OF WATER. 



In the Hawaiian Islands sugar cane is irrigated exclusively by 

 ditches and forrows. In laying out a field to be planted in sugar cane 

 the first step is to make a survey of the area and to determine its con- 



