CHAPTER YIL 



THE IRRIGATION OF THE CANE. 



A very large proportion of the cane crop is produced partially or entirely 

 tinder irrigation ; thus irrigation forms an important factor in the Hawaiian 

 Islands, in Java, in Egypt, in British India, and in Peru ; a few estates in 

 Mauritius are also irrigated. The West Indies, Louisiana, Piji, Australia, 

 and the island of Hawaii are districts which produce mainly under natural 

 conditions. It is only in the Hawaiian Islands (the writer believes) that 

 plantations have constructed and own independently their water supply ; in 

 the other irrigation districts the irrigation works are state-owned and 

 controlled. 



Unit of Measurement. Irrigation water is measured as a volume 

 flow per unit of time or as a depth per unit of area. In the first system the 

 cubic foot second or ' cusec ' is the generally adopted English unit ; this flow 

 is usually referred to the acre ; in the metric system the unit is a litre-second 

 referred to a hectare. The acre-inch is the usual unit of depth measurement 

 and this unit is equal to 101'5 tons, to 3652 cubic feet, to 22,736 imperial 

 gallons, to 27,294 U.S. gallons, and to 103,130 litres. In the Hawaiian 

 Islands, the plantation reckoning is in many million (U.S.) gallons per day, of 

 which 1,000,000 are estimated as necessary for each 100 acres in cultivation. 



Hawaii. On the islands of Oahu, Maui, and Kauai the crop is almost 

 entirely grown under irrigation. Irrigation was begun in Hawaii in 1907 and 

 is now developing. The system followed is one of short furrow irrigation, 

 the length of furrow being adopted to the nature of the soil. During the first 

 crop the water runs along the cane row ; in ratoon crops which are hilled up 

 the water runs between the row. 



The following data are based on a report of Maxwell 1 : 



During a period of growth of about 1 7 months the total water supplied to 

 the crop averages about 100 inches. Reference to the table below will show 

 that the young cane received less water than when more mature, but not so 

 much less as might be thought proportionate considering the different states of 

 young and of mature cane. The causes at work are twofold ; when the cane 

 is young the whole ground is exposed to the direct rays of the sun and to the 

 action of winds; when the cane is older the foliage shades the ground and 

 lessens loss due to evaporation, and to a large extent conserves water in the 



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