112 CHAPTER VII 



is one of furrow irrigation, differing in method in no way from those already- 

 described. 



Quantity of Water used in Irrigation. — In experiments made in Java, 

 Van der Heide^ concluded that 0-360 litre per second per bouw, or 0*0072 

 cubic foot per acre per second was required for cane irrigation. This quan- 

 tity is equivalent to a flow of 560,000 gallons per day per 100 acres, or to 

 62 inches per year, but, as irrigation only obtains from April to November, 

 the actual quantity of water used is about 36 inches. For an actual irrigation 

 at planting in Java, Mussenbroek^ estimates that 524 cubic metres are 

 required for a bouw, and for a watering afterwards 105 cubic metres. These 

 quantities are equivalent to 10,570 and 214 c. ft. per acre, or to 2 • 9 and o • 6 

 inches respectively. 



As compared with these quantities, O'Shaughnessy^ gives 1,000,000 

 U.S. gallons per day as required for the complete irrigation of 100 acres in 

 Hawaii. This quantity is equivalent to 134 inches, and does not include 

 the 50 inches of rain that may be expected to fall in a season of eighteen 

 months during which the cane will receive 22,800 tons of water and will 

 produce from 50 to 80 tons of cane. Of this quantity O'Shaughnessy 

 estimates that only one-third reaches the area of the cane roots, due to 

 leaky reservoirs, ditches, and careless application, but since this estimate 

 was made much more careful conservation is practised. 



In Egypt, Tiemann* estimates that for each irrigation 1,000 cubic metres 

 are required for a hectare, equivalent to 14,300 c. ft. per acre, or to 3 • 6 inches. 



At Poona, in British India, Mollison^" estimates that the cane over a 

 crop season receives 75 to 80 inches of water in twenty-eight applications, 

 together with some 30 inches of rain. 



The data fo lowing are based on a report by MaxwelP^ dealing with 

 experimental work on the irrigation of the cane in Hawaii. 



During a period of growth of about 17 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 consei-ves 

 water in the soil. At twelve months of age the crop actually constmies in 

 its economy ten times as much water as a crop one month old, but owing to 

 the causes mentioned above the apparent consumption is much less dis- 

 proportionate. 



It was found by experiment in Hawaii that the best results were obtained 

 when the young cane received o • 5 inch per week ; less favourable results 

 were obtained when the water supplied was one inch per week, and when the 

 furrows were filled with water the cane came up yellow and sickly. As the 

 cane comes away it requires about one inch weekly up to three or four 

 months, after which i • 5 inches are necessary until the crop is in full vigour, 

 when three inches and never more are required. These figures refer to 

 natural and artificial supplies combined. The reports quoted above give as 

 a general figure that 1,000 lbs. of water are required per lb. of sugar produced, 

 and mention that certain plantations in Hawaii use much more water than 

 the quantities cited with less favourable results. 



