IRRIGATION 113 



statistics, he estimates that the total irrigated area is not far 

 from 100,000,000 acres, or about the area of the state of 

 California. This area is being rapidly increased. 



Professor F. H. King states in his book, " Irrigation and 

 Drainage," published in 1907, that the area irrigated in 

 India was about 25,000,000 acres, in Egypt about 6,000,000 

 acres, in Italy 3,700,000 acres, in Spain 500,000 acres, and 

 in France 400,000 acres. 



The following data are taken from the preliminary report 

 of the United States Census of 1910. These figures are for 

 the arid states of the United States, and do not include rice 

 irrigation. 



Total acreage irrigated in 1909 13,739,499 acres 



Area irrigation enterprises were capable of irrigating 



in 1910 19,355,711 " 



Area included in irrigation projects 31,112,110 



Total cost of irrigation systems constructed $304,699,450 



Average cost per acre (based upon construction to July 1, 

 1910, and acreage enterprises were capable of supply- 

 ing in 1910) $15.76 



Average annual cost per acre of maintenance and opera- 

 tion $1-07 



PURPOSES OF IRRIGATION 



To Supply Moisture. By far the most important pur- 

 pose of irrigation is to supply moisture when needed for plant 

 growth, as has already been explained. In some localities 

 crops cannot be grown at all without irrigation, and in others 

 irrigation is practiced in order to supplement rainfall and 

 increase the crop. 



To Control Temperature. In some localities irrigation is 

 practiced chiefly to control the temperature. Cranberry 

 marshes are often flooded with water to protect the crop from 

 frost. In other localities the soil is warmed in winter by 



