OBJECTS OF IRRIGATION 127 



confined to dry regions, but this is not necessarily the case. In 

 arid climates, irrigation is absolutely necessary to produce any 

 crops at all, while in semi-arid sections, irrigation, where possible, 

 makes crop production sure, and greatly increases the yield. 

 In sub-humid and even in humid regions, because of the irregulari- 

 ties in the time and amount of rainfall, irrigation is practiced to a 

 greater or less extent. Both China and Japan, for example, have 

 a large and a well distributed rainfall, yet irrigation is generally 



FIG. 63. Furrow irrigation in orchard in dry climate. (U. S. D. A.) 



practiced. In Japan alone, water is artificially applied to at least 

 12,500 square miles of land, or about two-thirds of her culti- 

 vated area. 5 



Objects of Irrigation. The primary object of irrigation is to 

 supply needed water to crops. Without irrigation, many thou- 

 sands of square miles of land in the world would be deserts instead 

 of fit places to live in; and hundreds of square miles of desert 

 wastes are today being made to produce bountiful harvests just 

 by supplying water to these thirsty lands. 



In the United States irrigation is confined largely to the western 

 states, where many large irrigation projects are in operation or 



6 "In China and Japan, where they must raise large crops or starve, they 

 have been compelled to irrigate, although they have a larger summer rainfall 

 than we ... but they also fertilize heavily." King. 



