IMPROVEMENT OF THE SOIL 47 



subjected to continued washing and leaching. All 

 that is needed to make these lands exceedingly 

 productive is the artificial application of water. 

 This, when done on a considerable scale, is known 

 as irrigation. The name would hardly be applied 

 to the process of sprinkling small plots in a garden. 

 Many of the most famous agricultural reofions are 

 entirely dependent on irrigation for the production 

 of crops. It has been practiced for untold centuries 

 in Egypt, India, and China, and was used by the 

 Aztecs of Mexico long before the time of Columbus. 

 At the present day it is largely practiced in all these 

 countries, in Spain and Italy, in Hawaii, some of 

 the West India islands, and on the west coast of 

 Central and South America. Its most important 

 recent development, however, is in the drier parts 

 of the western United States, where great areas of 

 what formerly appeared on the maps as " The Great 

 American Desert " have been redeemed and brought 

 into profitable production. The work of building 

 reservoirs and of developing and controlling the 

 water supply in the West has now been taken up by 

 the national government and the development of 

 irrigation farming is likely to be still more rapid 

 in the future than it has been in the past. 



At present irrigation is for the most part confined 

 to what are known as the arid regions, wdiere the 

 rainfall is insufficient to produce crops. There are 

 many other regions, however, where the rainfall is 

 rather scanty, at least in what are known as dry 

 years, or that are subject to long droughts that injure 

 crops, where irrigation might be profitably employed 



