6 IRRIGATION PRACTICE 



highlands through the arid and semi-arid lands, together 

 with some of the underground waters, must be the source 

 of the water to be used in irrigation. When a world-sys- 

 tem of irrigation shall be perfected, all of the available 

 water will not, in all probability, cover more than one- 

 tenth to one-fifth of the thirsting land. The remainder 

 must be left to be conquered by dry-farming methods. 

 Yet, the possible area to be reclaimed by irrigation is 



FIG. 3. The value of water in an arid land. A Papago 

 squaw, in Arizona, utilizing the drip from her water 

 bottle to grow a few onion plants beneath, protected 

 by a paling of sticks. 



tremendous; and in view of its certainty of large crop 

 yield, farming under irrigation should be the most attrac- 

 tive of all modes of farming. (Fig. 2.) 



Irrigation will further find a limited application in 

 humid countries, the occasional dry years of which cause 

 injurious droughts. In many of the humid regions the 



