CHAPTER III 



THE EXTENT TO WHICH. TILLAGE MAY TAKE THE 

 PLACE OF BAIN OR IRRIGATION 



WERE it desirable to irrigate all agricultural lands 

 lying in humid climates, it would not be possible to 

 do so, on account of the insufficiency of water for the 

 purpose. The truth of this proposition will be evident 

 if we deal quantitatively with the problem. 



THE INSUFFICIENCY OF WATER TO IRRIGATE ALL 

 CULTIVATED LANDS 



Humphreys and Abbott have placed the mean an- 

 nual discharge of the Mississippi at 19,500,000,000,000 

 cubic feet, while the catchment area is placed at 1,- 

 244,000 square miles. Assuming that these quantities 

 are correct, then the mean annual run -off for the 

 whole Mississippi basin would be 6.747 inches. But 

 not all this run -off is available for irrigation, were it 

 desirable to so use it ; for during a large part of the 

 time this water is flowing away when the season does 

 not permit of its being used, and it is impracticable to 

 impound it and hold it until it might be used. If we 

 take the mean daily discharge of the river as -sir of 

 its annual amount, and allow that the whole of this is 



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