CHAPTER XV 

 ALKALI WATER FOR IRRIGATION 



ONE source of alkali trouble may be from irrigation 

 water which carries in solution large quantities of soluble 

 salts. Water passing over or seeping through alkali land 

 gradually dissolves the soluble material which it retains 

 in solution. Drainage water coming from land that is 

 high in soluble salts should therefore be thoroughly ex- 

 amined before being used for irrigation. 



Streams that flow through rock formations, such as the 

 Mancos shale, which contain large quantities of salts are 

 often so strongly impregnated that their waters are rendered 

 injurious for irrigation. Springs or wells are often found 

 containing sufficient soluble salts to make the use of their 

 waters dangerous. A limited quantity of alkali in the water 

 would not be so serious if it were not for the fact that the 

 land on which it is used may already have sufficient alkali 

 so that the addition of any more would make it unfit for 

 crops. 



Variation in the original salt content of the soil makes 

 it very difficult to determine just how much alkali can be 

 present in irrigation water before it becomes dangerous. 

 Notwithstanding the difficulty of giving exact figures, 

 the problem is so important that it merits the most pro- 

 found study. This is realized when the extensive use of 

 irrigation water is known. 



About 95,000,000 acres of land, or about 7 per cent of 

 the total area under cultivation in the world, is farmed 



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