32 IRRIGATION FARMING. 



gation, but careful investigation showed that these waters 

 were strongly alkaline and that their continued use 

 would deposit on the surface a sufficient coating of salt 

 to render the lands sterile. The beds of these lakes are 

 coated with a deep stratum of alkali. Similarly some 

 artesian waters, and even the waters from some flowing 

 streams, like the Salt creek in Southern Arizona, for in- 

 stance, would result in the production of alkali. 



Alkali is chiefly the result of defective irrigation by 

 permitting evaporation of sub-surface water, thereby leav- 

 ing alkali on the surface ; but the largest proportion of 

 damage is brought about by the rise of the sub-surface 

 water level by lateral soaking from high-line canals, and 

 the trouble is greatly aggravated and extended by the 

 extravagant use of water. 



In irrigating light soils very small streams of water 

 should be used ; otherwise, if the drainage is good there 

 is danger of washing out the soluble fertilizing elements, 

 leaving only the coarse mineral constituents, and render- 

 ing the soil less fertile and productive. This precaution 

 is especially necessary when using the clear pure water 

 from springs or artesian wells, which carries ordinarily 

 little of the rich fertilizing sediment characteristic of 

 streams which flow for long distances through alluvial 

 regions. In the employment of the latter, if well charged 

 with sediment, the use of a large irrigation head is fre- 

 quently advantageous, as it gives an opportunity for a 

 uniform settlement of the sediment while the water is 

 entering the soil. 



Remedies for Alkali. The remedies for the 

 improvement of soils surcharged with the neutral alka- 

 line salts, and whose texture is very compact and adhesive, 

 are through tillage, the leaching out of the alkali by irri- 

 gations combined with either natural or artificial drain- 

 age, and frequent irrigation of the soil, assuring the inter- 

 mixture of the surface deposit of alkali with the lower 



