TYPICAL ALKALI WATERS 231 



drainage water containing over n,ooo parts per million 

 of salts. The applications of water were large, sometimes 

 as much as 16 inches being applied at one time, which 

 makes a great difference in the retention of the salts by the 

 soil (5). Hawaiian experiments with water containing 

 2000 parts per million of salts show that on a moderately 

 porous soil there was very little accumulation of salt pro- 

 vided occasional heavy irrigation was given (4). Wash- 

 ing the salts out of the soil occasionally with the relatively 

 pure winter and spring waters has proved very beneficial 

 to some alkali districts. 



In semi-arid sections, the salt content of irrigation water 

 may be much higher than in the arid without causing trouble 

 because the amount of water necessary to supplement the 

 rainfall is smaller and the larger precipitation washes the 

 salts out of the soil much more readily. The U. S. Geo- 

 logical Survey (32) has attempted to classify irrigation 

 waters as good or bad by use of a formula based on the 

 toxicity of the individual alkali salts to field crops. Such 

 formulas, while instructive as to the relative injuriousness 

 of the waters, are subject to criticism because the factors 

 mentioned above modify the limits through a wide range. 

 A formula to be of much practical value must consider 

 these factors. 



Composition of Typical Alkali Waters. - To show the 

 variation in the salt content of some of the principal streams 

 of the West, the analyses given in Table XXII are pre- 

 sented. It should be kept in mind that these results will 

 not hold strictly for different seasons and different sections 

 of the stream, but they are useful in gaining a general 

 idea of the nature of the alkali in different streams. 



