ALKALI SOILS 



333 



to reach a concentration of 2200 parts per million. The quan- 

 tity of soluble salts that may be present in irrigation water 

 before it is unfit for use depends on certain conditions. This 

 amount will vary with the crop, the rainfall, the soil, the 

 composition of the alkali, and a number of other factors. 



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!FiG. 54. — ^Diagram showing the amount and composition of alkali salts 

 at various depths in a soil at Tulare^ California. (After Hilgard.) 



"Where the alkali is of the sodium sulfate type rather high 

 concentrations are admissible, running as high as 1000 parts 

 per million. Water carrying black alkali must be used with 

 great caution. Table LXXVI indicates the concentration that 

 may be expected in normal irrigation water. 



The preponderance of sodium chloride is almost always a 

 feature, not only in alkali water but also in soils affected with 

 alkali salts. This may be explained as due to differential ab- 



