436 



THE SMALL GRAINS 



ferent crops. The effect of heavy irrigation is to take up 

 these salts to a great depth, and leave them deposited at 

 the surface through evaporation during a dry period, 

 unless there is good drainage. They are strongly alkaline 

 in reaction, and known as alkali salts or alkalies. The 

 most destructive, sodium carbonate, because of its solvent 

 action on humus, is black in color, and known as " black 



FIG. 140. Field of wheat badly injured by alkali on Truckee-Carson 



Project. 



alkali." The more common white incrustations are 

 deposits of the white alkalies, sodium sulfate (glauber 

 salt) and sodium chloride (common salt). 



In many localities during the considerable time since 

 irrigation was established, alkali deposits have accu- 

 mulated to an alarming extent, because of needless exces- 

 sive applications of water, long continued, and lack of 

 proper drainage, if any at all. Black alkali, in addition 

 to its direct effect upon the crop, acts very injuriously 

 upon the soil, by puddling it and making it untillable, 



