OVER-IRRIGATION AND ALKALI 



393 



followed by sodium chloride, followed by sodium sulfate, 

 followed by magnesium sulfate. This is the general order 

 of tolerance of these four important salts, frequent con- 

 stituents of alkali. 



The injury from each salt depends upon the mixtures 

 of salts hi the alkali. The action of magnesium sulfate 

 is almost wholly destroyed, if there is mixed with it a 

 quantity of calcium sulfate. In fact, calcium sulfate is 

 the great neutralizer of the dangerous substances of 



FIG. 116. Vegetation on alkali lands. California. 



ordinary alkali. The salts found in alkali do not show 

 any specific effect upon the wilting coefficient. Any 

 of the alkali salts, present in large quantity, tends to 

 increase the water-cost of dry matter. Evaporation from 

 alkali soils is always reduced. In general, while alkali tends 

 to reduce the direct evaporation from the soil, it also tends 

 to increase the water-cost of dry matter. 



The concentration of alkali hi the soil that will injure 

 plants has not been finally determined. Most work on the 

 subject has been done by Hilgard and Loughridge of 

 the University of California. Loughridge has tabulated 

 the highest quantity of alkali salts endured by various 



