392 SOILS: PROPERTIES AND MANAGEMENT 



and chlorides of sodium, potassium, calcium, and mag- 

 nesium occur in the largest amounts. Sodium may be 

 present as carbonate, sulfate, chloride, phosphate, and 

 nitrate. Potassium may be similarly combined. Mag- 

 nesium is likely to appear as a sulfate or a chloride, and 

 calcium as a sulfate, a chloride, or a carbonate. One 

 salt will predominate in some soils, and other salts in other 

 soils. A base may be present in combination with several 

 different acids. The nature of the prevailing salt greatly 

 influences the effect on vegetation. The table on page 



393 gives the composition of the soluble salts from a 

 number of alkali soils. 



A few years ago Headden l called attention to large 

 accumulations of nitrates in certain localities in Colorado. 

 These salts dissolve in the soil water and are frequently 

 present in such large quantities as to be injurious to 

 vegetation. 



304. White and black alkali. Sulfates and chlorides 

 of the alkalies, when concentrated on the surface of the 

 soil, produce a white incrustation, which is very common 

 in alkali regions during a dry period as a result of evapora- 

 tion of moisture. Incrustations of this character are 

 called white alkali. 



Carbonates of the alkalies, particularly sodium car- 

 bonate, dissolve organic matter from the soil, thus giving 

 a dark color to the solution and to the incrustation. For 

 this reason alkali containing large quantities of these 

 salts is called black alkali. Black or brown alkali may 

 also be produced by calcium chloride or by an excess of 

 sodium nitrate. 



1 Headden, W. P. ' Deterioration in the Quality of Sugar 

 Beets due to Nitrates Formed in the Soil. Colorado Agr. 

 Exp. Sta., Bui. 183. 1912. 



