280 



SOIL PHYSICS AND MANAGEMENT 



Kinds of Alkali. The alkalies of arid regions are commonly 

 classified as black, white, and brown. The black consists of forms of 

 sodium carbonate, which owe their name to the color produced by 

 the solution of organic matter and its deposition on soil particles 

 during evaporation. There are at least two forme of sodium car- 

 bonate included in the black alkali, the bicarbonate (HNaC0 3 ) and 

 the normal carbonate (Xa-jCOg). 



The white alkalies are composed mainly of common salt ( NaCl ) 

 and sodium sulfate (Xa.,S0 4 ), together with some magnesium sul- 

 fate (MgS0 4 ), potassium chloride (KC1), magnesium chloride 

 (MgCl 2 ) and small amounts of many others. The brown alkali 

 consists of nitrates, which are found only occasionally in damag- 

 ing quantities. Different alkalies usually occur as mixtures in 

 various and indefinite proportions. A careful study of the follow- 

 ing table shows this fact. That from Kern county, number one, 

 contains sodium sulfate principally, but with some potassium sul- 

 fate; number two, sodium sulfate and chloride with some nitrate; 

 number three contains sodium and potassium carbonate or black 

 alkali largely; while four is a mixture of sodium sulfate, chloride, 

 carbonate, and nitrate. 



Percentage Composition of Some Typical Alkali Salts l (Hilgard) 



The amount of the different kinds of alkali is not constant, but 

 changes from week to week. 



Effect on Physical Condition of the Soil. The black alkali 

 defloccnlates the soil, producing a puddled condition due to the 

 solution of the organic matter. A very close rearrangement of the 

 particles occurs by which the soil becomes impervious to water and 

 practically untillable. This closer arrangement of particles de- 



