INFLUENCE OF SOIL ALKALI ON BACTERIA 191 



Kinds of Alkali. — The main injurious constituents in alkali 

 soils are sodium chloric! or common salt, sodium sulfate or Glau- 

 ber salt, sodium carbonate, and less frequently sodium nitrate. 

 Soils which have been the bed of seas or lakes contain in addition 

 to the above constituents magnesium chlorid or bittern, magnesium 

 sulfate or epsom salts, and calcium sulfate or gypsum. Where 

 there is a large quantity of any or all of the above salts except 

 sodium carbonate, it is known as white alkali. Such a soil is not 



Fig. 39. — Vegetation on alkali and alkali free soil. (After 



Kearney et al.) 



necessarily white but is nearly free from sodium carbonate. 

 Where there is considerable sodium carbonate or sodium nitrate 

 present we have what is known as black alkali. It is so-called 

 from the dark color which these constituents impart to the soil 

 when they react with its organic matter. Black alkali is very de- 

 structive to plants; it tends to puddle the soil, and the sodium 

 carbonate clings very tenaciously to the soil particles, thus being 

 very hard to wash out. 



Kind and Number of Microorganisms in Alkali Soil. — 



What a difference one observes in the native vegetation on look- 



