ALKALI SOILS. 



441 



precisely the same transformations experienced in California 

 and India, in presence of calcic carbonate (see below, p. 



450 ff). 



The accounts given by v. Middendorff of the nature and oc- 

 currence of alkali lands in Turkestan (Ferghana) agree en- 

 tirely with those given above for California and India ; as do 

 also the investigations made by other Russian observers on the 

 saline lands of the steppes of European Russia. 



COMPOSITION AND QUANTITY OF ALKALI SALTS. 



Black and White Alkali. Broadly speaking, the world over 

 alkali salts consist mainly of three chief ingredients, already 

 mentioned, namely, common salt, Glauber's salt (sulfate of 

 soda), and salsoda or carbonate 1 of soda. The latter causes 

 what is popularly known as " black alkali," from the black 

 spots of puddles seen on the surface of lands tainted with it, 

 owing to the dissolution of the soil humus ; 2 while the other 

 salts, often together with Epsom salt and bittern (Magnesium 

 chlorid), constitute " white alkali," which is known to be very 

 much milder in its effect on plants than the black. In most 

 cases all three are present, and all may be considered as prac- 

 tically valueless, or noxious, to plant growth. 



Nutritive Salts in Alkali. With them, however, there are 

 almost always associated, in varying amounts, snlfate of pot- 



1 In this designation are included, in this volume, both the normal (mono-) car- 

 bonate and the two other compounds, the bi- or hydrocarbonate and the inter- 

 mediate (so-called sesqui-) compound or trona; all of which are commonly present 

 simultaneously, but in utterly indefinite relative proportions, varying from day 

 to day and from inch to inch of depth, inasmuch as their continued existence 

 depends upon the greater or less formation of carbonic acid in the soil, and the 

 access of air. Hence their separate quantitative determination at any one time is 

 of little practical interest. All naturally occurring carbonate of soda contains, and 

 sometimes consists of, these " super-carbonates," according to the greater or less 

 exposure to air and solar heat. They are much milder in their action on plants 

 than the mono-carbonate, which unfortunately, in the nature of the case, always 

 predominates near the surface, and thus injures the root-crown. 



8 A wholly different kind of " black alkali " exists in some regions, especially in 

 the delta lands of the Colorado of the West and in the Pecos and Rio Grande 

 country in New Mexico. In these cases the dark tint is due, not to a humic 

 solution, but simply to moisture, which is tenaciously retained by the chlorids of 

 calcium and magnesium impregnating the land, thus contrasting strongly with the 

 gray tint of the general dry soil. 



