344 MISCELLANEOUS FARM SUBJECTS 



bonates of lime and magnesia and the sulphate of lime (gypsum, 

 or land plaster). 



It seldom, if ever, happens that only one kind of salt is pres- 

 ent. Alkali is almost always a mixture of several salts, the kinds 

 and the proportions in which they are mixed differing in different 

 localities. But often some one salt forms the bulk of the alkali, 

 and hence we can speak of sulphate alkali where Glauber's salt 

 and other sulphates are the chief ingredients, of chloride alkali 

 where common salt is the most abundant, and of "black alkali" 

 where a considerable quantity of sodium carbonate occurs. 



In many irrigated districts, especially in those situated east 

 of the Rocky Mountains, Glauber's salt (sodium sulphate) forms 

 the bulk of the alkali. But in some of the largest areas of alkali 

 land in the United States common salt (sodium cholorid) is the 

 most abundant compound present. Considerable quantities of so- 

 dium bicarbonate are often associated with both the sulphate and the 

 chlorid types. The areas where black alkali (sodium carbonate) pre- 

 dominates are much more restricted. 



The harmfulness of alkali depends upon the quantity as well aa 

 the kind of salts present. The alkali content of a soil is usually ex- 

 pressed in percentages of its total dry weight. Thus, if 100 pounds 

 of dry soil contains 1 pound of salts that are easily soluble in water, 

 its alkali content is said to be 1 per cent. As a rule, if the soil con- 

 tains more than one-half of 1 per cent of white-alkali salts, only de- 

 cidedly resistant plants can be grown. 



The sulphates, chlorids, and bicarbonates, collectively known as 

 white alkali, are much more abundant in most localities than the 

 carbonates, or black alkali. Black alkali, which can usually be recog- 

 nized by the dark color it imparts to the surface soil and to standing, 

 water, is far more injurious to plants than the white-alkali salts. 

 It is a strong corrosive, causing the decay of plant tissues. Trees 

 growing in black-alkali land are sometimes completely girdled at the 

 crown through the corrosive action of the sodium carbonate. This 

 salt also has a bad effect upon the texture of heavy soils, causing them 

 to become puddled. 



Where the soil contains considerable black alkali it is useless to 

 attempt to grow crops until this condition is remedied. If gypsum, 

 or land plaster, can be obtained at a reasonable cost, and the value 

 of the land warrants its use, the black alkali can often be converted 

 to less harmful salts by successive applications of this fertilizer. The 

 effect of the gypsum is to neutralize chemically the black alkali. 

 This results in loosening the soil, making it easier for water to pene- 

 trate, and aiding the washing down of the other salts. The presence 

 of more than one-tenth of 1 per cent of sodium carbonate is injurious 

 to the growth of practically all crop plants. For most species one- 

 twentieth of 1 per cent (0.05 per cent) of this extremely noxious salt 

 is too much for good crop production. 



The white-alkali salts are not corrosive, but when freely taken 

 up into the cells of the plant they cause serious disturbances in its 

 nutrition. If present in the soil in sufficient quantity, these salts also 



