66 SOILS 



other parts of the West, are large areas of alkali 

 soils. They are found almost entirely in arid or 

 semi-arid regions. These soils produce an insignifi- 

 cant growth of a few native plants and are wholly 

 unfit for cropping until properly treated. They are 

 called alkali soils because they contain large 

 quantities of various salts, mostly common salt and 

 carbonate of soda, which is ordinary washing soda. 

 Otherwise they are normal. Thousands of acres of 

 once valuable land have been made too alkaline for 

 crops by seepage waters. The surface of alkali soils 

 is often covered with crystals of the salts, making it 

 look whitish. This is caused by the evaporation 

 of water from the soil, leaving behind on the sur- 

 face the salt that was dissolved in it. Over-irri- 

 gation, especially on heavy lands, often makes them 

 alkaline and may ruin them. But all soils that are 

 white on the surface are not alkali. Excellent 

 limestone soils have sometimes been mistaken for 

 alkali, because they had a coating of carbonate of 

 lime on the surface. Quite frequently there are 

 alkali spots in an otherwise fertile field, the spots 

 varying from several feet to several acres in extent. 



There are two common types of alkali soils, 

 "black alkali'* and "white alkali." The former 

 contains chiefly carbonate of soda, which de- 

 composes the humus in the soil and makes it very 

 black; while the latter is a mixture of several salts, 

 chiefly common salt and sulphate of soda. Black 

 alkali is much more injurious to plants than white. 



The effect of alkali upon plants depends chiefly 

 upon the kind of plant and upon the amount of 

 salt in the first foot or two of soil. Some plants 

 cannot stand alkali at all, some are tolerant of it, 

 a very few prefer it. The plants that tolerate it 

 are mostly native salt busnes and grasses. Of 



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