CHAPTER XXH 



ALKALI LANDS AND THEIR RECLAMATION 



ALKALI lands are found in all regions of deficient rainfall. They 

 usually occur where the rainfall is less than 20 inches, but in India 

 alkali lands exist even with a rainfall of 28 inches. The effective- 

 ness of rainfall in removing alkali depends upon its character. If 

 the rainfall comes in very heavy showers, as is the case in India, 

 much will run off the surface without entering the soil, and hence 

 will do little toward removing the alkali. A small rainfall coming 

 as gentle showers so that it will enter the soil will he more effective. 



The effect, too, of the rainfall depends somewhat upon the char- 

 acter of the soil. Rainfall will penetrate a loose, sandy loam soil 

 much more readily than a clay. Hence, under the same rainfall a 

 clay soil or a clay loam soil may contain alkali, while the sandy loam 

 or sand would he free fron^ it. The amount of evaporation, too, 

 plays a somewhat important part in the amount present. Under 

 conditions of great evaporation the alkali may be brought to the sur- 

 face, while with less evaporation, as in a more northern climate, the 

 alkali would not be troublesome at all. 



Alkali does not usually occur in hill lands, although in small 

 level valleys among hills alkali may be found in considerable 

 amounts. It occurs abundantly in level uplands if the drainage is 

 in any way interfered with. Alluvial lands frequently contain 

 alkali, due to seepage from the upland and also from the water of 

 the stream. 



The Origin of Alkali. In the decomposition of rocks and the 

 further decomposition of soil material, many soluble substances are 

 formed which may not be leached out by the small rainfall of the 

 region but may be brought to the surface by capillary movement. 

 Many of the stratified rocks contained much salt, due to the fact 

 that they were formed in salt or brackish waters. When these be- 

 came dry land the salt was leached out later and carried into" tem- 

 porary lakes. This accumulation continued and ultimately the 

 lake became dry and a deposit of alkali was left (Fig. 127). Salt 

 springs sometimes occur, the waters of which carry considerable 

 amounts of alkali into depressions, where they may accumulate in 

 large quantities. Whatever the 'source of the alkali, its existence 

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