ALKALI LANDS 213 



the downward passage of water, is not unfrequently a further 

 condition determining the formation of an alkaline soil. 



On land moderately affected by alkali it is possible to 

 start the growth of crops at the close of the wet season, 

 and the crop at first grows with great luxuriance ; but as 

 summer advances saline matter accumulates at the surface, 

 and the crop withers, or yields but a stunted produce. Cereal 

 crops are particularly liable to injury. When the amount 

 of alkali is still greater, the seed sown will rot instead of 

 germinating. In the worst cases, even the natural weeds 

 cease to grow, and the land becomes bare. A white crust 

 or efflorescence of salts is seen upon the surface of the land 

 in summer time. In many cases also circular depressions 

 appear, destitute of plant growth, and characterized by a 

 blackish colour. 



Cases may now and then occur in which the source of 

 the alkali salts can be traced to some saline formation in 

 the neighbourhood, from which they have been transported 

 to the soil affected ; but in the majority of cases the salts 

 found in the soil have been derived from the soil and rain 

 alone. The salts, in fact, result from the accumulation in 

 the soil of the products of its own decomposition, plus the 

 saline matters brought by rain. Alkali lands are thus the 

 natural result of an arid climate, in which the rainfall is 

 insufficient to remove the annual production of soluble salts 

 in the soil. The formation of alkali land is of course how- 

 ever much favoured when, as in the case of the Yellowstone 

 Valley in Montana (Soils, Bulletin 14), the rocks of the 

 district, even in their undecomposed condition, contain much 

 gypsum and soluble salts of sodium and magnesium. 



The soluble salts occurring in alkali lands are very various. 



