CHAPTER XVII 

 'ALKALI SOILS "■ 



It has already been shown that soils are acted on by a ^reat 

 variety of weathering agents which gradually render soluble 

 a portion of the most susceptible constituents. This soluble 

 material becomes a part of the soil solution and may come in 

 contact with the roots of any crop growing on the land. In 

 humid regions, where a large quantity of water percolates 

 through the soil, this soluble matter has little opportunity to 

 accumulate.^ In arid regions, however, where loss by drainage 

 is slight, these salts may often collect in large amounts. Dur- 

 ing periods of dry weather they are carried upward by the 

 capillary rise of the soil-water, while during periods of rain- 

 fall they may move downward again in proportion to the leach- 

 ing action. At one time the lower soil may contain consid- 

 erably more soluble salt than the upper ; at another time the 

 condition may be reversed, in which case the solution in con- 

 tact with roots may contain so much soluble matter that vege- 

 tation is injured or destroyed. This excess of soluble salts 

 usually has a marked alkaline reaction, but in any case it pro- 

 duces what is termed an alkali soil. 



Large areas of land in every continent carry soluble salts 

 to such an extent that alkali injury is either actual or poten- 



*For a complete and satisfactory treatise on alkali see Harris, P. S,, 

 Soil Alkali, New Yori:, 1920. 



^Peat soils in humid regions may sometimes contain high concentra- 

 tions of salts, commonly non-toxie, and lower concentrations of ex- 

 tremely toxic salts. 



Conner, S. D., Bsscess Soluble Salts in Eumid Soils; Jour. Amer. Soc. 

 Agron., Vol. 9, No. 6, pp. 297-301, 1917. 



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