Soils 67 



Any soluble salt present in sufficient quantities may be 

 considered an alkali. The salts most commonly causing 

 injury are sodium chloride, or common salt ; sodium sul- 

 fate, or Glauber's salt ; sodium carbonate, or salsoda ; 

 and magnesium sulfate, or epsom salt. In addition 

 to these, sodium nitrate and a number of other salts 

 cause injiu"y in some districts. Sodium chloride is 

 injurious to beets when present in lower concentra- 

 tions than any of the other salts mentioned ; sodium 

 carbonate, or black alkali, injures the soil when present 

 in low concentrations by dissolving the organic matter and 

 causing a hard crust to form. Beets will grow in rela- 

 tively large quantities of the sulfates. 



The injury done to crops by alkali salts results largely 

 from the shutting off of water from the plant on account 

 of the soil solution's having a greater concentration than 

 the plant-cells. By the law of osmosis, water passes 

 from the dilute to the more concentrated solution. In a 

 normal soil the root has a cell-sap with a higher concen- 

 tration than the soil solution ; hence water passes from the 

 soil into the plant. When the soil solution is made too 

 concentrated, water passes out of the roots into the soil 

 and the plant dies. 



The permanent reclamation of alkali lands rests on the 

 removal of the excessive salts by drainage. The methods 

 of accomplishing this are discussed in Chapter X. Where 

 the accumulation of alkali results from the over-irriga- 

 tion of higher lands, the remedy is obviously the preven- 

 tion of percolating water, which carries soluble salts from 

 the higher and concentrates them in lower lands. Any 

 practice that reduces evaporation, such as cultivation, 



