196 THE LURE OP THE LAND 



chlorid. Its presence in very small quantity is suf- 

 ficient to prevent vegetation. 



TREATMENT OF BLACK ALKALI. 



This black alkali has been very successfully treated 

 by Hilgard by the application of gypsum which react- 

 ing with the sodium carbonate produces calcium car- 

 bonate and sodium sulfate, thus converting the black 

 into the white alkali and adding an ingredient in the 

 shape of lime carbonate to stiff soils which tends to 

 make them more pulverulent and easy of tillage. 



This method of treatment, however, as can be easily 

 seen, is only palliative, the whole amount of the alka- 

 line substances being still left in the soil, only in a less 

 injurious form. 



The only perfect remedy for alkaline soils, as has 

 been pointed out by Hilgard, is in the introduction of 

 underdrainage in connection with irrigation. The 

 partial irrigation of alkaline soils, affording enough 

 moisture to carry the alkali down to and perhaps par- 

 tially through the subsoil, can produce only a tempo- 

 rary alleviation of the difficulties produced by the alkali. 

 Subsequent evaporation may indeed increase the amount 

 of surface incrustation. For this reason in many cases 

 the practice of irrigation without underdrainage may 

 completely ruin an otherwise fertile soil by slowly in- 

 creasing the amount of alkali therein by the total amount 

 of the alkaline material added in the waters of irriga- 

 tion and brought to the surface by the evaporation of 

 the temporarily deeper percolation of the water. 



As Hilgard has pointed out, if a soil can be practically 

 freed from alkali by underdrainage connected with a 

 thorough saturation by irrigation, it may be centuries 

 before the alkali will accumulate in that soil again 



