2go CAUSES OF FERTILITY AND STERILITY [chap. 



1,000,000 acres of this region, now swamp, or salt 

 marsh, or otherwise uncultivable, which in ancient 

 times were the garden of Egypt." 



It has been the business of the English irrigation 

 officers since the occupation to restore and improve 

 the drainage system, and to begin the reclamation of 

 the salted areas by cutting drainage canals and passing 

 enough of the abundant winter flood water through 

 the soil to wash out the salts into these drains. 



Hilgard in California has also indicated that it is 

 impossible to wash the salts from the soil, even by 

 leaving the water to stand upon the surface for some 

 time, unless provision is made to remove the salted 

 water by underdrainage. In the case of black alkali 

 however, the soil has become too impervious to 

 allow water to percolate at all ; the first remedial 

 measure is to incorporate considerable quantities of 

 gypsum with the soil; this will interact with the 

 sodium carbonate, producing sodium sulphate and 

 calcium carbonate, at the same time precipitating the 

 humus in a flocculent form. If now underdrainage be 

 brought into practice the soluble salts can be washed 

 through, and a very fertile soil results, owing to the 

 presence of the finely divided humus and calcium car- 

 bonate. Where underdrainage is hardly practicable 

 because of the expense, irrigation water should be 

 used in as limited amounts as possible, and every 

 care should be taken to keep the surface tilled and 

 under crop, so as to minimise evaporation from the 

 bare ground. In humid countries like our own, 

 damage due to the accumulation of salts are rare ; 

 the author has, however, seen one case where the 

 vegetation of a lawn was destroyed during a hot dry 

 spell of weather by continuously applying water in 

 quantities which never washed down into the subsoil, 



