12 



OKOGRAPIIICAL DISTRIBUTION 



back into the Nile, and the crops are planted in the mud 

 without plowing. By this system only one crop is grown 

 each year, but the accumulation of alkali is prevented by 

 washing part of it to lower depths in the soil, by depositing 

 a fresh layer of salt-free silt on the surface, and by carrying 

 away with the water that is drained off any soluble material 

 that may have accumulated on the surface at the time of 

 flooding. 



In order to raise more than one crop a year and thereby 

 get greater profit from the land, the basin system of irri- 

 gation is being largely supplanted by the perennial system, 

 by means of which water is applied throughout the year. 

 This brings about almost continuous evaporation from the 

 surface and a consequent accumulation of soluble salts. 

 Of the 6,250,000 acres of irrigable land in Egypt, only 

 about 1,730,000 acres are irrigated by the old system of 

 basin irrigation. This means that the alkali problem 

 w r ill continue to be more acute in Egypt until suitable means 

 of coping with it are w r orked out. Already some rather 

 ingenious methods (23, 25) of drainage are in operation. 



The following analysis reported by Means (14) of an 

 alkali soil from Kom-el-Akhdar is typical of the alkali 

 land of lower Egypt: 



Table III. Chemical Analysis of Alkali Soil from Kom-el- 

 Akhdar, Egypt (Surface foot) 



Ions 



Calcium (Ca) 



Magnesium (Mg) 



Sodium (Na) 



Potassium (K) 



Sulphuric Acid (S0 4 ) .... 



Chlorine (CI) 



Bicarbonate Acid (HCO3) 



Conventional Combinations 



Calcium Sulphate (CaS0 4 ) .... 

 Magnesium Sulphate (MgS0 4 ) 

 Potassium Chloride (KC1) .... 



Sodium Chloride (NaCl) 



Sodium Bicarbonate (NaHC0 3 ) 



Sodium Sulphate (Na^SC^) .... 



Per cent Soluble 



Percent 



IO.43 

 9.90 

 3.62 



60.88 

 1. 41 



13.76 



..2 



