ALKALI PROBLEM IN IRRIGATION — SGOFIELD. 223 



that continued prosperity has been due to the quality of the water 

 supply. The water of the Nile is probably lower in salt content than 

 any other used extensively for irrigation. This water carries dur- 

 ing the flood season less than 150 parts per million of dissolved 

 salts, and about 75 per cent of these salts are compounds of calcium 

 and magnesium. Furthermore, the ancient system of irrigation, 

 which has been gradually replaced during the last half century, 

 was one in which it was absolutely essential to have an adequate 

 drainage system through which to draw off the water from the 

 flooded basins. As a result there was only a short period each year 

 when the flood waters percolated into the subsoil. With perennial 

 irrigation the subsoil has gradually become filled with water and 

 its relief calls for a much more comprehensive and expensive type 

 of drainage. 



In some of our own irrigation enterprises there exists a very dif- 

 ferent set of conditions. Some of our important irrigation streams 

 carry more than 1,000 parts per million of dissolved salts, of which 

 more than half are compounds of sodium. Too often irrigation has 

 been undertaken without making any provision for drainage until 

 the need for drainage became painfully apparent. In other situa- 

 tions where the water supply has been inadequate, or where it has 

 been necessary to lift it for long distances to reach suitable lands, it 

 has been used so sparingly that all the water applied has been used 

 by crop plants or evaporated from the soil surface. Under such 

 conditions it is inevitable that the salts carried to the land by the 

 water must remain in the upper layers of the soil and finally reach 

 concentrations that become toxic to the plants or by reacting with 

 the soil produce a condition of impermeability. 



There is no sound reason for doubting that irrigation farming 

 can be made as safe and as permanent as any other kind of farm- 

 ing if the essential conditions are complied with. In attempting to 

 understand these conditions we may learn some useful lessons from 

 the history of ancient irrigation enterprises as well as from the care- 

 ful observation of the tendencies in more recent projects. There can 

 be little doubt that the same fundamental laws of physics and 

 chemistry that are operating now have been operating during ages 

 long past. When the balance of salts in the irrigation water has 

 been such that the permeability of the soil has been impaired by 

 its use, the accumulation of salts has in time made crop production 

 impossible. Such results have occurred in the past and are taking 

 place at present. 



While the alkali problem presents many difficulties and complica- 

 tions it is by no means insurmountable. Experience and scientific 

 investigation are both contributing the knowledge with which the 

 problem may be solved. 



