OVER-IRRIGATION AND ALKALI 387 



232. Use of saline water. Another source of alkali is 

 the use of water charged with large quantities of soluble 

 salts. As shown in Chapter V, all natural waters contain 

 certain quantities of dissolved substances. Only when the 

 proportion of such soluble salts is too large does there 

 appear to be any danger hi the use of such waters. In 

 fact, saline waters have usually been undervalued for 

 purposes of irrigation. 



Plants can tolerate large quantities of soluble salts hi 

 irrigation water providing they are of the right mixture. 

 Thus Kearney and Cameron found that seventy parts of 

 magnesium sulphate in 1,000,000 parts of water repre- 

 sented the highest concentration hi which plant-roots 

 could survive; yet, hi the presence of a concentrated 

 solution of calcium sulfate, 33,600 parts of magnesium 

 sulphate in 1,000,000 parts of water could be tolerated. 

 Gypsum and common salt are both antidotes for mag- 

 nesium sulfate; magnesium carbonate is an antidote for 

 sodium carbonate and sodium chloride, raising their limit 

 two to four times; lime is an antidote for magnesium and 

 sodium, hi the form of sulfates, carbonates or chlorides, 

 raising the limit of these dangerous salts hundreds of 

 times. Kearney found that the native irrigationists of 

 northern Africa raised successfully many of the ordinary 

 crops with water containing 8,000 parts of soluble salts 

 for each 1,000,000 parts of water. Hilgard, as a result 

 of his long life of experimentation on such subjects, holds 

 that from 1,200 to 1,700 parts of soluble matters hi each 

 1,000,000 parts of water represent the highest limit of 

 endurance for ordinary plants. This, however, is much 

 lower than that observed by Kearney hi northern Africa, 

 or observed by other students hi other parts of the world. 

 The concentration of water that may be used for irrigation 



