9 

 CHAPTER XVI 



ALKALI AND SEEPAGE PROBLEMS 



In previous pages passing reference has already 

 been made to the alkali and seepage problems, 

 which comprise two of the greatest difficulties that 

 the irrigationist has to contend with. Seepage 

 troubles are caused by the concentration of drainage 

 waters in excess of plant requirements at places 

 where there is defective under-drainage ; while, the 

 alkali problem is due to the rising of alkalies or salts 

 injurious to plant life to the surface layers of the 

 soil. 



SALTS INJURIOUS TO VEGETABLE LIFE. 



Of the various chemical compounds contained 

 in the soil, the salts of chlorine, sodium, and mag- 

 nesium are usually the ones that cause injury to 

 plant life if present in any quantity. 



Of these, according to American experience, 

 sodium carbonate is the most injurious to vegeta- 

 tion, and less than 0.1 per cent, in the soil is detri- 

 mental to plant life. Fortunately this compound 

 has not, so far, been met with in excess on 

 Australian irrigation areas, and the salts that have 

 done the most damage are sodium chloride (com- 

 mon salt), sodium sulphate (Glauber's salt), and 

 magnesium sulphate (Epsom salts). 



ORIGIN OF SALTS IN SOIL. 



It is a widely accepted theory of science that 

 many if not all of the soluble salts found in soils, 

 rivers, lakes, and in sea water have in the course of 



