36 CHAPTER III 



BEAK SOILS. 



The two great factors withholding from cultivation 

 millions of acres of land in arid and semi-arid parts of the globe 

 are drought and brak ; and even if the drought factor is elimin- 

 ated by irrigation, the presence of brak may still prevent suc- 

 cessful crop production. In fact, practical experience has 

 demonstrated time and again that the brak evil may be greatly 

 aggravated by irrigation, and in many cases brak salts appear 

 in the surface soil in harmful quantities only after the land has 

 been brought under irrigation. 



Brak is commonly known as " alkali " in America and 

 other countries. It refers to the presence of soluble salts in the 

 soil in sufficient concentration to injure plants, and may include 

 salts which in smaller concentration are decidedly beneficial to 

 plant growth, e.g., nitrate of soda. 



All arid soils are, of course, not necessarily affected with 

 brak, but arid conditions in general are favourable to the 

 accumulation of brak salts, whereas humid conditions are not. 

 In the latter case abundant rainfall, coupled with natural drain- 

 age, will effectively prevent any harmful accumulation of 

 soluble salts. 



Arid and semi-arid conditions prevail over a great part of 

 South Africa, and brak is very commonly present in the soils 

 of these areas. Furthermore, irrigation is playing an ever- 

 increasingly important part in South African agriculture, so 

 that the brak problem demands, and must receive, particular 

 attention in this country. 



Frequently the concentration of brak salts in the surface 

 soil is not as yet sufficient to injure crops, but unless proper 

 precautions are observed, the almost invariable natural tendency 

 is for the concentration to increase. 



Crops vary greatly in their tolerance for brak soils, so that 

 concentrations which are decidedly injurious to certain crops 

 may have no harmful effect upon others. There is, however, 

 a limit to the amount of brak which can be tolerated by any 

 crop, and occasionally the concentration is so high that the 

 growth of ordinary farm crops is impossible. The natural 

 vegetation of such lands is generally confined to plants useless 

 to man, known commonly as " saline vegetation." Notable 

 exceptions occur, however, as instanced by much of the Karroo 

 vegetation which forms valuable pasture, and by Australian salt 

 bushes, which are readily eaten by all kinds of stock. In 



