SOIL MANAGEMENT. 37 



extreme cases brak lands are wholly destitute of vegetation, or 

 bear only such saline growth as is rejected by all domestic 

 animals. 



Keclamation of land badly affected with brak is very costly, 

 and frequently not worth attempting, save in the case of excep- 

 tionally valuable land ; but if the brak tendency is recognised 

 while the concentration is still small and comparatively 

 innocuous, the adoption of simple precautionary measures may 

 prevent further accumulation and maintain the crop producing 

 power of the land indefinitely. 



A noteworthy feature of brak soils is the fact that high 

 concentration of soluble salts generally coincides with richness 

 in plant food, so that these soils are characterised by high 

 potential fertility, which manifests itself in the good crop yields 

 following removal of the brak salts or their reduction to innocu- 

 ous concentration. 



Nature and Composition of Brak. — In general brak may 

 consist of carbonates (or bicarbonates), chlorides, sulphates and 

 nitrates of sodium, potassium, calcium and magnesium, with 

 the following reservations : — 



(1) Sodium salts are almost invariably the chief constitu- 

 ents, particularly the carbonate (or bicarbonate), chloride and 

 sulphate. 



(2) The bicarbonate and sulphate of calcium are not suffi- 

 ciently soluble to be directly injurious. 



(3) The quantity of potash salts present is generally low, 

 forming as a rule from 5 to 20 per cent, of the total salts. 



(4) Sodium phosphate is fairly frequently a constituent of 

 brak salts, though never present in large quantities. It may 

 form up to about 4 per cent, of the total salts present. 



Two general types of brak are recognised, the " black " 

 and the " white " varieties. 



Black Brak is characterised by the presence of sodium 

 carbonate (or bicarbonate) in considerable quantity. This sub- 

 stance has a solvent effect upon soil humus, thus imparting a 

 dark colour to the soil solution and any incrustation that may 

 appear on the surface of the soil. As a rule there are also pre- 

 sent more or less sodium chloride and sulphate, a little sodium 

 phosphate (due to the solvent effect of sodium carbonate upon 

 insoluble phosphates in the soil), and probably small amounts 

 of potash salts, but no sulphates or chlorides of calcium or 

 magnesium, and very little or not nitrates of any description. 



White Brak consists essentially of chloride and sulphate 



