278 DRY FARMING 



Black alkali is characterized by the presence of 

 sodium carbonate (sal soda, washing soda) although this 

 compound is almost always associated with one or more 

 of the chlorides and sulphates mentioned in the preced- 

 ing paragraph. Sodium carbonate is, as is well known, 

 white, but from the fact that it acts upon and dissolves 

 the decayed vegetable matter (humus) of the soil the 

 incrustation is tinged dark brown or black — hence the 

 name. "Water standing in pools on soils impregnated 

 with the carbonate is invariably of a darker color and 

 much resembles a strong infusion of coffee. 



232. Why Alkali is Harmful. — It is thought that the 

 harmful effects of alkali result from one or more of four 

 different actions: (1) the destruction of soil tilth, (2) 

 the corrosive effect of those alkalies containing sodium 

 carbonate, (3) the withdrawal of moisture from th? 

 plant cells by osmosis, and (4) the toxic effect of some 

 of the salts, 



233. The Reclamation of Alkali Soils. — In the dry lands 

 where alkali spots are found the chief means to im- 

 prove them are: (1) the application of manure, (2) 

 surface drainage, (3) thorough tillage to lessen evapora- 

 tion and (4) the use of grass crops where the alkali is 

 bad or the spots too numerous or too large to attempt to 

 reclaim. Manure improves the tilth and thus aids crops 

 to establish themselves. Surface drainage removes the 

 water carrying the alkali in solution and thus prevents 

 a further accumulation of salts. 



Thorough tillage aids in lessening evaporation and the 

 consequent rise of alkali with the water as the latter 

 comes to the surface. Manure also aids in lessening 

 evaporation. Thorough tillage and manure, by helping 

 to keep the soil filled with water, help also to wash the 



