ANTAGONISM BETWEEN ALKALI SALTS 113 



react readily with other salts and may form the relatively 

 insoluble carbonates. The well-known reaction Na 2 C0 3 

 + CaS0 4 = Na 2 S0 4 + CaC0 3 , or the conversion of black 

 alkali into white, is of the latter type of change. Black 

 alkali, however, is thought to remain practically in fairly 

 stable equilibrium where the soil has become so puddled 

 that air and carbon dioxide are largely excluded. Puddling 

 the soil apparently causes the conversion of sodium nitrate 

 into sodium carbonate where the conditions are favorable, 

 but this reaction is rapidly brought to an end because of 

 lack of sodium nitrate or the other agents under ordinary 

 conditions. 



Antagonism between Alkali Salts. - - In some of the early 

 work of Kearney and Cameron (5) it was noticed that 

 plants grown in solutions of single salts common in alkali 

 soils showed a much greater toxic effect for magnesium 

 sulphate and magnesium chloride than for the sodium salts 

 which ordinarily cause the greatest trouble on alkali land. 

 When there were two salts, especially where one was a 

 calcium salt, in the same solution, however, the toxic 

 effect was not the sum of the two separate toxicities but 

 was in some cases considerably less. This ameliorating 

 or antagonistic effect was shown differently for different 

 combinations of salts and for different concentrations of 

 the same combinations; but the greatest effect was for 

 combinations containing calcium and magnesium. The 

 antagonism between magnesium sulphate and calcium 

 sulphate was particularly strong and led to the belief that 

 a specific balance between calcium and magnesium must 

 exist for proper growth of plants despite the fact that in 

 soils such a relationship did not exist. Some of the 

 ameliorating effect, such as that where calcium chloride 

 and sodium carbonate were in the same solution, might 



