ALKALI LANDS 215 



According to his experiments, communicated to the American 

 Society for the Promotion of Agricultural Science in August, 

 1888, no reaction takes place between these salts unless 

 carbonic acid is also present *. The sodium carbonate is 

 usually most abundant in heavy soils, and in low moist 

 localities. 



The origin of the sulphates is attributed to the oxidation 

 of pyrites, or by some writers to the occurrence of gypsum in 

 the original rock. The possible accumulation of the sulphates 

 supplied by rain water does not seem to have been con- 

 sidered. 



The three sodium salts forming the principal constituents 

 of the soluble matter in alkali soils can hardly be reckoned 

 as plant foods, even under circumstances thoroughly favour- 

 able to the growth of plants. With these, however, there is 

 always associated some salts of potassium, some nitrates, and 

 not unfrequently soluble alkali phosphates. Alkali lands are 

 thus, generally speaking, exceedingly rich in soluble plant 

 food, and display a high degree of fertility when the special 

 hindrances to plant growth are removed. According to 

 Hilgard, potassium salts amount to 3-10 per cent, of the 

 total salts extracted by washing from the alkali soils of 



1 This question requires to be further elucidated. We shall see presently 

 that a reverse action readily occurs, and that gypsum is applied with great 

 advantage to land contaminated with sodium carbonate, and without difficulty 

 converts the carbonate into the far less injurious sodium sulphate. Are we 

 to assume that the result of the reaction in question is determined by mass ; 

 and that when calcium carbonate preponderates sodium carbonate is formed, 

 while when calcium sulphate preponderates the reaction is reversed ? If this 

 is so, the quantity of gypsum which must be applied to a soil to effect the 

 permanent removal of sodium carbonate will be found much larger than is 

 at present supposed. The removal from the sphere of the reaction of any one 

 of the products would suffice to determine a continuance of the course of 

 change in the same direction. 



