SOIL ACIDITY 349 



tration of calcium ions was provided. This relationship, 

 spoken of as synergism, may be seriously interfered with by 

 so-called soil acidity. 



187. The present status of the question. — Each of the 

 general hypotheses which have been advanced to explain the 

 detrimental influence of soil acidity has considerable plausible 

 evidence in its support. Cane-sugar, which is inverted only 

 in the presence of an acid, was found by Rice and Osugi * to 

 be inverted in soils, even when the water extracts from these 

 same soils were neutral or even alkaline. This seemed to indi- 

 cate that the acidity was actual and was inherent with the soil 

 mass rather than with the soil solution. This would also sug- 

 gest the presence of insoluble or absorbed acids that might be 

 liberated by hydrolysis, thus producing a harmful hydrogen 

 ion concentration. Other equally valuable data are available 

 on this phase of soil acidity. The work of Hartwell and Pem- 

 ber 2 and of Mirasol, 3 however, is even more conclusive in re- 

 gard to aluminum as a toxic agent, especially as they studied 

 the problem from the plant standpoint. 



Conner, 4 investigating the comparative influence of sulfuric 

 acid and aluminum sulfate on plants, has obtained some in- 

 teresting data corroborating the work of Hartwell and Pember. 

 By comparing a given hydrogen ion concentration with the 

 same hydrogen ion concentrations plus equivalent amounts of 

 aluminum ions, he was able to demonstrate the greater toxicity 

 of aluminum to barley and rye in water culture. Since soluble 

 aluminum so often accompanies an unfavorable hydrogen ion 



1 Eice, F. E., and Osugi, S., The Inversion of Cane Sugar by Soils 

 and Allied Substances and the Nature of Soil Acidity; Soil Sci., 

 Vol. V, No. 5, pp. 333-358, 1918. 



3 Hartwell, B. L., and Pember, F. E., The Presence of Aluminum 

 as a Reason for the Difference in the Effect of So-called Acid Soil on 

 Barley and Bye; Soil Sci., Vol. VI, No. 4, pp. 259-277, 1918. 



3 Mirasol, J. J., Aluminum as a Factor in Soil Acidity; Soil Sci., 

 Vol. X, No. 3, pp. 153-193, 1920. 



* Conner, S. D., Liming in Its Belation to Injurious Inorganic Com- 

 pounds in the Soil; Jour. Amer. Soc. Agron., Vol. 13, No. 3, pp. 113- 

 124, 1921. 



