PEOCEEDINGS OF 



THE ROYAL SOCIETY. 



Section B. — Biological Sciences. 



The Effect of Plant Growth and of Manures upon the Retention 



of Bases by the Soil. 

 By A. D. Hall, M.A., and K H. J. Miller, PhD. 



(Communicated by H. E. Armstrong, LL.D., Ph.D., F.KS. (From the Lawes 

 Agricultural Trust.) Eeceived March 30— Read May 11, 1905.) 



Introductory. 



The following investigation deals with the changes in the amount of calcium 

 carbonate, the chief substance in the soil acting as a base, which are brought 

 about by natural agencies, by manuring, and particularly by the growth of 

 plants. 



Since Cavendish discovered that calcium carbonate dissolves in water 

 charged with carbon dioxide, and ascertained the presence of calcium bicar- 

 bonate in many natural waters, it has been recognised that the calcium 

 carbonate present in most soils must be subject to regular loss. The air 

 enclosed in the soil contains a considerable proportion of carbon dioxide 

 derived from the roots of plants and decaying organic matter (Wollny, for 

 example, found amounts varying from 3 to 14 per cent, by volume), and the 

 soil water, after attaining a state of equilibrium with the gas at this partial 

 pressure, becomes an effective solvent of any calcium carbonate that may be 

 present, removing it as bicarbonate into the drains or the general stock of 

 underground water. That such dissolution does take place in the upper 

 layers of the soil is evident from the analyses made by A. Voelcker* and 



* ' Journ. Chem. Soc.,' 1871, p. 276. 



VOL. LXXVIL — B. 



B 



