THE COMPOSITION OF THE SOIL 125 



from the subsoil, on the other hand, the amount of calcium 

 showed less variation, except only for a rise at midsummer. 

 There was evidence of a transportation of calcium and 

 potassium from the subsoil to the surface during a prolonged 

 period of drought. No indication was obtained, however, 

 that soil adsorption exercised any regulating effect on the 

 concentration of the soil solution ; an exchange of bases took 

 place only when the proportions between the dissolved sub- 

 stances were altered. 



In van Zyl's experiments (323) the concentration of the 

 solution obtained also varied according to manurial treatment 

 and season of the year, but the percentage composition of the 

 ignited dry matter of the extract remained constant ; this 

 being the reverse of what Ramann obtained. 



A steel plunger was used by C. B. Lipman. 1 



An absorption method used by Briggs and McCall consists 

 in driving a Pasteur Chamberland filter into the soil and con- 

 necting it with an exhausted 2-litre bottle. 2 



A totally different method is adopted by Bouyoucos who 

 studies the changes in the soil solution in situ by determining 

 the changes in the freezing-point (49^). He finds the osmotic 

 pressure varies between 0*2 to I atmospheres in moist soils, 

 and 4'5 to 16*5 at low percentages of moisture. The con- 

 centration of the extracted solution was 0*04 to 0*18 per cent, 

 in moist soils and O'Q to 3 -o per cent, in drier soils. 



Some of his results are given in Table XXXVI. 



Hoagland and Sharp (136^) have applied the method to- 

 Californian soils with interesting results. 3 They find no evi- 

 dence that the soil water is a saturated solution : on the con- 

 trary, it appears to be dilute, probably containing less total 

 dissolved matter than the soil extract, and it varies in con- 

 centration with the conditions : in their experiments the range 



1 Univ. California Pubn. Ag. Sci., 1918, 3, 131. 



2 L. J. Briggs and J. R. McCall, " An Artificial Root," Science, 1904, 20, 

 566-569; Bull. 31, Bureau of Soils, 1901. 



3 For further results see J. C. Martin and A. W. Christie, Journ. Ag. Res.,. 

 1919, 18, 139. 



