3O THE SOII, SOLUTION 



some investigators 1 it would appear that the addition of soluble 

 fertilizer salts by causing a lowering of the vapor pressure of 

 the water induces a distillation to that region from other regions 

 of the soil as well as from the atmosphere above. This brings up 

 the problem of the diffusion of water and other vapors through 

 the soil. It has been shown that the soil "plug" retards the 

 rate at which diffusion takes place but induces no other effect 

 in the ordinary phenomenon of free diffusion. This fact is 

 obviously of the first importance in the theory of mulches, but 

 requires no further consideration here. 2 



1 Sur la diffusion des engrais salins dans le terre, par Mtmtz et 

 Gaudechon, Comptes rendus, 148, 253-258 (1909). 



1 See, Contribution to our knowledge of the aeration of soils, and 

 Studies of the movement of soil moisture, by Edgar Buckingham, Bulls. 

 Nos. 25, 1904, and 33, 1907, Bureau of Soils, U. S. Dept. of Agriculture. 



