70 



R. GREIG-SMITH. 



and nitrogenous substances go quicker into solution from 

 the dry than from the wet soil, as in the case of a soil 

 treated with a volatile disinfectant, but it is more likely 

 that the drying brings about an increased oxidation through 

 the water being displaced by air, some of which may be 

 adsorbed. This was brought forward by Fischer, 1 and 

 certainly the loss of activity upon moistening and storing 

 the soil appears to favour the idea. 



Konig, Hasenbaumen and Glenk 2 came to a different 

 conclusion. They found that all soils, with the exception 

 of clays, show a small but demonstrable increase of dialy- 

 sable materials when heated under diminished pressure. 

 They concluded that this results from an alteration of the 

 colloidal condition of the soil, which causes the adsorbed 

 materials to become soluble. Even air-drying of the soil, 

 under natural conditions, causes a partial destruction of 

 the colloidal state, and therefore an increase in the solu- 

 bility of the colloid-bound nutrients. They investigated 

 the crops grown upon various heated soils, and found that 

 the dry matter of the crops varied in the order of the 

 quantity of the dialysable substance of the soils. They 

 considered that this explained the value of repeated drying 

 and wetting in increasing plant growth. 



Buddin 3 showed that there was a certain relation 

 between the simple air-drying of soil and the treatment 

 with volatile disinfectants and with heat. It is possible 

 to trace a certain graduated intensity of effect between 

 disinfectants, from the strongest, such as formaldehyde, 

 through the more or less potent, down to the simple air- 

 drying of the soil in a thin layer. This suggests that the 

 alteration in the bacterial flora may be the chief reason for 

 the increased activity following the air-drying of the soil. 



1 Cent. Bakt. 2 te, 36, 346. 2 Ibid., 39, 184. 

 3 Journ. Agric. Sci., 6, 417. 



