52 SOILS AND FERTILIZERS 



tion. The organic matter of the soil is the principal 

 agent in the physical absorption of gases ; peat has the 

 power of absorbing large amounts. This action is sim- 

 ilar to that of a charcoal filter in removing noxious 

 gases from water. 



51. Relation of Soils to Electricity. There is always 

 a certain amount of electricity in both the soil and the 

 air. The part which it takes in plant growth is not 

 well understood. The action of a strong current upon 

 the soil undoubtedly results in a change in chemical 

 composition, but in order to change the composition of 

 the soil so as to render the unavailable plant food 

 available, a current destructive to vegetation would be 

 required. When plants are subjected to too strong a 

 current of electricity, they wilt and have all of the after- 

 effects of frost. A feeble current has either an indif- 

 ferent or a slightly beneficial effect upon crop growth, 

 but not sufficient to warrant its use in general crop 

 production on account of cost, and it is undoubtedly 

 physiological rather than chemical in its action unless 

 it be in the favorable influence exerted upon nitrifica- 

 tion. The electrical conductivity of soils has been taken 

 by Whitney as the basis for the determination of mois- 

 ture. 19 It is, however, dependent largely upon the nature 

 and amount of dissolved salts. 



52. Importance of the Physical Study of Soils. A 

 study of the physical properties of soils gives much val- 



