COLOR OF SOILS 47 



45. 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 cur- 

 rent upon the soil undoubtedly results in a change in 

 chemical composition; a feeble current has either an 

 indifferent or a slightly beneficial effect upon crop 

 growth. In order to change the composition of the 

 soil so as to render the unavailable plant food available, 

 would require a current destructive to vegetation. 

 When plants are subjected to too strong a current of 

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

 ance of frost. The slightly beneficial action upon 

 plant growth is not sufficient to warrant its use as yet 

 in general crop production on account of cost. The 

 action of a weak current of electricity upon plants is 

 undoubtedly physiological rather than chemical, unless 

 it be in the slightly favorable influence which it exerts 

 upon nitrification. The resistance which soils, when 

 wet, offer to electricity has been taken by Whitney as 

 the basis for the determination of moisture in soils. 18 



46. Importance of the Physical Study of Soils. — 



From what has been said regarding the physical prop- 

 erties of soils it is evident that such a study will give 

 much valuable information regarding their probable 

 agricultural value. While the physical properties 

 should always be taken into consideration, they should 

 not form the sole basis for judging the character of a 



