44 SOILS AND FERTILIZERS 



current of electricity is undoubtedly physiological 

 rather than chemical, unless it be in the slighty favor- 

 able influence which it exerts upon nitrification. The 

 electrical conductivity of soils has been taken by Whit- 

 ney as the basis for the determination of moisture ; I9 

 the conductivity of a soil, however, is dependent 

 largely upon the nature and amount of dissolved salts. 



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 

 soil, because two soils from the same locality frequently 

 have the same general physical composition and still 

 have entirely different crop-producing powers, due to 

 differences in chemical composition and amounts of 

 available plant food. 



Attempts have been made to over-estimate the value 

 of the physical properties of soils and to explain nearly 

 all soil phenomena on the basis of soil physics. Im- 

 portant as are the physical properties of a soil, it can- 

 not be said that they are of more importance than the 

 chemical or other properties. In fact the four sciences, 

 chemistry, physics, geology, and bacteriology, are all 

 closely connected and each contributes its part to our 

 knowledge of soils. 



