ESSAY, 



ON THE PHYSICAL PROPERTIES OF SOILS AS AFFECTING FERTILITY. 



BY SAMUEL W. JOHNSON, 



Professor of j^nalytical and Agricultural Chemistry in Yale College, and Che- 

 mist to the State xlgricultural Society of Connecticut. 



The fertility of a soil depends upon no one cause or class of 

 causes. The farmer who is acquainted with the results of gene- 

 rations of agricultural experience but who has not mastered the 

 principles of science; the chemist who regards only the revela- 

 tions of his reagents ; the geologist who merely traces the soil to 

 its original rock; the physicist who sees in it only a theater for 

 the play of mechanical forces — can each suggest some of the 

 conditions of fertility, and can account for the productiveness of 

 this and the barrenness of that soil; but none of them can give 

 accurate rules universally applicable to the valuation or improve- 

 ment of soils in general. There is hardly another subject of such 

 wide connection and extent. It involves the whole range of the 

 physical sciences; Geology, Chemistry, Botany, Physiology, Meteo- 

 rology, Mechanics, Hydrodynamics, the sciences of heat, light and 

 electricity, all are intimately related to it. That labors to illus- 

 trate such a topic should have only recently met with any degree of 

 success is not strange; neither are we to wonder that our present 

 knowledge of it is very limited, or that the opinions of those best 

 (jualifu'd to judge upon it, are divided. 



Tlie function of the soil is two-fold, first to serve as the station 

 or home of the plant, and second, to supply it with food. 



]n nature these two offices are not by any means separable. 

 The same materials that form the bed in which the })lant prefera- 

 bly fixes itself, in which it extends its roots most naturally, and 

 developes itself most healtht'ully, also contribute food to its 

 growth. 



The study of the physical characters of soils involves the 

 investigation of the first of these functions, that of their chemical 



