FARMERS' INSTITUTES. 29' 



SOIL PHYSICS. 



PROF. J. A. JEFFERY, AGRICULTURAL COLLEGE. 



The chemist and the bacteriologist have each spoken to you of the 

 soil from his point of view. 



I have been asked to speak to 3011 on the same subject and to give you 

 a few thoughts from the standpoint of the soil physicist. 



Soil Physics has for its object, among other things, the study and 

 mastery of those conditions which shall promote chemical, physiological, 

 bacteriological changes. Its realm is largely within the soil. Here lie 

 humus and minerals waiting the magic touch which shall change them 

 into forms such as the plant may use. The soil may be ever so abund- 

 antly supplied with materials, but unless these transformations take 

 place they cannot be used and the husbandman's labors are in vain — 

 they bring him no profits. 



All appreciate, to some extent at least, the importance of water in 

 agriculture. We have observed that in its absence plants droop and 

 die, and that in its presence, in normal quantities, they revive and take 

 up again and accomplish the work for which they were created. We 

 hardly realize why this is so, but our observations confirm the state- 

 ment.^ The reason lies in the fact that only when moisture conditions 

 are proper can the chemical, physiological and other changes take place. 

 There must be present also air, and a proper temperature must be 

 maintained in order that these changes may be accomplished. If these 

 conditions fail in any particular this work is handicapped. 



The moisture, air and temperature conditions depend primarily upon 

 the physical condition of the soil, while the air and temperature con- 

 ditions depend very much upon the moisture conditions. 



The physical condition of the soil will depend largely upon the size 

 of the ultimate grains of which it is composed and upon the manner in 

 which these grains are combined into compound grains. Upon the size- 

 of the ultimate soil grain will depend the amount of total surface which 

 a soil will present to the action of roots and to the action of solvents; 

 upon the manner in which these ultimate grains are compounded, or 

 aggregated, will depend the openness of the soil, its air content, its 

 water holding capacity, and the ease with which roots may reach out 

 through it for food aiid moisture. It is the study of these features of 

 the soils, and methods for handling them, that presents to the soil 

 physicists the most important field of labor. 

 A few facts concerning soils may be of interest: 



Some of our clay soils are so fine that to count the grains in the 1-28 

 part of an ounce, counting at the rate of one grain per second, ten hours 

 per day, 313 days per year, would require 525 years to accomplish the 

 undertaking. 



If the grains of a cubic inch of this soil were laid in a line, grain 

 touching grain, that line would reach over 500 miles. 



The total surface of a cubic foot of this, soil would" measore about 

 seven acres. 



