64 



An idea of the probable magnitude of the percentages 



concerned in the case of normal soils can be obtained 



from the following data of Russell. Percentages 



are by volume. 



Percent- Percentage of air 

 age of 



pore In nor- After 

 space mal, moist period of 

 condition drouth 



It has been noted above that the actual 

 composition of the soil air is the result of the 

 balance between the rate at which oxygen is consumed 

 and carbon dioxide produced by living matter and the 

 opposing rates at which oxygen can move inward from the 

 atmosphere and carboii dioxide can move outward, or be 

 disposed of otherwise. The most important investiga- 

 tions on the gas exchange between the soil and the atmo- 



p 

 sphere are those of Buckingham. As the result of care- 

 ful investigations, both theoretical and experimental, 

 this author concludes that the movement of gases in 

 the soil follows essentially the laws for diffusion in 



(1905). 



( 1904). 



1. Soil conditions and plant growth, p. 106 



2. U. S. Bureau of Soils, Bull. 25, 52 p, 



