480 SOILS: PBOPMRTIUS AND MANAGEMENT 



is in itself likely to prevent a proportional formation of 

 carbon dioxide, since the accumulation of the gas may 

 inhibit further activity of the decomposing organisms. 



Ramann ^ states that the percentage of carbon dioxide 

 in the soil air has the following relations : — 



1. The carbon dioxide increases with the depth. 



2. In general the percentage of carbon dioxide rises 

 and falls with the temperature, being higher in the warm 

 months and lower in the cold months. 



3. Changes in temperature and air pressure change the 

 percentage of carbon dioxide. 



4. In the same soil the content of carbon dioxide varies 

 greatly from year to year. 



5. An increase of moisture in the soil increases the per- 

 centage of carbon dioxide. 



6. The amount of carbon dioxide varies in different 

 parts of the soil. 



The movement of carbon dioxide from the soil depends 

 chiefly on diffusion into the outside atmosphere. The 

 conditions governing diffusion, which will be discussed 

 elsewhere (par. 400), therefore largely determine the 

 rate of loss of carbon dioxide from the soil. 



FUNCTIONS OF THE SOIL AIR 



Both oxygen and carbon dioxide, as they exist in the 

 air of the soil, have important relations to the processes 

 by which the soil is maintained in a habitable condition 

 for the roots of plants. Deprived of these gases, the soil 

 would soon become sterile. 



398. Oxygen. — An all-important process in the soil 

 is that of oxidation, because by it the organic matter 



1 Ramana, E. Bodenkunde. Seite 301. Berlin, 1905. 



