5y 



In brief these conclusions are that the content of 

 carbon dioxide is higher in soils in which active 

 plant growth is occurring and especially where the 

 plant cover is thick and during the season of most ac- 

 tive growth, usually the summer. In general it is higher 

 in soils containing much organic matter or recently 

 manured with organic fertilizers. The content of carbon 

 dioxide increases with depth, except in soils with very 

 actively growing plant-cover, in which cases the carbon 

 dioxide content may show a slight maximum 10 to 50 

 centimeters below the surface. The actual percentage 

 of carbon present may vary between wide limits. In 

 normal soils, down to 2 meters, it is seldom less than 

 .2 percent or over 3.0 percent. The oxygen varies, in 

 all cases, reciprocally with the carbon dioxide. When 

 the carbon dioxide is high the oxygen is low. Actual 

 percentages may vary from 15 to 20 percent. Even less 

 than 15 percent may be found in very deep soils or 

 soils possessing active plant or bacterial growth. The 

 nitrogen is comparatively constant, usually being be- 

 tween 79 and 80 percent. 



It is obvious that the facts of the composition 

 of the soil air are the result of the consumption of 

 oxygen and the production of carbon dioxide by the plant 

 toots, bacteria and other organisms in the 



