250 NATURE AND PROPERTIES OP SOILS 



Table LIU 



Chasacter 0¥ Soil 



Pebcentase by Volume 





CO, 



0, 



N, 



Sandy subsoil of forest . . 

 Loamy subsoil of forest 



Surface soil of forest 



Clay soil 



Soil one year after manuring 



Soil freshly manured 



Vegetable mold compost 



.24 

 .79 

 .87 

 .66 

 .74 

 1.54 

 3.64 



19.66 

 19.61 

 19.99 

 19.02 

 18.80 

 16.45 



79.55 

 79.52 

 79.35 

 80.24 

 79.66 

 79.91 



Tile differences in the composition of the atmosphere of 

 different soils and the variability noticeable within the same 

 soil are due primarily to two factors: (1) the production of 

 carbon dioxide, and (2) oxidation. These will be discussed 

 in the above mentioned order. 



130. The carbon dioxide of the soil air. — The presence 

 of carbon dioxide in soils may be due in small part to in- 

 filtration from the atmospheric air, there being a tendency 

 for the carbon dioxide, which is heavier than nitrogen and 

 oxygen, to settle out. It may also have a purely chemical 

 origin. The latter source is much more probable. The ab- 

 sorption of the bases of carbonates or bicarbonates would 

 obviously release carbon dioxide. This probably does not take 

 place, however, to any great extent in a natural soil. When 

 ground limestone is added, such a reaction does occur.^ Car- 

 bon dioxide in appreciable amounts might for a short time 

 thus be liberated through chemical reaction. The addition 



^Maelntire, W. H., The Carhonation of Burnt Lime in Soils; Soil 

 Sci., Vol. YII, No. 5, pp. 325-446, 1919. See also, The Non-existence 

 of Magnesmm Carbonate in Sumid Soils; Tenn. Agr. Exp. Sta., Bui. 



