110 NATURE AND PROPERTIES OF SOILS 



58. Simple products of organic decomposition. — As the 



processes of chemical and biological change of the soil organic 

 matter proceed, the simple compounds already noted begin 

 to appear. This change is of course coordinate with a certain 

 amount of synthetic action, but compounds thus built up 

 must ultimately succumb to the agencies at work and suffer a 

 splitting-up and reduction to simple bodies. Carbon dioxide 

 is one of the most important of these compounds, always being 

 a product of bacterial activity. Its importance has already 

 been noted in the discussion of weathering. Here it heightens 

 the solvent power of water and tends to increase the amount of 

 nutrient material carried in the soil solution. Carbonation 

 is a direct result of its presence. 



With increased organic matter in any soil, greater bacterial 

 action and an increase in the carbon dioxide evolved may well 

 be expected. In fact, the carbon dioxide production of a 

 soil is considered by some authors ^ to be a measure of bacterial 

 activity. "With this increase in carbon dioxide, the soil air 

 is markedly reduced in its free oxygen and an alteration in 

 bacterial and plant relationships may thereby be induced. 

 The following figures by WoUny ^ show the composition of 

 the soil atmosphere and the effects of additional organic ma- 

 terial on the carbon dioxide content : 



Table XXI 



Soms 



Percentage by Yolume of 





COa 







Atmospheric air 



.04 

 2.54 

 1.06 

 9.74 



20.96 



Soil air (average 19 analyses) 



A sandy soil 



18.33 

 19.72 



Sandy soil plus manure 



10.35 







^Stoklasa, J., and Ernest, A., lyher den Ur sprung, die Menge, und die 

 Bedeuiimg des KoMendioxyds im Boden; Centrlb. Bakt., II, 14, Seite 

 723-736, 1905. 



^WoUny, E., Die ZersetBung der OrganiscJien Stoffe; Seite 2, Heidel- 

 berg, 18^7, 



