THE ORGANIC MATTER OF THE SOIL 



139 



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 becomes 

 more heavily charged and an alteration in bacterial and 

 plant relationships may thereby be induced. The fol- 

 lowing figures, by Wollny, 2 show the composition of the 

 soil atmosphere and the effects of additional humous 

 material on the carbon dioxide content : — 



Percentage by 

 Volume of 



Soil air (average of 19 analyses) 



Atmospheric air 



A sandy soil 



A sandy soil plus manure 



18.33 

 20.96 

 19.72 

 10.35 



While carbon dioxide may be evolved by the splitting-up 

 of both carbohydrate and nitrogenous bodies, ammonia 

 results only from the latter. It is really the first ex- 

 tremely simple nitrogenous body produced. It can be 

 utilized by some plants as a source of nitrogen, as is also 

 true with certain simple humic bodies, but ordinarily 

 it must undergo oxidation. This oxidation results in 

 nitrites (N0 2 ) and ultimately in nitrates (N0 3 ), the 

 latter being usually considered as the chief source of 

 the nitrogen utilized by plants. 



1 Stoklasa, J., and Ernest, A. Ueber den Ursprung, die 

 Menge, und die Bedeutung des Kohlendioxyds im Boden. 

 Centrlb. Bakt., II, 14, Seite 723-736. 1905. 



2 Wollny, E. Die Zersetzung der Organischen Stoffe, 

 Seite 2. Heidelberg, 1897. 



