682 PRINCIPLES OF SOIL MICROBIOLOGY 



A detailed study of the carbon dioxide content of the soil atmosphere 

 is given elsewhere (p. 640). A discussion of the evolution of C0 2 in 

 the soil as an index of the availability of the soil organic matter is also 

 discussed elsewhere (p. 717). It is sufficient to point out here that 

 the evolution of C0 2 from the soil and its content in the soil atmosphere 

 depend upon a number of other factors outside of the actual carbon 

 content of the soil. Kissling and Fleischer, 26 as far back as 1891, used 

 C0 2 production of peat soils as an index of the rapidity of decomposi- 

 tion going on in the soil. The addition of sand was found to stimulate 

 oxidation greatly, while temperature was found to be one of the 

 most important factors. As a measure of oxidation taking place in 

 the soil, Deherain and Demoussy 27 used the amount of C0 2 present in 

 the atmosphere of a closed 100-cc. tube containing the soil. The tube 

 of soil was kept at constant temperature for a certain period of time. 

 They demonstrated that the production of carbon dioxide in basic soil 

 (1) is due almost wholly to bacteria; (2) it increases with temperature to 

 about 65°C, then decreases, and at higher temperatures (90°C.) in- 

 creases again; (3) it increases with the amount of water present up to a 

 certain point and then decreases, the optimum amount varying with 

 the soil; and finally (4) it is greatly influenced by the state of division of 

 the soil and aeration. Sterile soil produces small amounts of carbon 

 dioxide, but, when reinoculated with soil extract, it forms twenty-five 

 times as much C0 2 . 28 Sterilized and inoculated soil gives two to five 

 times as much carbon dioxide as unsterilized and inoculated soil. 



When manure is treated with disinfectants (thymol, phenol, HgCl 2 ), 

 little C0 2 is produced; this proves that the process of decomposition of 

 organic matter in the rotting of manure and the evolution of carbon 

 dioxide are biological in nature. Since microorganisms are influenced 

 in their activities by the temperature and moisture content of the 

 medium, one would expect that a change in temperature and moisture, 

 within certain limits, influences the evolution of C0 2 . Decomposition 

 of the organic matter was found to vary roughly with the amount of 

 oxygen available, although some C0 2 is formed in the complete absence 



26 Kissling, R., and Fleischer, M. Die Bodenluft in besandeten und nicht 

 besandeten Hochmoor und Niederungsmoorboden. Landw. Jahrb., 20: 876- 

 889. 1891. 



27 Deherain, P. P., and Demoussy, E. Sur l'oxydation de la matiere organ- 

 ique du sol. Ann. Agron., 22: 305-337. 1896. 



28 Sewerin, S. A. Die Mobilisierung der Phosphorsauren des Bodens unter 

 dem Einflusz der Lebenstatigkeit der Bakterien. Centrbl. Bakt. II, 13:616; 

 28: 561. 1910; 32: 498. 1912. 



