ENERGY TRANSFORMATION 425 



Energy transformation in the soil. The microbiological processes in 

 the soil can be considered from the point of view of energy transfor- 

 mation, 83 by determining the calorific value of the organic matter 

 present in the soil. "When organic matter is added to the soil, in the 

 form of manures, green manures, plant stubble, etc., a certain amount of 

 potential energy is introduced. A part of this is liberated as heat and dis- 

 sipated into space as a result of the activities of microorganisms, a part 

 is stored in the microbial cells, and a part is left in the form of unde- 

 composed organic matter or various intermediary products. The 

 energy stored away in the microbial cells and that left in the unde- 

 composed or partially decomposed organic matter go to increase the 

 energy content of the soil. This energy is only gradually liberated as 

 a result of the activities of microorganisms. 



TABLE 30 

 Relation between COi and energy liberation in some typical microbiological processes 



1 GRAM OP CO: LIBERATES IN 



Butyric acid "fermentation" 



Oxidation of sugar to oxalic acid. 



Complete oxidation of sugar 



Alcoholic "fermentation" 



Methane fermentation 



The calorific value of the soil organic matter represents the minimum 

 energy available for the activities of microorganisms, since the auto- 

 trophic bacteria can obtain their energy also from inorganic substances 

 in the soil. 



Since the organic matter added to the soil has a calorific value of 

 4.6 to 5.0 Cal. per gram, the addition of 3 tons of dry ash-free organic 

 matter, in the form of manure or green manure, per acre of soil, in- 

 troduces 13,000,000 Cal. available for the activities of microorganisms. 

 Considering the average content of organic matter in the soil as 2 to 

 3 per cent, the potential energy available in one acre of soil (12 inches 

 deep) is about 200,000,000 Cal., equivalent to about twenty-four tons 

 of anthracite coal. The freshly introduced organic matter begins to 

 decompose immediately in the soil, at first rapidly, then more and 

 more slowly, until a certain equilibrium is established, as shown by the 



83 van Suchtelen, F. H. H. Energetic und die Mikrobiologie des Bodens. 

 Centrbl. Bakt. II, 58: 413^30. 1923. 



