Products of Microbial Decomposition 



107 



The rate of decomposition of plant and animal materials can be 

 measm-ed by a number of different methods. These are based upon 

 the products of decomposition; the disappearance of specific plant 

 and animal constituents, such as the sugars, the cellulose, the pento- 

 sans, or some of the nitrogenous bodies; the formation of resistant 

 products of decomposition, such as accumulation of lignins and their 

 transformation into humus compounds. As shown in Table 20, the 

 accumulation of the ash may be used as a measure of total decom- 

 position. 



Products of Microbial Decomposition 



When plant and animal residues undergo decomposition in the 

 soil and in composts, the various constituent elements, especially the 

 carbon, nitrogen, sulfur, and phosphorus, are liberated in mineralized 

 forms. 



15 



45 50 



65 



Fig. 50. 



25 30 35 40 

 Days of composting 



Course of decomposition of stable manure as measured by temperature 

 chans;es (from Waksman and Nissen). 



The carbon is liberated, under aerobic conditions, as COj, and 

 under anaerobic conditions, as methane, organic acids and alcohols, 

 and COo. Even imder the most favorable conditions of decomposi- 

 tion, however, the carbon of the organic matter is not all transformed 

 to COo at once. This is due to the assimilation of a large part of 

 the carbon by the microorganisms concerned in the decomposition 



