106 Decomposition of Plant and Animal Residues 



stances by these organisms, (c) formation of resistant complexes by 

 various processes of condensation and polymerization. During the 

 process of decomposition, a considerable amount of microbial cell 

 substance is synthesized. This substance is later attacked again by 

 other microorganisms. The processes of decomposition are contin- 

 ued until most of the organic complexes in the original plant ma- 

 terials are gradually changed into simple elements or inorganic 

 compounds. The final processes of decomposition of organic matter 

 by microorganisms and the final liberation of the elements in min- 

 eralized form complete the cycle of transformation of the essential 

 chemical elements which are used for the building up of organic life 

 in nature. The microbes thus tend to complete the cycle begun by 

 plants. 



The plant and animal residues do not decompose as a whole. The 

 various chemical constituents are attacked at different rates. The 

 sugars and starches, some of the hemicelluloses, and some of the 

 proteins undergo a most rapid decomposition by a great variety of 

 microorganisms. The cellulose, certain hemicelluloses, and some 

 of the fats, oils, and other plant constituents are decomposed more 

 slowly and, commonly, by specific orgauisms. The lignins and some 

 of the waxes and tannins are most resistant to decomposition; some 

 of the lignins may even afl^ect the decomposition of the proteins by 

 rendering the latter more resistant to attack. This is illustrated in 

 Table 20. 



Table 20. Chemical Changes in Corn Stalks as a Resi'lt of Decomposition by 

 Microorganisms (from Tenney and Waksman) 



On basis of dry material. 



Original After Days of Decomposition 

 Chemical Corn < ■ < 



Constituent Stalks 27 68 20.5 405 



per per per per per 



cent cent cent cent cent 



Ether-soluble 1.80 2.22 0.80 0.64 0.2") 



Cold-water-soluble 10.58 3.43 5.27 JJ.OG 4.59 



Hot-water-soluble 3.56 2.45 3.20 5.36 8.71 



Hemicelluloses 17.63 15.56 16.41 10.68 10. .39 



Cellulose 29.67 23.80 21.93 6.28 5.05 



Lignin 11.28 17.70 19.12 23.83 21.30 



Crude protein 2.50 4.81 6.84 10.93 12.13 



Ash 7.53 26.12 29.43 



