446 PRINCIPLES OF SOIL MICROBIOLOGY 



transformation of organic substances into a mixture of brown and 

 black substances with a high content of carbon such as is characteristic 

 of fossil coals. But whatever the mechanism of these transformations, 

 the active participation of microorganisms in the latter cannot be 

 denied." According to Pringsheim, 54 thermophilic bacteria are also 

 active in the decomposition of cellulose in manure, with the formation 

 of acetic and formic acids, C0 2 , hydrogen and methane. 



The pentosans may be acted upon even before the celluloses are 

 decomposed. When fresh manure is allowed to compost, the bacteria 

 and fungi transform the celluloses, pentosans and pectins of the straw 

 into various organic substances and carbon dioxide. The organisms 

 thereby absorb a great deal of the available nitrogen present in the 

 urine for the synthesis of their protoplasm. When fresh manure is 

 applied to the soil directly, it may not stimulate and may even injure 

 plant growth. This is due to the assimilation of the available nitrogen 

 in the manure and in the soil by the microorganisms which use the 

 carbohydrates of the manure as sources of energy. The composting 

 of the manure brings about a great reduction in the nitrogen-free 

 compounds and the transformation of the available nitrogen into 

 microbial proteins. 55 



Importance of cellulose decomposition in the soil. According to 

 Mutterlein's 56 calculation, 1 acre of soil in Germany receives yearly 

 about 200 kgm. of cellulose in the form of manure. When we add to 

 that the amount introduced by green manuring, plant stubble, root 

 residues, weeds, etc., quite appreciable quantities are obtained. Some 

 of the plant constituents are attacked more readily than others. The 

 sugars and starches and, to a more limited extent, the proteins are 

 acted upon first, then the pentosans and celluloses; then the oils, fats 

 and lignins; and finally the waxes which may persist in the soil for a 

 long time unaltered. 



Cellulose was considered by older investigators and even some re- 

 cent ones 57 to be the mother substance of soil "humus." On the 

 other hand, Hoppe-Seyler 5S and others have demonstrated that since 



64 Pringsheim, 1913 (p. 202). 



65 Heinze, B. tlber die Verrottung des Stalldungers. Centrbl. Bakt. II, 

 25: 503-504. 1910. 



66 Mutterlein, 1913 (p. 434). 



67 Marcusson, J. Torfzusammensetzung und Lignintheorie. Ztschr. angew. 

 Chem., 38: 339. 1925. 



48 Hoppe-Seyler, 1889 (p. 700). 



