Chapter IX — ^153 — Decomposition of Residues 



their ability to attack native lignin, actinomycetes might be assumed also 

 to be capable of attacking humus materials. This was actually found 

 to be the case for peat (Table 40). A pure culture of an actinomyces 

 and a strain of Trichodervia decomposed more of the peat than the com- 

 plex soil population, as shown by the greater amount of COo liberated 

 and of ammonia produced. The ratio of the carbon to the nitrogen 

 liberated was less for the pure cultures than for the complex microbiolog- 

 ical population, pointing to the fact that the former attacked more of 

 the nitrogenous constituents than did the total population. 



Macj^ has shown that actinomycetes, through their ability to decom- 

 pose proteins into amino acids and ammonia, bring about the formation 

 of humus in the soil. In view of the fact that actinomycetes synthesize 

 considerably less mycelium than do fungi, only small quantities of nitro- 

 gen are assimilated, and most of the nitrogen is liberated free in the 



Table 41 : Decojnposition of stable manure by pure cultures of thermophilic microorganisms and 



by a mixed thermophilic population (459) : — 



Per cent of dry material left after decomposition 



form of ammonia. Nonnitrogenous organic materials are utilized for 

 cell synthesis, but they do not exert such a depressing effect upon am- 

 monia liberation by actinomycetes as in the case of bacteria and fungi. 

 The accumulation of humus in the soil is an index of the great 

 resistance of this group of organic substances to decomposition by micro- 

 organisms. Since humus contains the larger part of the soil nitrogen, 

 its decomposition is of great importance to soil fertility. Actinomycetes 

 seem to be capable of attacking this resistant material and bringing about 

 its decomposition. Liming of soil and draining of swampy soil favor 

 the development of actinomycetes and also the decomposition of the soil 

 organic matter. According to Fousek (125), an increase in plant 

 growth is obtained by adding mycelium of actinomycetes to the soil; this 

 is due to increased decomposition of the organic matter thus brought 

 about. 



Thermophilic Composts:— As was pointed out above, the actinomy- 

 cetes comprise a number of thermophilic types. In the decomposition 



