Decomposition of Stable Manures 305 



that nun be present, and to t)btain a piodnct whieh ean be readily 

 pulverized, such manures are sometimes composted before their 

 introduction into the soil. Although stable manures contain appre- 

 ciable amounts of plant nutrients, their value as sources of humus 

 increases their importance in soil. A large part of the organic mat- 

 ter in some of the manures decomposes rapidly and, therefore, has 

 a relatively short period of effectiveness. Poultry manure and sheep 

 manure particularly are frequently used as organic fertilizers and 

 not as sources of soil organic matter. As fertilizers they are gen- 

 erally expensive; they are applied to the soil directly or mixed with 

 certain proportions of peat or soil. 



Decomposition of Stable Manures 



When placed in a compost that is kept under conditions of favor- 

 able moisture and aeration, the various organic constituents of stable 

 manures are immediately attacked by a great variety of microorgan- 

 isms, including not only fungi, actinomycetes, and aerobic and an- 

 aerobic bacteria, but also protozoa and other forms of life. These 

 organisms do not attack the manures as a whole or all the chemical 

 constituents of the manures at the same rate. The decomposition of 

 the compost and the various changes brought about in its specific 

 organic constituents depend to a large extent upon the nature and 

 composition of the manure and upon the conditions under which 

 the decomposition of the manure is taking place. 



The microorganisms bringing about the decomposition of stable 

 manures either inhabit the manures or are derived from the soil. 

 These microorganisms bring about a rapid destruction of the carbo- 

 hydrates and some of the proteins; this is accompanied by synthesis 

 of considerable microbial cell substance. Although the various 

 processes involved in the decomposition of stable manures are 

 closely interrelated, they may be considered from three distinct 

 angles: (a) the decomposition of the organic matter as a whole in 

 the manures and the formation of humus; (b) the liberation, oxida- 

 tion, reduction, and synthetic processes involving the nitrogen com- 

 plexes; (c) the influence of the microorganisms found in the manures 

 upon the microbiological population of the soil and upon soil 

 processes. 



The transformation of the nitrogen in the manures, leading to its 

 final liberation in a form available for the growth of higher plants. 



