122 Decomposition of Plant and Animal Residues 



in a compost and only 14.5 per cent of the cellulose were decom- 

 posed. Other fleshy fungi, like Coprimis, are also capable of attack- 

 ing lignin; from fresh horse manure, C. radians removed, in 51 days, 

 22 per cent of the total lignin and 70 per cent of the cellulose. 



Decomposition of Other Plant Constituents 



Plant and animal materials contain organic compounds that 

 undergo rapid or slow decomposition by microorganisms. Of par- 

 ticular importance are the oils, fats, and waxes, the sterols and alco- 

 hols, the organic acids and tannins, the paraffins, cutins, and gums, 

 and a variety of compounds that occur in varying concentrations 

 from a fraction of 1 per cent to more than 2 per cent. These are all 

 decomposed, sooner or later, giving rise to numerous products. Oils 

 and fats, for example, are hydrolyzed to glycerol and fatty acids; the 

 glycerol is readily oxidized to COo and water, and the fatty acids may 

 give rise to certain resistant and, sometimes, toxic products. 



The transformation of fatty substances under anaerobic conditions 

 is a process that is beheved to have contributed materially to the 

 origin of petroleum. Clostridium perfringens, for example, has been 

 shown to form, from alkaline oleates prepared from olive oil, a black 

 combustible liquid immiscible with water and resembling a petroleum 

 fraction. 



Decomposition of Plant Materials as a Whole 



Rapid decomposition of plant materials is favored by the following 

 conditions : 



1. A low lignin and wax content of the plant material. 



2. The presence of an adequate supply of available nitrogen. 



3. A fine state of mechanical disintegration. 



4. A favorable pH. 



5. Favorable aeration and an adequate supply of moisture. An- 

 aerobic conditions result in a restricted bacterial population, with 

 lower nitrogen requirements. 



6. A high temperature, usually within the range of 30-45° C. 

 Mixed materials frequently decompose more quickly than single 



types of materials. This is true, for example, of a mixture of straw 

 and alfalfa, bedding and excreta in animal manures, and mixed 

 litter from several species of trees. 



