510 NATURE AND PROPERTIES OF SOILS 



the temperature falls to as low as 80° or 90° F. New organ- 

 isms may now function, although many of those active under 

 aerobic conditions may continue to be effective. The prod- 

 ucts become changed to a considerable degree. Carbon diox- 

 ide, of course, continues to be evolved in large amounts, but 

 instead of ammonia being formed, the nitrogenous matter is 

 converted into the usual putrefactive products, such as indol, 

 skatol, and the like. If sufficient reduction occurs, free nitro- 

 gen may escape. 



The carbonaceous matter is resolved into numerous hydro- 

 carbons, of which methane (CH 4 ) is prominent; and as a by- 

 product of the breaking-down of the proteins, hydrogen sul- 

 fide (H 2 S) and sulfur dioxide (S0 2 ) are evolved. The com- 

 plex nitrogenous and carbohydrate bodies are attacked with 

 the splitting-off, not only of simpler materials, but often of 

 those more complex. Such compounds may be listed in gen- 

 eral as organic acids and humous bodies. They, of course, ul- 

 timately succumb to simplification. 



The general changes 1 in any manure pile can readily be 

 recapitulated. First is the aerobic action, with the escape of 

 ammonia and carbon dioxide. Next the manure is wetted, 

 it compacts, and the slow, deep-seated decay sets in with a 

 simplification of some compounds, with the production of 

 acids, and with a gradual formation of humous materials. 

 As the manure becomes alternately wet and dry, the two gen- 

 eral processes may follow each other in rapid succession, the 

 anaerobic bacteria attacking the complex materials, the 

 aerobic affecting both the complex and the simpler com- 



1 The proteid compounds, which are the most important group in farm 

 manures, split up in the soil or compost heap into amino-acids. These 

 amino-acids undergo deaminisation and decarboxylation. The former 

 takes place either under aerobic or anaerobic conditions producing am- 

 monia and a complex acid. The decarboxylation occurs only when oxygen 

 is excluded giving either ammonia and an organic acid as in deaminisa- 

 tion, or carbon dioxide and a complex amine, which may be rather stable. 

 Deaminisation and decarboxylation go on together, the former generally 

 predominating. 



