FARM MANURES 593 



food. In other words, the whole mass of the manure 

 tends to simpler forms. The mass becomes decayed, 

 humus is produced, and available plant-food is evolved. 



496. Anaerobic action. — As the manure becomes 

 compacted, especially if it is left moist, oxygen is grad- 

 ually excluded within the heap and its place is taken by 

 carbon dioxide, which is given off during the process of 

 any form of bacterial activity. The fermentation now 

 changes from aerobic to anaerobic, it becomes slower, and 

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

 organisms may now function, and even some of the same 

 ones that were active under aerobic conditions may con- 

 tinue to be effective. The process is now a deep-seated 

 one and the products become changed to a considerable 

 degree. Carbon dioxide, of course, continues to be evolved, 

 but instead of ammonia being formed the nitrogenous 

 matter is converted into the usual putrefactive products, 

 such as indol, skatol, and the like. The carbonaceous 

 matter is resolved into numerous hydrocarbons, of which 

 methane (CH 4 ) is prominent; and as a by-product of 

 the breaking-down of the proteins, hydrogen sulfide 

 (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 general as organic acids and humic bodies. 

 They of course ultimately succumb to simplification. 



497. Fermentation in general. — In any process of 

 fermentation, acids tend to form which if not neutralized 

 will render the mass acid and impede bacterial activity. 

 This occurs when the solid excrement decomposes alone. 

 The liquid manure, however, is alkaline and will tend 

 to correct any acidity due to fermentation. The advan- 



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