CHAPTER VII 



THE DECOMPOSITION OF ORGANIC MATTER 

 IN THE SOIL 



Almost every conceivable organic compound is added to 

 the soil in the plant and animal matter that finds its way 

 therein. All is grist for the mill of the microorganisms of 

 the soil. So far as is known, no substance is able to resist 

 their action; even such resistant substances as chitin, horn, 

 and gums ultimately disappear, as do the bones of animals 

 that are placed in the upper layers of the soil. If, in some 

 way, they have been deposited in the lower layers of the 

 earth or in a place where they are protected from the action 

 of microorganisms, they will persist for ages. 



From the standpoint of the action of the decomposing 

 matter on the fertility of the soil and from the viewpoint 

 of the farmer, all organic matter may be divided into two 

 great groups : first, those compounds that contain only car- 

 bon, hydrogen, and oxygen, of which the sugars and starches 

 are examples; second, the nitrogen-containing substances 

 that are best illustrated by the proteins. These latter com- 

 pounds also contain sulphur and phosphorus, the cycles of 

 which are of interest to the farmer. 



The decomposition of all of these substances, with the 

 formation of those compounds in which the various ele- 

 ments are available to the green plant, is an intricate proc- 

 ess from the standpoint of the chemical reactions concerned 

 and the organisms involved. Knowledge of the complete 

 process is yet fragmentary and incomplete. Only a few 

 general facts are known, and little of the details of the 



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