A CHEMICAL CLASSIFICATION OF THE ACTIVITIES 
OF SOIL MICROORGANISMS 
PAUL EMERSON 
At the present time it may be said that the process of decom- 
position with its resultant complex chemical changes taking place 
in the soil is controlled primarily by the activities of micro- 
organisms and that Soil Fertility is mainly dependent upon these 
microscopic forms. At first the action is probably limited to a 
comparatively few forms and is entirely biological in nature, due 
to the efforts of the organism to digest the organic matter with 
which it is in intimate contact. The organism is interested only 
in securing the proper amount of food for its metabolic processes. 
But in the process of digestion it splits off certain substances, for 
instance carbon dioxide, which cause an appreciable chemical 
reaction in the soil. As the digestive action continues, the com- 
plex organic molecules are subjected to the attacks of a greater 
variety of soil organisms and are split in various ways with the 
subsequent formation of hundreds of simpler compounds. Some 
of these compounds may be in such a form that they are capable 
of being again assimilated by the growing plants. Others may be 
in such a condition that they form an acceptable food for other 
forms of microorganisms and are changed to such a form that 
they ultimately become available for plant use or are lost to the 
soil in various ways. During the process many compounds are 
formed that react with the insoluble constituents of the soil, 
changing them to the soluble form, thus forming more and more 
available plant food. It is seen, therefore, that while the decom- 
position of the complex organic plant remains in the soil with its 
attendant influence on Soil Fertility is dependent upon the activity 
of microorganisms, the action is not entirely biological, as there are 
many chemical actions and reactions involved. In fact, the micro- 
organisms are in reality the instigators and accelerators of various 
reactions, which, when well started may proceed to some extent 
without them. Apparently the chemical products have the ability 
to continue the process of decomposition for some time. Recent 
investigations at this Station have shown that sterile soils give off 
