30 



Microbiological Population of the Soil 



Table 1. Composition' of a Gray Forest or Podzol Soil (from Glinka) 



soil a living system and not a mere dead mass of mineral matter and 

 organic residues. This can be clearly seen in Fig. 18. 



The quantitative composition of the population and its qualita- 

 tive nature depend largely upon the origin and nature of the soil 

 and the relative composition of its inorganic and organic constitu- 

 ents. The prevailing climate and the growing vegetation also influ- 

 ence greatly the nature and abundance of the microorganisms that 

 inhabit the particular soil. Among the other factors that have a 

 marked effect upon the relative composition of the microbiological 

 population, it is sufficient to mention the reaction of the soil, its 

 moisture content, and the conditions of aeration. 



Microbiological Population of the Soil 



Study of the soil population has progressed along several distinct 

 lines. Some investigators have devoted their major attention to the 

 quantitative composition of the microbiological population; others 

 were interested in the nature of the organisms making up this popu- 

 lation; still others were concerned with the chemical processes 

 brought about in the soil by the various organisms and their im- 

 portance in soil fertility and in plant growth. 



The methods for the enumeration of bacteria and other micro- 

 organisms in the soil have undergone various changes during the 

 last fifty years. The same is true of the concepts concerning the 

 relative importance of the various constituent groups of micro- 

 organisms inhabiting the soil. These facts, as well as the discovery 



