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Recent Developments in Soil Microbiology 



General Trends 



Soil microbiology is a borderline science. It deals with micro- 

 organisms and their importance in soil processes. It involves prob- 

 lems in ecology, physiology, and biochemistry. Since it is concerned 

 with soils as the natural substrate for the growth of microorgan- 

 isms, it embraces physical, chemical, and biological phenomena. An 

 understanding of the relationships of microorganisms to higher plants 

 and of the effect of microorganisms upon the activities of other 

 microorganisms is essential. 



Soil microbiology has certain theoretical and practical considera- 

 tions. It involves (a) knowledge of the microscopic, ultramicro- 

 scopic, and near-microscopic populations of the soil, as influenced by 

 the nature and composition of the soil, by climatic and environmental 

 conditions, and by plant growth; (b) knowledge of the activities of 

 these microorganisms, which result in a variety of processes and in the 

 formation of numerous metabolic products, influencing directly or 

 indirectly the nature and composition of the soil and the growth of 

 cultivated and uncultivated plants; ( c ) methods of control of micro- 

 biological activities, and their domestication, thus harnessing them 

 for the service of man as well as of those plants and animals upon 

 whom man has come to depend for his existence. 



Although the numerous groups of microorganisms inhabiting the 

 soil form only a very small part of the soil mass, they are responsible 

 for many of the chemical transformations, and even for some of the 

 physical changes, that take place in the soil. They result in making 

 the soil a living system rather than a mass of dead debris. The 

 microbiological population is largely distributed through the upper 

 layers of the soil mass, where the living plants send down their roots 

 and where they obtain the necessary nutrients. When the roots 

 die, they are rapidly attacked by the soil organisms, with the result 

 that some of the nutrient elements are returned to circulation and 



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