PREFACE 



Although the biochemical processes in the soil as well as the nature 

 of the microorganisms present there have received considerable atten- 

 tion from various points of view and although an extensive literature has 

 accumulated, not only dealing with soil processes in general but even 

 with certain specific activities of the organisms, our present knowledge 

 of the soil microflora and microfauna and of the numerous transforma- 

 tions that they bring about has not advanced beyond a mere beginning 

 of a systematic study. The isolation of numerous microorganisms from 

 the soil, their identification and cultivation upon artificial media is 

 very important but such data do not tell what role they play in the soil. 

 A knowledge of the activities of certain organisms isolated from the soil 

 is certainly necessary, but that is not a knowledge of the extent to 

 which these processes take place in the soil itself. A book on soil 

 microbiology should include a study of the occurrence of microorganisms 

 in the soil, their activities and their role in soil processes. It is this 

 last phase which has been studied least and where the information 

 available is far from satisfactory in explaining what is taking place in 

 the soil. This is due largely to the limitations of the subject which 

 depends for its advance on botany, zoology, bacteriology, chemistry, 

 including biological and physical, and especially upon the advance of 

 our understanding of the physical and chemical conditions of the soil. 



There are various kinds of audiences to which a book on soil micro- 

 biology may appeal. There is the scientific farmer who may search for 

 a better understanding of the processes taking place in the soil, those 

 processes which control the growth of his crops and indirectly influence 

 the growth of his animals. There is the agronomist, who is interested 

 in the fundamental reactions controlling soil fertility, by reason of the 

 need of directing such processes towards a greater utilization of the 

 nutrients added to the soil or stored away in the soil organic matter. 

 There is the investigator, the soil chemist or the soil microbiologist, who, 

 in attacking problems dealing with the occurrence of microorganisms 

 in the soil, their activities, and especially with the relation of these 

 activities to the physical and chemical soil conditions, seeks for specific 

 or general information. These investigators may deal with organisms 



