The Influence of Depth of Cultivation upon 

 Soil Bacteria and Their Activities. 



By 



WALTER E. KING, Bacteriologist. 

 CHARLES J. T. DORYLAND, Assistant in Soils. 



INTRODUCTION. 



THERE are those who believe that future work in soil bac- 

 teriology will have considerable bearing upon the problem of 

 maintaining soil fertility. This belief is founded upon the ex- 

 isting knowledge of soil bacteria, and the suggested part that 

 bacterial action plays in preparing the soil for plant growth. 



Granting that our present rather limited knowledge por- 

 tends to show that soil bacteria and their activities are useful 

 and essential attributes of fertile soil, it seems justifiable that 

 attempts should be made to determine the influence of different 

 conditions upon the number and specific activities of the bac- 

 teria living in various types of soil. 



The consideration of the influence of depth of cultivation 

 upon the soil bacteria and their activities is a broad subject, 

 which embraces a host of minor problems. The whole prob- 

 lem can be determined only by an immense amount of experi- 

 mental work and years of patient labor. The experiments out- 

 lined in the following pages, therefore, must be considered as 

 preliminary and the suggested results as only forerunners of 

 definite conclusions. 



Part I. 



PRELIMINARY EXPERIMENTS. 



This work was designed and carried out as a preliminary 

 experiment for the basis of further research in soil bacteri- 

 ology under field conditions. The work was begun on March 7, 

 1908, and was continued fifteen weeks. At the end of this 

 time the plan was broadened out, including more details of soil 

 conditions. The first three weeks of the experiment were used 

 in determining the number of bacteria in the soil under the 

 existing conditions, so that the comparative results by differ- 



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