Methods of Studying the Soil Population 



51 



f^^^^^oW II with phosphorus 



1000 2000 3000 4000 5000 7500 10,000 



Pounds calcium carbonate per 2,000,000 pounds soil 



Fig. 25. Effect of CaCOs upon bacterial numbers in soil (from Bear). 



results show great ^'ariability. These methods, however, may find 

 certain applications in the solution of special problems. 



Table 7. Abuxdanxe of Physiological Groups of Bacteria in Soil 

 Numbers per gram soil. 



Table 7 shows the results obtained by two investigators. They 

 are rather consistent and tend to throw some light upon the rela- 

 tive abundance of different physiological groups of bacteria in the 

 soil. 



Soil Enrichment Methods. These methods consist in adding 

 various organic and inorganic nutrients to portions of soil placed in 

 beakers or tumblers. The soil is adjusted to moisture and kept in 

 an incubator for varying periods. The chemical changes that have 



