SOIL MICROBIOLOGICAL EQUILIBRIUM 



755 



struction of protozoa following partial sterilization with the increase 

 in the numbers of bacteria and their activities and subsequently soil 



200 



100 • 



19 40 70 



130 19 40 70 



130 

 Days 



250 



150 



Bacterial Numbers. 



Toluened Soil 



Untreated Soil 



500 



300 



100 



310 



Fig. 68. Influence of toluene upon numbers of bacteria and available nitrogen 

 (ammonia and nitrate) formed in the soil; upper figures from a soil in which 

 small amounts of available nitrogen were initially present; lower figures from a 

 soil in which large amounts of available nitrogen were initially present (after 

 Russell). 



fertility. They suggested that the protozoa are responsible for keeping 

 down bacterial numbers in an untreated soil and, therefore, affect 



