FACTORS INFLUENCING NUMBER 



163 



however, the possibility that the freezing breaks up the clumps of 

 bacteria and the noted increase is apparent and not real. Little 

 relationship has been found between the moisture and cropping of a 

 soil and the bacterial count- 



The number of organisms in the soil vary greatly with the depth. 

 Due to the lack of moisture and the germicidal action of light, the 

 number of bacteria in the uppermost inch or two of soil is lower than 

 in the layers of soil immediately below. Beyond the depth of eight 

 or nine inches, the number diminish rapidly, and in humid regions 

 the number below two feet is extremely low. This is illustrated by 

 results reported by Chester: 



Depth. Number of colonies. 



2 inches 981,000 



4 inches . 1,632,000 



6 inches 1,623,000 



12 inches 73,000 



18 inches 21,000 



24 inches 4,000 



The conditions, however, are quite different in the arid regions 

 where we have the slow formation of clay substances in the soil, 

 and, therefore, the absence of the cementing substances in the soil. 



