Aug. 1909.] Soil Bacteriology. 221 



soil, of low humus content, in the most favorable growing 

 area. 



If, however, the field were stirred to a depth of ten inches 

 for several years, so as to incorporate humus into the surface 

 ten inches of soil, it is reasonable to suppose that extra deep 

 plowing might be more favorable for the development of bac- 

 teria in the sandy soil than it appears to be from the above 

 table. At the same time, however, several years of deep plow- 

 ing would also be more beneficial to bacterial development in 

 the heavier soils. 



These preliminary experiments show that when plowed land 

 is compared with unplowed land it is found that : 



Silt 



Plowed 4 inches deep increases the number of bacteria 15.46% 



Plowed 6 inches deep increases the number of bacteria 10.94 



Plowed 8 inches deep increases the number of bacteria 24.20 



Plowed 10 inches deep increases the number of bacteria 26.89 



Sand 



"Plowed 4 inches deep increases the number of bacteria 35.( 



Plowed 6 inches deep increases the number of bacteria 13.53 



Plowed 8 inches deep increases the number of bacteria 22.90 



Plowed 10 inches deep increases the number of bacteria 5.11 



