Aug. 1909.] 



Soil Bacteriology. 



217 



TABLE XI PLOT 5B. Stirred to depth of 8 inches. 



TABLE XII-PLOT 6B. Stirred to a depth of ten inches. 





The great variation in the results is at once apparent. This 

 fluctuation, however, generally occurs in quantitative soil bac- 

 teriological work. Samples taken 100 feet apart may often 

 show a variation of 20 to 40 per cent., while those taken from 

 the same depth, only a few feet apart, may vary from 10 to 20 

 per cent. Commencing at the surface, bacteria increase in 

 number up to the fifth or sixth inch, depending upon the depth 

 of plowing, then rapidly decrease, and disappear at a depth 

 of about seven feet below the surface foot. 



Some of the exceptional irregularities in the table can be 

 explained. For instance, on April 23, plot 2A showed twenty- 

 nine million bacteria per cubic centimeter at six inches, thir- 

 teen million at eight inches, and eighteen million at ten inches 

 in depth. These high numbers are due to a portion of manure 



