26 



SOIL BACTERIOLOGY 



5. Cover the soils with Petri dishes and incubate at room 

 temperature. 



6. Determine the number of bacteria after one and 

 three weeks. 



7. Before drawing the sample for counts mix the contents 

 of the tumblers thoroughly. This may be done with a 

 sterile spatula. In the case of treated soils plate from the 

 dilutions i : 100,000 and i : 1,000,000. 



8. Tabulate results. 



Table 4 — Effect of Manures on Number of Bacteria 



Time 



Treatment 



Dilution 



Bacteria per plate 



Bacteria m i gm. 

 of dry soil 



Days. 



7 



Per cent 

 None. 



do. 



do. 





Total 



Average 



Average 



7 



I clover, 

 do. 

 do. 











7 



I manure 

 do. 

 do. 











21 



None. 

 do. 

 do. 











21 



I clover, 

 do. 

 do. 











21 



I manure 

 do. 

 do 











