40 



SOIL BACTERIOLOGY 



4. Bring the moisture content of the soil to two- thirds 

 saturation. 



Note.—ln order to secure the proper moisture content it is necessary to 

 take into account the water-holding capacity of the added substances, c. (r ^ 

 I gram of casein or blood-meal requires about 2 c.c. of water; i gram of 

 clover, about 5 c.c. of water. 



Allow the soil to stand for one hour or more and remix 

 with a sterile spatula. 



5. Determine the amount of ammonia nitrogen in samples 

 I, 2, 5, 6, 9; and 10 at once. The ammonia nitrogen of 

 these cultures or controls is to be subtracted from the am- 

 monia nitrogen found at the final analysis. This gives the 

 figures '^blank substracted." 



6. Cover the remainiitg tumblers with Petri dishes and 

 incubate for four to bix days at 28° C. Now determine the 

 ammonia content of all of the soils. The percentage of 

 nitrogen in the different substances is given on the label. 



7. Tabulate results. 



Table ii. — Ammonification of Various Substances 



No. 



> 

 Treatment. 



AmmoEia nitrogen m 100 gm. of 

 soil 



Average. 



Nitrofen 



Total 



Blank 

 subtracted. 



ammonified. 



I 



3 

 4 



5 

 6 



Casein. 



do. 



Blood-meal. 



do. 



Clover. 



do. 



Mgm, 



Mgm. 



Mgm 



Per cent. 



