46 



SOIL BACTERIOLOGY 



Exercise 12 

 Ammonification by Pure Cultures of Bacteria 



1. Prepare ten portions, 50 grams each, of field soil. 



2. Add I gram of clover and bring the moisture to two- 

 thirds saturation. 



3. Cover the tumblers with Petri dishes and sterilize 

 in the autoclave at 15 pounds' pressure for two hours on 

 two consecutive days. 



4. When cool, inoculate each tumbler of soil with a 

 i-c.c. suspension of the bacterial culture to be tested. 



Note — Prepare a suspension of bacteria by shaking a forty-eight-hour-old 

 culture of the organism in sterile water. 



(a) I and 2, uninoculated 



(b) 3 and 4, unknown ammonifier (i). 

 {c) 5 and 6, unknown ammonifier (2). 

 {d) 7 and 8, Bacillus subtilis. 



(e) 9 and 10, Bacillus tumescens 



5. Numbers i and 2 should be analyzed at once. 



6. Incubate for ten days at 28° C. 



7. At the end of this time analyze. 



Table 17. — A^nmonificaUon by Fwe Culktres of Bacteria 



No 



Culture 



Ammonia nitrogen m loo gm of soil 



Nitrogen 





Total. 



Blank 

 subtracted 



Average 



ammonified 



I 



2 



3 

 4 



5 

 6 



7 

 8 



No. I 



do. 



No. 2 



do. 



B. subtilis 



do. 



B, tumescens 



do. 



Mgm 



Mgm. 



Mgm. 



Per cent 



