SECTION II 



RELATION OF MICROORGANISMS TO THE NITROGEN 



CYCLE 



Exercise i 

 Ammonification of Urea 



1. Prepare six 2oo-c.c. Erlenmeyer flasks with 50 c.c. 

 each of urea solution (m. 19). 



2. After sterilizing, arrange as follows: 



(a) i and 2, control. 



(&) 3 and 4, inoculate with i gm. of soil. 



(c) 5 and 6, inoculate with i gm. of fresh manure. 



It is not necessary to weigh accurately the soil or manure. 



3. Incubate the cultures at 28 C. 



4. After two days remove from each flask 5 -c.c. portions 

 of the solution, with a sterile pipet, to a 5oo-c.c. Erlenmeyer 

 flask. 



5. Add about 50 c.c. of distilled water to the urea solu- 

 tion in the large flask, a few drops of methyl red or cochineal, 

 and titrate against N/i4 sulphuric acid. 



6. From the results of the titrations calculate the amount 

 of ammonia nitrogen in 100 c.c. of the different urea solu- 

 tions. In order to find the amount of ammonia formed by 

 bacterial action, subtract the untreated from the treated 

 series. 



7. Determine the percentage of urea transformed into 

 ammonia. 



35 



