so 



SOIL BACTERIOLOGY 

 Table 19. — Nitrification in Solution {Quantitative). 



No. 



Inoculum. 



Nitrate nitrogen in 100 c.c of solution. 



Nitrified. 



Total. 



Blank 

 subtracted. 



Average. 



I 

 2 



3 

 4 



Field soil. 



do. 



Garden soil. 



do. 



Mgm. 



Mgm. 



Mgm. 



Per cent. 



Exercise 14 



Isolation of Nitrifying Organisms 



1. Prepare eight tubes of acid sodium potassium silicate 

 (m. 30). 



2. Dilute the second enrichment cultures, nitrite, and 

 nitrate organisms untif i c.c, represents i : 1000, i : 10,000, 

 I : 100,000, and i : 1,000,000 of the original culture. 



3. Pour the acid silicate into a sterile Petri dish with 

 the culture dilutions; add the nutrient salts and enough 

 sodium carbonate to harden the silicate. 



4. When hard, invert the plates and incubate under a 

 moist bell jar for three to six weeks. 



5. Examine at weekly intervals, using the low-power 

 objective. As soon as small colonies appear, make trans- 

 fers to sterile nitrite or nitrate solution. 



6. The nitrifying organisms may be grown on washed 

 agar (m. 31). 



Exercise 15 



Nitrification of Various Substances 



I. Prepare six portions of field soil, 100 grams each, in 

 tumblers or flasks. Mix and sieve the soil well before using. 



