RELATION OF PROTOZOA TO SOIL BACTERIA 



427 



shows the total ammonia and nitrate nitrogen present in the 

 untreated, heated, and heated and reinoculated soils. 



Here the introduction of the supposedly harmful factor, the 

 protozoa, into the soil did not seem to have any depressing effect 

 on the bacteria as far as their production of ammonia and sub- 

 sequent oxidation of the same was concerned. 



NITRIFICATION 



Flask experiments were carried out somewhat similar to the 

 ammonification tests, except that at the time of inoculation with 

 soil containing protozoa and soil free from protozoa, the soil was 

 also inoculated with cultures of Nitrosomonas and Nitrohacter 

 free from ciUates and flagellates. The nitrifying organisms were 

 obtained by inoculation and subsequent occasional transfer into 

 media suitable to their growth and unfavorable to the growth of 

 other organisms. After the inoculation of the sterilized soil as 

 previously stated, ammonium sulphate was added in quantities 

 equal to 20 mgm. of nitrogen as ammonia per 100 grams (dry 

 weight) of the soil. The ammonia and nitrate content was de- 

 termined at the end of fourteen and twenty-eight days. 



The figures in tables 5 and 6 show the results of these deter- 

 minations. 



In the case of the soil with protozoa at fourteen days the aver- 

 age ammonia content was approximately 18.6 mgm. and at 

 twenty-eight days, 16.0 mgm. Where the protozoa were ab- 



TABLE 5 

 Rate of conversion of ammonia to nitrate in soil with and without protozoa 



ANALYSES 



TBEATMENT 



With protozoa. . . 

 With protozoa ... 

 With protozoa. . . 

 Without protozoa 

 Without protozoa 

 Without protozoa 



NITROGEN AS AMMONIA PER 100 

 GRAMS DRY SOIL 



After 14 days After 28 days 



mgm. 



20.58 

 19.02 

 16.10 

 21.14 

 23.24 

 20.16 



mgm. 



15.82 

 15.96 

 16.24 

 19.32 

 19.18 

 19.32 



