RELATION OF PROTOZOA TO SOIL BACTERIA 



425 



tent naturally increased since the nitrifying organisms were 

 present and the ammonia as it was formed was oxidized to nitrites 

 and further to nitrates. Where the soil contained no protozoa, 

 the nitrate content remained practically unchanged because of 

 the absence of the nitrifying bacteria. 



In order to show the correlation between ammonia formation 

 and nitrate formation the following table giving the total ammonia 

 and nitrate nitrogen was compiled. 



TABLE 2 

 Total ammonia and nitrate nitrogen in soils with and without protozoa 



TREATMENT 



With protozoa 



Without protozoa. 



AMMONIA AND NITRATE NITROGEN PER 100 

 GRAMS DRY SOIL 



After 4 wesks 



■nigm. 



12.62 



12.20 



12.55 



11.79 



11.70 



11.72 



After 8 weeks 



mgm. 



12.17 

 12.38 

 13.29 

 11.83 

 11.76 

 11.76 



After 12 weeks 



mgm. 



14.62 

 14.90 

 14.20 

 12.53 

 12.53 

 12.42 



From the summary data in table 2 it is very evident that the 

 presence or absence of protozoa has very little effect on the sum 

 total of ammonia and nitrate nitrogen. 



On account of the absence of the nitrifying bacteria in the 

 protozoa-free soil it is hardly fair to draw very definite conclu- 

 sions from these results. Therefore, other experiments were 

 made, in which three sets of the same soil were used : (1) untreated, 

 (2) heated to 90°C. for one hour and (3) heated to 90°C. for one 

 hour and later reinoculated with 1 per cent of normal soil, thus 

 introducing the nitrifying organisms and also the protozoa. 

 These soils were incubated at room temperature and the am- 

 monia and nitrate nitrogen determined every ten days for a 

 period of thirty days. 



The following results were obtained. 



