RELATION OF PROTOZOA TO SOIL BACTERIA 



429 



ter incubating at room temperature for one week, the soils in 

 the plates were treated with 1 per cent of mannite. The 

 mannite was thoroughly mixed with the soil by means of a 

 sterile spatula. The plates were then incubated for three 

 weeks at 25°C. The moisture content was kept as near one- 

 half saturation as possible by the addition of sterile distilled 

 water. At the expiration of the incubation period, the soils 

 were placed in a 30°C. incubator until air dry. They were then 

 ground in a mortar and thoroughly mixed and finally sieved. 

 Duplicate total nitrogen analyses were made according to the 

 modified Gunning method. 



The results of the analyses are given in the following table. 



TABLE 7 

 Rate of fixation of free nitrogen in soil with and without protozoa 



TREATMENT 



With protozoa. . . . 

 With protozoa. . . , 

 With protozoa. . . 

 Without protozoa 

 Without protozoa 

 Without protozoa 



TOTAL NITROGEN PER 100 

 GRAMS OP DRY SOIL 



After 21 days 



mgm. 



148.40 

 145.60 

 150.50 

 144.20 

 149.10 

 144.90 

 147.00 



144.20 

 144.90 

 140.00 

 147.00 



> 



Average 



147.45 



145.02 



From the data above it will be seen that there is a difference 

 in total nitrogen in favor of the soil containing the protozoa. 

 However, it is probably not marked enough to cause any dif- 

 ference in the fertility of the soil. 



From these results it seems probable that the protozoa do 

 not have any particularly harmful effect on the fixation of free 

 nitrogen in the soil. 



Liquid cultures. One hundred cubic centimeters of mannite 



