428 



T. L. HILLS 



TABLE 6 

 Rate of nitrate formation in soil with and without protozoa 



ANALYSES 



TREATMENT 



With protozoa. . . 

 With protozoa. . . 

 With protozoa. . . 

 Without protozoa 

 Without protozoa 

 Without protozoa 



NITROGEN AS NITRATE PER 100 

 GRAMS DRY SOIL 



After 14 days After 28 daya 



mgm. 



9.90 

 11.90 

 11.76 

 7.52 

 6.57 

 8.20 



mgm. 



13.88 



13.88 



13.51 



7.81 



8.06 



8.06 



sent the relative decrease in the amount of ammonia was about 

 the same, 21.5 mgm. at fourteen days to 19.3 mgm. at twenty- 

 eight days. There seemed to be practically no difference in 

 the rate of conversion of ammonia into nitrate in the two soils. 



Where the rate of nitrate formation was determined the in- 

 crease in nitrate formation seemed to be slightly in favor of 

 the soil which contained the protozoa. 



From the small amount of work done on the effect of protozoa 

 on nitrification in soil, it seems that their presence is at 

 least not detrimental to the process as determined by these 

 experiments. 



FREE NITROGEN FIXATION 



Some very interesting results were obtained in this part of 

 the work. Here both soil and liquid cultures were employed. 

 The liquid medium gave the protozoa an environment better 

 adapted to their growth and activity than did the soil cultures. 



Soil cultures. Four hundred grams of soil were weighed out 

 and spread in approximately one inch layers on six flat porcelain 

 plates. These were then carefully covered with parchment 

 paper and tied and then steriUzed at 15 pounds for one hour. 

 Upon cooling each culture was inoculated with a suspension 

 of Azotohacter in sterile distilled water. Then one-half were 

 inoculated with a suspension of soil containing protozoa and the 

 remaining half with the same amount of protozoa-free soil. Af- 



