Dec. i6, 1918 



Nitrogen-Fixing and Nitrifying Organisms 



609 



In another experiment a local soil which had shown vigorous Azoto- 

 bacter development and nitrogen fixation was used. The moisture con- 

 tent varied in different samples, being 3 per cent, 12 per cent, 24 per cent, 

 and 36 per cent, respectively. After three days' treatment with carbon 

 disulphid and toluol the samples to be evaporated were treated as in the 

 preceding experiment. The moisture content of those samples con- 

 taining 24 per cent of water decreased very slowly, it being necessary to 

 leave them for two weeks before they were air-dry. The other evapora- 

 ted samples were left the same length of time before the moisture was 

 made up to the required amount. No attempt was made to evaporate 

 the samples containing 36 per cent of water. After evaporation the 

 moisture content of all samples, except those containing 36 per cent, 

 was made up to 24 per cent. During incubation the loss of water due to 

 evaporation was restored. 



Cultures for Azotobacter were made six weeks after the soil had been 

 treated, and seven weeks later the nitrate content was determined. A 

 number of quantitative nitrogen determinations were lost through acci- 

 dent, but the qualitative results are sufficient for present needs. The 

 results are given in Tables V and VI. 



Table V. — Effect of carbon disulphid upon nitrogen fixation and nitrate accumulation 



NOT EVAPORATED 



EVAPORATED 



" Nitrogen fixed in milligrams per 50 cc. of culture. ^ Nitrates in milligrams per 100 gm. of soil. 



