BIOLOGICAL SOIL PROCESSES 



607 



Experiment IX. Nitrogen fixation in soils. Nitrogen in milligrams per 10 

 grains of soil. 



Aerobic 



Anaerobic 



Greenhouse. 



Loam 



Clay 



8.50 

 5.29 

 4.69 



In these experiments greater amounts of nitrogen are fixed 

 under anaerobic conditions than under aerobic conditions. There 

 is a gradation shown under anaerobic conditions, most nitrogen 

 being fixed by the greenhouse soil, less by the loam and least 

 by the clay. 



In the following experiment soil was sterilized in the autoclave 

 and mass cultures grown under aerobic and anaerobic conditions 

 in mannite solution were added. 



Experiment X. Nitrogen fixation in sterile soil. Nitrogen in milligrams per 

 10 grams of soil. 



Aerobic 



Greenhouse. 



Loam 



Clay 



NITROGEN AT END 



24.67 



12.50 



5.60 



NITROGEN AT 

 BEGINNING 



26.32 

 9.32 

 4.34 



LOSS OH GAIN 



-1.65 

 3.10 

 1.26 



Anaerobic 



Greenhouse. 



Loam 



Clay 



The number of bacteria per gram of soil, capable of growing 

 on nitrogen poor media, was estunated on three different media 

 under aerobic and anaerobic conditions. The following media 

 were used: 



