14 University of California Publications in Agricultural Sciences [Vol. 1 



show quantitative as well as qualitative figures iu these as well 

 as other experiments, that in the absence of Azotobacter only 

 very slight fixations of nitrogen or none are obtained. 



From the results set forth in table III, it appears that only 

 one soil of the eleven tested shows the presence of Azotobacter 

 as deep down as the fourth foot and six others show the pres- 

 ence of these organisms in the third foot. Most of them, how- 

 ever, show the presence of Azotobacter in vigorous form only 

 in the first two feet. It is therefore not sufficient, evidently, for 



TABLE III 



NiTROGEX Fixation ix Soil Columns 



Soil No. 1 2 3 4 5 G 7 8 9 10 11 



1st ft. + + + + + + + + + + + + + + + — + + + — — — + + 



2mlft. ++ + + + + + + + + + + + + — + + + — — — + + 



3rd ft. + — ++ + + + + + + — ++ — — — + + 



4th ft. _ _ — — + + + — — — — — + 



5th ft. — — — — — — — _ — — — 



6th ft. — — — — — — — -___ 



7th ft. — — — — — — — — — — — 



8th ft. — — — — — — — _ — — — 



9th ft. — — — — — — — — — — _ 



10th ft. — — — — — — — — — — — 



11th ft. — — — — — — — — — — — 



12th ft. — — — — — — — — — — — 



soils to be chemically and physically as favorably constituted as 

 these soils are for ammonification and nitrification to encourage 

 the deeper penetration of Azotobacter. As is well known, these 

 organisms are extremely sensitive to a lack of oxygen and it 

 would appear that this circumstance regulates and controls the 

 penetration of Azotobacter organisms as above portrayed. I think 

 in addition, however, it may fairly be argued that the presence 

 of Azotobacter in more than half of these soils in the third foot 

 is. in itself, a favorable indication of the nature of the soils in 

 question. It is of intere-st also that, iu soil No. 5, Azotobacter 

 organisms, with the nitrogen-fixing power as vigorous as those 

 above, were found in the fourth foot. This, so far as the writer is 



