BIENNIAL RETORT, 1927 AND 1928 305 



DEPARTMENT OF BACTERIOLOGY AND PHYSIOLOGY 

 G. E. Gage in Charge 



Nitrogen-Fixation in Relation to Legumes and Non-legumes under De- 

 fined Agronomic Conditions. (James E. Fuller'). The plan followed has 

 been to study soils of different units to determine tlie ability of these 

 units to fix atmospheric nitrogen; to isolate organisms from the units and 

 study the distribution of nitrogen-fixing organisms as compared with the 

 nitrogen-fixing power of the soil units; and lastly to study factors which 

 may influence the presence and activity of nitrogen-fixing organisms 

 isolated in these studies. 



The units, as suggested above, were obtained by dividing the experi- 

 mental j)lot into twenty-four units, so treated as to give the following 

 experimental conditions: 



1. LTnits planted with legumes and receiving fertilizer. 



2. LTnits planted with legumes but not receiving fertilizer. 



3. Units receiving fertilizer but not planted with legumes. 



4. Units not receiving fertilizer and not planted with legumes. 

 The fertilizers used were ammonium sulfate, sodium nitrate or dry 



ground fish. 



Each season, after the crops were harvested, nitrogen determinations 

 were made on both soil and croj). It had been expected that units imder 

 No. 1 would show the highest nitrogen content, under No. 4 the lowest, 

 and under Nos. 2 and 3 somewhere between. However, the results have 

 been inconsistent. It was assumed from this that the reason might pos- 

 sibly be found by making a biological survey of the plots to determine 

 the possible influence of micoorganlsms on the nitrogen content of the 

 soil. 



The nitrogen-fixing ptiwer of the soil units has been determined. An 

 organism belonging to the genus Azotobacter has been isolated and desig- 

 nated as 9A. It has been found to possess definite nitrogen-fixing power 

 and to be widely distributed in the plot units showing the greatest nitro- 

 gen-fixing power. Other organisms have been isolated and studied, among 

 them being several strains of Actinomyces. These Actinomyces exhibit a 

 tendency to use the nitrogen fixed by Azotobacter 9 A and other strains of 

 Azotobacter when cidtured with them in a synthetic medium. 



Studies are now under way to determine whether the nitrogen-fixation 

 in the different soil units is constant and also to establish how imiformly 

 distributed in the units is this new species Azotobacter 9A. Studies are 

 also being made of factors which influence the presence and activity of 

 Azotobacter 9A. These include hydrogen-ion values of the soil, availabil- 

 ity of various carbohydrates as sources of energy, and the effect of organic 

 and inorganic compoimds. 



It is hoped that the data accumulated in this study may furnish the 

 basis of practical methods by which the nitrogen-fixing organisms naturally 

 pretient In s-oil may be stimulated to greater activity. 



Laboratory Service. (Raljih L. France). This service was established 

 July 1, 1928, for the purpose of supplying to the residents of Massachusetts 

 information concerning problems of sanitation and bacteriology; of pro- 

 viding laboratory service for the study and solution of bacteriological 

 problems; and of improving methods of analysis and procedure. 



^ Mf. Fuller took charge of the work in 1928 ; previous to that time it was carried 

 on by Dr. Leon A. Bradley. 



