BACTERIA OF OLD SOILS 



111 



Kjeldahl method. Duplicates and sterile controls were run on 

 each soil. Macroscopic observations were also made on the con- 

 ditions of growth in the flasks. The results are given in table 4. 



Soil No. 2 possesses a very remarkable flora for it is the best 

 ammonifyer and now it proves to be first in nitrogen fixing power, 

 though it is an alkali soil. However, nitrogen fixation^^ as a 

 soil function has proved much more resistant to the alkali salts 

 than either ammonification or nitrification. The striking fixing 

 power of soil No. 2 is largely due to Clostridium pastorianum, 

 as indicated by gas production and formation of butyric acid 

 and corroborated by examination under the microscope. As 

 previously cited Lafar had observed the long Uved tendencies of 

 spores of this organism and my results give evidence of even 

 greater resistance than recorded by him. 



TABLE 4 



Nitrogen fixation 



NO. OF SOIL 



Mg. OP N 



ORIGINALLY 

 PRESENT IN SOIL 



Mg. OF N 



FOUND 



Mg. OF N 



FIXED 



CONDITION OP 

 FLASK 



1 



3.92 



5.18 



1.26 



No membrane 



2 



9.17 



13.05 



3.88 



Gas production 



3 



6.02 



8.49 



2.47 



Xo membrane 



4 



6.02 



7.98 



1.96 



No membrane 





4.41 



4.76 



0.35 



No membrane 



6 



lost 



10.50 





Gas production- 



7 



5.18 



6.65 



1.47 



No membrane 



8 



6.16 



8.00 



1.84 



Azotobacter 



9 



7.14 



8.61 



1.47 



No membrane 



In soil No. 8, Lipman" has previously isolated Azotobacter 

 Hilgardii which is still prevalent but has Httle fixing power. He 

 also isolated a spore-bearing nitrite-forming organism but was 

 unable to find Nitrobacter or Bacillus radicicola. In soil No. 2 

 the anaerobic form is present and in soil No. 8 the aerobic spe- 

 cies of the prominent nitrogen fixing organisms persists; with 

 these two exceptions all other Azotobacter types and Clostridium 



In a paper to appear in the near future Lipman and Sharp have shown that 

 the nitrogen fixation flora resists to a far greater degree the presence of alkali 

 salts in the soil than either the ammonification or nitrification floras. 

 " Science, June, p. 942. 1909. 



