494 



Journal of Agricultural Research 



Vol. XII. No. 8 



The data for this test, presented in Table XVI, showed that i}4 mag- 

 nesium — carbonate treatment after one week gave a greater increase in 



the number of Bacil- 



2,500,000 



lus azotobacter cells 

 than was obtained by 

 the iX application; 

 after two and three 

 weeks, the iX treat- 

 ment gave a greater 

 increase than was ob- 

 tained by the i}4 

 treatment. In every 

 case the heaviest ap- 

 plication of magne- 

 sium carbonate caused 

 less increase in the 

 number of these or- 

 ganisms than did the 

 lighter treatments. 

 However, as compared 

 with the control, the 

 heavy application also 

 gave a great increase. 

 In comparing the 

 data of Table XVI 

 with those of Table 

 XV, it will be seen 

 that iX ^^^ ill most 

 cases i}4 magnesium- 

 carbonate treatment 

 caused a greater in- 

 crease in the number 

 of Bacillus azotobacter 

 organisms in sterilized 

 Colby silt loam than 

 the full treatment. It 

 is difficult to explain 

 why such an enor- 

 mous increase in the 

 number of these or- 

 ganisms was obtained 

 when more than 

 enough magnesium 

 carbonate was added 

 to neutralize the soil acids. From the data in Table XVI, one is led to 

 believe that this great multiplication in Bacillus azotobacter cells was due 



12 3 4 

 lUTeek 



t Z 3 -t- 

 BU/eeh 





Fig. II.— Diagram showing the influence of large applications of mag- 

 nesium carbonate on Bacillus azotobacter in sterile Colby silt loam. 



I— no treatment. 



9=» il4 magnesium carbonate. 



3= 1^2 magnesium carbonate. 

 4= double magnesium carbonate. 



