Feb. as. 1918 



Influence of Carbonates on Soil Bacteria 



495 



to something besides the correction of the soil acidity, 

 in Table XVI are presented graphically in figure 1 1 . 



The entire data 



Table XVI. — Influence of large applications of magnesium carbonate on Bacillus azoto- 

 bacter in Colby silt loam treated with fnannit 



INFLUENCE OF MAGNESIUM CARBONATE ON BACILLUS AZOTOBACTER IN 

 STERILE NEUTRAL SOIL 



Miami silt loam. — Since magnesium carbonate increased the number 

 of Bacillus azoiobacter cells in an acid soil when more than enough of the 

 carbonate was added to neutralize the acidity, an experiment was planned 

 to determine the effect this compound would have on Bacillus azoiobacter 

 in a neutral soil. The soil selected for this work was Miami silt loam, 

 previously described. Magnesium carbonate, along with i per cent 

 mannit, was added in one-fourth, one-half, and full neutralization based 

 on the acidity of Colby silt loam. The data for this test are tabulated in 

 Table XVII. 



Table XVII.- 



-Influence of magnesium carbonate on Bacillus azoiobacter in sterile 

 Miami silt loam treated with m,annit 



In studying the data in this table, it will be seen that in Miami silt 

 loam, a neutral soil, where magnesium carbonate was applied in an 

 amount great enough to neutralize all the active acidity in Colby soil, 

 there was a great increase in the number of Bacillus azoiobacter cells. 

 At this time no explanation can be offered to account for the drop in 

 number after two weeks where one-half and full magnesium carbonate 

 were applied, since the other counts, made after one and three weeks 

 with the one-half and full application gave a decided increase. The 

 count made after the 3-week period showed the greatest increase. From 

 the results of Table XVII it is clear that magnesium carbonate plaj's some 

 role in stimulating the B. azoiobacter organism other than that of 

 neutralization. 



27811°— 18 3 ' 



