Feb. 2$, 1918 



Influence of Carbonates on Soil Bacteria 



493 



INFLUENCE OF CALCIUM CARBONATE, MAGNESIUM CARBONATE, AND LIME- 

 STONE ON BACILLUS AZOTOBACTER IN STERILIZED SOIL 



Colby silt loam. — Dry soil in 200-gm. portions was treated with cal- 

 cium carbonate, with magnesium carbonate, and limestone, and placed 

 in 500-c. c. Erlenmeyer flasks. To each flask was added i per cent of 

 mannit by weight of dry soil. The flasks were plugged, sterilized, and 

 sterile water was added to bring the soil to the proper moisture content. 

 Inoculations of Bacillus azotobacier in pure culture were then made by 

 adding a i-c. c. suspension of the organisms to each flask. The entire 

 set of flasks was incubated at 27° C, and after one, two, and three weeks 

 plate counts, using mannit agar, were made. The results for this experi- 

 ment are recorded in Table XV. 



Table XV. — Influence of calcium carbonate, magnesium carbonate, and limestone on 

 Bacillus azotobacter in Colby silt loam treated with mannit 



Treatment. 



Number of bacteria in i gm. of dry soil. 



After I week. 



After 2 weeks. 



After 3 weeks. 



None 



One-fourth calcium carbonate 



One-half calcium carbonate 



Full calcium carbonate 



One-fourth limestone 



One-half limestone 



Full limestone 



One-fourth magnesium carbonate 

 One-half magnesium carbonate. . 

 Full magnesiiun carbonate 



602, 

 200, 

 400, 

 <i. 

 <i, 

 <i, 

 200, 

 150, 

 800, 



<i,ooo 



4, 170,000 

 12,500,000 

 11,350,000 



<I,000 



<i,ooo 



850,000 



3, 620, 000 



47, 000, 000 



477,000,000 



<I,000 



2,440,000 



32,300,000 



45,500,000 



<i,ooo 



<i,ooo 



26, 000, 000 



10,350,000 



268, 000, 000 



355,000,000 



The results of this experiment showed the striking effect of magnesium 

 carbonate on the multiplication of Bacillus azotobacter cells in Colby silt 

 loam soil. Calcium carbonate caused an increase in the number of these 

 organisms, but the increase was not as great as that obtained with mag- 

 nesium carbonate. With limestone the increase was very small. This 

 great gain with magnesium carbonate was obtained where amounts 

 equal to full neutralization were applied. After the third week the one- 

 half neutralization by magnesium carbonate also gave a large increase, 

 while two weeks after treatment the greatest gain was shown. 



INFLUENCE of large APPLICATIONS OF MAGNESIUM CARBONATE ON 

 BACILLUS AZOTOBACTER IN STERILE SOIL 



Colby silt loam.— Because magnesium carbonate when applied to give 

 neutralization, increased the number of Bacillus azotobacter in sterilized 

 Colby silt loam soil to a great extent, a further test was made to deter- 

 mine if heavier applications, enough added to give a distinct alkaline 

 reaction, would continue to increase the reproduction of Bacilhis azoto- 

 bacter. These applications were made by adding magnesium carbonate 

 suflBcient to make iXi iX» ^^^ double neutralization. 



