Feb. 2Si 1918 



Influence of Carbonates on Soil Bacteria 



497 



Table XIX. — Influence oj calcium carbonate and magnesium carbonate on Bacillus 

 radicicola {lupine) in sterile Colby silt loam treated with mannit 



From the data given in Table XIX it is evident that the lupine strain 

 of Bacillus radicicola was benefited to as great an extent as the alfalfa 

 strain when Colby soil was treated with magnesium or calcium carbo- 

 nate. After the second and third weeks the counts showed that mag- 

 nesium carbonate gave better results than did calcium carbonate. The 

 untreated soil gave a slightly higher number than was obtained with the 

 alfalfa strain under similar conditions. This difference may be due to 

 the fact that the lupine strain is slightly tolerant to an acid reaction. 



Here, as in the tests made with unsterilized soil, the smaller applications 

 stimulated multiplication to a greater extent, in proportion to the 

 amounts applied, than did the larger treatments. However, the maxi- 

 mum gain in number of bacteria was obtained with full magnesium- 

 carbonate treatment. From the data obtained in this and the preceding 

 experiment it is clearly evident that either magnesium or calcium car- 

 bonate (the magnesium to a somewhat greater degree than the calcium) 

 greatly increased the number of legume bacteria, alfalfa and lupine 

 strains, in an acid soil. 



CONCLUSIONS 



From a general review of the results of the experiments just described 

 It is clearly shown that carbonates of calcium and magnesium when 

 applied to acid Colby silt loam, acid Plainfield sand, and neutral Miami 

 silt loam increase the number of bacteria. A greater increase was 

 obtained in the acid soils than in the neutral Miami silt loam. These 

 carbonates increased the number of bacteria in both sterilized and un- 

 sterilized soil. The sterilized soil was inoculated with an organism in 

 pure culture. Not only was the number of bacteria in the soils increased 

 by applications of magnesium and calcium carbonates, but an increase 

 in activity of the various groups of bacteria was shown. 



The form of carbonate which gave the best results was magnesium 

 carbonate. There was an enormous increase in the number of bacteria 

 produced by the magnesium carbonate over that of calcium carbonate. 

 Ground dolomitic limestone did not prove quite as efficient as calcium 



