Feb. 25. 1918 Influence of Carbonates on Soil Bacteria 499 



in the number of bacteria. In the neutral soil magnesium phosphate 

 proved superior to calcium phosphate in stimulating the bacteria; in 

 acid soil neither compound appeared to benefit the soil flora. 



SUMMARY 



(i) The number of bacteria in acid Colby silt loam and acid Plain- 

 field sand is increased by the applications of calcium carbonate, mag- 

 nesium carbonate, or limestone. 



(2) Magnesium carbonate increases the number to a much greater 

 extent than does either calcium carbonate or limestone. 



(3) Monocalcium phosphate and dibasic magnesium phosphate slightly 

 increase the total number of bacteria in neutral soil. 



(4) Nitrification is benefited by limestone, calcium-carbonate, and 

 magnesium-carbonate treatment. Magnesium carbonate in soil to 

 which no nitrogenous substance was added favors nitrate accumulation 

 more than does either calcium carbonate or limestone. The phosphates 

 increase the accumulation of nitrate nitrogen to a very small extent. 

 When gelatin was applied to the soil, magnesium carbonate did not 

 benefit nitrification any more than calcium carbonate or limestone. 



(5) Ammonification in Colby soil is benefited by all three forms of 

 the carbonates, while in Plainfield sand a decrease in ammonia is shown. 

 Monocalcium phosphate increases ammonification in both soils. 



(6) Pure cultures of Bacillus tuinescens and B. suhtilis ammonify 

 blood meal better when sterile Colby soil is treated with any one of the 

 three forms of carbonates. 



(7) A culture of B. azotobacter in the two soils treated with the car- 

 bonates and mannit fails to show an increase in total nitrogen in the 

 sand and only a slight gain in the Colby soil. 



(8) Pure cultures of B. radicicola, of both alfalfa and lupine strains, 

 and B. azotobacter are greatly benefited when inoculated into sterile 

 Colby soil previously treated with magnesium or calcium carbonate. 

 Limestone barely increases the number of B. azotobacter in Colby soil. 

 In neutral and acid soils treated with magnesium carbonate until the 

 soils were strongly alkaline, B. azotobacter is greatly increased in munber 

 over that of the untreated. 



(9) From the data considered as a whole, magnesium carbonate is 

 superior to calcium carbonate or limestone in stimulating the reproduc- 

 tion of bacteria in Colby gilt loam and Plainfield soils. In general, the 

 smaller applications of either compound give better results than do the 

 heavier applications. 



