48o 



Journal of Agricultural Research 



Vol. XII, No. 8 



on the bacteria is derived from the basic part of these compounds, then 

 the salts of these substances — namely, magnesium and calcium chlorid — 

 should increase the number of bacteria in a similar manner. These salts 

 were added in quantities equivalent to o.i per cent of the dry weight of 

 the soil. The data for this experiment are presented in Table VI. 



The chlorids of calcium and magnesium failed to increase the number 

 of bacteria in Colby silt loam. Instead, the majority of cases showed a 

 loss, especially with calcium chlorid. Calcium and magnesium carbo- 

 nates, in agreement with a previous study, increased the number of 

 microorganisms. Magnesium carbonate stimulated the development of 

 the bacteria far greater than did calcium carbonate. 



When the dibasic magnesium phosphate and monocalcium phosphate 

 were applied alone there did not seem to be any gain in the number of 

 bacteria. The mixtures of monocalcium phosphate and dibasic mag- 

 nesium phosphate with magnesium carbonate resulted in all except one 

 period in an increase in the number of bacteria beyond that obtained by 

 the use of magnesium carbonate alone. The mixtures made by adding 

 these same phosphates with calcium carbonate did not result in an 

 increase in the number of bacteria beyond that noted where calcium car- 

 bonate was used alone. 



From the data of this experiment, which are diagramed in figures 7 

 and 8, it seems safe to conclude that neither the phosphates nor the 

 chlorids of magnesium and calcium alone caused a marked multiplica- 

 tion of the bacteria in Colby silt loam. 



Miami silt loam. — A similar test of these different compounds was 

 made with Miami silt loam, a neutral soil. The chlorids of magnesium 

 and calcium were eliminated in this experiment. Since the effect of a 

 carbonate on the number of bacteria in Miami silt loam soil was not 

 known, the carbonates were added in amounts equal to the one-half and 

 full calcium carbonate requirement of Colby silt loam. The data for 

 this experiment are presented in Table VII. 



Table VII. — Influence of calcium carbonate, magneshim carbonate, dibasic magnesium 

 phosphate, and monocalcium phosphate on the number of bacteria in Miami silt loam 



Treatment. 



None 



One-half calcium carbonate 



Full calcium carbonate 



One-half magnesium carbonate 



Full magnesium carbonate 



0.1 per cent monocalcium phosphate 



0.1 per cent dibasic magnesium phosphate. . 

 0.1 per cent monocalcium phosphate -h full 



calcium carbonate 



0.1 per cent dibasic magnesium phosphate 



-t-full calcium carbonate 



0.1 per cent monocalcium phosphate + full 



magnesium carbonate 



0.1 per cent dibasic magnesium phosphate 



+full magnesium carbonate 



Number of bacteria in i gm. of dry soil. 



After 1 week, 



10, 000, 000 

 10,300,000 

 13,800,000 

 17,000,000 

 27,000,000 

 10,600,000 

 15, 700,000 



12,400,000 



II, 100,000 



20, 000, 000 



21,600,000 



Rela- 



100 

 103 

 13S 

 170 

 270 

 106 

 157 



200 

 216 



After 2 

 weeks. 



18,500,000 

 18,500,000 

 23 , 700, 000 

 25,400,000 

 52,400,000 

 20. 400, 000 

 27,000,000 



24, 000, 000 



20, 000, 000 



35,000,000 



43 , Soo, 000 



Rela- 

 tive. 



100 

 100 

 128 

 137 

 283 

 no 

 146 



130 



108 



1S9 



236 



After 3 Rela- 

 weeks. tive. 



9, 600, 000 

 13,800,000 

 15, 100,000 

 15, 500,000 

 21,600,000 

 12,300,000 

 14,300,000 



13 , 500, 000 



14, 600, 000 



19, 000, 000 



II, 700,000 



100 

 143 

 IS7 

 161 

 22s 

 12S 

 ISO 



140 



isa 



198 



