474 



Journal of Agricultural Research 



Vol. XII, No. 8 



phosphate and one-fourth calcium carbonate requirement was used. It 

 is surprising that this combination should favor the development of bac- 

 teria more than a heavier application of the same combination (fig. 4). 



INFI^UENCE OF MAGNESIUM CARBONATE ON THE NUMBER OP BACTERIA 



IN SOIIv 



Colby silt loam. — Since pure calcium carbonate or dolomitic lime- 

 stone failed to give a large increase in the total number of bacteria, an 

 attempt was made to determine what effect magnesium carbonate would 

 have on the soil flora. Accordingly an experiment was planned in which 

 pure magnesium carbonate was added to the soil. The magnesium car- 



12 3 4 5 6 7 



i Weeh 



12 3 4 5 6 7 



2U/eeki 



I 2 3 4 5 6 r 

 3 ureehs 



1^34567 



<3 Uree/o 



I 2 3 4 5 b 7 

 20 UreeAa 



Fig. 4. — Diagram showing the influence of calcium carbonate and monocalcium phosphate on the number 



of bacteria in Plainfield sand. 

 x«>no treatment. 



9=0.5 gm. monocalcium phosphate. 

 3= 1 gm. monocalcium phosphate. 



4=>o.s gm. monocalcium phosphate+one-fourth calcium carbonate. 

 5—0.5 gm. monocalcium phosphate+full calcium carbonate. 

 6= a gm. monocalcium phosphate+one-fourth calcium carbonate. 

 fee 2 gm. monocalcium phosphate+full calcium carbonate. 



bonate was applied to the soil in the gram-molecular equivalent of cal- 

 cium carbonate. The procedure in this experiment was similar to that 

 just described. The results of this test are presented in Table III. 



TablS III. — Influence of magnesium carbonate on the number of bacteria in Colby silt 



loam 



Treatment. 



None , 



One-fourth mag- 

 nesiiun carbon- 

 ate 



One-half magne- 

 sium carbonate. 



Full magnesium 

 carbonate 



Number of bacteria in i gm. of dry soil. 



After 

 I week. 



Rela- 

 tive. 



25, 200, 00c 



36, 600, 000 

 44, 800, 000 

 156,000,000 



14s 

 178 

 61S 



After 

 2 weeks. 



21,000,000 



29, 700, 000 

 41,000,000 

 125,000,000 



Rela- 

 tive. 



After 

 3 weeks. 



19,300,000 



30, 500, 000 

 45, 200,000 

 74, 500, 000 



Rela- 

 tive. 



157 

 234 

 386 



After 

 8 weeks. 



Rela- 

 tive. 



14, 000, 000 



17. 200.000 



19.400.0001 138 

 59,100,000 422 



After 

 20 weeks. 



8, 600, 000 



II, 700,000 

 12,200,000 

 26,000,000 



Rela- 

 tive. 



136 

 141 

 30a 



