478 



Journal of Agricultural Research 



Vol. XII, No. 8 



mixtures of calcium and magnesium carbonates are not favorable to the 

 development of soil bacteria. 



To study the effect of a mixture of calcium and magnesium carbonates 

 on the total number of bacteria in both Colby silt loam and Plainfield 

 sand, a series of tests was made. This mixture was employed in amounts 

 equivalent to the neutralizing power of calcium carbonate — that is, 

 enough of the mixture was added to neutralize one-fourth, one-half, and 

 all of the soil acids. Each mixture was made by adding che carbonates 

 in gram-molecular equivalent amounts. The results are presented in 

 Table V. 



Table V. — Influence of a mixture of calcium and m,agnesiiim, carbonates on the number 

 of bacteria in Colby silt loam and Plainfield sand 



COLBY SILT LOAM 



PLAINFIELD SAND 



It will be seen from the figures of the table that a mixture of calcium 

 and magnesium carbonates increased the number of bacteria in CoBby 

 silt loam and Plainfield sand. The most interesting fact ascertained 

 from this test is that magnesium carbonate plus calcium carbonate is 

 less efficient in its efifect on the reproduction of bacteria than the equiva- 

 lent weight of magnesium alone. 



