Feb. 35, 1918 



Infltience of Carbonates on Soil Bacteria 



473 



The results reported in Table II differ somewhat from those obtained 

 with Colby silt loam. One week after the treatment there was a decrease 

 in the number of bacteria in the soil treated with both the calcium car- 

 bonate and limestone. However, after the first week the treated soil 

 showed an increase in the number of bacteria. 



In contrast with the results of the Colby silt-loam experiment, the 

 Plainfield sand, to which one-fourth calcium carbonate or limestone was 

 added, did not give any marked gain in the total number of bacteria 

 after i and 2 weeks. After 3, 8, and 20 weeks, one-fourth calcium car- 

 bonate caused a slight increase in the number of soil organisms. It is 

 evident that one-half or full neutralization of the soil acids by the calcium 

 carbonate was required to give the greatest increase in the number of 

 bacteria (fig. 3). 



12 3-^567 



I Week 



I Z i ^ 5 6 7 



2 U/ee/(s 



12^^567 



3 U/eeki 



12 3-9 567 



d UreeJts 



I Z 3 i 5 6 7 



20 WeeAi 



Fio. 3.— Diagram showing the influence of calcium carbonate and limestone on the number of bacteria in 



Plainfield sand. 



I— no treatment. 

 3= one-fourth calcium carbonate. 

 3— one-half calcium carbonate. 

 4= full calcium carbonate. 



S= one-fourth limestone. 

 6= one-half limestone. 

 7=full limestone. 



In general, light applications of limestone gave a greater increase in 

 the number of microorganisms than did calcium carbonate. A difference 

 in the nature of the soil acid in Colby and Plainfield sand probably ac- 

 counts for the difference in quantity of calcium carbonate required to 

 stimulate the reproduction of bacteria. 



Where monocalcium phosphate was added alone to the sandy soil, 

 practically no increase in the number of bacteria was obtained. A com- 

 bination of the phosphate with calcium carbonate apparently did not 

 stimulate the multiplication of bacteria any better than did calcium 

 carbonate alone except where a combination of 0.5 gm. of monocalcium 



