Feb. 2s. 1918 Influence of Carbonates on Soil Bacteria 



471 



as compared with limestone was due probably to the difference in solu- 

 bility of the two compounds; pure calcium carbonate is more soluble 

 than the dolomitic limestone. 



The monocalcium phosphate in small amounts apparently did not in- 

 crease the total number of bacteria, whereas in larger amounts, applied 

 alone, it was slightly beneficial. In two instances a combination of 

 calcium carbonate and phosphate showed an increase in the total num- 

 ber of microorganisms. However, in most cases the increase was no 

 greater than that obtained with calcium carbonate alone. 



I 2 i 4 5 e 7 



I U/eeA 



/ 2 3 4 5 6 7 

 ZWeehs 



I 2 i t 5 b 1 



3 U/ee/(i 



I z i4 5 b r 



t 2 3 ■^ 5 b 7 



FiO. I. — Diagram showing the influence of calcium carbonate and limestone on the number of bacteria in 



Colby silt loam. 



i=- no treatment. 

 2"=one-fotirth cacium carbonate. 

 3= one-half calcium carbonate. 

 4= full calcium carbonate. 



5= one-fourth limestone. 

 6= one-half limestone. 

 7= full limestone. 



A comparison of the influence of calcium from calcium phosphate 

 with that from calcium carbonate on the number of bacteria in Colby 

 silt loam is shown in figure 2. Although there are many fluctuations, 

 the results indicate that calcium phosphate alone or with calcium car- 

 bonate increases the number of bacteria much sooner than does the 

 carbonate alone. Here the maximum gain with the phosphate was 

 noted 3 weeks after treatment instead of 20 weeks, as in the case of cal- 

 cium carbonate. 



PLAiNFiEiyD SAND. — ^The preceding experiment was repeated with a 

 Plainfield sand, a soil very low in organic matter. The results obtained 

 in this test are presented in Table II. 



