470 



Journal of Agricultural Research 



Vol. XII, No. 8 



Table I. — Influence of calcium carbonate, limestone, and monocalcium phosphate on the 

 number of bacteria in Colby silt loam 



Treatment. 



None 



One-fourth calcium 

 carbonate 



One-half calcium 

 carbonate 



Full calcium car- 

 bonate 



One - fourth lime- 

 stone 



One-half limestone. . 



Full limestone. . . . . . 



o.s sm. monocalcitmi 

 phosphate 



9 gm. monocalcium 

 phosphate 



0.5 gm. monocalcium 

 phosphate + one- 

 fourth calcium car- 

 bonate 



o.s gm. monocalcium 

 phosphate + full 

 calcium carbonate . 



s gm. monocalcium 

 phosphate + one- 

 f ointh calciimi car- 

 bonate 



3 gm. monocalcium 

 phosphate -f full 

 calcium carbonate . 



Number of bacteria in i gm. of dry soil. 



After I 

 week. 



iS, 600, 000 

 21,000,000 



20, 500, 000 



18, 100, 000 



21,000,000 

 25,300,000 

 22,300,000 



14, 300, 000 

 22,300,000 



16,000,000 

 21,300,000 



14, 300, 000 



16, 100,000 



Rela- 

 tive. 



After 2 

 weeks. 



100 xg, 

 113 

 III 

 97 



120 18. 



200,000 



400,000 



000,000 



200,000 



500,000 

 500,000 

 100,000 



15,500,000 



21,000,000 



15,000,000 

 31,700,000 



21,100,000 

 20, 900, 000 



Rela- 

 tive. 



100 

 116 

 I3S 

 110 

 127 



lOI 



94 

 80 

 109 



78 



109 



108 



After 3 

 weeks. 



Rela- 

 tive. 



12,800,000 

 21,300,000 

 14,000,000 

 13,100,000 



15,000,000 



15,500,000 

 20,700,000, 



18,000,000 



20, 200, 000 



18,300,000 



33,500,000 



26,200,000 

 35,600,000 



204 



278 



After 8 

 weeks. 



000,000 



000,000 



000,000 



000,000 



,000,000 

 ,900,000 

 , 100,000 



,500,000 



,600,000 



17,300,000 

 15,400,000 



15,300,000 



12, 500,000 



Rela- 

 tive. 



100 



138 



100 



138 



123 

 114 

 131 



X03 



104 



132 

 119 



117 



97 



After 20 

 weeks. 



Rela- 

 tive. 



, 700, 000 



,400,000 



, 700, 000 



,600,000 



,500,000 

 ,500,000] 

 , 700,000 



, 400, 000 



,300,000' 



100 

 »4S 



230 



203 



20t 

 173 

 189 



95 



134 



17,400,000 365 

 i4f3°o>o<'<' 2*S 



11,600,000 



11,000,000 



173 

 164 



It will be seen from the figures in Table I that in practically every case 

 calcium carbonate, either pure or in the form of limestone (dolomitic), 

 increased the growth of bacteria to a considerable extent. As compared 

 with the untreated soil, the favorable influence of the calcium compounds 

 on the number of bacteria was greatest 3, 8, and 20 weeks after treat- 

 ment. Apparently these compounds of calcium, especially the carbonate, 

 have little influence on the soil flora for the first week. This is to be 

 expected, since calcium carbonate is very slowly soluble. 



The most striking fact noted from the results of this experiment is 

 the marked stimulation of the microorganisms following small applica- 

 tions of calcium carbonate. Figure i is a diagram showing the effect 

 of calcium carbonate and limestone on the total number of bacteria. 

 One-fourth enough calcium carbonate to neutralize the entire soil acidity, 

 with only one exception, showed the greatest increase in the number of 

 bacteria. If grouped according to their effect on the number of soil 

 organisms, one-fourth calcium carbonate gave the greatest gain in the 

 number of bacteria, one-half, the next greatest, and full, the least. The 

 beneficial effect of calcium carbonate extended over the entire period of 

 five months — that is, the treated soil gave a decided increase in the total 

 number of bacteria as compared with the untreated soil. In general, 

 pure calcium carbonate proved superior to limestone in its effect on the 

 bacteria of Colby silt loam soil. This superiority of calcium carbonate 



