464 Journal of Agricultural Research volxii.no.s 



REVIEW OF LITERATURE 



A complete review of the literature, showing the effect of lime (CaO).. 

 calcium carbonate (CaCOg), and magnesium carbonate (MgCOg) on soil 

 microorganisms, is not attempted in this paper. Only a brief resume of 

 certain of the more important papers is given. 



Although this paper is primarily concerned with the relation of soil 

 microorganisms to calcium and magnesium carbonates, it was deemed 

 worth while to include a brief review of results obtained from the use of 

 lime and limestone. Under ordinary soil conditions, calcium oxid, or 

 lime, is soon converted into calcium carbonate. Because of the frequent 

 occurrence of magnesium in limestone, this substance was included in 

 the discussion. 



NUMBKR OF ORGANISMS 



In 1 90 1 Chester (7)^ made plate counts of an acid soil which had re- 

 ceived lime at the rate of i ,000 to 4,000 pounds per acre. In every case 

 the lime increased the total number of bacteria; the greatest gain was 

 noted where the largest amount of lime was applied. 



Fischer {18) treated soil with lime and calcium carbonate at the rate 

 of 0.1 to 3.0 per cent by weight of soil. The calcium carbonate and lime 

 were added in gram-molecular equivalents. His results showed that 

 0.1 and 0.2 per cent of lime after three days gave an increase in the 

 total number of bacteria. Treatments amounting to 0.5 per cent and 

 more were harmful at first, but later gave an increase beyond that of the 

 control. The data showed that a slight increase in the number of bac- 

 teria occurred when calcium carbonate was added to the soil. 



Several years later, Hutchinson (25) made somewhat similar experi- 

 ments, using lime and calcium carbonate. He also found that lime at 

 first exerted a depressing effect but later gave rise to an increase in the 

 number of bacteria. He concluded that the reduction in the number of 

 bacteria immediately after treatment with lime was due to the caustic 

 effect of the oxid, since no injury was noted after the oxid changed to 

 carbonate. He believed the benefit from liming was due in part to the 

 gain in soluble organic matter, to the improvement in the physical con- 

 dition, and to the correction of the acid reaction of a soil, all of which 

 tended to bring about a better environment for the development of bac- 

 teria. However, this investigator held that these changes brought 

 about by the action of liming did not seem sufficient to account for the 

 enormous increase in plant growth. He assumed, therefore, that the 

 action of lime was much the same as an antiseptic — that is, it caused a 

 partial sterilization. 



In a later publication, Hutchinson and MacLennan (24) reported the 

 results of experiments with lime and calcium carbonate on five different • 

 soils. The range of reaction in these soils varied from neutral to strongly 



1 Reference is made by number (italic) to " Literature cited," pp. 500-504. 



