BACTERIA OF FROZEN SOIL.* 



H. JOEL CONN. 



SUMMARY. 



i. The number of bacteria in frozen soil is generally larger than in 

 unfrozen soil. This fact was first noticed by the writer in 1910-11 

 when connected with the Cornell University Agricultural Experi- 

 ment Station. Recently it has been observed at a different locality 

 and in two other soils, one very different from the first. It is true 

 not only of cropped soil, as shown in the previous work, but also 

 of sod and fallow soil. 



2. The increase in number of bacteria after freezing is not due to 

 the increase in soil moisture which usually occurs in winter. 



3. The same increase in germ content may take place in potted 

 soil, where there is no possibility that the bacteria are carried up 

 mechanically from lower depths during the process of freezing. 



4. The facts noted under the headings 2 and 3 make it very 

 probable that the phenomenon is due to an actual growth of bacteria 

 after the soil is frozen. Its influence on fertility is still an unknown 

 factor. 



5. The results given in this bulletin were obtained in a different 

 laboratory and under quite different conditions from those previously 

 reported, thus partly eliminating errors which might have crept 

 in because of peculiarities of technique. 



INTRODUCTION. 



Until recently considerable attention was given to variations in 

 numbers of bacteria in soil at different seasons and under various 

 conditions; but it is now realized that quantitative work alone is of 

 small significance, and this line of investigation has been largely 

 abandoned. As a result we know very little about the seasonal 

 variation in either kinds or numbers of the bacteria in soil. A study 

 of qualitative seasonal variations has never been undertaken. 

 Samples for quantitative study have often been secured from green- 

 house soil; or, if from the field, they have not been taken frequently 

 enough or for a sufficiently long period to yield complete data. The 

 flora of winter soil, in particular, has scarcely been studied. 



It was assumed, for a long time, that bacterial activity was almost, 

 if not completely, absent while soil was frozen. This assumption 

 was supported by both theoretical and experimental evidence. 



* Reprint of Technical Bulletin No. 35, July. 



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