﻿THE OCCURRENCE OF BACTERIA IN FROZEN SOIL 



E. C. Harder 



(with two graphs) 

 Introduction 



The results of various investigators, notably Conn and Brown, 

 have shown that the actual number of bacteria in the soil often 

 increases with a decrease in temperature. This phenomenon is 

 not confined to a gain in the number of bacteria alone, but is accom- 

 panied by a stimulation of the activity of the microorganisms. 

 Many bacteriological processes, as ammonification, denitrification, 

 and free nitrogen fixation, have shown an increase in frozen soils. 



Because of the practical importance of this problem for agri- 

 cultural practice it was thought advisable to note the effect of 

 cold and moisture on the number of bacteria in Madison soil. 

 Here the variations in temperature are greater than those recorded 

 by former investigators. 



In order to study what effect these great variations would exert 

 on the number of bacteria, a series of plate counts was made. 

 If the number of bacteria in the soil increases with freezing, there 

 should be a parallel increase in available plant food. Many ques- 

 tions arise. Do all soils when sampled in the winter show the same 

 general increase? What effect does stimulation of bacteria have 

 on soil fertility ? It has been noted that an increase in bacterial 

 activity results in an increase in food for higher plants. The 

 increase in the number of bacteria during the winter probably plays 

 an important part in soil fertility. This is decidedly at variance 

 with the earlier idea that frozen soils are dormant. 



Previous work 



The more recent experiments on the activity of bacteria in 

 frozen soil were conducted by Conn 1 and Brown and Smith. 2 



• Conn, H. J., Bacteria in frozen soil. I and II. Centralbl. Bakt. 28:422-434. 

 1 Brown, P. E., and Smith, R. E., Bacterial activities in frozen soils. Agric. 

 507] [Botanical Gazette, vol. 61 



