THE MICRO-ORGANIC POPULATION OF THE SOIL 277 



of CO 2 in the soil air, at frequent intervals for a period of two 

 seasons on several of the plots. The experimental data do not 

 represent the amounts of production but only of accumulation ; 

 nevertheless the curves are found to give useful information as 

 to production. 



TABLE LXXIV. BACTERIA IN GARDEN SOIL, NEW JERSEY, MILLIONS PER 

 GRAM. WAKSMAN (2920). 



These figures are for the top inch : samples were taken at six different 

 depths with similar results. 



In the first instance it is observed that the curves are all 

 sufficiently alike to justify the view that in the soil, as in the 

 laboratory, the phenomena of nitrate production and CO 2 

 evolution are closely related to the numbers of bacteria. When 

 the bacterial numbers rise there is a rise in the amount of COg 

 and of nitrate. But the nitrate curve does not sharply agree 

 with the others : it is displaced, showing a lag of two or three 

 weeks. 



The general results are illustrated by the curves in Fig. 26. 

 During the winter months there is very little activity. But 

 as soon as the temperature rises above 5 C. change sets in : 

 bacterial numbers, COg, 1 and nitrates all increase. The rise, 

 however, is not long sustained ; it is followed by a fall, not- 

 withstanding the continuance of favourable temperature con- 

 ditions. To some extent this is due to lack of moisture, for 

 the curves now begin to resemble the soil moisture curves. 

 It is also due to lack of something supplied by rain presum- 

 ably dissolved oxygen for the rainfall curves more closely fit 

 the CO 2 and bacterial number curves. This period of summer 



1 The very sharp rise of CO 2 in May and August appears to be associated 

 with the crop (241^). 



