720 



PRINCIPLES OF SOIL MICROBIOLOGY 



it was also found to run parallel with nitrification. Rahn 21 used sugar 

 solutions containing CaC0 3 , so that he measured not only C0 2 formed 

 by bacteria but also that produced from the interaction of the organic 

 acids formed with the CaC0 3 . Drying of soil was found to exert a 

 decidedly favorable influence. 



Van Suchtelen 22 placed upon the bottom of a jar pure sand and upon 

 it 6 kgm. of soil. Through this he passed air, usually 16 liters in 24 

 hours. The intensity of C0 2 production was found to be much greater 

 in the beginning of the experiment but it decreased rapidly after a 

 short time. Carbon dioxide was measured until a definite intensity 



Fig. 60. Method for determining the ability of soil to decompose organic 

 matter (from Waksman and Starkey). 



has been attained. The average production of carbon dioxide in a 

 unit of time was used as a measure. It was concluded that the com- 

 parison of the carbon dioxide production of different soils furnishes a 

 better means for the estimation of their relative bacterial activities 

 than the bacterial content. Soil cultivation was found to have a 

 favorable influence upon the carbon dioxide evolution, well sieved 



11 Rahn, O. Bakteriologische Untersuchungen liber das Trocknen des Bodens. 

 Centrbl. Bakt. II, 20: 38-S1. 



22 Van Suchtelen, F. H. H. tlber die Messung der Lebenstiitigkeit der aero- 

 biotischen Bakterien im Boden durch die Kohlensiiureproduktion. Centrbl. 

 Bakt. II, 28: 45-89. 1910. 



