MICROBIOLOGICAL ANALYSIS OF SOIL 



721 



soils producing 177 per cent as much C0 2 as unsieved soils. An increase 

 in aeration brought about an increase in CO2 production in soil to which 

 organic matter had been or had not been added. Moisture was found 

 to be one of the most important factors. The influence of salts upon 

 the evolution of carbon dioxide is seen from the following table. CS 2 

 was found to serve first as a check and then as a stimulant upon carbon 

 dioxide production. 



TABLE 77 

 CO2 formed in 5 days, at 10° to 12°C.,from 6 kgm. of soil, with and without 



different salts 



TREATMENT 



Soil alone 



Soil + 90 grams MgSO* 



Soil + 6 grams CaO 



Soil + 30 grams ammonium sulfate. 

 Soil + 6 grams superphosphate . . . 



MILLIGRAMS OF 

 CO2 



145 

 408 

 62 

 864 

 306 



TABLE 78 

 Nmnbers of bacteria and evolution of CO2 in different soil types 



By using C0 2 as an index, it was found that similar soils behave the 

 same under similar conditions. When glucose is added, the abundant 

 production of CO2 tends to obliterate any differences, hence the briefest 

 possible period (12 hours) should be used in this connection. A certain 

 parallelism was obtained between the numbers of bacteria and the 

 evolution of carbon dioxide in different soils, as shown in table 78. 



The curves for bacterial numbers, nitrate content and carbon dioxide 

 in the soil air were found 23 to be sufficiently similar to justify the view 



23 Russell, E. J., and Appleyard, A. The atmosphere of the soil: its com- 

 position and the cause of variation. Jour. Agr. Sci., 7: 1. 1915. 



