Tue Carson DioxipE oF THE Sort AIR 321 
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FACTORS AFFECTING THE AMOUNT OF CARBON DIOXIDE IN THE SOIL AIR 
Soil organisms 
Most investigators consider that soil-organisms play a large part in the 
production of carbon dioxide in the soil. Pettenkofer (1858, 1871, 1873, 
1875) concluded, as a result of his investigations, that most of the carbon 
dioxide in the soil is due to living organisms. 
Later, E. Wollny (1880b) found that there is only a small production 
of carbon dioxide in an atmosphere of hydrogen gas, while chloroform 
almost completely stops the power of the soil to form carbon dioxide. 
He concluded that carbon dioxide is produced largely by bacteria. 
Further confirmation of this is to be found in the studies of Dehérain 
and Demoussy (1896), which showed that sterile soil at a temperature of 
22° C. produces only insignificant amounts of carbon dioxide. Stoklasa 
and Ernest (1905), after working with beets, clover, oats, and other plants, 
noted that a bare soil produced, in one hundred and fifty days, more than 
twice the carbon dioxide produced by a crop of wheat on the same area in 
sixty days. They observed also a correlation between the numbers of 
bacteria and the carbon dioxide produced at different depths in the 
soil. Hutchinson (1912) concluded that carbon-dioxide production is a 
reliable measure of bacterial activity. 
Soil conditions 
Where soil conditions are favorable to the action of bacteria, the carbon- 
dioxide content is usually high. For example, Stoklasa (1911) obtained the 
greatest production of this gas in a soil that was well aerated, slightly 
alkaline, and well supplied with readily available plant nutrients. This 
was found by E. Wollny (1897), Russell and Appleyard (1915), and others, 
to be especially true in the case of soils having readily available organic 
matter. Very small amounts of carbon dioxide were found in the swamp 
rice lands of India by Harrison and Aiyer (1913), showing that unfavorable 
soil conditions are associated with a low content of carbon dioxide. 
Seasonal conditions 
Russell and Appleyard (1915, 1917) emphasized the importance of 
seasonal conditions on the carbon-dioxide content of the soil. In their 
investigations they observed that a rise of temperature is accompanied 
