ae 
THE CARBON DIOXIDE OF THE SOIL AIR 
H. W. Turpin 
Carbonic acid has long been recognized as an important soil solvent. 
On this point, at least, authorities are well agreed, but from the data 
available it is not yet clear what factors are most important in controlling 
the production of carbon dioxide in the soil. It is generally conceded, 
however, that a large proportion of the carbon dioxide found is due to 
soil microorganisms. The significance of plant roots in this connection 
has been recognized by some investigators, while others appear to be not 
quite decided as to how important plant-root excretions are. 
HISTORICAL REVIEW 
IMPORTANCE OF THE CARBON DIOXIDE IN THE SOIL 
That carbon dioxide in solution is an important soil solvent has been 
shown by Stoklasa and Ernest (1909).!| These workers point out that 
when ground gneiss and basalt are mixed with nutrient solutions, the 
amount of phosphorus and potassium absorbed by the plants grown 
is directly proportional to the carbon dioxide produced per gram of dry 
matter of the roots. 
Aberson (1910) concluded, as a result of studies with young plants, that, 
while the excretions from plant roots may not be sufficiently concentrated 
(in carbon dioxide) to have a marked effect in dissolving insoluble materials, 
still the mucilaginous covering of the root hairs, containing a saturated 
solution of carbon dioxide, is entirely sufficient to bring into solution the 
insoluble soil constituents with which it comes in contact, especially the 
phosphates. 
The limited usefulness, as a solvent, of the carbon dioxide secreted by 
plant roots is pointed out by Pfeiffer and Blanck (1912), who show that 
in soils treated with phosphates the carbon dioxide given off by plant 
roots is not a sufficient solvent to account for all the mineral nutrients 
obtained by the plant from the soil. 
1Data in parenthesis refer to Bibliography, page 349. 
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