252 NATURE AND PROPERTIES OP SOILS 



volved: (1) the pliysiological action of bacteria by wliieh 

 they absorb oxygen and give off carbon dioxide, and (2) the 

 excretion of carbon dioxide by roots. (See Pig. 47.) 



Recent work^ has clearly shown that higher plants, espe- 

 cially during their most rapid growth, markedly increase the 

 amount of carbon dioxide gas in the soil. Stoklasa^ concluded 

 that the microorganisms in an acre of soil to a depth of four 

 feet may produce between sixty-five and seventy pounds of 

 carbon dioxide a day for two hundred days in the year, and 

 that during the growing period the roots of oats or wheat 

 would give off nearly as much more. Turpin^ finds that the 

 crop often produces, during its period of active growth, many 

 times as much carbon dioxide as is produced by soil organ- 

 isms. He minimizes the influence of the decaying root par- 

 ticles of the crop occupying the soil on the carbon dioxide 

 content of the soil air. 



In any particular soil, the two major controls of carbon 

 dioxide production seem to be temperature and rainfall.* The 

 former apparently is dominant in a temperate humid region 

 from November to May. During the remainder of the year, 

 the moisture content of the soil and the amount of rainfall 

 are the direct controls. Bacterial numbers and nitrate ae- 



^Stoklasa, J., and Ernestj A., Beitrage zur Lbsung der Frage der 

 Cliemischen Natur des Wurzelse'kretes ; Jahr. Wiss. Bot., Bd. 46^ Seite 

 55-102, 1909. 



Aberson, J. H., Bin Beitrag mr Kermtms der Natiir der Wurselaus- 

 scheidunger; Jahr. Wiss. Hot., Bd. 47, Seite 41-56, 1910. 



RusseU, E. J., and Appleyard, A., The Influence of Soil Conditions 

 071 the Decomposition of Organic Matter in the Soil; Jour. Agr. Sci., 

 Vol. YII, Part 3, pp. 385-417, 1917. 



BizzeH, J. A., and Lyon, T. L., The Effect of Certain Factors on 

 the Carbon Dioxide Content of Soil Air; Amer. Soc. Agron., Yol. 10, 

 No. 3, pp. 97-112, Mar. 1918. 



^Stoklasa, J., MetJioden sur Bestimmung der Atmungsmtensitdt der 

 Bahterien im Boden. Zeit, f. d. Landw. Yersuehswesen in Oesterreieh, 

 Band 14, Seite 1243-79, 1911. 



^Turpin, H. W., The Carbon Dioxide of the Soil Air; Cornell Agr. 

 Exp. Sta., Memoir 32, April 1920. 



*Eussell, E. J., and Appleyard, A., The Atmosphere of the Soil: Its 

 Composition and the Causes of Variation; Jour. Agr. Sci., Yol. YII, 

 Part 1, pp. 1-48, 1915. 



