TRANSFORMATION OF ORGANIC MATTER 681 



solution, at 15 pounds pressure for 30 minutes, and boiled with 

 2 per cent H2SO4 solution, washed and dried and extracted with 

 Schweizer's reagent. 



These methods permit one to observe the processes of decomposition 

 of the various constituents of natural organic substances added to soil 

 or to sand media, the rapidity with which each is decomposed, and the 

 nature of the constituents which contribute to the formation of the com- 

 plex mass of soil organic matter or "humus." But when, in addition to 

 the original organic substances, the end products of decomposition are 

 also measured, a clearer picture is obtained of the mechanism of trans- 

 formation of organic matter in the soil. In view of the fact that these 

 can frequently be measured, as in the case of the evolution of C0 2 , 

 without disturbing the soil in which decomposition is taking place, they 

 are especially important. 



Evolution of carbon dioxide as an index of decomposition of organic 

 matter in the soil. In determining the power of the soil to decompose 

 organic matter as indicated by the evolution of C0 2 , the terms "oxida- 

 tive capacity," "carbon dioxide producing capacity," "respiratory 

 capacity of soils" are often used. They all designate the decomposition 

 of organic matter in the soil by microorganisms, whereby energy is 

 liberated. However, carbon dioxide may be formed without the libera- 

 tion of energy, as in the decomposition of pyruvic acid : 



CH 3 -COCOOH -> CH 3 -COH + C0 2 

 pyruvic acid acetaldehyde 



On the other hand, energy may be liberated without the formation of 

 carbon dioxide, as in the case of the anaerobic fermentations of sugars. 



C 6 H 12 6 = 2 CH 3 -CHOH-COOH 

 Glucose Lactic acid 



C 6 H 12 6 = 3 CH 3 -COOH 

 Acetic acid 



Some C0 2 undoubtedly also originates in normal soils from carbonates 

 interacting with organic or mineral acids formed by biological agencies. 

 The absorption of oxygen can be only a partial index of energy trans- 

 formation, since some energy is liberated without the intervention of 

 free oxygen, as in the case of anaerobic decomposition of organic matter. 

 A more accurate index of energy transformation would be the calorific 

 changes in the soil (the liberation of heat) as a result of the activities of 

 microorganisms. 25 



"Van Suchetelen, 1923 (p. 425). 



