DECOMPOSITION OF NON-NITROGENOUS ORGANIC MATTER 463 



Decomposition of fats and waxes. Fats are widely distributed in the 

 plant and animal residues added to the soil. They are also synthe- 

 sized by the different groups of soil microorganisms. The amount of 

 fat synthesized and the nature of the fat will depend upon the type of 

 organisms and stage of growth. The fat is a reserve substance and is 

 readily utilized by the organisms in the absence of other available 

 sources of energy. 112 



Fats decompose only slowly in moist soils, and almost not at all in 

 dry soils. According to Rubner, 113 only 22.9 per cent of butterfat 

 added to soil (4.5 grams of fat to 200 grams of soil) was decomposed 

 during a period of one year and 38.1 per cent in twelve years; other 

 fats were decomposed at a different rate. The fats are first hydrolyzed, 

 according to the general reaction: 



CsHsOs-Rs + 3H 2 = C 3 H 8 3 + 3R-OH 



The glycerol or corresponding alcohols are readily utilized by various 

 groups of microorganisms as sources of energy, while the fatty acids 

 are decomposed further. A typical fat is decomposed in the soil as 

 follows: 



CH3(CH 2 ) 7 CH = CH(CH 2 ) 7 CO,H + H 2 + h(0 2 )-> 

 Oleic acid 



CH 3 (CH 2 ) 7 • CHOH • CHOH(CH 2 ) 7 C0 2 H 

 Dioxystearic acid 



This last substance has been demonstrated in the soil 114 and was 

 also found in the cells of fungi. Fats are decomposed chiefly by fungi, 

 with the possible formation of ketones, and by a number of aerobic 



112 Dubaquie. Recherches sur les matieres grasses des vegetaux inferieurs. 

 Mem. Soc. Sci. Phys. Nat. Bordeaux (6). 1910. 



113 Rubner, N. Notiz liber die Zersetzung von Fetten im Boden. Arch. Hyg., 

 91: 290. 1922. 



114 Schreiner, O., and Shorey, E. The isolation of harmful organic substances 

 from soils. Bur. Soils, U. S. Dept. of Agr. Bui. 53. 1909. 



