THE DECOMPOSITION OF CELLULOSE IN SOILS 477 



of native vegetation has been limited by the meager rainfall, the humus 

 content of the virgin soil may be as low as 0.30 per cent or even less. 

 When such soils are brought under intensive cultivation by means of irri- 

 gation, the scarcity of humus soon manifests itself by the development of 

 injurious changes in the tilling qualities of the land. Many such lands 

 soon fail to give satisfactory crops or respond to the application of com- 

 mercial fertilizers unless the supply of organic matter is maintained by 

 liberal applications of barnyard manure, green manures, etc. 



As the larger part of carbonaceous matter added to soils in plant re- 

 sidues, stable manure, etc. is cellulose, — the gradual decomposition of 

 the cellulose in soils in association w^ith the nitrogenous compounds must 

 play a very prominent role not only in maintaining the humus content of 

 soils, but in securing the proper development of the many important bio- 

 logical processes. The humus content of the soil is considered by many to 

 serve as the depository of the insoluble nitrogen of the soil w^hich consti- 

 tutes the reserve supply for crops. It is probable but not certain 

 that this insoluble nitrogen through the process of nitrification fur- 

 nishes the main nitrogen supply to plants. The fixation of atmos- 

 pheric nitrogen in the soil is dependent upon the development of micro- 

 organisms which requires large quantities of organic carbon as food. Dur- 

 ing recent years, investigations by Koch (34), Pringsheim (63), and 

 McBeth (42) have shown that cellulose may serve as a valuable source 

 of energy for these organisms. However, cellulose is an extremely in- 

 ert compound and the carbon contained therein can be utilized by the 

 nitrogen fixing bacteria only after the cellulose has been converted into 

 less refractory compounds by the cellulose-dissolving bacteria. It is ob- 

 vious, therefore, that the work performed by these organisms is of fimda- 

 mental importance in releasing the great store of energy locked up in 

 cellulose. In view of the fact that the cellulose added to the soil repre- 

 sents a large amount of potential energy, the value of which depends 

 upon the nature of the compounds formed in its decomposition, it be- 

 comes quite important to inquire into the nature of the compounds pro- 

 duced by the celFulose-dissolving bacteria. Earlier investigations by 

 Popoff (61), Toppeiner (78), Hoppe-Seyler (25), Gayon (15), Deherain 

 (13), Schloesing (74), Van Senus (76), Omeliansky (50), and others 

 seemed to indicate that cellulose undergoes a direct gaseous fermentation 

 in which a very large percentage of the carbon is converted into carbon 

 dioxide and methane. Hoppe-Seyler was of the opinion that cellulose 

 was dissolved according to the following formula: 



(1) The hydration of the cellulose with the formation of a hexose, 



CeHjoO, -f H^O = CeHj.Oe ; and 



(2) The destruction of the carbohydrate with the formation of equal 

 quantities of carbon dioxide and methane, 



C^H,,0, = 3CO, -f 3CH,. 



