THE ORGANIC MATTER OF THE SOIL 111 



While carbon dioxide may be evolved by the splitting-up 

 of both carbohydrate and nitrogenous bodies, ammonia re- 

 sults only from the latter. It is really the first extremely 

 simple nitrogenous body produced. It can be utilized by 

 some plants as a source of nitrogen, as is also true of certain 

 products of partial decomposition such as urea, but ordinarily 

 it must undergo oxidation. This oxidation results in nitrites 

 (N0 2 ) and ultimately in nitrates (N0 3 ), the latter usually 

 being considered as the chief source of the nitrogen utilized 

 by plants. 



Other simple products, such as methane (CH 4 ), hydrogen 

 disulphide (H 2 S), carbon disulphide (CS 2 ), and the like, may 

 also result. They are relatively unimportant, however, as 

 regards the plant, in comparison with the role played by car- 

 bon dioxide, ammonia, the nitrites, and the nitrates. The 

 production of the nitrates from ammonia is very closely cor- 

 related with good soil conditions, especially optimum moisture 

 and adequate aeration. The proper handling of the soil, then, 

 will not only tend to eliminate toxic matter and prevent its 

 further formation but will encourage the proper decay of the 

 soil organic matter and the production of simple compounds 

 w T hich will function directly or indirectly as nutrients. 



59. Carbonized materials of soil. — After the extraction 

 of the soil for the study of the ordinary organic compounds, 

 a considerable mass of material remains, which is insoluble 

 in water, alkali, and other ordinary solvents. By the extrac- 

 tion of a large amount of soil, Schreiner and Brown x were 

 able to study this material. They found it susceptible to *di- 

 vision into six groups, as follows: (1) plant tissue, (2) insect 

 and other organized material, (3) charcoal particles, (4) lig- 

 nite, (5) coal particles, and (6) materials resembling natural 

 hydrocarbons, as bitumen, asphalt, and the like. Such ma- 



1 Schreiner, O., and Brown, B. E., Occurrence and Nature of Carbon- 

 ized Material in Soils; U. S. Dept. Agr., Bur. Soils, Bui. 90, 1912. 



