THE ORGANIC MATTER OF THE SOIL 103 



55. Decomposition^ of organic matter in soils.— AYliile 

 the general trend of organic degradation in soils is towards 

 simplification, the process is by no means a progressive one. 

 Many products are built up that are much more complex 

 than the original tissue. Most of the fermentation and putre- 

 faction is due to that great group of organisms called bacteria, 

 although molds, fungi, and the like also are important. The 

 action of these organisms may be direct, but is more likely 

 to be enzymie.^ A cycle is therefore set up, in which the 

 higher plants and animals are occupied in building up, while 

 bacteria are tearing down and reducing the residue of plant 

 action to simple forms, such as can be ultimately utilized again 

 in plant nutrition. The importance of soil organisms is thus 

 evident, and the encouragement of their grow^th and function 

 is clearly a part of good soil management. (See Pig. 21.) 



When the complex molecules that make up plant tissue 

 break down, they split along definite lines of cleavage, de- 

 pending on the structure of the original molecule. These 

 bodies, which are usually simpler in nature than those from 

 which they have sprung, are called cleavage products, and 

 without a doubt their appearance is the first step in organic 

 decomposition. These compounds are subject to still further 

 change, and because of the great number of agencies at work 

 the secondary products that result may be simpler or more 

 complex, according to conditions. Some bacteria have a tend- 

 ency, while tearing down organic matter, to produce syn- 

 thetic compounds, which present a very complicated molecule 

 until they are in turn degraded. The tendency for the sec- 

 ondary products to react both among themselves and with the 



^ Deeomposition and decay are general terms referring to all of the 

 degradation processes through which the original tissue passes in the 

 soil. Fermentation refers to the decomposition of carbohydrates while 

 putrefaction has to do usually with nitrogenous materials. 



^A catalytic agent is a material capable of hastening or retarding a 

 chemical reaction, the catalyst emerging unchanged from the transforma- 

 tion. Enzymes are catalysts produced by living organisms and may be 

 active within or without the cell. They are generally colloidal in nature. 



