122 THE PRINCIPLES OF SOIL MANAGEMENT 



These original compounds are broken down in the pro- 

 cess of decay into other successively simpler com- 

 pounds. The end of the process is always essentially 

 the same the reduction of the elements to their sim- 

 plest and most stable forms, the carbon to carbon dioxid, 

 the nitrogen to nitrates, ammonia or even free nitrogen, 

 and the mineral elements to their simple salts. The 

 soil constituents which are termed humus, mold, peat, 

 muck, etc., simply represent stages in the transition 

 process from the fresh materials to the native elements. 

 There is no single compound or group of compounds 

 which imparts definite characteristics. These are the 

 result of the mixture; and this fact of an infinitely 

 complex mixture is exceedingly important to keep in 

 mind, in considering the effects of the organic matter 

 of the soil. Many of them are acids. Some as ammonia 

 and marsh gas function as bases. They react with 

 each other in many ways, and, what is more important, 

 they react with the mineral elements of the soil to form 

 organic salts. It is by this union that organic matter 

 has not only a direct effect as a food, but also an indirect 

 effect in releasing food elements from their less soluble 

 mineral combinations. Aside from the production of 

 many complex organic acids, the two most significant 

 facts of their composition are the per cent of nitrogen 

 present and the chemical form of part of the carbon. 

 Nitrogen, which is not a constituent of rocks, is made 

 available to all higher forms of plants through this or- 

 ganic decay process, and these various compounds 

 constitute the soil store-house of the element from which 

 it gradually changes over into the available forms. The 



