LAND AND OTHER AGENTS OF PRODUCTION 171 



about this decay in the soil. Various groups of universally distributed 

 organisms are involved. In the first place, the insoluble proteins are 

 changed into soluble peptones; these are changed into amino acids, 

 and these in turn to ammonia. This ammonification constitutes a 

 vital stage in the production of nitrates in the soil. It is important 

 also in that it brings about the formation and later the destruction 

 of humus. 



Humus is decaying organic matter in the soil. We know that the 

 presence of a proper amount of humus and also the best rate of 

 destruction are important factors from the physical and chemical 

 standpoint in determining the fertility of a soil. Introduction of 

 barnyard manure brings about vastly increased bacterial action, due 

 to the large amount of organic matter added and also the large number 

 of bacteria introduced. Thus the ammonifying power of a soil is 

 increased by addition of manure. 



Ammonium compounds produced in the soil as just described 

 never accumulate to any appreciable extent, but are transformed into 

 nitrates almost as rapidly as they are formed. This transformation 

 is called nitrification and includes two stages: the change of ammonia 

 to nitrites and then the oxidation of nitrites to nitrates. Two distinct 

 classes of organisms are involved in the process and they are both of 

 practically universal distribution. 



All the farming operations which increase ammonification have 

 a similar effect on nitrification, since nitrification starts where ammo- 

 nification leaves off. Particularly necessary for nitrification, however, 

 is the presence of lime in soils. This is due to the fact that nitrous 

 and nitric acids are produced in the process of nitrification and if they 

 are not neutralized by lime they accumulate and very quickly stop 

 bacterial action. The activities of both the ammonifying and the 

 nitrifying bacteria are governed very closely by the climatic and 

 farming conditions with regard to moisture, temperature, acidity, 

 aeration, and food supply. 



Bacteria and minerals in the soil. In the process of decay of which 

 we have spoken, the destruction of the organic nitrogenous materials 

 leads to the production of other compounds than ammonia and 

 nitrates. Chief among these is carbon dioxide. Furthermore, the 

 organic non-nitrogenous substances, such as starches, sugars, cellulose, 

 etc., are destroyed in the general decay which occurs in the organic 

 matter, and among the variety of products which result we find various 

 organic acids and particularly carbon dioxide. These organic acids and 



