90 SOILS AND FERTILIZERS 



fertile field sprinkled on ' alkali ' spots will do much to 

 encourage nitrification, by introducing the nitrifying 

 organisms. 



THE ORGANIC COMPOUNDS OF SOILS 



96. Sources of the Organic Compounds of Soils. 



— The organic compounds of soils are derived from 

 accumulated vegetable and animal matter which has 

 been acted upon by micro-organisms. The organic 

 matter of the soil originally consisted of the same 

 compounds, as cellulose, proteid bodies, and organic 

 acids that are found in living plants and animals. By 

 the action of various micro-organisms the cellulose, 

 proteid bodies, and other compounds have undergone 

 chemical changes, and produced the organic com- 

 pounds of the soil which are mixtures of animal and 

 vegetable matter in various states of decomposition. 

 The organic compounds of the soil may exist in 

 various forms ranging from cellulose to the final oxi- 

 dation products as carbon dioxide and water. 27 



97. Classification of the Organic Compounds. — 



Various attempts have been made to classify the or- 

 ganic compounds of the soil, but those which have 

 been described are without doubt mixtures of various 

 bodies, and not distinct compounds. An old classifi- 

 cation by Miilder 28 was humic, ulmic, crenic, and ap- 

 procrenic acids. This classification does not include 

 any nitrogenous matter containing more than four per 

 cent, nitrogen, while organic matter with eight to ten 



