86 SOILS AND FERTILIZERS 



acids. Acid soils are made productive by using lime 

 and other alkaline matter to neutralize the humic 

 acid before applying farm and other manures. Acid 

 soils are not suitable for the production of clover and 

 legumes. 



THE ORGANIC COMPOUNDS OF SOILS 



i oi Sources of the Organic Compounds of Soils. 



The organic compounds of soils are composed of the 

 elements carbon, hydrogen, oxygen, and nitrogen. 

 When vegetable and animal matter undergo decay in 

 contact with the soil, compounds as carbon dioxide, 

 water, ammonia, 28 organic acids, and various derivatives 

 are formed, while some of the organic acids unite with 

 the mineral matter of the soil to form humates. 

 Micro-organisms take an important part in the decay 

 of animal and vegetable matter and the production of 

 organic compounds in soils. In some soils, the or- 

 ganic compounds of plants, as cellulose, proteids, and 

 carbohydrates like pentosans, are present, while in 

 other soils these compounds have undergone partial 

 oxidation. Some authorities claim (see Section 137) 

 that a portion of the initial organic matter of soils is 

 the result of the workings of carbon assimilating 

 nitro-organisms. The main source of the soil's or- 

 ganic matter, however, is the accumulated animal and 

 vegetable remains which exist in various stages of 

 decay. The organic matter of soils is a mechanical 

 mixture of a large number of organic compounds, 

 many of which have not as yet been studied. 



102. Classification of the Organic Compounds. 

 Various attempts have been made to classify the or- 



