NITROGEN COMPOUNDS OF THE SOU, 1 07 



with nitrogen for food purposes until the process 

 known as nitrification takes place. The nitrogenous 

 organic compounds in cultivated soils are derived 

 mainly from the undigested protein compounds of 

 manure and from the nitrogenous compounds in crop 

 residues, and are present mainly as insoluable pro- 

 teids. 85 When decomposition occurs, arnides, organic 

 salts, and other allied bodies are without doubt pro- 

 duced as intermediate products before nitrification 

 takes place. The organic nitrogen of the soil may be 

 present in exceedingly inert forms similar to leather. 

 In fact, in many peaty soils there are large amounts of 

 inactive organic compounds rich in nitrogen. In 

 other soils the nitrogen is present in less complex 

 forms. The organic nitrogen of the soil may vary in 

 complexity from forms like the nitrogen of urea to 

 forms like that of peat. 



127. Amount of Nitrogen in Soils. The fertility 

 of any soil is dependent, to a great extent, upon the 

 amount and form of its nitrogen. In soils of the 

 highest degree of fertility there is usually present 

 from 0.2 to 0.3 per cent, of total nitrogen, equivalent 

 to from 7,000 to 10,000 pounds per acre to the depth 

 of one foot. Many soils of good crop-producing power 

 contain as low as 0.12 per cent. There is usually two 

 or three times more nitrogen in the surface soil than 

 in the subsoil. In sandy soils which have been 

 allowed to decline in fertility, there may be less than 

 0.04 per cent. Of the total nitrogen in soils there is 

 rarely more than 2 per cent, at any one time, in forms 



