68 FIRST PRINCIPLES OF AGRICULTURE. 



CHAPTEE VI. 

 Artificial and Concentrated Manures; Nitrogenous Materials. 



As farm lands become exhausted of their essential 

 plant-food constituents by the continual sale of crops, 

 the manures available to the farmer, both from the 

 natural wastes of the farm and from such materials as 

 lime, ashes, etc., are often insufficient to keep up their 

 original fertility. At the present time, too, the tendency 

 of farming in this country, especially in the Eastern 

 States, and in the vicinity of large cities, is toward 

 special crop farming, which requires that soils should 

 be abundantly supplied with active plant-food. 



These conditions have caused a rapid development of 

 the sources of supply of suitable materials that furnish 

 the constituents liable to be lacking, or contained in too 

 small amounts, in the soil ; viz., nitrogen, phosphoric acid, 

 and potash. 



Classes of Materials. These materials are divided 

 into three distinct classes, namely, nitrogenous, furnish- 

 ing nitrogen ; phosphatic, furnishing phosphoric acid j and 

 potassic, furnishing potash. 



Manures made from these materials are called "arti- 

 ficial," " concentrated," or " commercial." They differ 

 from the natural manures mainly in being more con- 

 centrated, though frequently the constituents in them 



