fertilizer inspection. 6j 



Constituents of Fertilizers.* 



The only ingredients of plant-food which we ordinarily 

 need to consider in fertilizers are potash, lime, phos- 

 phoric acid, and nitrogen. The available supply of lime 

 is often insufficient ; hence one reason for the good effect 

 so often observed from the application of lime, and of 

 plaster, which is a compound of lime and sulphuric acid. The 

 remaining substances, nitrogen, phosphoric acid and potash, are 

 the most important ingredients of our common commercial fer- 

 tilizers, both because of their scarcity in the soil and their high 

 cost. It is in supplying these that phosphates, bone manures, 

 potash-salts, guano, nitrate of soda, and most other commercial 

 fertilizers are chiefly useful. 



The term "form" as applied to a fertilizing constituent has 

 reference to its combination or association with other constit- 

 uents which may be useful, though not necessarily so. The 

 form of the constituent, too, has an important bearing upon its 

 availability, and hence upon its usefulness as plant food. Many 

 materials containing the essential elements are practically worth- 

 less as sources of plant-food because the form is not right ; the 

 plants are unable to extract them from their combinations ; they 

 are "unavailable." In many of these materials the forms may 

 be changed by proper treatment, in which case they become val- 

 uable not because the element itself is changed, but because it 

 then exists in such form as readily to feed the plant. 



Nitrogen is the most expensive of the three essential fertiliz- 

 ing elements. It exists in three different forms, organic nitro- 

 gen, ammonia and nitrate. 



Organic nitrogen exists in combination with other elements 

 either as vegetable or animal matter. All materials containing 

 organic nitrogen are valuable in proportion to their rapidity of 

 decay, because change of form must take place before the nitro- 

 gen can serve as plant food. Organic nitrogen differs in availa- 

 bility not only according to the kind of material which supplies 

 it, but according to the treatment it receives. The nitrogen in the 



* Farmers Bulletin 44 of the U. S. Dept. of Agriculture. "Commercial 

 Fertilizeres, Composition and Use." can be had free by applying to your 

 Congressman. Bulletin 107. Home Mixed Fertilizers, of this Station 

 will be sent on application. 



