444 NATURE AND PROPERTIES OF SOILS 



phosphates are exported, while sodium nitrate and potash 

 salts are imported in large amounts. Fifty per cent. o£ the 

 fertilizers sold in the United States are applied in the south 

 Atlantic states within three or four hundred miles of the 

 seaboard. Nearly one-half of the remainder is purchased by 

 the New England and middle Atlantic states. West of the 

 Mississippi River, the use of fertilizers, especially those car- 

 rying phosphoric acid, is increasing rapidly. 



The primary function of a commercial fertilizer is to supply 

 plant nutrients to the soil in such a form that the plant may 

 be directly influenced by such an application. The secondary 

 influences of fertilizers may be beneficial or detrimental. The 

 exact nature of the secondary influences depends on the par- 

 ticular fertilizer applied and especially on the type of soil 

 and the crop management in vogue. 



Prepared fertilizers, as found on the market, are usually 

 composed of a number of ingredients. Since these ingredi- 

 ents are the carriers of the nutrient constituents, and since 

 it is on their composition and solubility that the value of a 

 fertilizer depends, a knowledge of the properties of these 

 materials is not only of interest to every one who uses fer- 

 tilizers but is also a valuable aid in their purchase. 



FERTILIZERS USED FOR THEIR NITROGEN 



Nitrogen is usually the most expensive constituent of ma- 

 nure and is of great importance, since it is very likely to be 

 deficient in soils. A commercial fertilizer may have its nitro- 

 gen in the form of soluble inorganic salts or in organic com- 

 bination. On the form depends to a certain extent the agri- 

 cultural value of the nitrogen, as the soluble inorganic salts 

 are very readily available to the plant, while the organic forms 

 must pass through the various biological processes before 

 the plant can use the nitrogen so contained. Only the best- 

 known fertilizer carriers need receive particular attention 

 here. 



