COMMERCIAL FERTILIZERS 493 



414. Fertilizer constituents. — Prepared fertilizers, as 

 found on the market, are usually composed of a number 

 of ingredients. Since these are the carriers of the fertiliz- 

 ing material, and since it is on their composition and solu- 

 bility that the value of a fertilizer depends, a knowledge 

 of the properties of these constituents is of interest to 

 every one who uses fertilizers and is a valuable aid in their 

 purchase. 



FERTILIZERS USED FOR THEIR NITROGEN 



Nitrogen is the most expensive constituent of manures 

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

 deficient in soils. A commercial fertilizer may have its 

 nitrogen in the form of soluble inorganic salt, or combined 

 as organic material. On the form of combination de- 

 pends to a certain extent the 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 processes leading to nitrification before the 

 plant can use the nitrogen so contained. The inorganic 

 nitrogen fertilizers are sodium nitrate, ammonium sulfate, 

 calcium nitrate, and calcium cyanamide. 



415. Forms in which nitrogen exists in soils. — There 

 are several forms in which nitrogen exists in soils. The 

 uncombined nitrogen of the soil air constitutes the largest 

 supply because of its diffusibility with the atmospheric 

 air. Next in quantity is the nitrogen of organic com- 

 pounds, ranging from 0.05 to 0.3 per cent in ordinary 

 arable land and slightly, but appreciably, soluble in soil 

 water. In upland cultivated soils the nitrogen of nitrate 

 salts forms the next largest supply, but rarely exceeds 

 20 per cent of the total combined nitrogen of the soil. 



