November, 1921] fertilizer ikspection, 1&21. ^ 



of commercial fertilizers depends, therefore, upon their 

 available content of these three elements. For this reason 

 manufacturers are required to state upon their label the 

 guaranteed content of these three materials. 



Nitrogen. Pure nitrogen is a colorless, odorless, tasteless 

 gas which makes up about four-fifths of the air siUTOunding 

 us. In this form, however, it is not available to plants with 

 the exception of a few, such as legumes, which are able to 

 get nitrogen from the air by means of the bacteria which ex- 

 ist upon their roots. In order to be available for plants 

 nitrogen must be in the form of a compound known as a 

 nitrate. 



In commercial fertilizers the nitrogen occurs in three dif- 

 ferent forms as follows: (i) nitrate, (2) ammonia and (3) 

 organic nitrogen. The nitrate nitrogen is readily soluble in 

 water and immediately available to the plant. The ammonia 

 nitrogen and organic nitrogen must be converted into the 

 nitrate form before they are available to the plant. The 

 ammonia nitrogen becomes available quite rapidly during 

 the growing season and so can be considered as an avail- 

 able form. Some types of organic nitrogen such as are con- 

 tained in dried blood, cottonseed meal, tankage, etc., are 

 also rapidly converted into nitrate nitrogen in the soil and 

 made available to the plant. Other types of organic nitrogen 

 like those contained in hoof, hair and leather waste, how- 

 ever, are only very slowly converted into nitrate nitrogen 

 and are not readily available. 



Phosphorus occurs in the various fertilizer materials in 

 the greater part as phosphoric acid in combination with 

 calcium (or lime). In order to be available to plants these 

 compounds of lime and phosphorus must be soluble or made 

 soluble. The amount of lime combined with the phosphcJc 

 acid determines the solubility of the material ; that contain- 

 ing the smallest amount of lime being most soluble. That 

 part of the phosphoric acid which is readily soluble in water 

 is immediately available to the plant during the growing 

 season. This is known as "water soluble" phosphoric acid. 



