November, 1920] fertilizer inspection, 1920. 3 



reason manufacturers are required to state upon their label 

 the guaranteed content of these three materials. 



Nitrogen. Pure nitrogen is a colorless, odorless, taste- 

 less gas which makes up about four-fifths of the air sur- 

 rounding 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 exist upon their roots. In order to be 

 available for plants nitrogen must be in the form of & 

 compound known as a nitrate. 



In commercial fertilizers the nitrogen occurs in three dif- 

 ferent forms as follows: (1) nitrate, (2) ammonia and (3) 

 organic nitrogen. The nitrate nitrogen is readily soluble 

 in water and immediately available to the plant. The am- 

 monia 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 

 available form. Some types of organic nitrogen such as 

 are contained 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, however, 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 

 phosphoric acid determines the solubility of the material; 

 that containing the smaller amount of lime being more 

 soluble. That part of the phosphoric acid which is readily 

 soluble in water is immediately available to the plant dur- 

 ing the growing season. This is known as "water soluble" 

 phosphoric acid. A part of the phosphoric acid which is 

 insoluble in water is soluble in a certain strength of am- 

 monium citrate solution. This^ is also available to the 

 plant. In the analysis the "available" phosphoric acid 

 includes the "water soluble" and the "citrate soluble." 

 The insoluble may be obtained by subtracting the avail- 

 able from the total in the tables of analyses. The ' ' insolu- 

 ble" phosphoric becomes available to the plant only very 

 slowly. 



