October, 1922] fertilizer inspection, 1922 3 



MEANING OF THE CHEMICAL ANALYSIS 



Three of the ten elements essential for plant growth are 

 most likely to be lacking in suiRcient available quantity for 

 best crop growth in our usual soils. These are nitrogen, 

 phosphorus and potassium. Sometimes calcium, magne- 

 sium and sulphur may be deficient, but because these de- 

 ficiencies have apparently not been marked and widespread, 

 our fertilizer practices have dealt largely with the applica- 

 tion of nitrogen, phosphorus and potassium. The value of 

 commercial fertilizers depends, therefore, upon their avail- 

 able content of these three elements. For this reason man- 

 ufacturers are required to state upon their label the guar- 

 anteed 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 bac- 

 teria which exist upon their roots. In order to be available 

 for most plants nitrogen must be in the form of a compound 

 known as a nitrate. 



In commercial fertilizers the nitrogen occurs in three 

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

 (3) organic nitrogen. The nitrate nitrogen is readily sol- 

 uble 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 dur- 

 ing 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 nitro- 

 gen like those contained in hoof, hair and leather waste, 

 however, are only very slowly converted into nitrate nitro- 

 gen and are not readily available. 



