November, 1924] fertilizer inspection, 1924 3 



you in purchasing fertilizer. If you need further help 

 write to the Department of Agricultural Chemistry, The 

 University of New^ Hampshire Agricultural Experiment 

 Station, Durham, N. H. 



MEANING OF THE CHEMICAL ANALYSIS. 



Three of the ten elements essential for plant growth 

 are most likely to be lacking in sufficient 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- 

 ficiences 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 manu- 

 facturers are required to state upon their label the guar- 

 anteed content of these three materials. 



Nitrogen. . Pure nitrogen is a colorless, odorless, 

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

 surrounding 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 on 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 

 soluble in water and immediately available to the plant. 

 The ammonia nitrogen and organic nitrogen must be con- 

 verted 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 consid- 

 ered as an available form. Some types or organic nitrogen 

 such as are contained in dried blood, cotonseed meal, tank- 



