SOILS AND FERTILIZERS 459 



erning the use of fertilizers and become familiar with the specific 

 requirements of their soils and crops, they will less frequently call for 

 general compound fertilizers and will buy the raw materials of known 

 origin and properties which are required for their special purpose. 



Nature and Causes of Variations. All manufactured products 

 or brands of fertilizers are made up of a mixture of the various 

 kinds and forms of fertilizing materials and the differences that exist 

 in the brands of different manufacturers are due both to differences 

 in the character and to variations in the proportions of the materials 

 used to form the different brands; that is, while all manufacturers 

 must go to the sources of supply indicated, they may select either 

 good or poor products and may vary the proportions of the different 

 materials used. 



The difference between a good brand of fertilizer and a poor 

 one lies not so much in differences that may exist in the total amount 

 of plant food contained as in the quality of the materials of which 

 the two are made. For instance, in one brand the nitrogen may 

 have been derived entirely from insoluble organic materials and the 

 phosphoric acid from untreated phosphates rather than superphos- 

 phates ; while in another the nitrogen may have been derived from 

 the three sources of nitrogen, viz, nitrates, ammonia salts, and or- 

 ganic matter, and the phosphoric acid entirely from superphosphates. 

 The total plant food contained in the first brand may be quite as 

 great as it is in the other, yet the immediate results obtained from 

 its use would be less satisfactory than those obtained from the one 

 containing the more active forms of fertilizing constituents. 



A fertilizer containing foreign substances, of themselves worth- 

 less as a source of plant food, is not necessarily adulterated. It may 

 contain the full quantity of the fertilizer ingredients guaranteed, and 

 the foreign substance in question may act only as a filler. On the 

 other hand, a fertilizer may contain one or more of the plant food 

 constituents in forms so inert, and so difficultly available, as to make 

 them practically worthless as a source of the constituents in question. 

 This would apply, for instance, to peat, which in a finely ground 

 state is known to have been used as a source of nitrogen iri mixed 

 fertilizers. Because of its resistance to the agencies of decay, it 

 possesses scarcely any value as a source of nitrogen, and hence its 

 use under such conditions could justly be designated as adulteration. 



What Chemical Analyses Show. The differences that exist be- 

 tween good and poor fertilizers are quite clearly shown by the chem- 

 ical analyses made by the various experiment stations, provided the 

 analysis is carried far enough to show both the amount and form 

 of the nitrogen, phosphoric acid, and potash. For instance, an 

 analysis which shows that a considerable proportion of the nitrogen 

 exists as nitrates or as ammonia is positive evidence that good nitrog- 

 enous materials have been used ; if it shows that the phosphoric acid 

 is largely in a soluble form, the consumer knows that superphos- 

 phates have been used. On the other hand, if all the nitrogen is 

 shown to be in the form of organic matter, and a large proportion 

 of the phosphoric acid is found to be insoluble, it is evident that 



