97 



16 termed " commercial value," or cost in market. This value is deter- 

 mined by market and trade conditions, as cost of production of the 

 crude materials, methods of manipulation required, etc. Since there 

 is no strict relation between agricultural and commercial or market 

 value, it frequently happens that an element in its most available form, 

 and under ordinary conditions of high agricultural value, costs less in 

 market than the same element in less available forms and of a lower 

 agricultural value. The cost of production in the one case is lower 

 than in the other, though the returns in the field are far superior. 



The commercial value has reference to the material as an article of 

 commerce, hence commercial ratings of various fertilizers have refer- 

 ence to their relative cost and are used largely as a means by which the 

 different materials may be compared. 



VARIATIONS IN THE COMPOSITIONS OF MANUFACTURED FERTILIZERS. 



All manufactured products or brands of fertilizers are made up of a 

 mixture of the various kinds and forms of the fertilizing materials just 

 described, and the differences that exist in the brands of different 

 manufacturers are due both to differences in the character and to varia- 

 tions in the proportions of the materials used to form the different 

 brands ; that is, while all manufacturers must go to the sources of sup- 

 ply 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 in it as in the quality of the materials of which it is 

 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 superphosphates ; while in another 

 the nitrogen may have been derived from . the three sources of nitrogen, 

 viz., nitrates, ammonia salts, and organic matter, and the phosphoric 

 acid entirely from superphosphates. In the first brand the total food 

 contained may be quite as great as in the other, yet the immediate results 

 obtained from its use would be less satisfactory than that obtained from 

 the one containing the more active forms of fertilizing constituents. 



The differences that exist between good and poor fertilizers are quite 

 clearly shown by the chemical 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 in- 

 stance, an analysis which shows that a considerable proportion of the 

 nitrogen exists as nitrates or as ammonia is positive evidence that good 

 nitrogenous 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 that a large proportion of the 

 phosphoric acid is insoluble, it is evident that materials containing less 

 active forms of plant food have been used. In the next place, it is the 

 quality and amount of plant food that is contained in a fertilizer which 

 determines its value rather than the relative proportion of the various 

 constituents, though under certain well-known conditions the latter is 

 of very considerable importance. Special crop brands are particularly 

 useful only when an abundance of all the plant-food constituents are 

 present in the soil. 



