COMMERCIAL FERTILIZERS AND THEIR USE 237 



of the same general composition, may have widely 

 different crop-producing powers. 



283. Inert Forms of Plant Food in Fertilizers. A 



fertilizer of the same general composition as the first 

 example, but of different availability of the elements, 

 could be made from feldspar rock, apatite rock, and 

 leather. The leather contains nitrogen, the apatite 

 contains phosphoric acid, and the feldspar, potash. 

 Such a fertilizer would have no value when used on a 

 crop, because all the plant food elements are present 

 in unavailable forms. Hence, in purchasing fertilizers, 

 it is necessary to know not only the percentage com- 

 position, but also the nature of the materials from which 

 the fertilizer was made. Inert forms of plant food are 

 akin to indigestible forms of animal food ; it is the food 

 which is assimilated that is of value whether it be by 

 animals or by plants. 



284. Inspection of Fertilizers. -- In many states, laws 

 have been enacted regulating the manufacture and sale 

 of commercial fertilizers, and provision is made for 

 inspection and analysis of all brands offered for sale. 

 The label on the fertilizer package must specify the 

 percentage amounts of available nitrogen, phosphoric 

 acid, and potash. Inspection has been found necessary 

 in order to protect the farmer and the honest manu- 

 facturer. As the result of inspection and analysis, 

 occasionally a fraud is revealed like the following : 71 



