COMMERCIAL FERTILIZERS 199 



So concentrated a fertilizer as the preceeding is 

 rarely, if ever, found on the market, although the 

 price, $45.15 per ton, is frequently charged. This 

 example is given to show the composition and cost 

 of one of the most concentrated fertilizers that can 

 be produced. 



Any one of the different materials mentioned in the 

 chapters on special fertilizers could be used in making 

 commercial fertilizers, as dried blood, tankage, nitrate 

 of soda, sulphate of ammonia, raw bone, dissolved 

 bone, raw phosphate rock, dissolved phosphate rock, 

 basic slag, kainit, muriate or sulphate of potash, and 

 many others. Inasmuch as each of these materials 

 has a different value, it follows that fertilizers, even 

 of the same general composition, may have widely 

 different crop-producing powers. 



269. Inert Forms of Plant Food in Fertilizers. 



A fertilizer of the same general composition as the first 

 example 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 of the plant food elements 

 are present in unavailable forms. Hence, in purchas- 

 ing fertilizers, it is necessary to know not only the 

 percentage composition, 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 ; in each it is the part which is assimi- 

 lated that is of value. 



