178 Fertilizers 



was certainly not drawn from a superphosphate, or it 

 would have shown a higher percentage of available, a cer- 

 tain proportion of which whould have been soluble, and 

 the percentage of insoluble would have been very much 

 less. In the case of potash, it is quite evident that it was 

 drawn from kainit, inasmuch as the percentage of chlorin 

 exceeds the percentage of the potash, as would be the case 

 if the potash had been drawn from that source. 



Thus it is that a complete chemical analysis of a fer- 

 tilizer indicates very clearly the source of the materials 

 by the form in which the constituents exist in the mixture. 



THE AGRICULTURAL VALUE OF A FERTILIZER 



It is obvious, from what has already been pointed 

 out, that the value of a fertilizer to the farmer depends 

 not so much upon what is paid for it as upon the character 

 of the materials used to make it. This value is termed 

 the " agricultural value," and it is measured by the value 

 of the increased crop produced by its use. It is, therefore, 

 a variable factor, depending first, upon the availability of 

 its constituents, and second, upon the value of the in- 

 creased crop produced. 



For example, in the first place, the agricultural value of 

 a pound of soluble phosphoric acid is likely to be greater 

 than that of a pound of insoluble when applied under the 

 same conditions as to soil and crop, because in the one case 

 the element is in its most available form, while in the 

 other it is least available. In the second place, the solu- 

 ble phosphoric acid may exert its full effect and cause 

 a greatly increased yield on a certain crop, and still not 

 cause an increase in its value sufficient to pay the cost of 

 the application, while for another crop the same applica- 



