PURCHASE AND USE OF FERTILIZERS 



317 



an equal amount of insoluble phosphoric acid, when used under 

 the same conditions, because it is much more easily used by plants. 

 But the water-soluble phosphoric acid may produce an increased 

 yield of a crop on some soils and still not cause an increase in 

 value sufficient to pay the cost of the application, while on an- 

 other crop the application may result in a very great increase in 

 value. On a soil which needs phosphoric acid its use may be 

 profitable, while on one which does not need this form of plant 

 food, it will have no effect. A fertilizer may produce a com- 

 paratively small effect upon a crop of high selling price, and yet 

 be profitable ; while on a crop of low selling price the increase may 

 not offset the cost of the fertilizer. 



Basis of Purchase. Large sales of fertilizing material are 

 usually at a certain price per unit. A unit means one per cent, on 

 the basis of a ton. That is 20 pounds. For example, $1.00 per 

 unit for phosphoric acid would be $1.00 for 20 pounds, or 5 cents 

 per pound. 



The ton basis of purchase is used for the sale of manufactured 

 fertilizers. The purchaser must consider the guarantee, and 

 valuation of the fertilizer before purchasing. For example, sup- 

 pose fertilizer A is offered for $21.00 a ton, and fertilizer B for 

 $24.00 a ton : 



Taking the valuations given elsewhere, we have the following : 



