124 NATURE STUDY REVIEW [10:4— April, 1914 



per cent potash. If the percentage of available basic ingredients 

 is known it is an easy matter to calculate the value of a fertilizer. 



Directions: 



The percentages of ingredients are indicated on the fertilizer 

 tag or label if sold in a state where fertilizers must be guaranteed. 

 The list of ingredients on a fertilizer tag or label is often mislead- 

 ing or at least confusing. Only the lowest stated amount of avail- 

 able nitrogen, phosphoric acid, and potash should be considered. 

 The following example of list printed on fertilizer tag will illustrate 

 this point : 



Nitrogen 1.64 to 2.46 per cent 



Nitrogen as ammonia 2 " 3 " 



Soluble phosphoric acid 5 " 6 " 



Reverted phosphoric acid 3 " 4 " 



Insoluble phosphoric acid i " 2 " 



Total phosphoric acid 10 " 12 " 



Phosphate of lime 22 "24 " 



Available phosphoric acid 8 "10 " 



Potash 3 " 4 " 



Sulphate of potash 6 " 8 " 



In this fertilizer the lowest stated amount of nitrogen is 1.64 per 

 cent, of available phosphoric acid 8, of potash 3. In other words, 

 this is a 1.64-8-3 fertilizer. Sometimes nitrogen is expressed in 

 terms of ammonia. Ammonia contains 82 per cent of nitrogen. 

 Two per cent ammonia would therefore contain .82 of 2 or 1.64 

 per cent nitrogen. 



In order to determine the value of the plant food in a fertilizer 

 three easy calculations are necessary: (i) Determine in pounds 

 from the percentages given in the guaranteed analysis the amoimts 

 of nitrogen, phosphoric acid, and potash in one ton (2000 pounds). 

 For example, the above fertilizer contains 1.64 per cent nitrogen, 

 8 per cent phosphoric acid, and 3 per cent potash. 



(2) Calculate the value of each ingredient at average market 

 value per pound for nitrogen, phosphoric acid and potash. These 

 values change somewhat from year to year, but are published 

 annually in state fertilizer inspection circulars. For 19 13, the 



