October, 1922] fertilizer inspection, 1922 ,5 



The per cent, of ammonia multiplied by 0.82247 gives the 

 per cent, of nitrogen. Do not be misled by thinking that a 

 tag stating 3.29 per cent, of nitrogen and nitrogen equiva- 

 lent to 4 per cent, of ammonia means that the fertilizer con- 

 tains the sum of these two. It does not. It means that the 

 fertilizer contains 3.29 per cent, of nitrogen only. 



For convenience, phosphorus is expressed as per cent, of 

 "phosphoric acid" or PoOr, (Phosphorus pentoxide). The 

 tag usually gives the total per cent, of "phosphoric acid," 

 the "water soluble," "citrate soluble" and "insoluble." For 

 the purpose of figuring out the value of these we can take 

 the sum of the "water soluble" and the "citrate soluble" and 

 call it available phosphoric acid. The per cent, of avail- 

 able phosphoric acid is the figure to use in determining the 

 value of the fertilizer. Potassium is expressed as per cent, 

 of available K.O or potash. This is water soluble and 

 available to the plant. 



METHOD OF CALCULATING THE RELATIVE 

 COMMERCIAL VALUE 



Because of the variations of prices during the season and 

 the differences in freight costs, etc., it is difficult to calculate 

 accurately the values of the different brands of fertilizer. 

 The commercial value of a fertilizer is based upon the con- 

 tent of available nitrogen, phosphoric acid (P2O5) and 

 potash (KoO). If we know the guaranteed analysis and 

 assign approximate commercial values for a pound of each 

 of the plant foods, we can calculate the relative values of 

 fertilizers. 



The terms "unit" of nitrogen, "unit" of phosphoric acid 

 and "unit" of potash are sometimes used to express the 

 amounts instead of the per cent. The term "unit" means 

 20 pounds per ton (2,000 pounds) or 1 per cent. One unit 

 means 1 per cent, of a ton or 20 pounds. A fertilizer hav- 

 ing 4 per cent, of nitrogen has four units of nitrogen or 80 

 pounds per ton. 



