November, 1921] fektilizeb inspection, 1921. c 



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 available 

 phosphoric acid is the figure to use in determining the value 

 of the fertilizer. Potassium is expressed as per cent of avail- 

 able K.iO or potash. This is water soluble and available to 

 the plant. 



METHOD OF CALCULATING THE RELATIVE 

 COMMERCIAL VALUE. 



The commercial value of a fertilizer is based upon the 

 content of available nitrogen, phosphoric acid (P0O5) 

 and potash (K2O). If we know the guaranteed analysis 

 and the commercial value of 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 or 

 unit of potash are sometimes used to express the amounts 

 instead of the per cent. The term "unit" means 20 lbs. per 

 ton (2000 lbs.) or i per cent. One unit then means i per 

 cent of a ton or 20 lbs. A fertilizer having 3 per cent 

 nitrogen has three units of nitrogen per ton, or 60 lbs. per 

 ton. 



Prices of Plant Materials. It is impossible to give ac- 

 curate figures for the cost of the diflr'erent plant foods be- 

 cause the cost of mixing, bagging, freight and the manu- 

 facturers' and dealers' profits vary with the quantity pur- 

 chased, distance shipped and number of persons through 

 whose hands the material has passed. It is possible, how- 

 ever, to arrive at figures which are sufficiently accurate for 

 use in comparing the relative value of fertilizers. 



Acid phosphate containing 16 per cent of available phos- 

 phoric acid was purchased for $28.00 per ton. One ton then 

 contained 0.16 times 2000 lbs. or 320 lbs. of available phos- 

 phoric acid. The cost per lb. was $28.00-^320 or $o.o8| and 

 one unit of available phosphoric acid cost 2oX$o.o85 or 



$1.75- _ 



Muriate of potash averaging 51.5 per cent of water 



