October, 1923] FERTILIZER INSPECTION, 1923 3 



however, are only very slowly converted into nitrate nitro- 

 gen and are not readily available. 



Phosphorus occurs in the various fertilizer materials 

 principally as phosphoric acid in combination with calcium 

 (lime) . In order to be available to plants these compounds 

 of lime and phosphorus must be soluble or be made soluble. 

 The amount of lime combined with the phosphoric acid de- 

 termines the solubility; the material containing the small- 

 est amount of lime is the most soluble. That part of the 

 phosphoric acid which is readily soluble in water is imme- 

 diately available to the plant during the growing season. 

 This is known as "water soluble" phosphoric acid. A part 

 of the phosphoric acid which is insoluble in water is sol- 

 uble in a certain strength of ammonium citrate solution. 

 This is known as "citrate soluble" or "reverted" phosphoric 

 acid. This is also available to the plant. In the analysis 

 the "available" phosphoric acid includes the "water soluble" 

 and the "citrate soluble." The insoluble may be obtained 

 by subtracting the available from the total in the table of 

 analyses. The "insoluble" phosphoric acid becomes avail- 

 able to the plant only very slowly. 



Potassium occurs in commercial fertilizers usually in 

 the form of chloride (muriate) or sulphate. Only the 

 water soluble potassium is readily available to plants. The 

 analysis, therefore, expresses the percentage of "water sol- 

 uble" potash (KoO). 



Statement of the Analysis. There are numerous ways 

 of expressing the amounts of nitrogen, phosphoric acid and 

 potash contained in a fertilizer. The purchaser should not 

 be rnisled by these statements.. For instance, if a fertilizer 

 contains 3 per cent, of nitrogen, it may be expressed as 

 nitrogen 3 per cent., as nitrogen equivalent to 3.65 per cent, 

 ammonia or as nitrogen equivalent to 14.1 per cent, of 

 ammonium sulphate. The per cent, of nitrogen is the thing 

 which is important and is the figure which should be used 

 in calculating the value of a fertilizer. The following 

 shows how to calculate the per cent, of nitrogen from the 



