4 N. H. AGR. EXPERIMENT STATION [Bulletin 196 



Potassium occurs in commercial fertilizers usually in the 

 form of a 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 (K2O). 



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 mislead 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 3.63 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 the fertilizer. The following 

 shows how to calculate the per cent of nitrogen from the 

 per cent of ammonia and vice versa. Nitrogen per cent mul- 

 tiplied by 1.21584 gives the per cent of ammonia. The 

 per cent of ammonia multiplied by 0.82247 gives the per 

 cent of nitrogen. Do not be mislead by thinking that a tag 

 stating 3.29 per cent of nitrogen and nitrogen equivalent 

 to 4 per cent of ammonia means that the fertilizer contains 

 the sum of these two. It does not. It means that the fer- 

 tilizer contains 3.29 per cent of nitrogen only. 



For convenience phosphorus is expressed as per cent of 

 "phosphoric acid" or PoOg (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 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 K2O or potash. This is water soluble and 

 available to the plant. 



AGRICULTURAL VALUE. 



The commercial value of the fertilizer is determined 

 largely by the cost of producing the materials and getting 

 them into the hands of the consumer. The agricultural 

 value is based upon the return in money which the fer- 

 tilizer yields to the farmer by increased crop production. 

 The commercial value is therefore not necessarily closely 

 related to the agricultural value. It is possible that a 



