4 N. H. AGR. EXPERIMENT STATION [Bulletin 214 



* 



age, etc., are also rapidly converted into nitrate nitrogen 

 in the soil and made available to the plant. Other types 

 of organic nitrogen like those contained in hoof, hair and 

 leather waste, however, are only very slowly converted into 

 nitrate nitrogen and are not readily available. 



Phosphorus occurs in the various fertilizer materials 

 principally as phorphoric 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 

 determines the solubility; the material containing the 

 smallest 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 solu- 

 ble in a certain strength of ammonium citrate solution. 

 This is known as "citrate soluble" or "reverted" phos- 

 phoric 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 

 available 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 

 soluble" 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 misled 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 am- 



