oFFiciAi, inspe;ctions 42. 123 



decay, because change of form must take place before the nitro- 

 gen can serve as plant food. Organic nitrogen differs in availa- 

 bility not only according to the kind of material which supplies 

 it, but according to the treatment it receives. 



Nitrogen as ammonia usually exists in commercial manures in 

 the form of sulphate of ammonia and is more readily available 

 than organic nitrogen. While nitrogen in the form of ammonia 

 is extremely soluble in water, it is not readily removed from the 

 soil by leaching, as it is held by the organic compounds of the 

 soil. 



Nitrogen as nitrate exists in commercial products chiefly as 

 nitrate of soda. Nitrogen in this form is directly and imme- 

 diately available, no further changes being necessary. It is 

 completely soluble in water, and diffuses readily throughout the 

 soil. It differs from the ammonia compounds in forming no 

 insoluble compounds with soil constituents and may be lost by 

 leaching. 



Phosphoric acid is derived from materials called phosphates, 

 in which it may exist in combination with lime, iron, or alumina 

 as phosphates of lime, iron or alumina. Phosphate of lime is 

 the form most largely used as a source of phosphoric acid. 

 Phosphoric acid occurs in fertilizers in three forms : That solu- 

 ble in water and readily taken up by plants ; that insoluble 

 in water but still readily used by plants and known as "re- 

 verted ;" and that soluble only in strong acids and consequently 

 very slowly used by the plant. The "soluble" and "reverted" 

 together constitute the "available" phosphoric acid. The phos- 

 phoric acid in natural or untreated phosphates is insoluble in 

 water, and not readily available to plants. If it is combined 

 with organic substances as in animal bone, the rate of decay is 

 more rapid than if with purely mineral substances. The insol- 

 uble phosphates may be converted into soluble forms by treat- 

 ment with strong acids. Such phosphates are known as acid 

 phosphates or superphosphates. The "insoluble phosphoric 

 acid" of a high cost commercial fertilizer has little or no value 

 to the purchaser because at the usual rate of application the 

 quantity is too small to make any perceptible effect upon the 

 crop, and because its presence in the fertilizer excludes an equal 

 amount of more needful and valuable constituents. 



Potash in commercial fertilizers exists chiefly as muriates and 

 sulphates. With potash the form does not exert so great an 



