68 MAINE AGRICULTURAL EXPERIMENT STATION. 1 902. 



upon the treatment it receives. The nitrogen in the tables of 

 analyses marked "insoluble in water" is organic nitrogen. 



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 com- 

 pletely 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. 

 The "Nitrogen soluble in water" of the tables includes both the 

 nitrogen as ammonia and as nitrate. 



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, also known as "reverted ;" 

 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 phosphoric acid 

 ,in natural or untreated phosphates is insoluble in water, and not 

 readily available to plants. If it is combined with organic sub- 

 stance, as in animal bone, the rate of decay is more rapid than if 

 with purely mineral substances. The insoluble phosphates may 

 be converted into soluble forms by treatment with strong acids. 

 Such products are known as acid phosphates or superphosphates. 

 The "insoluble phosphoric acid" of a high cost commercial fer- 

 tilizer has little or no value to the purchaser because at the usual 

 rate of application the quantity is too small to make any percep- 

 tible effect upon the crop, and because its presence in the fertilizer 

 excludes an equal amount of more needful and valuable con- 

 stituents. 



Potash in commercial fertilizers exists chiefly as muriates and 

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



