76 Fertilizers 



in good bone, is equivalent to 43.60 per cent of phosphate 

 of lime. 



All phosphates are insoluble in water, but, as phos- 

 phates, they are not capable of feeding the plant directly ; 

 they must first decay. Hence, the usefulness of a phos- 

 phate depends upon the rate of decay, or time required 

 to change to such a form as to become available to the 

 plant. The rapidity with which a phosphate will feed 

 the plant depends upon a number of conditions, chief 

 among which are, first, the character of the substance 

 itself; second, the fineness of its division; third, the 

 character of the soil to which it is applied ; and fourth, 

 the kind of crop for which it is used. 



The influence of source of phosphate upon availability. 



The chief point to be observed in the first case is 

 whether the substance is animal or vegetable, or whether 

 it is mineral. Phosphates of immediate animal or vege- 

 table origin decay more rapidly than purely mineral 

 phosphates, because of the greater tendency of the organic 

 matter with which the phosphate is associated to respond 

 to the action of the natural agencies which cause decay. 

 A bone, for example, if kept in a suitable condition of 

 moisture and warmth, will soon begin to rot, the rotting 

 affecting not only the animal matter, but more or less the 

 phosphatic matter with which it is so closely identified, 

 the fermentation primarily attacking the organic sub- 

 stances, but exercising a greater or less solvent effect 

 upon the phosphates. 



In the case of the mineral substances, the rate of decay 

 is usually much slower, because there is no organic fer- 

 mentation. The material changes or is broken up only 

 by virtue of the action of the natural solvents, air and 



