154 BOARD OF xVGRK'ULTUKE. [Pub. Doc 



phoric acid from bone and fish, and who would not be sup- 

 posed to ein})loy it. Its more general introduction into 

 conmiercial fertilizers at i)resent, than formerly, is said to be 

 in res})onse to the demands of the consumer for a fertilizer 

 which drills readily. At all events, the manufacturer should 

 sell this phosphate for use only on limestone soils, or the 

 consumer must run the risk that he will not receive full 

 returns from its use. The consumer should also make sure 

 that his soil does not lack lime, if he expects to receive full 

 returns from ready-mixed commercial manures which con- 

 tain phosphoric acid in this material. Even then it is a 

 serious proposition if it would not be more profitable to mix 

 his own fertilizers, rather than to i)urchase ready-mixed 

 goods, unless he can be assured of the source of the organic 

 nitrogen, and that this particular phosphate is not used in 

 their manufacture. 



It should be borne in mind by every consumer of ferti- 

 lizers that the term " available," as applied to the phosphoric 

 acid of the commercial manures, has reference to the sum 

 of the phosphoric acid which is soluble in pure water (soluble 

 phosphoric acid) and in ammonium citrate solution (reverted 

 phosphoric acid) . The term ' ' available " has therefore come 

 to be a "trade name," and it is not to be inferred that all 

 of the phosphoric acid known as "available" is necessaril}^ 

 readily available to plants, or, in other and more apjn-opriate 

 words, that it is readily "assimilable" by them. To make 

 this more plain, if ])ossible, let us assume that in a given 

 case all of the reverted and hence the "available" phos- 

 phoric acid of a fertilizer is present in ignited iron and 

 aluminum phosphate ; then little or none of it would be 

 available to the plant, or, in other words, little or none of it 

 would be assimilable, provided it were used upon very acid 

 soil. 



In view of the foregoing, it would seem as if the time 

 may have arrived when the agricultural chemists of the 

 United States will find it necessary to modify either the 

 solution enn)loyed in the determination of reverted phos- 

 phoric acid, or the method of treatment, so as to dissolve 

 less of the phos[)horic acid of the ignited iron and aluminum 



