S86 ANNUAL REPORT OF THV. Off. Doc. 



jilioi'ic acid fioiii a mineral source is just as valuable as a pound from 

 an oi'gauic source. With this fact confronting us there seems to be 

 nothing to warrant the purchase of a dissolved bone instead of a dis- 

 solved rock, unless the phosphoric acid in the bone costs no more 

 tiian that in the rock. In other words, a farmer can not alford to 

 pay more per pound for available phosphoric acid in dissolved bone 

 than he can for that in dissolved rock any more than he would pay 

 more for sugar from cane than he would for sugar from beets. In 

 either case the only justification that could be given would be that 

 Ihere was no departure from the traditions of his grandfathers. 



The results of both field and plot experiments show that certain 

 classes of phospliates are more available and hence have a higher 

 agricultural value than would be given them by official methods of 

 analysis. This condition would seem to warrant some modified 

 method for analyzing such materials. This is particularly true of 

 the tetra-phosphates when used on some soils. 



The best advice and general rule which can be given in the matter 

 of the intelligent use of phosphates is, to study the special conditions 

 that surround the particular case in hand, observe the methods of 

 nature and compare these circumstances with those of the experi- 

 ments given, then apply the results with such modification as good 

 common sense would seem necessary' to meet the demands of local 

 conditions. 



