JSo. 1. DEPARTMENT OF AGRICULTURE. 141 



especially turnips, quite readily. The source and general character 

 of the phosphates themselves will influence the degree of their availa- 

 bility^ while the phosphoric acid, as has already been noted, is pre- 

 sent in bone and in phosphate rock in the same condition — that is as 

 tri-calcium phosphate, or, as we say, in an insoluble form, the phos- 

 phoric acid of bone is much more easily available than that of the 

 rock. This is due to the fact that in the bone the phosphate is as- 

 sociated with more or less organic matter, the decaying of which aids 

 very materially in accomplishing the solubility of the phosphoric 

 acid of the bone. In the rock the phosphates are associated almost 

 entirely with mineral matter there being nothing present to aid de- 

 composition. The degree of fineness will also affect its availability. 



The Rhode Island Experiment Station gives in their report of 

 1897, partial results of an experiment designed, if possible, to as- 

 certain the most economical form in which to apply phosphoric acid. 

 All the plots in the experiment received like amounts of potash and 

 nitrogen and the same money value of phosphoric acid in its various 

 forms with the exception of two check plots which, of course, re- 

 ceived no phosphoric acid. The plots were seeded to grass in 1895. 

 The iijsoluble phosphates — fine ground bone, slag, phosphate and 

 floats — were applied as a full ration at that time and each spring 

 for three years each received a one-third dressing of nitrate of soda 

 and potash and also a one-third ration of soluble phosphates. 



By a full ration, is meant at the rate of 600 pounds per acre of dis- 

 solved bone black and as many pounds of the other forms of phos- 

 phate as the cost of that would purchase. Application was made in 



this way on the assumption that the insoluble phosphates, being 

 much less available, would remain in the soil through the period of 

 three years while the soluble, more readily available material, should 

 be supplied from year to year as required. At the end of three years 

 all the plots would have then received a like money value of fertili- 

 zer. At the time this report was made the last one-third of the 

 ration of soluble phosphates had not yet been applied so that the 

 soluble and insoluble forms of phosphoric acid were not on the same 

 basis, but the summary given of the results at that time was that 

 *'the three insoluble phosphates, fine ground bone, floats and slag 

 maintained the lead and that while there was one more dressing of 

 soluble phosphates to be given, the lead held by the insoluble forms 

 would doubtless even then give the latter the advantage." 



The Maine Station in their report of 1891 reports a trial of differ- 

 ent forms of phosphoric acid extending through a period of 6 years. 

 They came to the conclusion that dissolved phosphates were more 

 efificacious than the insoluble forms. In the field trial in which three 

 crops of oats and one of hay and* peas were grown, insoluble phos- 

 phoric acid was second in hay and third in oats and peas. 



