No. 6. 



DEPARTMENT OF AGRICULTURE. 



867 



TABLE 20. 

 Value of Average Incre-ase From Different Sources of Phosphoric Acid. 



By consolidating the values given in the above table and regarding 

 it as representing the probable outcome of an average rotation in 

 which the four crops have followed each other as in the actual ro- 

 tation, then the value of the total increase per acre due to the various 

 sources of phosphoric acid, when supplemented witli uniform 

 amounts of nitrogen and potash, will be represented by the follow- 

 ing figures: 



Value of increase from basic slag 



Value of increase from dissolved bone black 



Value of increase from raw bone meal 



Value of Increase from acid phosphate, 



Per Acre. 



$19 14 

 U S2 

 16 63 

 IS 63 



Taking basic slag phosphate as 100, we find the follow'ing as the 

 proportionate values of these materials as sources of phosphoric 

 acid: 



Basic slag phosphate, 2 00 



Dissolved bone black, 9t) 



Kaw bone meal, 87 



Acid phosphate, 87 



While these results are very close together in some cases, and more 

 work will be necessary to determine their relative value, yet there 

 seems to be no doubt that most crops have ability to utilize phos- 

 phoric acid that is insoluble in water to a larger extent than is 

 commonly recognized. 



