396 



Y. KOZAI, M. TOYOXAGA AND M. NAGAOKA. 



Relative iiiaiiurial value 





ill the 1st 

 season. 



in the isl 

 and 2n(l 

 seasons. 



in the isl, 

 2nd and 

 3rd sea- 

 sons. 





seasons. | 



0 ;i 0 



Double superphosphate 



loo 



100 



100 



100 





100 



Precipitated phosphate 



1 06 



112 



121 



"S 





"5 



Thomas phosphate 



53 



71 



79 



79 





82 



Crude bone dust 



60 



73 



76 



75 





75 





56 



73 



7S 



75 





75 





39 



52 



58 



56 





61 





28 



33 



39 



36 





36 



Phosphorite 



10 



17 



20 



22 





22 



From these figures and the explanations given in the joreceding 

 pages the results of the five years' experiments on various phosphatic 

 manures with paddy rice may be summarized as follows. 



(i.) Of the various phosphatic manures in our experiments, pre- 

 cipitated calcic phosphate, which in our case consisted chiefly of 

 dicalcic phosphate mixed with some tricalcic phosphate was the 

 most effective. Its action was most efficient in the first year of its 

 application, while in subsequent years the efiect was considerably 

 diminished and in the fifth year not the least action was to be seen. 

 The superiority of this manure over superphosphate, though not 

 great, was distinctly seen. This fact has been frequentl}- observed by 

 several investigators and may be due in our case to the extreme rich- 

 ness of the soil in hydrated sesquioxides of iron and aluminium, by 

 which the easily soluble monocalcic phosphate of the superphosphate 

 is more readily converted into the basic comjiounds which are diffi- 

 cultly assimilable than the dicalcic phosphate contained in precipit- 

 ated calcium phosphate. Considering that precipitated phosphate 

 can be obtained cheaper per unit of phosphoric acid than superphos- 

 phate, the conclusion is unavoidable, that the former is a more 

 economical source of phosphoric acid for paddy rice than the latter. 



(2.) Very similar though somewhat inferior to precipitated phos- 

 phate was superphosphate, whose action thougli great in the begin- 

 ning did not continue long and was wholly inefficient in the fifth 

 year after its application. The great solubility of the phosphoric 



