EXPEPJMENTS ON TUENIPS. 



315 



the increase by addition of superphosphate is due to its assisting 

 the plant with sohible phosphoric acid during its earlier stages 

 of growth, and probably a much less quantity than 5 cwt. per 

 acre would effect this purpose. 



IT. Ground against Dissolved Phosphates. — The second inquiry 

 proposed was, whether it is more economical in this soil to apply 

 phosphates in a finely ground state or dissolved by treatment 

 with acid. Table XIII. shows the plots in which they are 

 compared. Each plot on the left hand received superphosphate, 

 while the one opposite it on the right got the same manure, 

 except that the superphosphate was replaced by an equal 

 money vahie of ground mineral phosphates. The basis of equal 

 money value being subject to fluctuation, may be thought 

 inferior to the one usually adopted, that of equal weights of 

 phosphoric acid. The soluble phosphates, as has been often 

 pointed out, become insoluble in the soil, but in a very much 

 finer state of division than any mechanical grindiug can effect. 

 Indeed, 10 per cent, to 30 per cent, of the ground mineral 

 phosphate is comparatively coarse powder. The effect therefore 

 to the crop to which equal amounts of phosphoric acid are 

 applied should be more or less in favour of dissolved phos- 

 phates. It is merely a question of amount, and experiment on 

 the whole has borne this out. The practical question to solve 

 for any soil is whether the larger amount of phosphoric acid, 

 that can be purchased as the cheaper ground phosphate, will 

 overcome the superiority in form of the superphosphate. It 

 seems better to test this directly than by calculations which 

 have given room for discussion. The superphosphate contains 

 sulphate of lime which is not present in the ground mineral, and 

 in other circumstances it would have been advisable to add 

 this to the latter manure, as in some cases the superiority of 

 superphosphate has been attributed to deficiency of sulphates in 

 the soil. It was unnecessary, however, to do this in these experi- 

 ments as the 5 tons of lime, of which analysis will be found 

 at the end of this paper, supplied a suiliciency of sulphates. 



The comparative trial stands thus — 



1SS2, 



Without Dung. 



Weight 



Applied, 



per Acre. 



Tricalcic 

 IMios- 



Cost, 



With Duntj, 



phatc, jper Acre.' 

 per Acre.i \ 



Wclfirht 

 AppliL'd, 



Tricalcic 

 I'hos- 



Cost, 



ptrAcio.p-7-^1 



phntc, per Acre. 



Sn])er|>liositlmte, 

 Ground coj)rolite8, 



cwt. 

 8 



lbs. 



250 



412 



30/ 

 30/ 



cwt. 

 ;") 



3^ 



lbs. 



157 

 257 



18/9 

 18/9 



