1864.] CHEMISTRY OF MANURES, 207 



cultiyated soils for the most part do) potash remains, conformahly 

 with Liehig's law, the characteristic manure for the leguminosae. 



The root-crops, however, and particularly turnips, are brought 

 forward as contradictory to Liebig's law, and confirmatory ( f the 

 theory of manurial " specifics"; because, though the ash of the 

 turnip contains more potash than phos, horic acid, this plant is 

 nevertheless found to benefit, conversely, more by artificial supplies 

 of phosphoric acid than of potash. 



"It must be admitted," say the principal champions of the 

 doctrine specific, " that the extraordinary effect of superphosphate 

 of lime cannot be accounted for by the idea of merely supplying 

 it in the actual constituents of the crop, but that it is due to some 

 special agency in developing the assimilative processes of the 

 plant.'' ^ And again they say, " It is at any rate certain that 

 phosphoric acid, though it forms so small a proportion of the ash 

 of the turnip, has a very striking effect on its growth when applied 

 as manure. "f 



On these statements it is first to be remarked that the experi- 

 mental results on which they are founded, and which were obtained 

 at Rothamstead, are at variance with those obtained on other soils 

 by other equally trustworthy observers. According to the best 

 analyses of the ash of turnips (swedes), these plants may be taken 

 to contain about 0*1 per cent, of phosphoric acid. On the odier 

 hand, ordinary superphosphate of lime contains about 16 per cent. 

 of this ingredient in the soluble form of combination ; so that three 

 cwt. of this manure contain between fifty-three and fifty-four lbs. 

 of immediately-available phosphoric acid. Mr. J, Russell | divided 

 a turnip-field into plots : upon one plot he applied three cwt, of 

 superphosphate ; upon two others five cwt. ; upon two others seven 

 cwt. and ten cwt. respectively. On comparing the crops yielded by 

 the two plots equally manured, a difference of 38 cwt. was observed 

 between their respective weights. The figure fixes the limit of variar 

 tion fairly attributable in this case, to causes other than the quan- 

 tity of manure employed. The plot manured with three cwt. of super- 

 phosphate yielded to Mr. Russell 480 cwt. of swedes. These would 



• On Agricultural Chemistry, especially in Relation to the Mineral 

 Theory of Baron Liebig. Journ. Roy. Ag. Soc. of England, vol. xii, 

 part i, 1851. 



t Ibid. 



X Journ. Roy. Ag. Soc, rol. xxii, p. 86. 



