On Agricultural Chemistry. 



33 



accumulating nitrogen from the atmosphere during its growth, 

 taking up the minerals which the grasses, from their more 

 limited power in this respect, could not appropriate, an abundance 

 of provision of the nitrogenous manure so effective in the growth 

 of the grasses, which are observed to spring up with great 

 luxuriance wherever the fungus has grown or fallen. 



But again, judging from the composition of the ash of the 

 turnip, which shows, both in the leaf and in the bulb, a pro- 

 portion of alkalies to phosphoric acid of from four or five to one, 

 we might be led to decide that the former, rather than the latter, 

 were usually and specially the more appropriate manures for the 

 turnip. Common practice has, however, definitely determined 

 in favour of phosphoric acid rather than of the alkalies, as the 

 special manure to be provided for the turnip, from sources 

 external to the farm itself. 



The striking effect of phosphoric acid upon the growth of the 

 turnip, indeed, is a fact so well known to every intelligent agri- 

 culturist in Great Britain, that it would seem quite superfluous 

 to attempt to illustrate it by any direct experiments of our own. 

 However, as Professor Liebig has again, in the recent edition of 

 his ' Letters,' expressed an opinion entirely inconsistent with 

 such a result, we will refer to one or two of the results obtained 

 in our experimental turnip-field, which bear upon the opinion 

 he has reiterated as follows : — thus, speaking of the exhaustion of 

 phosphate of lime and alkaline phosphates by the sale of flour, 

 cattle, &c., he says : — " It is certain that this incessant removal of 

 the phosphates must tend to exhaust the land and diminish its 

 capability of producing grain. The fields of Great Britain are in 

 a state of progressive exhaustion from this cause, as is proved 

 by the rapid extension of the cultivation of turnips and mangold- 

 -wurzel, plants which contain the least amount of the phosphates, 



AND THEREFORE REQUIRE THE SMALLEST QUANTITY FOR THEIR 



DEVELOPMENT I"* Now we do not hesitate to say that, however 

 small the quantity of phosphates contained in the turnip, the 

 successful cultivation of it is more dependent upon a large 

 supply of phosphoric acid in the manure than that of any other 

 crop. 



In the following table, then, is given the amounts of bulbj since 

 1843, of— 



First, the continuously unmanured plot ; 



Secondly, that with a large amount of superphosphate of lime 

 alone each year ; and 



* See the third edition of the ' Letters on Chemistry,' page 522. 

 t Norfolk Whites in 1843.4-5-6-7-8, and Swedes in 1849 and 1850. 

 VOL. XIL D 



