Experiments upon Sicedes. 155 



slate, not near enough acid having been employed for dissolving 

 the coprolite powder. Indeed the coprollte manure contained 

 but little soluble phosphate ; and as insoluble phosphate, in the 

 shape of coprolite powder, has as little effect upon vegetation as 

 sand, whilst the insoluble phosphates in bones, partially decom- 

 posed by acid, unquestionably are sufficiently available to produce 

 an immediate effect on the turnip crop,— the difference in the 

 result obtained by dissolved bones and dissolved coprolites, there- 

 fore, may have been due to the larger amount of available phos- 

 phates, and not to the ammonia contained in the former. On the 

 other hand, the addition of some guano to dissolved coprolites 

 having produced a beneficial effect, it may be inferred that the 

 ammonia in the guano produced this effect ; but since Peruvian 

 guano contains both soluble phosphates and bone-earth, in a 

 highly finely-divided state, it may be maintained with equal force 

 that the additional produce resulted from the additional quantity 

 of available phosphates in guano. In short, my former experi- 

 ments, of which a detailed account will be found in vol. xvi., 

 of this Journal, are not calculated to decide the question 

 whether or not ammonia can be dispensed with as a manuring 

 constituent in a turnip manure, nor do they show that superphos- 

 phate is a more economical manure for roots than guano ; for it 

 is quite possible that an excess of ammonia will do harm to 

 turnips, whilst a small quantity is likely to benefit the same crop, 

 provided available phosphates are present at the same time. It 

 also occurs to me that the assimilation of phosphates may be much 

 facilitated by the presence of a quantity of ammonia not large 

 enough to injure the roots. In other words, it is possible that 

 whilst 2/.-worth of guano per acre produces a less favourable 

 result than 2/. -worth of dissolved bones, IZ.-worth of guano per 

 acre may be found a more economical dressing, and lOs.-worth 

 of guano and lO.f.-worth of superphosphate may give a more 

 favourable result than either guano or superphosphate separately. 

 It may appear a simple matter to ascertain the comparative 

 value of ammonia as a fertilizing agent for root-crops, but this is 

 not the case. Notwithstanding all the experiments that have 

 been made with various ammoniacal and phosphatic manures, 

 our knowledge on this subject is so imperfect, that those who are 

 best acquainted with the experience of good farmers in different 

 parts of England will hesitate to give a definite answer when the 

 question is asked, Is ammonia a useful or necessary fertilizing 

 constituent in a turnip manure ? I do not think Ave are at present 

 in a position to give a satisfactory answer to this question, for 

 the simple reason that, important as it is, it has not yet been 

 sufficiently investigated in all its bearings. The contradictory 

 testimony of equally good and intelligent agriculturists — some 



