Experiments upon Swedes. 5 



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, l/.-worth of guano per 

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

 of guano and lOs.-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 we 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 

 maintaining that ammonia has a decidedly beneficial effect upon 

 turnips, others that it is of no use whatever for that crop shows 

 plainly enough that we have still a good deal to learn before it 

 can be decided on what soils and under what system of cultivation 

 ammonia can be dispensed with in a turnip manure, and what 

 the conditions are that render the direct supply of ammoniacal 

 matters to roots necessary or desirable. 



We hear constant discussions as to whether guano is better 

 than superphosphate, or whether a mixture of guano and super- 

 phosphate should be used ; and these discussions are never brought 



