4 Experiments upon Swedes. 



increased the efficacy of the latter as a turnip manure. The pro- 

 duce obtained with other manures poor in phosphate fell short 

 of the crops raised with phosphatic manures. 



The legitimate conclusions which may be drawn from these 

 field experiments are 



1. That on the particular soil, in the season in which the ex- 

 periments were made, and the quantities of manures employed, 

 guano was a less economical manure for swedes than bone-super- 

 phosphate. 



2. That phosphatic manures greatly increased the yield of the 

 root-crop, and much more so than other kinds of artificials. 



3. That the form in which the phosphates were employed very 

 much indeed affected the result, since superphosphate gave more 

 than 2i times as much increase per acre as an equal money value 

 of bone-dust. 



4. That a purely mineral phosphate, when dissolved in acid 

 and perfectly free from ammonia, under favourable circumstances 

 may produce as large a return as guano, a manure rich in am- 

 monia. 



It does not appear, however, from these experiments whether 

 ammonia had any share in the final result or not. The fact that 

 bone-superphosphate, containing from 2 to 2i per cent, of am- 

 monia, gave a much larger return than the mineral superphosphate, 

 and also the equally important fact that the addition of a small 

 quantity of guano to dissolved coprolites had a very beneficial 

 effect, would seem to indicate that ammonia, in moderate pro- 

 portion, is a desirable fertilizing ingredient of a turnip manure. 

 A critical examination of these facts, however, I think neither 

 proves nor discountenances the conclusion that ammonia has had 

 a beneficial effect in the recorded experiments ; for when com- 

 paring the effects of bone-superphosphate with dissolved copro- 

 lites, no account was taken of the proportion of soluble phos- 

 phate contained in each. I have since ascertained that the dis- 

 solved coprolites contained most of the phosphate in an insoluble 

 state, not near enough acid having been employed for dissolving 

 the coprolite powder. Indeed the coprolite 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 



