154 Experiments upon Swedes. 



phosphate gave an increase of 8 tons 8 cwt. 16 lbs., whilst the 

 same amount of money expended in bone-dust yielded only an 

 increase of 3 tons 12 cwt. 



Guano produced 2 tons less of swedes per acre than home- 

 made superphosphate — a difference,' considering the small crop 

 xurnished by the unmanured land, which is considerable. On the 

 other hand, dissolved coprolites gave an increase of 6 tons 8 cwt., 

 or very nearly the same increase as guano alone ; and a mixture of 

 guano and dissolved coprolites an increase of 7 tons 12 cwt. 16 lbs. 

 The purely mineral superphosphate, made by dissolving copro- 

 lites in acid, thus produced a less favourable effect than the bone- 

 superphosphate, but, when added to guano, dissolved coprolites 

 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 2^ 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 



