DR. DAUBENY ON THE ROTATION OF CROPS, ETC. 



233 



The following Table will show the composition of the three crops of beans, after 

 deducting the extraneous matters present in the ash. 



Having now, with reference to the six plants above-mentioned, stated, not only the 

 amount of every year's crop, but also the composition of the last of each which had 

 been obtained, we seem to be in a position to calculate the amount of the several 

 inorganic ingredients contained in them, which will have been abstracted from the 

 ground during the time the experiments were carried on. 



This indeed is a question of little interest, so far as regards the acids and bases 

 that are predominant ingredients in the soil, but in the case of the alkalies, the mag- 

 nesia, and the phosphates, which exist there in more limited quantity, its determina- 

 tion may afford us a clew towards the main object of our inquiry, namely, the 

 cause of the falling off of a crop after frequent repetition. 



In the case of the barley, it will be seen, that the produce of the same plot of ground 

 amounted in the course of ten years to 289*65 lbs., including straw as well as grain, 

 and that, taking the last year's crop as the criterion, this quantity would have yielded 

 25*2 lbs. of ash. 



For as 100— 8*7— 289*65— 25*2. 



Now 25*2 lbs. of ash would contain nearly as follows, according to the analyses 

 given above : — 



Sand and charcoal ") 



„ . , ^ . y extraneous . . . 6*25 



Peroxide or iron J 



Silica 6*30 



Phosphoric acid ........ 1*84 



Sulphuric acid 0*53 



Carbonic acid 0*47 



Chloride of sodium 1*18 



Potass 4-36 



Magnesia 1'15 



Lime 3*52 



25*60 



