for Twenty Years in succession on the same Land. 281 
1866 ; and in total produce, 1859, 1862, 1865, 1866, and 1871. 
For information as to the characters of season, under the influence 
of which these results were obtained, we must refer to the descrip- 
tion of the respective seasons in Section 1. 
Whilst the unmanured land gave an average annual produce 
of only 21 bushels of dressed corn, and about 12 cwts. of straw, 
the farmyard manure gave 48^- bushels of dressed corn, and 28|- 
cwts. of straw ; or an average increase over the mean unmanured 
of 21 \ bushels of corn, and 16|^ cwts. of straw. 
During the 20 years, 280 tons of dung, containing from 80 to 
90 tons of dry solid matter, have been applied per acre. But 
the produce has only amounted to about 24| tons of corn, and 
28j tons of straw, or in all to only 53 tons ; and the increase, over 
the produce without manure, has only been about 14^J tons of 
corn, and 16-i- tons of straw — in all 30 J tons of total increase ; 
which certainly would contain less than one-third as much dry 
solid matter as was supplied in the dung. The manure would, 
in fact, supply to the soil very much more of carbon, of nitrogen, 
of phosphoric acid, of potass, of lime, of magnesia — indeed, pro- 
bably of every constituent, than the total produce contained ; and, 
of course, a still greater excess over the amounts taken off in the 
increase of produce. 
It is evident that there must be a very great accumulation of 
constituents in the soil of the dunged plot. Of nitrogen, for 
example, from 3 to 4 times as much has ^been applied as to any 
of the artificially manured plots; and, judging from the deter- 
minations of nitrogen in the soil of the dunged plot in the wheat- 
field, it is probable that the percentage of that substance in the 
surface-soil of the dunged barley plot has, during the 20 years, 
been nearly doubled. Yet, mixtures of mineral manure and am- 
monia-salts, or nitrate of soda, supplying nitrogen in so much less 
quantity, but in a more readily available condition, frequently 
gave about the same, and sometimes more, produce than the dung. 
It is obvious, too, that the large amount of nitrogen accumulated 
in the soil of the dunged plot is in a far less available or effective 
condition than the much smaller quantities annually supplied as 
ammonia-salts or nitrate of soda. 
In order to ascertain in what degree the accumulated nitrogen 
and other constituents will be annually available, and for what 
length of time any residue will remain effective, the dunged plot 
has, since the removal of the twentieth crop, been divided into 
two portions — one to receive dung annually, as before, and the 
other to be left unmanured, probably until the produce on it 
approximates to that of the continuously unmanured plot. 
The following Table shows the results obtained by the annual 
application of 14 tons of dung per acre, for barley, and for wheat, 
