144 Report of Experiments on the Growth of Wheat. 
though a diminution in the produce of straw, still some in- 
crease of total produce, during the later years. Finally, with 
farmyard-manure there is an increase of both corn and straw 
in the latter as compared with the former half of the twelve 
years, but in a much less degree than over the last ten as 
compared with the first ten years of the whole period of the 
experiments. 
The general result over the final twelve years is, then, that 
the average annual yield was, without manure, much the same 
over the whole period ; that, notwithstanding the exhausting 
effects of applying ammonia-salts every year, the annual diminu- 
tion of produce under their influence was proportionally less 
during the latter half of the last twelve, than of the whole nine- 
teen years of their use ; that where ammonia-salts and all mine- 
ral constituents, except silica, were liberally supplied every year, 
the produce of corn increased, and that of the straw somewhat dimi- 
nished ; lastly, that where an excess of every constituent recpaired 
by the crop was annually applied, as in the farmyard manure, the 
rate of increase from year to year was not so great during the 
later as during some of the earlier years. 
That the unmanured produce should keep up its yield during 
the later years, and that the produce by the exhaustive process of 
applying ammonia-salts every year should diminish less during 
the latter half of the twelve than of the whole nineteen years, seems 
sufficient indication that the later seasons of the experiments were, 
upon the whole, more favourable than the earlier ones. But to 
this evidence may be added that derivable from the fact, that 
although the average weight per bushel of dressed corn without 
manure, and with ammonia-salts alone, was considerably less 
during the latter than during the earlier half of the whole period, 
it was, nevertheless, without manure considerably higher, and 
with ammonia-salts alone about as high, during the latler as dur- 
ing the earlier half of the last twelve years. It is, therefore, clear, 
that even under the most defective soil conditions the crop has 
either not deteriorated, or has done so in a less degree, in the 
later years. 
Upon the whole, then, it must be concluded, that the later years 
of the experimental period were, on the average, slightly more 
favourable to the crop than the earlier ones. Assuming this to 
have been the case, it must be admitted, that the fact of the un- 
manured plot maintaining its produce throughout the whole 
twenty years is probably in some degree due to the better average 
of the seasons themselves in the later years ; and, consequently, 
that had it been otherwise, the unmanured produce would have 
shown some slight decline in the later years, or rather, some slight 
t 
