Experiments on the Growth of Wheat. 
219 
matter is of itself of no practical utility as a manure for wheat. 
It may be mentioned that this is a result precisely similar in 
character to that which has been obtained in the Rothamsted 
experiments. 
The next and last Experiment is No. 7, in which 14 tons of 
farm-yard manure were applied per acre annually. It has already 
been stated that this amount of farm-yard dung would supply 
more of every constituent than would be contained in the increase 
of crop due to its employment. It would contain, in fact, from 
3 to 4 tons of carbonaceous organic substance, whilst the annual 
increase of produce did not contain 1 ton of such matter. The 
minerals in the dung would also very far exceed those in the 
increased produce yielded, and its nitrogen would be greater in 
amount than that supplied in the ammoniacal salts of Experi- 
ments 3, 4, and 5, or in the rape-cake of Experiment 6. There 
would, however, be this difference as regards the nitrogen — 
namely, that whilst that which was supplied in the ammoniacal 
salts would be the most readily dissolved in the soil, that in 
the rape-cake would be so in a less degree, though much 
more rapidly in a light soil than in a heavy one. Part of the 
nitrogen of the dung too would also be rendered easily available, 
but that portion which entered into the composition of the straw 
would probably require some years before the whole was liberated 
and applicable for the growth of the crop. The result of the 
experiment with the dung is, that we get an average annual in- 
crease by it of about lO^^ bushels of corn and 1300 lbs. of straw, 
which is less by nearly 3 bushels of corn and about 150 lbs. of 
straw than was obtained by the rape-cake. The weight per 
bushel of the corn grown by the dung was, however, on the 
average about | lb. heavier than that by the rape-cake, which will 
account for part of the deficiency. Now, as we have seen by the 
other experiments, that neither minerals alone, nor carbonaceous 
organic matter, had any influence in the increase of the crop, but 
that wherever there was a supply of nitrogen in the manure there 
was always a very considerable increase, we have every reason to 
conclude that it was the amount of nitrogen liberated from the 
dung in a form applicable by the plants which fixed the limit to 
the increase of produce obtained by its use. And in confirma- 
tion of this conclusion, it may be recalled to mind how very 
small would be the amount, both of the carbonaceous organic 
matter and of mineral matter, in the increase of produce obtained 
in proportion to the amount of either of them supplied by the 
farm-yard manm-e. It is true, that neither is the amount of 
nitroffen contained in the increased produce of wheat ever equal 
to that supjilied in the manure which yielded that increase ; but 
it must be remembered that, besides any liability to loss by 
