Agricultural Chemistry. 
407 
Taking together, then, the now established facts, th,at the 
supply of available nitrogen to a cultivated soil, greatly increases 
the produce of wheat, — that the clover, which has the same effect, 
has rendered the soil much poorer in all the important mineral 
constituents required by the wheat, except silica, — and that the 
clover again is known to yield twice or three times as much 
nitrogen per acre as a cereal grain Avhen equally provided with it 
by manure, and that it also leaves a large amount of organic 
residue in the land, — have we not in these facts, sufficient ground 
for concluding, that the beneficial effect of the leguminous clover 
has been the accumulation from atmospheric sources within the 
soil itself, of available nitrogen for the increased groxoth of the cereal 
grain ? And have we not in this fact, taken in connection with 
that of the much larger amount of nitrogen required in m.anure 
than is obtained in an increased produce of wheat obtained by 
its use, the clearest key to the benefits of the so-called /a/Zozo C7vps 
in alternation with grain ? Have we not in these facts the 
clearest proofs, that the rotation of crops does 7iot depend " on the 
unequal quantity and quality (solubilitv, &c.) of the mineral con- 
stituents, and on the unequal proportions in which they are re- 
quired for tlie development of the different cultivated crops ? " 
And liow, we would ask, if an adequate increased growth of corn 
be only attainable by the accumulation of available nitrogen toitliin 
the soil — and if one of the chief moans of the farmer to this end 
were a rotation of crops, by which he is enabled " to produce 
manure for his corn crops, that is, for the growth of his s.aleable 
produce" — and if the great object to be attained in our time is 
" to substitute for a rotation of crops a rotation of the proper 
manures'" — how, we would ask, would an adequate increase of grain 
be possible under such circumstances, by the supply of a rotation 
of manures from ivithout, founded on a knowledge of the compo- 
sition of the ashes of crop to be grown ? ! 
To resume — as the result of our whole inquiry we conclude : — 
1. That the manure indicated by the resultant requirements of 
British agriculture has no direct connection with the composition 
of the mineral substances collectively found in the ashes of the 
produce grown on, or exported from the farm ; and that the 
direct mineral manures which are required, are not advan- 
tageously applied for the direct reproduction of the exported corn, 
but should be used for the green or fallow crops — one of whose offices 
it is, to collect from the atmosphere, or to conserve on the farm, 
available nitrogen, for the increased gi'owth of the cereal grains. 
2. That the nitrogen required to be provided icithia the soil for 
this purpose, is far greater than that contained in the increase of 
produce obtained by it. 
3. That the chemical effects fallow, in increasing the growth 
