s. But its fertility remains unimpaired, with a due supply
of animal excrements, fluid and solid, and it not only remains the
same, but may be increased by a supply of mineral substances alone,
such as remain after the combustion of ligneous plants and other
vegetables; namely, ashes. Ashes represent the whole nourishment
which vegetables receive from the soil. By furnishing them in
sufficient quantities to our meadows, we give to the plants growing
on them the power of condensing and absorbing carbon and nitrogen by
their surface. May not the effect of the solid and fluid excrements,
which are the ashes of plants and grains, which have undergone
combustion in the bodies of animals and of man, be dependent upon
the same cause? Should not the fertility, resulting from their
application, be altogether independent of the ammonia they contain?
Would not their effect be precisely the same in promoting the
fertility of cultivated plants, if we had evaporated the urine, and
dried and burned the solid excrements? Surely the cerealia and
leguminous plants which we cultivate must derive their carbon and
nitrogen from the same source whence the graminea and leguminous
plants of the meadows obtain them! No doubt can be entertained of
their capability to do so.

In Virginia, upon the lowest calculation, 22 pounds weight of
nitrogen were taken on the average, yearly, from every morgen of the
wheat-fields. This would amount, in 100 years, to 2,200 pounds
weight. If this were derived from the soil, every morgen of it must
have contained the equivalent of 110,000 pounds weight of animal
excrements (assuming the latter, when dried, at the temperature of
boiling water, to contain 2 per cent.).

In Hungary, as I remarked in a former Letter, tobacco and wheat have
been grown upon the same field for centuries, without any supply of
nitrogenised manure. Is it possible that the nitrogen essential to,
and entering into, the composition of these crops, could have been
drawn from the soil?

Every year renews the foliage and fruits of our forests of beech,
oak, and chesnuts; the leaves, the acorns, the chesnuts, are rich in
nitrogen; so are cocoa-nuts, bread-fruit, and other tropical
productions. This nitrogen is not supplied by man, can it indeed be
derived from any other source than the atmosphere?

In whatever form the nitrogen supplied to plants may be contained in
the atmosphere, in whatever state it may be when absorbed, from the
atmos