it possible to postpone
for a year or two the reapplication of lime. All these circumstances
have their influence in bringing its action to an end, but the most
important is, that after a time it has exhausted its decomposing effect
on the soil, having destroyed all the organic matter, or liberated all
the insoluble mineral substances which the quantity added is competent
to do, and so the soil passes back to its old state. It does even more,
for unless active measures are taken to sustain it by other means, it is
found that the fertility of the soil is apt to become less than it was
before the use of lime. And that it should be so is manifest, if we
consider that the lime added has liberated a quantity of inorganic
matter, which, in the natural state of the soil, would have become
slowly available to the plant, and that it must have acted chiefly in
those very portions which, from having already undergone a partial
decomposition, were ready to pass into a state fitted for absorption,
and thus as it were must have anticipated the supplies of future years.
This effect has been frequently observed by farmers, and is indeed so
common, that it has passed into a proverbial saying, that "lime enriches
the fathers and impoverishes the sons." But this is true only when the
soil is stinted of other manures, for when it is well manured the
exhausting effect of lime is not observed; and it must be laid down as a
practical rule, that its use necessitates a liberal treatment of the
soil in all other respects. But when lime has been once employed it
becomes almost necessary to resort to it again; and generally so soon as
its effects are exhausted a new quantity is applied, not so large as
that which is used when the soil is first limed, but still considerable.
When this is done very frequently, however, bad effects ensue; the soil
gets into a particular state, in which it is so open that the grain
crops become uncertain, and such land is said, in practical language, to
be overlimed. The explanation of this state of matters commonly assumed
by those unacquainted with chemistry is, that the land has become too
full of lime; but a moment's consideration of the very small fraction of
the soil which even the largest application of lime forms, will serve to
shew that this cannot be the cause. Ten tons of lime per acre amounts to
only one per cent of the soil, and as a considerable part of the lime is
carried off by drainage in the course of