Lime is used either to prepare the seed for germination, or to prepare
the soil for the better growth of the seed. This latter operation it
does, either by adding itself as a new ingredient, or by acting
chemically upon the ingredients already in the soil.
When lime is applied _to the seed_ (the seed being moist) the oxygen
of the water, combining with carbon of the seed, forms carbonic acid;
which, having a powerful affinity for lime, unites with it, forming a
carbonate of lime. The escape of a portion of its carbon constitutes
the natural preparation of a seed for growth; but why, chemists have
not been able to explain.
Air-slaked lime, is lime which has combined with carbonic acid
existing in the atmosphere. Unburnt limestone is a carbonate of lime;
air-slaked lime is the same, and they do not materially differ.
Air-slaked lime, having no longer an affinity for carbonic acid,
withdraws none from the grain to which it may be applied; and in
nothing helps the germinating process. Our readers will therefore see
the reason why wheat does not sprout any quicker when it is limed,
than when it is not. Precisely the same thing is true of other
substances applied to grains. Magnesia, existing naturally as a
carbonate, like lime, has its carbonic acid expelled by strong heat,
and in that state applied to seeds, will assist the germination. If
exposed to the air it attracts carbonic acid and becomes again a
carbonate, and useless to seeds.
Where lime is employed _upon the soil_, it is either as a mere article
of vegetable food, or, as a chemical agent, to change the condition of
other ingredients of the soil. All good soils contain lime; of
ninety-four different cultivated soils in Rhode Island, analyzed by
Professor C. T. Jackson, _eighty-nine_ contained lime. Ruffin, in his
essay on calcareous manures, says, after a large induction of fact,
“that all soils naturally poor, are certainly destitute of calcareous
earth.” When there exists in the soil, already, enough lime for the
wants of vegetation, the addition of more will produce no effect upon
the crop. New lands, and old land not run down, and naturally rich in
lime, may require none. But lime is applied not alone as food directly
offered to vegetation, but to act upon and change the soil itself.
It _neutralises_ free acids which exist in the soil. This is done with
quick-lime or air-slaked; the first combining directly with the
acid—the second by liberating its carbonic acid and then combining
with the acid of the soil, leaving the carbonic acid to be food for
plants. It is very well known by those accustomed to use peaty
substances for manures, and meadow mud, that they will rather injure
than benefit soils, until their acid has been neutralized.
Lime _decomposes_ vegetable fibre, and reduces tough ligneous
substances, to a consideration in which they can be appropriated by
plants. For this purpose _quick-lime_ should be used and may be
applied at the rate of from twenty to thirty bushels to the acre.
Lime enters into combination with sand or silex, forming a substance
different from either of them. Even strong clays will be found to
contain much silex; and lime, by combining with it, makes the soil
friable or crumbling.