DIFFERENT KINDS OF SOIL
(Continued)
“Limestone is the rock from which lime is obtained. It is composed of
carbonic acid and lime. To obtain the latter, the limestone is
subjected to intense heat in a furnace or lime-kiln. The carbonic acid
escapes, is dissipated in the air, and only the lime remains. In arable
land limestone is found rather often in smaller or larger pieces, but
more frequently as a fine powder which the eye can scarcely distinguish
from the other constituents, especially clay. The water of rivers and
other streams almost always contains a small proportion of dissolved
limestone. Thence comes the thin layer of stone that accumulates little
by little on the inner surface of bottles, coating the glass. Some
waters contain enough of this dissolved limestone to deposit a mineral
crust on objects immersed in them, as mosses and aquatic plants, and to
obstruct their aqueducts. The clearest water, in which no foreign
substance can be seen, absolutely none, nevertheless contains dissolved
limestone, just as sweetened water contains invisible sugar. In
drinking a glass of water we drink a little stone at the same time. Our
body, in order to grow strong and increase in size, needs considerable
calcareous matter for the formation of bones, which are to us what its
solid framework is to a building. This material, so necessary to us, is
not created by us; we obtain it from our food and drink. Water plays
its part in furnishing this limestone, which it furnishes also to
plants; they all contain a greater or less proportion of this mineral
matter.
“Calcareous soils are whitish from their chief constituent, chalk.
Entirely sterile when the proportion of limestone is excessive, they
are tolerably productive when clay is added. They are especially
suitable for vineyards and for raising lucerne, sainfoin, and clover.
Champagne and the south of France offer examples of this kind of soil.
Its principal varieties are chalky soil, which is nearly sterile,
containing as much as ninety-five per cent of chalk, and marly soil
which is composed of clay and chalk.
“The plant-life characteristic of calcareous soils comprises the
box-tree, whose compact and fine-grained wood is so esteemed by
turners; the wild cornel, whose red, olive-shaped fruit is one of the
best-liked autumn products that nature offers us; and the alkekengi, or
winter cherry, whose yellow berries are used for coloring butter. These
berries are encased in a large, gorgeously red membranous bag.
“Wood, leaves, herbage, left a long time in contact with air and
moisture, undergo a slow combustion; in other words, they rot. The
result of this decomposition is a brown substance called humus or
vegetable mold. The heart of old hollow willows is converted into
humus; it is the same with leaves that fall from the trees and rot on
the ground. Humus from the remains of earlier generations of plant-life
nourishes the plant-life of to-day, and this in turn will become mold
from which future plants will spring. It is in this way that vegetation
is maintained in places not cultivated by man. Humus, then, is nature’s
manure. Where it is allowed to form freely, vegetation never loses its
vigor, using over and over again the same material, which takes
alternately the two forms of plant and humus. But hay from the field is
stored in the hay-loft, and the annual harvest of wheat is taken to the
granary. Thus the land is robbed of the mold that would be formed
naturally by the rotting of this hay and wheat; therefore we must give
back to it, under some form or other, this mold that has been taken
away, since otherwise the soil will become less and less productive
until finally it is quite sterile. This restitution is made in the form
of animal manure, which is a sort of humus produced by digestive
processes instead of by natural decay.
“Humus plays a twofold part in the soil. First, it mellows the land, or
in other words makes it more easily permeable by air and water.
Secondly, by the slow combustion taking place in the humus there is
constantly being liberated a small quantity of carbonic acid gas, which
is taken up by the adjacent roots. Agriculture can succeed only in so
far as the soil contains humus. Wheat requires nearly eight per cent,
oats and rye only two per cent. In poor, sandy soils, to increase the
amount of vegetable mold, it is customary to plow certain green crops
under, as the farmers express it; that is, the surface soil is turned
over and the growing crop intended for manuring purposes is buried and
left to decay in the ground. That is what is done when the plowman
turns under a field of growing grass or a stretch of clover. When it is
proposed to improve a piece of land by this process, it is the practice
to begin by raising a crop (which will later be turned under) that
derives the greater part of its nourishment from the air, since the
soil in this instance cannot of itself furnish this nourishment. Among
the plants satisfying these conditions are buckwheat, clover, lupine,
beans, vetches, lucerne, and sainfoin.
“Soils rich in humus have for their chief constituent the brown
substance that results from the decaying of leaves and other vegetable
matter. Turf land stands first as rich in humus. Turf is a dark, spongy
substance that forms in moist lowlands from the accumulation of
vegetable refuse, especially mosses. Turf, or peat, as it is also
called, is used for fuel. To turn such a soil to account, it must first
be made wholesome by drainage, it must be mellowed by paring and
burning and by the addition of sand and marl, and a proportion of lime
must be mixed in to hasten the decomposition of all vegetable matter.
Turf lands are recognized by their sphagnei, great mosses that grow
with their roots in the water; and by their flax-like sedges, from the
tops of which hang beautiful tufts of down having the softness and
whiteness of the finest silk.”