Clovers As Soil Improvers
All things considered, no class of plants
grown upon the farm are so beneficent in the influence which they exert
upon the land as clovers. They improve it by enriching it; they improve
it mechanically; and they aid plant growth by gathering and
as it were, food for other plants.
All clovers have the power of drawing nitrogen from the air and
depositing the same in the tubercles formed on the roots of the plants.
These tubercles are small, warty-like substances, which appear during
the growing season. They are more commonly formed on the roots within
the cultivable area, and therefore are easily accessible to the roots of
the plants which immediately follow. Clovers are not equally capable of
thus drawing nitrogen from the air, nor are the same varieties equally
capable of doing this under varying conditions. The relative
capabilities of varieties to thus deposit nitrogen in the soil is by no
means equal, but up to the present time it would seem correct to say
that relative capability in all of these has not yet been definitely
ascertained. With reference to the whole question much has yet to be
learned, but it is now certain that in all, or nearly all, instances in
which clovers are grown on land, they leave it much richer in nitrogen
than it was when they were sown upon the same.
They also add to the fertility of the surface soil by gathering plant
food in the subsoil below where many plants feed. They have much power
to do this, because they are deep rooted and they are strong feeders;
that is, they have much power to take up food in the soil or subsoil.
Part of the food thus gathered in the subsoil helps to form roots in the
cultivable area and part aids in forming top growth for pasture or for
hay. If grazed down or if made into hay and fed so that the manure goes
back upon the land the fertility of the same is increased in all leading
essentials. This increase is partly made at the expense of the fertility
in the subsoil. But the stores of fertility in the subsoil are such
usually as to admit of thus being drawn upon indefinitely.
Clovers improve soils mechanically by rendering them more friable, by
giving them increased power to hold moisture, and by improving drainage
in the subsoil. Of course, they have not the power to do this equally,
but they all have this power in degree and in all the ways that have
Clovers send down a tap root into the soil and subsoil as they grow.
From the tap roots branch off lateral roots in an outward and downward
direction. From these laterals many rootlets penetrate through the soil.
When the plants are numerous, these roots and rootlets fill the soil.
When it is broken up, therefore, particles of soil are so separated that
they tend to fall apart, hence the soil is always made more or less
friable, even when it consists of the stiffest clays. The shade
furnished by the clover also furthers friability. This friability makes
the land easier to work, and it is also more easily penetrated by the
roots of plants. The influence on aeration is also marked. The air can
more readily penetrate through the interstices in the soil, and, in
consequence, chemical changes in the soil favorable to plant growth are
The roots of clovers are usually so numerous that they literally fill
the soil with vegetable matter. This matter, in process of decay,
greatly increases the power of the soil to hold moisture, whether it
falls from the clouds or ascends from the subsoil through capillary
attraction. The moisture thus held is greatly beneficial to the plants
that immediately follow, especially in a dry season and in open soils,
and the influence thus exerted frequently goes on, though with
decreasing potency, for two, three or four seasons.
Reference has already been made to the tap root which clover sends down
into the soil and subsoil. In the strong varieties this tap root goes
down deeply. When the crop is plowed up, the roots decay, and when they
do, for a time at least, they furnish channels down which the surface
water percolates, if present in excess. Thus it is that clover aids in
draining lands under the conditions named. The channels thus opened do
not close immediately with the decay of the clover roots, hence the
downward movement of water in the soil is facilitated for some time
It has been stated that clovers have more power than some other plants
to gather plant food in the soil. In some instances they literally fill
the soil with their roots. When other plants are sown after the clover
has been broken up they feed richly on the decaying roots of the clover.
Thus it is that clover gathers food for other plants which they would
not be so well able to gather for themselves, and puts it in a form in
which it can be easily appropriated by these. The nitrogen in clover is
yielded up more gradually and continuously as nitrates than it could be
obtained from any form of top dressings that can be given to the land.
In this fact is found one important reason why cereal grains thrive so
well after clover.
Since the roots of clovers act so beneficently on soils, it is highly
important that they be increased to the greatest extent practicable.
Owing to the relation between the growth of the roots of plants and the
parts produced above ground, development in root growth is promoted much
more when the clover is cut for hay than when it is fed off by grazing.
Experiments have also demonstrated that the development of root growth
is much enhanced in medium red clover by taking a second cutting for
hay or seed. They have also demonstrated that more nitrogen is left in
the soil by clover roots after a seed crop than after a crop of hay.
From what has been said, it will be apparent that the extent to which
clovers enrich the soil will depend upon the strength of the growth of
the plants and certain other conditions. It will not be possible to
reduce to figures the additions in plant food which clovers add to the
soil other than in a comparative way. Dr. Voelker has stated that there
is fully three times as much nitrogen in a crop of clover as in the
average produce of the grain and straw of wheat per acre. Dr. Kedzie is
on record as having said that in the hay or sod furnished by a good crop
of clover, there is enough nitrogen for more than four average crops of
wheat, enough phosphoric acid for more than two average crops and enough
of potash for more than six average crops. He has said, moreover, that
the roots and stubble contain fully as much of these elements as hay.
It will also be apparent that where clover grows in good form no cheaper
or better way can be adopted in manuring land, and that in certain areas
the judicious use of land plaster on the clover hastens the renovating
process. It is thought that in some instances the mere loading and
spreading of barnyard manure costs more than the clover and plaster.
Especially will this be true of fields distant from the farm steading.
It is specially important, therefore, that in enriching these, clover
will be utilized to the fullest extent practicable.
Next: Clover As A Weed Destroyer
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