DRAINAGE ADAPTS THE SOIL TO GERMINATION AND VEGETATION.
Process of Germination.--Two Classes of Pores in Soils, illustrated
by Cuts.--Too much Water excludes Air, reduces Temperature.--How
much Air the Soil Contains.--Drainage Improves the Quality of
Crops.--Drainage prevents Drought.--Drained Soils hold most
Water.--Allow Roots to go Deep.--Various Facts.
No apology will be necessary for the long extract which we are about to
give, to any person who will read it with attention. It is from a
lecture on Agricultural Science, by Dr. Madden, and we confess ourselves
incompetent to condense or improve the language of the learned author.
We think we are safe in saying that it has never been before published
in America:
"The first thing which occurs after the sowing of the seed is, of
course, _germination_; and before we examine how this process may
be influenced by the condition of the soil, we must necessarily
obtain some correct idea of the process itself. The most careful
examination has proved that the process of germination consists
essentially of various chemical changes, which require for their
development the presence of air, moisture, and a certain degree of
warmth. Now it is obviously unnecessary for our present purpose
that we should have the least idea of the nature of these
processes: all we require to do, is to ascertain the conditions
under which they take place; having detected these, we know at once
what is required to make a seed grow. These, we have seen, are air,
moisture, and a certain degree of warmth; and it consequently
results, that wherever a seed is placed in these circumstances,
germination will take place. Viewing matters in this light, it
appears that soil does not act _chemically_ in the process of
germination; that its sole action is confined to its being the
vehicle, by means of which a supply of air and moisture and warmth
can be continually kept up. With this simple statement in view, we
are quite prepared to consider the various conditions of soil, for
the purpose of determining how far these will influence the future
prospects of the crop, and we shall accordingly at once proceed to
examine carefully into the _mechanical relations of the soil_. This
we propose doing by the aid of figures. Soil examined mechanically,
is found to consist entirely of particles of all shapes and sizes,
from stones and pebbles, down to the finest powder; and, on account
of their extreme irregularity of shape, they cannot lie so close to
one another as to prevent there being passages between them, owing
to which circumstance soil in the mass is always more or less
_porous_. If, however, we proceed to examine one of the smallest
particles of which soil is made up, we shall find that even this is
not always solid, but is much more frequently porous, like soil in
the mass. A considerable proportion of this finely-divided part of
soil, _the impalpable matter_ as it is generally called, is found,
by the aid of the microscope, to consist of _broken-down vegetable
tissue_, so that when a small portion of the finest dust from a
garden or field is placed under the microscope, we have exhibited
to us particles of every variety of shape and structure, of which a
certain part is evidently of vegetable origin. In these figures I
have given a very rude representation of these particles; and I
must beg you particularly to remember that they are not meant to
represent by any means accurately what the microscope exhibits, but
are only designed to serve as a plan by which to illustrate the
mechanical properties of the soil. On referring to Fig. 91, we
perceive that there are two distinct classes of pores; first, the
large ones, which exist _between_ the particles of soil, and
second, the very minute ones, which occur in the particles
themselves; and you will at the same time notice, that whereas all
the larger pores--those between the particles of soil--communicate
most freely with each other, so that they form canals, the small
pores, however freely they may communicate with one another in the
interior of the particle in which they occur, have no direct
connection with the pores of the surrounding particles. Let us now,
therefore, trace the effect of this arrangement. In Fig. 91, we
perceive that these canals and pores are all empty, the soil being
_perfectly dry_; and the canals communicating freely at the surface
with the surrounding atmosphere, the whole will of course be filled
with air. If in this condition, a seed be placed in the soil, as at
_a_, you at once perceive that it is freely supplied with air, _but
there is no moisture_; therefore, when soil is _perfectly dry_, a
seed cannot grow.
[Illustration: Fig. 91.]
[Illustration: Fig. 92.]
"Let us turn our attention now to Fig. 92. Here we perceive that
both the pores and canals are no longer represented white, but
black, this color being used to indicate water; in this instance,
therefore, water has taken the place of air, or, in other words,
the soil is _very wet_. If we observe our seed _a_ now, we find it
abundantly supplied with water, but _no air_. Here again,
therefore, germination cannot take place. It may be well to state
here, that this can never occur _exactly_ in nature, because water
having the power of dissolving air to a certain extent, the seed
_a_ in Fig. 92 is, in fact, supplied with a _certain_ amount of
this necessary substance; and, owing to this, germination does take
place, although by no means under such advantageous circumstances
as it would were the soil in a better condition.
[Illustration: Fig. 93.]
[Illustration: Fig. 94.]
"We pass on now to Fig. 93. Here we find a different state of
matters. The canals are open and freely supplied with air, while
the pores are filled with water; and consequently you perceive
that, while the seed _a_ has quite enough of air from the canals,
it can never be without moisture, as every particle of soil which
touches it, is well supplied with this necessary ingredient. This,
then, is the proper condition of soil for germination, and in fact
for every period of the plant's development; and this condition
occurs when soil is _moist_ but not _wet_--that is to say, when it
has the color and appearance of being well watered, but when it is
still capable of being crumbled to pieces by the hands, without any
of its particles adhering together in the familiar form of mud.
"Turning our eyes to Fig. 94, we observe still another condition of
soil. In this instance, as far as _water_ is concerned, the soil is
in its healthy condition--it is moist, but not wet, the pores alone
being filled with water. But where are the canals? We see them in a
few places, but in by far the greater part of the soil none are to
be perceived; this is owing to the particles of soil having adhered
together, and thus so far obliterated the interstitial canals, that
they appear only like pores. This is the state of matters in every
_clod of earth_, _b_; and you will at once perceive, on comparing
it with _c_, which represents a stone, that these two differ only
in possessing a few pores, which latter, while they may form a
reservoir for moisture, can never act as vehicles for the _food_ of
plants, as the roots are not capable of extending their fibres into
the interior of a clod, but are at all times confined to the
interstitial canals.
"With these four conditions before us, let us endeavor to apply
them _practically_ to ascertain when they occur in our fields, and
how those which are injurious may be obviated.
"The first of them, we perceive, is a state of too great dryness,
_a very rare_ condition, in this climate at least; in fact, the
only case in which it is likely to occur is in very coarse sands,
where the soil, being chiefly made up of pure sand and particles of
flinty matter, contains comparatively much fewer pores; and, from
the large size of the individual particles, assisted by their
irregularity, the canals are wider, the circulation of air freer,
and, consequently, the whole is much more easily dried. When this
state of matters exists, the best treatment is to leave all the
stones which occur on the surface of the field, as they cast
shades, and thereby prevent or retard the evaporation of water.
"We will not, however, make any further observations on this very
rare case, but will rather proceed to Fig. 92, a much more
frequent, and, in every respect, more important condition of soil:
I refer to an _excess of water_.
"When water is added to perfectly dry soil, it, of course, in the
first instance, fills the interstitial canals, and from these
enters the pores of each particle; and if the supply of water be
not too great, the canals speedily become empty, so that the whole
of the fluid is taken up by the pores: this, we have already seen,
is the _healthy_ condition of the soil. If, however, the supply of
water be too great, as is the case when a spring gains admission
into the soil, or when the sinking of the fluid through the canals
to a sufficient depth below the surface is prevented, it is clear
that these also must get filled with water so soon as the pores
have become saturated. This, then, is the condition of _undrained
soil_.
"Not only are the pores filled, but the interstitial canals are
likewise full; and the consequence is, that the whole process of
the germination and growth of vegetables is materially interfered
with. We shall here, therefore briefly state the injurious effects
of an excess of water, for the purpose of impressing more strongly
on your minds the necessity of thorough-draining, as the first and
most essential step towards the improvement of your soil.
"The _first_ great effect of an excess of water is, that it
produces a corresponding diminution of the amount of air beneath
the surface, which air is of the greatest possible consequence in
the nutrition of plants; in fact, if entirely excluded, germination
could not take place, and the seed sown would, of course, either
decay or lie dormant.
"_Secondly_, an excess of water is most hurtful, by reducing
considerably the _temperature_ of the soil: this I find, by careful
experiment, to be to the extent of six and a-half degrees
Fahrenheit in Summer, which amount is equivalent to an elevation
above the level of the sea of 1,950 feet.
"These are the two chief injuries of an excess of water in soil
which affect the soil itself. There are very many others affecting
the climate, &c.; but these not so connected with the subject in
hand as to call for an explanation here.
"Of course, all these injurious effects are at once overcome by
thorough-draining, the result of which is, to establish a direct
communication between the interstitial canals and the drains, by
which means it follows, that no water can remain any length of time
in these canals without, by its gravitation, finding its way into
the drains.
"The 4th Fig. indicates badly-cultivated soil, or soil in which
large unbroken clods exist; which clods, as we have already seen,
are very little better than stones, on account of their
impermeability to air and the roots of plants.
"Too much cannot be said in favor of pulverizing the soil; even
thorough-draining itself will not supersede the necessity of
performing this most necessary operation. The whole valuable
effects of plowing, harrowing, grubbing, &c., may be reduced to
this: and almost the whole superiority of _garden_ over _field_
produce is referable to the greater perfection to which this
pulverizing of the soil can be carried.
"The whole success of the drill husbandry is owing, in a great
measure, to its enabling you to stir up the soil well during the
progress of your crop; which stirring up is of no value beyond its
effects in more minutely pulverizing the soil, increasing, as far
as possible, the size and number of the interstitial canals.
"Lest any one should suppose that the contents of these
interstitial canals must be so minute that their whole amount can
be of but little consequence, I may here notice the fact, that, in
moderately well pulverized soil, they amount to no less than
one-fourth of the whole bulk of the soil itself; for example, 100
cubic inches of _moist_ soil (that is, of soil in which the pores
are filled with water while the canals are filled with air),
contain no less than 25 cubic inches of air. According to this
calculation, in a field pulverized to the depth of eight inches, a
depth perfectly attainable on most soils by careful tillage, every
imperial acre will retain beneath its surface no less than
12,545,280 cubic inches of air. And, to take one more element into
the calculation, supposing the soil were not properly drained, the
sufficient pulverizing of an additional inch in depth would
increase the escape of water from the surface by upwards of one
hundred gallons a day."
_Drainage improves the quality of crops._ In a dry season, we frequently
hear the farmer boast of the quality of his products. His hay-crop, he
says, is light, but will "spend" much better than the crop of a wet
season; his potatoes are not large, but they are sound and mealy.
Indeed, this topic need not be enlarged upon. Every farmer knows that
his wheat and corn are heavier and more sound when grown upon land
sufficiently drained.
_Drainage prevents drought._ This proposition is somewhat startling at
first view. How can draining land make it more moist? One would as soon
think of watering land to make it dry. A drought is the enemy we all
dread. Professor Espy has a plan for producing rain, by lighting
extensive artificial fires. A great objection to his theory is, that he
cannot limit his showers to his own land, and all the public would never
be ready for a shower on the same day. If we can really protect our land
from drought, by under-draining it, everybody may at once engage in the
work without offence to his neighbor.
If we take up a handfull of rich soil of almost any kind, after a heavy
rain, we can squeeze it hard enough with the hand to press out drops of
water. If we should take of the same soil a large quantity, after it was
so dry that not a drop of water could be pressed out by hand, and
subject it to the pressure of machinery, we should force from it more
water. Any boy, who has watched the process of making cider with the
old-fashioned press, has seen the pomace, after it had been once pressed
apparently dry and cut down, and the screw applied anew to the "cheese,"
give out quantities of juice. These facts illustrate, first, how much
water may be held in the soil by attraction. They show, again, that more
water is held by a pulverized and open soil, than by a compact and close
one. Water is held in the soil between the minute particles of earth. If
these particles be pressed together compactly, there is no space left
between them for water. The same is true of soil naturally compact. This
compactness exists more or less in most subsoils, certainly in all
through which water does not readily pass. Hence, all these subsoils are
rendered more permeable to water by being broken up and divided; and
more retentive by having the particles of which they are composed
separated, one from another--in a word, by pulverization. This increased
capacity to contain moisture by attraction, is the greatest security
against drought. The plants, in a dry time send their rootlets
throughout the soil, and flourish in the moisture thus stored up for
their time of need. The pulverization of drained land may be produced,
partly by deep, or subsoil plowing, which is always necessary to perfect
the object of thorough-draining; but it is much aided, in stiff clays,
also, by the shrinkage of the soil by drying.
Drainage resists drought, again, by the very deepening of the soil of
which we have already spoken. The roots of plants, we have seen, will
not extend into stagnant water. If, then, as is frequently the case,
even on sandy plains, the water-line be, in early Spring, very near the
surface, the seed may be planted, may vegetate, and throw up a goodly
show of leaves and stalks, which may flourish as long as the early rains
continue; but, suddenly, the rains cease; the sun comes out in his June
brightness; the water-line lowers at once in the soil; the roots have no
depth to draw moisture from below, and the whole field of clover, or of
corn, in a single week, is past recovery. Now, if this light, sandy soil
be drained, so that, at the first start of the crop, there is a deep
seed-bed free from water, the roots strike downward, at once, and thus
prepare for a drought. The writer has seen upon deep-trenched land in
his own garden, parsnips, which, before midsummer, had extended downward
three feet, before they were as large as a common whiplash; and yet,
through the Summer drought, continued to thrive till they attained in
Autumn a length, including tops, of about seven feet, and an
extraordinary size. A moment's reflection will satisfy any one that, the
dryer the soil in Spring, the deeper will the roots strike, and the
better able will be the plant to endure the Summer's drought.
Again, drainage and consequent pulverization and deepening of the soils
increase their capacity to absorb moisture from the atmosphere, and thus
afford protection against drought. Watery vapor is constantly, in all
dry weather, rising from the surface of the earth; and plants, in the
day-time, are also, from their leaves and bark, giving off moisture
which they draw from the soil. But Nature has provided a wonderful law
of compensation for this waste, which would, without such provision,
parch the earth to barrenness in a single rainless month.
The capacity of the atmosphere to take up and convey water, furnishes
one of the grandest illustrations of the perfect work of the Author of
the Universe. "All the rivers run into the sea, yet the sea is not
full;" and the sea is not full, because the numerous great rivers and
their millions of tributaries, ever flowing from age to age, convey to
the ocean only as much water as the atmosphere carries back in vapor,
and discharges upon the hills. The warmer the atmosphere, the greater
its capacity to hold moisture. The heated, thirsty air of the tropics
drinks up the water of the ocean, and bears it away to the colder
regions, where, through condensation by cold, it becomes visible as a
cloud; and as a huge sponge pressed by an invisible hand, the cloud,
condensed still further by cold, sends down its water to the earth in
rain.
The heated air over our fields and streams, in Summer, is loaded with
moisture as the sun declines. The earth has been cooled by radiation of
its heat, and by constant evaporation through the day. By contact with
the cooler soil, the air, borne by its thousand currents gently along
its surface, is condensed, and yields its moisture to the thirsty earth
again, in the form of dew.
At a Legislative Agricultural Meeting, held in Albany, New York, January
25th, 1855, "the great drought of 1854" being the subject, the secretary
stated that "the experience of the past season has abundantly proved
that thorough-drainage upon soils requiring it, has proved a very great
relief to the farmer;" that "the crops upon such lands have been far
better, generally, than those upon undrained lands, in the same
locality;" and that, "in many instances, the increased crop has been
sufficient to defray the expenses of the improvement in a single year."
Mr. Joseph Harris, at the same meeting, said: "An underdrained soil will
be found damper in dry weather, than an undrained one, and the
thermometer shows a drained soil warmer in cold weather, and cooler in
hot weather, than one which is undrained."
The secretary of the New York State Agricultural Society, in his Report
for 1855, says: "The testimony of farmers, in different sections of the
State, is almost unanimous, that drained lands have suffered far less
from drought than undrained." Alleghany county reports that "drained
lands have been less affected by the drought than undrained;" Chatauque
county, that "the drained lands have stood the drought better than the
undrained." The report from Clinton county says: "Drained lands have
been less affected by the drought than undrained." Montgomery county
reports: "We find that drained lands have a better crop in either wet or
dry seasons than undrained."
B. F. Nourse, of Orrington, Maine, states that, on his drained land, in
that State, "during the drought of 1854, there was at all times
sufficient dampness apparent on scraping the surface of the ground with
his foot in passing, and a crop of beans was planted, grown and gathered
therefrom, without as much rain as will usually fall in a shower of
fifteen minutes' duration, while vegetation on the next field was
parching for lack of moisture."
A committee of the New York Farmers' Club, which visited the farm of
Prof. Mapes, in New Jersey, in the time of a severe drought, in 1855,
reported that the Professor's fences were the boundaries of the drought,
all the lands outside being affected by it, while his remained free from
injury. This was attributed, both by the committee and by Prof. Mapes
himself, to thorough-drainage and deep tillage with the subsoil plow.
Mr. Shedd, in the _N. E. Farmer_, says:
"A simple illustration will show the effect which stagnant water,
within a foot or two of the surface, has on the roots of plants.
"Perhaps it will aid the reader, who doubts the benefit of
thorough-draining in case of drought, to see why it is beneficial.
[Illustration: Fig. 95. Section of land before it is drained.]
[Illustration: Fig. 96. Section of land after it is drained.]
"In the first figure, 1 represents the surface soil, through which
evaporation takes place, using up the heat which might otherwise go
to the roots of plants; 2, represents the water table, or surface
of stagnant water below which roots seldom go; 3, water of
evaporation; 4, water of capillary attraction; 5, water of
drainage, or stagnant water.
"In the second figure, 1 represents the surface-soil warmed by the
sun and Summer rains; 2, the water-table nearly four feet below the
surface--roots of the wheat plant have been traced to a depth of
more than four feet in a free mold; 3, water of capillary
attraction; 4, water of drainage, or stagnant water."