TEMPERATURE AS AFFECTED BY DRAINAGE.
Drainage Warms the Soil in Spring.--Heat cannot go down in Wet
Land.--Drainage causes greater Deposit of Dew in Summer.--Dew warms
Plants in Night, Cools them in the Morning Sun.--Drainage varies
Temperature by Lessening Evaporation.--What is Evaporation.--How it
produces Cold.--Drained Land Freezes Deepest, but Thaws Soonest,
and the Reasons.
_Drainage raises the temperature of the soil, by allowing the rain to
pass downwards._ In the growing season, especially in the Spring, the
rain is considerably warmer than the soil. If the soil be saturated with
the cold snow-water, the water which falls must, of course, run away
upon the surface. If the soil be drained, the rain-water finds ready
admission into it, carrying and imparting to it a portion of its heat.
The experiments of Count Rumford, showing that heat is not propagated
downward in fluids, may be found at page 273. This is a principle too
important to be overlooked, especially in New England, where we need
every aid from Nature and Art, to contend successfully against the
brevity of the planting season. Soil saturated with cold water, cannot
be warmed by any amount of heat applied to the surface. Warm water is
lighter than cold water, and stays at the surface. In boiling water in a
kettle, we apply fire at the bottom, and no amount of heat at the
surface of the vessel would produce the desired effect. So rapid is the
passage of heat upward in water, that the hand may without injury be
held upon the bottom of a kettle of boiling water one minute after it
has been removed from the fire.
The following experiments and illustrations, from the _Horticulturist_
of Nov. 1856, beautifully illustrate this point:
"RATIONALE OF DRAINING LAND EXPLAINED.
"The reason why drained land gains heat, and water-logged land is
always cold, consists in the well-known fact that heat cannot be
transmitted _downwards_ through water. This may readily be seen by
the following experiments:
[Illustration: Fig. 97.]
"_Experiment No. 1._--A square box was made, of the form
represented by the annexed diagram, eighteen inches deep, eleven
inches wide at top, and six inches wide at bottom. It was filled
with peat, saturated with water to _c_, forming to that depth
(twelve and a half inches) a sort of artificial bog. The box was
then filled with water to _d_. A thermometer _a_, was plunged, so
that its bulb was within one inch and a half of the bottom. The
temperature of the whole mass of peat and water was found to be
39-1/2 deg. Fahr. A gallon of boiling water was then added; it raised
the surface of the water to _e_. In five minutes, the thermometer,
_a_, rose to 44 deg., owing to the conduction of heat by the
thermometer and its guard tube; at ten minutes from the
introduction of the hot water, the thermometer, _a_, rose to 46 deg.,
and it subsequently rose no higher. Another thermometer, _b_,
dipping under the surface of the water at _e_, was then introduced,
and the following are the indications of the two thermometers at
the respective intervals, reckoning from the time the hot water was
supplied:
_Thermometer b._ _Thermometer a._
20 minutes 150 deg. 46 deg.
1 hour 30 " 101 deg. 45 deg.
2 hours 30 " 80-1/2 deg. 42 deg.
12 " 40 " 45 deg. 40 deg.
"The mean temperature of the external air to which the box was
exposed during the above period, was 42 deg., the maximum being 47 deg.,
and the minimum 37 deg..
"_Experiment No. 2._--With the same arrangement as in the preceding
case, a gallon of boiling water was introduced above the peat and
water, when the thermometer _a_, was at 36 deg.; in ten minutes it rose
to 40 deg.. The cock was then turned for the purpose of drainage, which
was but slowly effected; and, at the end of twenty minutes, the
thermometer _a_, indicated 40 deg.; at twenty-five minutes, 42 deg., whilst
the thermometer _b_, was 142 deg.. At thirty minutes, the cock was
withdrawn from the box, and more free egress of water being thus
afforded, at thirty-five minutes the flow was no longer continuous,
and the thermometer _b_, indicated 48 deg.. The mass was drained, and
permeable to a fresh supply of water. Accordingly, another gallon
of boiling water was poured over it; and, in
3 minutes, the thermometer _a_, rose to 77 deg..
5 " " fell to 76-1/2 deg..
15 " " " 70-1/2 deg..
20 " " remained at 71 deg..
1 hour 50 " " " " 70-1/2 deg..
"In these two experiments, the thermometer at the bottom of the box
suddenly rose a few degrees immediately after the hot water was
added; and it might be inferred that the heat was carried downwards
by the water. But, in reality, the rise was owing to the action of
the hot water on the thermometer, and not to its action upon the
cold water. To prove this, the perpendicular thermometers were
removed. The box was filled with peat and water to within three
inches of the top, a horizontal thermometer, _a f_, having been
previously secured through a hole made in the side of the box, by
means of a tight-fitting cork, in which the naked stem of the
thermometer was grooved. A gallon of boiling water was then added.
The thermometer, a very delicate one, was _not in the least
affected_ by the boiling water in the top of the box.
"In this experiment, the wooden box may be supposed to be a field;
the peat and cold water represent the water-logged portion; rain
falls on the surface, and becomes warmed by contact with the soil,
and, thus heated, descends. But it is stopped by the cold water,
and the heat will go no further. But, if the soil is drained, and
not water-logged, the warm rain trickles through the crevices of
the earth, carrying to the drain-level the high temperature it had
gained on the surface, parts with it to the soil as it passes
down, and thus produces that bottom heat which is so essential to
plants, although so few suspect its existence."
Water, although it will not conduct heat downwards, is a ready vehicle
of cold from the surface towards the bottom. Water becomes heavier by
cooling till it is reduced to about 39 deg., at which point it attains its
greatest density, and has a tendency to go to the bottom until the whole
mass is reduced to this low temperature. Thus, the circulation of water
in the saturated soil, in some conditions of the temperature of the
surface and subsoil, may have a chilling effect which could not be
produced on drained soil.
After water is reduced to about 39 deg., instead of obeying the common law
of becoming heavier by cooling, it forms a remarkable exception to it,
and becomes lighter until it freezes. Were it not for this admirable
provision of Nature, all our ponds and rivers would, in the Winter,
become solid ice from the surface to the bottom. Now as the surface
water is chilled it goes to the bottom, and is replaced by warmer water,
which rises, until the whole is reduced to the point of greatest
density. Then the circulation ceases, and the water colder than 39 deg.
remains at the surface, is converted into ice which becomes still
lighter, by crystallization, and floats upon the surface.
No experiments, showing the temperature of undrained soils at various
depths, in the United States, have come to our knowledge. Mr. Gisborne
says: "Many experiments have shown that, in retentive soils, the
temperature, at two or three feet below the surface of the water-table,
is, at no period of the year, higher than from 46 deg. to 48 deg. in
agricultural Britain." Prof. Henry states in the Patent Office Report
for 1857, that in the cellars of the observatory, at Paris, at the depth
of sixty-seven and a half feet, in fifty years, the temperature has
never varied a tenth of a degree from 53 deg. 28', in all that period,
Summer or Winter.
Mr. Parkes gives the results of a valuable series of experiments, in
which he compared the temperature of drained and undrained portions of a
bog. He found the temperature of the undrained portion to remain
steadily at 46 deg., at all depths, from one to thirty feet; and at seven
inches from the surface, the temperature remained at 47 deg. during the
experiments. During the same period, the temperature of the drained
portion was 48-1/4 deg. at two feet seven inches below the surface, and at
seven inches, reached as high as 66 deg. during a thunder-storm; while, on a
mean of thirty-five observations, the temperature at the latter
depth was 10 deg. higher than at the same depth in the undrained portion of
the bog.
We find in the "Agriculture of New York," the results of observations
made at Albany and at Scott, in that State, in the year 1848, upon
temperature at different depths. The condition of the soil is not
described, but it is presumed that it was soil naturally drained in both
cases. A few of the results may give the reader some idea of the range
of underground temperature, as compared with that of the air.
Temperature at Albany at two feet depth.
" " " highest August 17 and 18, 70 deg.
" " " lowest February 28, 32-3/4 deg.
----
" " " Range, 37-1/4 deg.
----
" " " at four feet depth.
" " " highest July 29, 64-1/2 deg.
" " " lowest February 25, 35-1/2 deg.
----
" " " Range, 29 deg.
----
" " " of the air, February 12, -3 deg.
" " " " " August, 3, P. M., 90 deg.
----
" " " Range, 93 deg.
Temperature at Scott at two feet depth.
" " " highest, August 17 and 18, 64 deg.
" " " at four ft. depth, 17 days in Aug. 60 deg.
" " " of the air, at 3, P. M., highest 90 deg.
The temperature of falling rain, however, in the hot season, is many
degrees cooler than the lower stratum of the atmosphere, and the surface
of the earth upon which it falls. The effects of rain on drained soil,
in the heat of Summer, are, then, two-fold; to cool the burning surface,
which is, as we have seen, much warmer than the rain, and, at the same
time, to warm the subsoil which is cooler than the rain itself, as it
falls, and very much cooler than the rain-water, as it is warmed by its
passage through the hot surface soil. These are beautiful provisions of
Nature, by which the excesses of heat and cold are mitigated, and the
temperature of the soil rendered more uniform, upon land adapted, by
drainage, to her genial influences.
Upon the saturated and water-logged bog, as we have seen, the effect of
the greatest heat is insufficient to raise the temperature of the
subsoil a single degree, while the surface may be burned up and
"shrivelled like a parched scroll."
Drainage also raises the temperature of the soil by the admission of
warm air. This proposition is closely connected with that just
discussed. When the air is warmer than the soil, as it always is in the
Spring-time, the water from the melting snow, or from rain, upon drained
land, passes downward, and runs off by its gravitation. As "Nature
abhors a vacuum," the little spaces in the soil, from which the water
passes, must be filled with air, and this air can only be supplied from
the surface, and, being warmer than the ground, tends to raise its
temperature. No such effect can be produced in land not drained, because
no water runs out of it, and there are, consequently, no such spaces
opened for the warm air to enter.
Drainage equalizes the temperature of the soil in Summer by increasing
the deposit of dew. Of this we shall speak further, in a future
chapter.
_Drainage raises the temperature in Spring by diminishing evaporation._
Evaporation may be defined to be the conversion of liquid and solid
bodies into elastic fluids, by the influence of caloric.
By heating water over a fire, bubbles rise from the bottom of the
vessel, adhere awhile to the sides of it, and then ascend to the
surface, and burst and go off in visible vapor, or, in other words, by
evaporation. Water is evaporated by the heat of the sun merely, and even
without this heat, in the open air. It is evaporated at very low
temperatures, when fully exposed to the air. Even ice evaporates in the
open air. We often observe in Winter, that a thin covering of ice or
snow disappears from our roads, although there has been no thawing
weather.
In another chapter, we have considered the subject of "Evaporation and
Filtration," and endeavored to give some general idea of the proportion
of the rain which escapes by evaporation. We have seen, that evaporation
proceeds much more rapidly from a surface of water, as a pond or river,
than from a land surface, unless it be fully saturated, and that
evaporation from the water exceeds the whole amount of rain, about as
much as evaporation from the land falls short of the amount of rain.
Thus, by this simple agency of evaporation, the vast quantities of water
that are constantly flowing, in all the rivers of the earth, into the
sea, are brought back again to the land, and so the great system of
circulation is maintained throughout the ages.
As evaporation is greatest from a water-surface, so it is greater, other
things being equal, according to the wetness of the surface of any given
field. If the field be covered with water, it becomes a water-surface
for the time, and the evaporation is like that from a pond. If, as is
often the case, the water stands on it in spots, over half its surface,
and the rest is saturated, the evaporation is scarcely less, and has
been said to be even more; while, if the surface be comparatively dry,
the evaporation is very little.
But what harm does evaporation do? and what has all this scientific talk
to do with drainage? These, my friend, are very practical questions, and
just the ones which it is proposed to answer; but we must bear in mind
that, as Nature conducts her grand affairs by systematic laws, the small
portion of her domain which for a brief space of time we occupy, is not
exempted from their operation. Some of these laws we may comprehend, and
turn our knowledge of them to practical account. Of others, we may note
the results, without apprehending the reasons of them; for it is true--
"There are more things in Heaven and earth, Horatio,
Than are dreamt of in your philosophy."
Discussions of this kind may seem dry, though the subject itself be
moisture. They belong, certainly, to the topic under consideration.
Evaporation does harm in the Spring-time, because it produces cold, just
when we most want heat. How it produces cold, is not so readily
explained. The fact may be made as evident as the existence of sin in
the world, and, possibly, the reason of it may be as unsatisfactory.
The books say, that heat always disappears when a solid body becomes a
liquid; and so it is, that the air always remains cool while the snow
and ice are melting in Spring. Again, it is said that heat always
disappears, when a fluid becomes vapor. These are said to be laws or
principles of nature, and are said to explain other phenomena. To a
practical mind, it is perhaps just as satisfactory to say that
evaporation produces cold, as to state the principle or law in the
language of science.
That the fact is so, may be proved by many illustrations. Stockhardt
gives the following experiment, which is strikingly appropriate:
"Fill a tube half full of water, and fasten securely round the bulb
of it, a piece of cloth. Saturate the cloth with cold water, and
then twirl the tube rapidly between the hands; presently the water
in the tube will become sensibly colder, and the degree of cold may
be accurately determined by the thermometer. Moisten the cloth with
ether, a very volatile liquid, and twirl it again in the same
manner as before; by which means, its contents, even in Summer, may
be converted into ice."
It is very fortunate for us, that our Spring showers are not of ether;
for then, instead of thawing, our land would freeze the harder! The heat
of the blood is about 98 deg.; yet man can endure a heat of many degrees
more, and even labor under a Summer sun, which would raise the
thermometer to 130 deg., without the temperature of his blood being
materially affected, and it is because of perspiration, which absorbs
the surplus heat, or, in other words, creates cold. It is said, too,
that on the same principle, if two saucers, one filled with water warm
enough to give off visible vapor, the other filled with water just from
the well, are exposed in a sharp frosty morning, that filled with the
warm water will exhibit ice soonest. Wine is cooled by evaporation, by
wrapping the bottle in wet flannel, and exposing it to the air.
If, after all this, any one doubts the fact that evaporation tends to
produce cold, let him countenance his skepticism, by wetting his face
with warm water, and going into the air in a Winter's day, and his faith
will be greatly strengthened.
We have, in the northern part of America, most water in the soil in the
Spring of the year, just at the time when we most need a genial warmth
to promote germination. If land is well drained, this water sinks
downward, and runs away in the drains, instead of passing upward by
evaporation.
Drainage, therefore, diminishes evaporation simply by removing the
surplus snow and rain-water by filtration. It thus raises the
temperature of the soil in that part of the season, when water is
flowing from the drains; but, in the heat of Summer, the influence of
the showers which refresh without saturating the soil, and are retained
in it by attraction, is not lessened. As a good soil retains by
attraction about one-half its weight of water that cannot be drained
out, there can be no reasonable apprehension that the "gentle Summer
showers" will be wasted by filtration, even upon thorough-drained land,
while an avenue is open, by the drains, for the escape of drowning
floods.
To show the general effect of drainage, in raising the temperature of
wet lands in Summer, the following statement of Mr. Parkes is valuable.
An elevation of the temperature of the subsoil ten degrees, will be seen
to be very material, when we consider that Indian corn will not vegetate
at all at 53 deg., but will start at once at 63 deg., 55 deg. being its lowest point
of germination:
"As regards the temperature of the water derived from drainage at
different seasons of the year, I am unacquainted with any published
facts. This is a subject of the highest import, as thermometric
observations may be rendered demonstrative, in the truest manner,
of the effect of drainage on the climate of the soil. At present, I
must limit myself to saying, that I have never known the water of
drainage issue from land drained at Midsummer, to depths of four
and five feet, at a higher temperature than 52 deg. or 53 deg. Fahrenheit:
whereas, in the following year and subsequent years, the water
discharged from the same drains, at the same period, will issue at
a temperature of 60 deg., and even so high as 63 deg., thus exhibiting the
increase of heat conferred during the Summer months on the
terrestrial climate by drainage. This is the all-important fact
connected with the art and science of land-drainage."
Besides affecting favorably the temperature of the particular field
which is drained, the general effect of the drainage of wet lands upon
the climate of the neighborhood has often been noticed. In the paper
already cited, emanating from the Board of Health, we find the
following remarks, which are in accordance with all observation in
districts where under-drainage has been generally practiced:
"Every one must have remarked, on passing from a district with a
retentive soil to one of an open porous nature--respectively
characterized as cold and warm soils--that, often, whilst the air
on the retentive soil is cold and raw, that on the drier soil is
comparatively warm and genial. The same effect which is here caused
naturally, may be produced artificially, by providing for the
perfect escape of superfluous water by drainage, so as to leave
less to cool down the air by evaporation. The reason of this
difference is two-fold. In the first place, much heat is saved, as
much heat being required for the vaporization of water, as would
elevate the temperature of more than three million times its bulk
of air one degree. It follows, therefore, that for every inch in
depth of water carried off by drains, which must otherwise
evaporate, as much heat is saved per acre as would elevate eleven
thousand million cubic feet of air one degree in temperature. But
that is not all. Not only is the temperature of the air reduced,
but its dew point is raised, by water being evaporated which might
be drained off; consequently, the want of drainage renders the air
both colder and more liable to the formation of dew and mists, and
its dampness affects comfort even more than its temperature. It is
easy, then, to understand how local climate is so much affected by
surplus moisture, and so remarkably improved by drainage. A farmer
being asked the effect on temperature of some new drainage works;
replied, that all he knew was, that before the drainage he could
never go out at night without a great coat, and that now he could,
so that he considered it made the difference of a great coat to
him."
_Drainage increases the coldness of the subsoil in Winter._ Whether this
is a gain or loss to the agriculturist, is not for us to determine. The
object of our labor is, to lay the whole subject fairly before the
reader, and not to extol drainage as the grand panacea of bad husbandry.
Although water will not conduct heat downwards, yet it doubtless
prevents the deep freezing of the ground. It has already been seen, that
the temperature of the earth, a few feet below the surface, is above the
freezing point, at all times. The fact that the ground does not freeze,
usually, even in New England, where every Winter brings weather below
Zero, more than four or five feet deep, in the most exposed situations,
shows conclusively the comparatively even temperature of the subsoil.
The water which flows underground is of this subsoil temperature, and,
in Winter, warms the ground through which it flows. In land thoroughly
drained, this warm water cannot rise above the drains, and so cannot
defend the soil from frost.
Drained land will, undoubtedly, freeze deeper than undrained land, and
this is a fact to be impressed upon all who lay tiles in a cold climate.
It is a strong argument for deep drainage. "Drain deep, or drain not,"
is a convenient paraphrase of a familiar quotation. How often do we hear
it said, "My meadow never freezes more than a foot deep; there will
never be any trouble from frost in that place, if the tiles are no more
than two feet deep." Be assured, brother farmer, that the frost will
follow the water-table downward, and, unless the warm water move in
sufficient quantity through your pipes to protect them in Winter, your
work may be ruined by frost. So long as much water is flowing in pipes,
especially if it be from deep springs, they will be safe from frost,
even at a slight depth.
Dr. Madden says, that it has been proved that one great source of health
and vigor in vegetation, is the great difference which exists between
the temperature of Summer and Winter, which, he says, in dry soils,
often amounts to between 30 deg. and 40 deg.; while, in very wet soils, it
seldom exceeds 10 deg.. This idea may have value in a mild climate; but,
probably, in New England, we get cold enough for our good, without
artificial aids. In another view, drainage is known to be essential,
even in Winter.
Fruit trees are almost as surely destroyed by standing with their feet
in cold water all Winter, as any of us "unfeathered bipeds" would be;
while the solid freezing of the earth around their roots does not harm
them. Perhaps the same is true of most other vegetation.
The deep freezing of the ground is often mentioned as a mode of
pulverization--as a sort of natural subsoiling thrown in by a kind
Providence, by way of compensation for some of the evils of a cold
climate. Most of those, however, who have wielded the pick-axe in laying
four-foot drains, in clay or hard-pan, will have doubts whether Jack
Frost, though he can pull up our fence-posts, and throw out our Winter
grain, has much softened the earth two feet below its surface.
That the frost comes out of drained land earlier than undrained, in
Spring, we are satisfied, both by personal observation, and by the
statements of the few individuals who have practiced thorough-drainage
in our cold climate.
B. F. Nourse, Esq., whose valuable statement will be found in a later
chapter, says, that, in 1858, the frost came out a week, at least,
earlier from his drained land, in Maine, than from contiguous undrained
land; and that, usually, the drained land is in condition to be worked
as soon as the frost is out, quite two weeks earlier than any other land
in the vicinity. Our observations on our own land, fully corroborate the
opinion of Mr. Nourse.
The reasons why the frost should come out of drained land soonest, are,
that land that is dry does not freeze so solid as land that is wet, and
so spaces are left for the permeation of warm air. Again, ice, like
water, is almost a nonconductor of heat, and earth saturated with water
and frozen, is like unto it, so that neither the warmth of the subsoil
or surface-soil can be readily imparted to it. Dry earth, on the other
hand, although frozen, is still a good conductor, and readily dissolves
at the first warm breath of Spring above, or the pulsations of the great
heart of Nature beneath.