Farm drainage Part 28

"The mean temperature of the external air to which the box was exposed during the above period, was 42, the maximum being 47, and the minimum 37.

"_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; in ten minutes it rose to 40. The c.o.c.k 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; at twenty-five minutes, 42, whilst the thermometer _b_, was 142. At thirty minutes, the c.o.c.k was withdrawn from the box, and more free egress of water being thus afforded, at thirty-five minutes the flow was no longer continuous, and the thermometer _b_, indicated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. The ma.s.s 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.

5 " " fell to 76-1/2.

15 " " " 70-1/2.

20 " " remained at 71.

1 hour 50 " " " " 70-1/2.

"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 pa.s.ses 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, at which point it attains its greatest density, and has a tendency to go to the bottom until the whole ma.s.s 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, 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 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 to 48 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 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, at all depths, from one to thirty feet; and at seven inches from the surface, the temperature remained at 47 during the experiments. During the same period, the temperature of the drained portion was 48-1/4 at two feet seven inches below the surface, and at seven inches, reached as high as 66 during a thunder-storm; while, on a mean of thirty-five observations, the temperature at the latter depth was 10 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 " " " lowest February 28, 32-3/4 ---- " " " Range, 37-1/4 ---- " " " at four feet depth.

" " " highest July 29, 64-1/2 " " " lowest February 25, 35-1/2 ---- " " " Range, 29 ---- " " " of the air, February 12, -3 " " " " " August, 3, P. M., 90 ---- " " " Range, 93

Temperature at Scott at two feet depth.

" " " highest, August 17 and 18, 64 " " " at four ft. depth, 17 days in Aug. 60 " " " of the air, at 3, P. M., highest 90

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 pa.s.sage 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, pa.s.ses downward, and runs off by its gravitation. As "Nature abhors a vacuum," the little s.p.a.ces in the soil, from which the water pa.s.ses, 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 s.p.a.ces 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 diminis.h.i.+ng 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 quant.i.ties 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 s.p.a.ce 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 ill.u.s.trations. 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; yet man can endure a heat of many degrees more, and even labor under a Summer sun, which would raise the thermometer to 130, 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 pa.s.sing 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, but will start at once at 63, 55 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 or 53 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, and even so high as 63, 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 pa.s.sing 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 a.s.sured, brother farmer, that the frost will follow the water-table downward, and, unless the warm water move in sufficient quant.i.ty 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 and 40; while, in very wet soils, it seldom exceeds 10. 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 s.p.a.ces 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.