"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 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° 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.