Farm drainage / The Principles, Processes, and Effects of Draining Land with Stones, Wood, Plows, and Open Ditches, and Especially with Tiles

by Henry F. French

First: The drained land comes into condition for working, a week or ten days earlier in the Spring than other lands.

Secondly: The growth of the crops is quickened all through the Summer by an increase of several degrees in the temperature of the soil.

Thirdly: The injurious effects of frost are kept off several days later in the Fall.

Of the value of these conditions, the farmer, who has lost his crops for lack of a few more warm days, may make his own estimates. In Roxbury, Mr. I. P. Rand heats up a portion of his land, for the purpose of raising early plants for the market, by means of hot water carried by iron pipes under the surface of the ground. In this manner he heats an area equal to 100 feet by 12 feet, by burning about one ton of coal a month. The increase of temperature which, in this case, is caused by that amount of coal, can, in the absence of direct measurement, only be estimated; but it, probably, will average about 30°, day and night, throughout the month. In an acre the area is 36.4 times as great as that heated by one ton of coal; the cost being in direct proportion to the area, 36.4 tons of coal would be required to heat an acre; which, at $6 per ton, would cost $217.40. To heat an acre through 10°, would cost, then, $72.47. It may be of interest to consider how much coal would be required to evaporate from an undrained field that amount of water which might be carried off by under-drains, but which, without them, is evaporated from the surface. It may be taken as an approximate estimate, that the evaporation from the surface of an undrained retentive field, is equal to two inches vertical depth of water for each of the months of May, June, July, and August; which is equal to fifty-four thousand three hundred and five gallons, or eight hundred and sixty-two hogsheads per acre for each month. If this quantity of water were evaporated by means of a coal fire, about 22⅔ tons of coal would be consumed, which, at $6 a ton, would cost $136. The cost of evaporating the amount of water which would pass off in one day from an acre would be about $4.53. It is probable that about half as much water would be evaporated from thorough-drained land, though, by some experiments, the proportion has been made greater—in which case the loss of heat resulting from an excess of moisture evaporated from undrained retentive land, over that which would be evaporated from drained land, would be equal to that gained by 11⅓ tons of coal, which would cost $68; and this for each acre, in each of the three months. At whatever temperature a liquid vaporizes, it absorbs the same total quantity of heat.

The latent heat of watery vapor at 212° is 972°; that is, when water at 212° is converted into vapor at the same temperature, the amount of heat expended in the process is 972°. This heat becomes latent, or insensible to the thermometer. The heat rendered latent by converting ice into water is about 140°. There are 7.4805 gallons in a cubic foot of water which weighs 62.38 lbs."

We have seen that a sea of water, more than three feet deep over the whole face of the land, falls annually from the clouds, equal to 4,000 tons in weight to every acre. We would use enough of this water to dissolve the elements of fertility in the soil, and fit them for the food of plants. We would retain it all in our fields, long enough to take from it its stores of fertilizing substances, brought from reeking marshes and steaming cities on cloud-wings to our farms. We would, after taking enough of its moisture to cool the parched earth, and to fit the soil for germination and vegetable growth, discharge the surplus, which must otherwise stagnate in the subsoil, by rapid drainage into the natural streams and rivers.

Evaporation proceeds more rapidly from a surface of water, than from a surface of land, unless it be a saturated surface. It proceeds more rapidly in the sun than in the shade, and it proceeds again more rapidly in warm than in cold weather. It varies much with the culture of the field, whether in grass, or tillage, or fallow, and with its condition, as to being dry or wet, and with its formation, whether level or hilly. Yet, with all these variations, very great reliance may be placed upon the ascertained results of the observations already at our command.

We have seen that evaporation from a water surface is, in general, greater than from land, and here we may observe one of those grand compensating designs of Providence which exist through all nature.

If the same quantity of water fell upon the sea and the land, and the evaporation were the same from both, then all the rivers running into the sea would soon convey to it all the water, and the sea would be full. But though nearly as much water falls on the sea as on the land, yet evaporation is much greater from the water than from land.

About three feet of rain falls upon the water, while the evaporation from a water surface far exceeds that amount. In the neighborhood of Boston, evaporation from water surface is said to be 56 inches in the year, and in the State of New York, about 50 inches; while, in England, it is put by Mr. Dalton at 44.43 inches, and, by others, much lower.