Draining for Profit, and Draining for Health

by George E. Waring

An idea of the amount of heat lost to the soil, in the evaporation of water, may be formed from the fact that to evaporate, by artificial heat, the amount of water contained in a rain-fall of two inches on an acre, (200 tons,) would require over 20 tons of coal. Of course a considerable—probably by far the larger,—part of the heat taken up in[pg 035] the process of evaporation is furnished by the air; but the amount abstracted from the soil is great, and is in direct proportion to the amount of water removed by this process; hence, the more we remove by draining, the more heat we retain in the ground.

The season of growth is lengthened by draining, because, by avoiding the cooling effects of evaporation, germination is more rapid, and the young plant grows steadily from the start, instead of struggling against the retarding influence of a cold soil.

Temperature.—The temperature of the soil has great effect on the germination of seeds, the growth of plants, and the ripening of the crops.

Gisborne says: "The evaporation of 1 lb. of water lowers the temperature of 100 lbs. of soil 10°,—that is to say, that, if to 100 lbs. of soil, holding all the water it can by attraction, but containing no water of drainage, is added 1 lb. of water which it has no means of discharging, except by evaporation, it will, by the time that it has so discharged it, be 60° colder than it would have been, if it had the power of discharging this 1 lb. by filtration; or, more practically, that, if rain, entering in the proportion of 1 lb. to 100 lbs. into a retentive soil, which is saturated with water of attraction, is discharged by evaporation, it lowers the temperature of that soil 10°. If the soil has the means of discharging that 1 lb. of water by filtration, no effect is produced beyond what is due to the relative temperatures of the rain and of the soil."

It has been established by experiment that four times as much heat is required to evaporate a certain quantity of water, as to raise the same quantity from the freezing to the boiling point.

It is, probably, in consequence of this cooling effect of evaporation, that wet lands are warmest when shaded,[pg 036] because, under this condition, evaporation is less active. Such lands, in cloudy weather, form an unnatural growth, such as results in the "lodging" of grain crops, from the deficient strength of the straw which this growth produces.

In hot weather, the temperature of the lower soil is, of course, much lower than that of the air, and lower than that of the water of warm rains. If the soil is saturated with water, the water will, of course, be of an even temperature with the soil in which it lies, but if this be drained off, warm air will enter from above, and give its heat to the soil, while each rain, as it falls, will also carry its heat with it. Furthermore, the surface of the ground is sometimes excessively heated by the summer sun, and the heat thus contained is carried down to the lower soil by the descending water of rains, which thus cool the surface and warm the subsoil, both beneficial.

Mr. Josiah Parkes, one of the leading draining engineers of England, has made some experiments to test the extent to which draining affects the temperature of the soil. The results of his observations are thus stated by Gisborne: "Mr. Parkes gives the temperature on a Lancashire flat moss, but they only commence 7 inches below the surface, and do not extend to mid-summer. At that period of the year the temperature, at 7 inches, never exceeded 66°, and was generally from 10° to 15° below the temperature of the air in the shade, at 4 feet above the earth. Mr. Parkes' experiments were made simultaneously, on a drained, and on an undrained portion of the moss; and the result was, that, on a mean of 35 observations, the drained soil at 7 inches in depth was 10° warmer than the undrained, at the same depth. The undrained soil never exceeded 47°, whereas, after a thunder storm, the drained reached 66° at 7 inches, and 48° at 31 inches. Such were the effects, at an early period of the year, on a black bog. They suggest some[pg 037] idea of what they were, when, in July or August, thunder rain at 60° or 70° falls on a surface heated to 130°, and carries down with it, into the greedy fissures of the earth, its augmented temperature. These advantages, porous soils possess by nature, and retentive ones only acquire them by drainage."

Drained land, being more open to atmospheric circulation, and having lost the water which prevented the temperature of its lower portions from being so readily affected by the temperature of the air as it is when dry, will freeze to a greater depth in winter and thaw out earlier in the spring. The deep freezing has the effect to greatly pulverize the lower soil, thus better fitting it for the support of vegetation; and the earlier thawing makes it earlier ready for spring work.

Drought.—At first thought, it is not unnatural to suppose that draining will increase the ill effect of too dry seasons, by removing water which might keep the soil moist. Experience has proven, however, that the result is exactly the opposite of this. Lands which suffer most from drought are most benefited by draining,—more in their greater ability to withstand drought than in any other particular.