The worst of all drains is an open ditch, of equal width from top to bottom. It cannot stand a single season, in any climate or soil, without being seriously impaired by the frosts or the heavy rains. All open drains should be sloping; and it is ascertained, by experiment, what is the best, or, as it is sometimes expressed, the natural slope, on different kinds of soil. If earth be tipped from a cart down a bank, and be left exposed to the action of the weather, it will rest, and finally remain, at a regular angle or inclination, varying from 21° to 55° with the horizon, according to the nature of the soil. The natural slope of common earth is found to be about 33° 42'; and this is the inclination usually adopted by railroad engineers for their embankments.
If the banks of the open ditch are thus sloped, they will have the least possible tendency to wash away, or break down by frost.
Again: where open ditches are adopted in mowing fields, they may, if not very deep, be sloped still lower than the natural slope, and seeded down to the bottom; so that no land will be lost, and so that teams may pass across them.
This amounts, in fact, to the old ridge and furrow system, which was almost universal in England before tiles were used, and is sometimes seen practiced in this country. The land, by that system, is back-furrowed in narrow lands, till it is laid up into beds, sloping from the tops, or backs, to the furrows which constitute the drains. This mode of culture is very ancient, and is probably referred to in the language of the Psalmist, in the Scriptures: "Thou waterest the ridges thereof abundantly, thou settlest the furrows thereof, thou makest it soft with showers."
The objections to open ditches, as compared with under-drains, may be briefly stated thus:
1. They are expensive. The excavation of a sloping drain is much greater than that of an upright drain. An open drain must have a width of one or two feet at the bottom, to receive the earth that always must, to some extent, wash into it. An open drain requires to be cleaned out once a year, to keep it in good order. There is a large quantity of earth from an open drain to be disposed of, either by spreading or hauling away. Thus, a drain of this kind is costly at the outset, and requires constant labor and care to preserve it in working condition.
2. They are not permanent. A properly laid underdrain will last half a century or more, but an open drain, especially if deep, has a constant tendency to fill up. Besides, the action of frost and water and vegetation has a continual operation to obstruct open ditches. Rushes and water-grasses spring up luxuriantly in the wet and slimy bottom, and often, in a single season, retard the flow of water, so that it will stand many inches deep where the fall is slight. The slightest accident, as the treading of cattle, the track of a loaded cart, the burrowing of animals, dams up the water and lessens the effect of the drain. Hence, we so often see meadows which have been drained in this way going back, in a few years, into wild grass and rushes.
3. They obstruct good husbandry. In the chapter upon the effects of drainage on the condition of the soil, we suggest, in detail, the hindrances which open ditches present to the convenient cultivation of the land, and, especially, how they obstruct the farmer in his plowing, his mowing, his raking, and the general laying out of his land for convenient culture.
4. They occupy too much land. If a ditch have an upright bank, it is so soft that cattle will not step within several feet of it in plowing, and thus a strip is lost for culture, or must be broken up by hand. If, indeed, we can get the plow near it, there being no land to rest against, the last furrow cannot be turned from the ditch, and if it be turned into it, must be thrown out by hand. If the banks be sloped to the bottom, and the land be thus laid into beds or ridges, the appearance of the field may, indeed, be improved, but there is still a loss of soil; for the soil is all removed from the furrow, which will always produce rushes and water-grass, and carried to the ridge, where it doubles the depth of the natural soil. Thus, instead of a field of uniform condition, as to moisture and temperature and fertility, we have strips of wet, cold, and poor soil, alternating with dry, warm, and rich soil, establishing a sort of gridiron system, neither beautiful, convenient, nor profitable.
5. The manure washes off and is lost. The three or four feet of water which the clouds annually give us in rain and snow, must either go off by evaporation, or by filtration, or run off upon the surface. Under the title of Rain and Evaporation, it will be seen that not much more than half this quantity goes off by evaporation, leaving a vast quantity to pass off through or upon the soil. If lands are ridged up, the manure and finer portions of the soil are, to a great extent, washed away into the open ditches and lost. Of the water which filters downwards, a large portion enters open ditches near the surface, before the fertilizing elements have been strained out; whereas, in covered drains of proper depth, the water is filtered through a mass of soil sufficiently deep to take from it the fertilizing substances, and discharge it, comparatively pure, from the field. In a paper by Prof. Way (11th Jour. Roy. Ag. Soc.), on "The Power of Soils to retain Manure," will be found interesting illustrations of the filtering qualities of different kinds of soil.