This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
Underground or sub-drains serve to relieve the land of free water, which is harmful to most plants if left to stagnate in the surface soil or subsoil. They serve not only to dry the land in early spring, but indirectly to warm it, for if the water is removed the sun's heat warms the soil instead of cooling it by evaporating the surplus water. Tenacious lands devoted to gardening and small-fruits are made more productive, warmer and earlier by sub-drainage. Drains promote nitrification, assist in liberating mineral plant-food and cheapen tillage. They serve not only to remove deleterious stagnant water, but they promote aeration as well, and this hastens beneficial chemical changes in the soil. Drainage promotes the vigor, healthfulness and fruitfulness of plants. Tenacious soils are made more friable by drains, thereby giving easier access to plant roots, while the percolation through the soil of rainwater, which carries some plant-food, is hastened. Rain-water in the spring is warmer than the soil; in midsummer it is cooler than the soil: therefore, percolation of rain-water warms the soil in the spring and cools it in extremely hot weather.
Drains serve not only to relieve land of free water, but they impart to it power to hold additional available moisture, which materially benefits plants during droughts.
Fig. 1347. Diagrams to explain the effect of lowering the water-table by means of under-draining. On the undrained soil, the roots do not penetrate deep; and when droughts come, the plants suffer.
Drainage is of two kinds, surface and sub-drainage. On land on which large outlays of money are to be expended, as in horticultural plantations, it is of the utmost importance that the soil be freed to considerable depths from stagnant water. Trees, many shrubs, and even some garden crops send their roots deeper into the subsoil than most of the cereals, hence they require a greater depth of drained feeding-ground. In horticulture the planting may often precede the harvest by five to ten years, while with many farm crops the harvest follows the planting in a few months. If the grain-raiser loses one crop, an annual, by planting on wet land, the loss is not great, but if the orchardist loses fifteen to twenty years of labor by planting on undrained lands, before the mistake is discovered, the losses are serious. Some lands require little more than to be relieved from surplus surface water in early spring. This may be accomplished by forming ridges and open furrows as far asunder as the rows of trees are to be placed. But it is only rarely that surface drainage fully prevents serious damage from surplus moisture. Surface drainage may be considered a cheap way of temporarily alleviating undesirable conditions. It does not always eradicate them.
Fig. 1347 illustrates how sub-drainage lowers the water-table (or the area of standing water), and thereby ameliorates the soil.
Sub-drainage consists in placing conduits of tile or other material in the ground at depths varying from 2 1/2 to feet, and at such distances apart as will serve to relieve the subsoil of deleterious stagnant water. When suitable stones are at hand, they are sometimes used instead of tile for forming drainage conduits. If such use is made of them, the drains should be somewhat deeper than tile drains, since the stones which form the drain occupy nearly a foot of the depth of the ditch and are more likely to become obstructed, especially if placed near the surface, than are tile drains. The throats or openings of stone drains are irregular in size, while those of tile drains are smooth and uniform in size, and are, therefore, most desirable. Years ago, various flat-bottomed tiles (Fig. 1348) were employed, but the style in general use at present is the cylindrical unglazed tile shown in Fig. 1349. They should be hard-burned. Because of the low cost of cement, tiles made of sand and hydraulic cement have recently come into use; they require no burning, are stronger than tiles made of clay and are just as efficient, except in alkali and where frost penetrates very deep.
In semi-arid districts in which irrigation is practised, if there is a hardpan, nearly or quite impervious to water, located within
31/2 to 4 1/2 feet of the surface, the land will in time become sour or charged with injurious alkaline salts, and in many cases ruinously unproductive. Lands of this description are, for the most part, situated west of the 100th meridian. A striking illustration of raising the water-table by too liberal irrigation may be found in a tract of several thousand acres in Tulare County, California, which formerly produced grapes and peaches abundantly but now yields nothing except a little hardy forage. The water table in this region was once 30 to 40 feet below the surface, but as a result of constant irrigation has risen to within 2 or 3 feet and, in low places, even to the surface, forming a sort of tule swamp. Since the water-table could not be lowered enough to restore the land by under drainage, for lack of an outlet within reasonable distance, it is probable that the only way to reclaim it would be to sink a well and pump the surplus water into a surface ditch. Irrigation with pure water would then sweeten the soil and render it again productive; and the whole process of restoration need not be excessively expensive.
Fig. 1348. Old-fashioned drain-tile.
Fig. 1349. Common cylindrical drain-tile; and a scoop for preparing the bed for the tile.
If the hardpan is less than 2 feet in thickness, the land may be improved greatly for orchard and vineyard purposes by the use of dynamite. Blasting should be deep enough to allow the surplus water to escape into the porous earth or gravelly soil beneath the hardpan. On the Pacific coast this method of draining orchard and vineyard land has been quite successful. In any case, unless the soil has good natural sub-drainage, it is both wise and economical to blast out holes for trees and vines; for the cost of digging holes, if they are as large and deep as they should be, is lessened by an amount almost equal to the cost of blasting.
Recently, powerful tractors have solved, to some extent, the problem of drainage in many cases by making deep plowing possible before planting and during the first few years of subsequent tillage of the orchard or vineyard. This machine with the tillage implement turns easily at the ends of the field within the space allowed for turning a span of horses and a plow; it can pass under limbs where a 14-hand horse (56-inch) can pass, and as close to the plants as a span of horses can. It furnishes also power and locomoton for spraying and for opening trenches to a considerable depth (18 to 44 inches) for the reception of drain-tile.
Fig. 1350. Improper method of draining a field.
In some regions, drains are placed 200 to 300 feet apart, and serve their purpose well. In others they should not be placed farther apart than 20 to 30 feet. Wherever the subsoil is composed of tenacious fine clay, through which the water moves upward or downward with difficulty, the narrower intervals are necessary. In some instances the surplus water in the subsoil is under pressure by reason of water which finds its way into it from higher levels, and if this is not removed, the water has a constant tendency to rise to the surface. In many such cases drains placed at wide intervals may serve to relieve the pressure and drain the land. Since sub-drains are designed to be permanent, are expensive to construct and difficult to repair, the principles of drainage should be well understood, and the work should be undertaken only after a most careful inspection of the land and after the fundamental principles of the subject have been mastered.
Mains and sub-mains should be avoided so far as possible, since they greatly increase cost, tend to become obstructed, and are often unnecessary. The three long mains in Fig 1350 are not drains, strictly speaking, since the land may be as fully drained without them, as shown in Fig. 1351; therefore, they serve only to conduct the water of the drains proper. Tiles of 3 to 4 and 5 inches diameter should be used when the drains are infrequent and the flow of water considerable. Smaller ones, 2 to 3 inches in diameter, will suffice when the intervals between the drains are narrow.
Fig. 1351. Best method of draining a field.
Drains should have as uniform a fall as possible, and no abrupt lateral curves or sharp angles should occur as are seen in many places in Fig. 1350. If the drain has a rapid fall in its upper reaches, as is often the case, and but slight fall in the lower, a silt basin should be constructed at the point at which the rapid changes into the slight fall, if obstructing silt is present. All drains which may be necessary should be placed before the planting occurs. Orchard lands may be drained in the spring, fallowed in the summer, and planted in the fall or the following spring. Drains placed at frequent intervals because of the tenacity of the soil should be comparatively shallow, for if placed deep or at wide intervals, the water will be too long reaching them. If drains are placed at wide intervals they should be at least 3 1/2 feet deep to be most efficient. If the parallel system is adopted (Fig. 1351), there may be more outlets to construct and maintain than is desirable; if so, the system might be modified by constructing a sub-main, one side of which will serve also as a drain, and but one outlet will be required (Fig. 1352). Drains through which water runs for the greater part of the year are likely to become obstructed by roots, if water-loving trees, such as the willow, soft maple, and elm, are allowed to grow near them.
If floating silt is present, the joints of the tiles should be protected for two-thirds of their upper circumferences by a narrow strip of tarred building paper (Fig. 1353), or collars should be used. Stone drains should receive a liberal covering of straw or some similar material before they are filled.
Fig. 1352. Showing how the drains may be gathered into one when there is only one place at which an outlet can be secured.
I. P. Roberts.
Fig. 1353. Covering a joint.