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16 or 18 inches with small stones, over which a thin covering of turf or heath should be laid, to prevent the earth from getting in; and the drain must be then filled in and levelled, taking care to have 16 or 18 inches of earth above the stones, in order that the drain may not be disturbed in ploughing. This is the most common and durable sort of drain : but tiles and other materials are often used ; and so long as a free outlet for the water is secured, leaving the surface dry for cultivation, it matters little how this is accomplished.
In some stiff wet clay lands, it has been the practice to drain with thorns, by cutting a narrow trench of the depth of about 3 feet, with a small groove or gutter at bottom, in which a rope of straw is laid from end to end of the drain, and over it the thorns are placed, and the trench is then filled in. This mode of draining costs but little, and will answer for several years, and in stiff clays perhaps affords a readier means of escape for the surface-water than tile draining: but where the land is once well tile-drained, it lasts for ever, whereas the thorns decay in 15 or 16 years, and the whole process will then have to be done anew.
In filling in the drains, however they may have been made, care should be taken to use the lighter portions of the earth thrown out in forming them, in order that the surface-water may pass more readily through it, and be carried off in the drain below. The heavier portions of the earth may be scattered over the surface, where it will soon become mellowed by the action of the atmosphere. This is especially necessary to be attended to in draining stiff clay lands.
There are other modes of draining practised in different parts of the country, each probably suited to the circumstances of the district, and effective for its object; for if a free outlet is provided for the spring and surface water, it matters little, except on the score of expense, how this object is accomplished, always presuming that at least 16 inches' depth of soil is left above the drain for the purposes of cultivation.
Care must likewise be taken to carry off the rain and surface water, by means of open drains, which should
always be kept clean, and the outlets and watercourses must be scoured out as often as necessary, and always at least once a year.
If the surface-soil rests upon a shallow compact subsoil, the latter forms a kind of dam or reservoir for retaining the water, and the remedy in such case is, to cut through this obstruction, and thus to give the water a free passage to a lower level.
When water rests upon and overspreads the surface, the carrying it away in open channels is termed surface-draining. When water has penetrated the upper surface, but is unable to escape, being retained there by the tenacious subsoil, and kept soaking through, and rendering cold, wet, and unproductive all that is above it, the process of cutting through the obstruction, and collecting the water into a fixed channel, is called under-draining.
In the case of springs, the line where moisture appears on the sloping surface of a field, is generally perceptible, by the change of colour and other indications of wetness, as the production of rushes, coarse grasses, &c. By cutting a drain along the upper side of this line, sufficiently deep to intercept the water before it reaches the surface, it may be carried away to some convenient outlet. In such case, one drain well laid out, and of adequate dimensions, will often in this way effect a purpose which no multiplication of smaller drains could so cheaply and effectually accomplish.
The surface-water should be carried away in open drains. These consist of the ditches, which ought to be so made as to facilitate the escape of the water—the open furrows, which are formed by the ridges and open trenches, cut in places necessary for giving the water a free passage. A good arrangement of ridges and furrows will generally of itself effect the purpose of surface-draining a field; but before the approach of winter, a few open drains, a foot wide and six inches deep, or more, according to the quantity of water expected, should be cut with a spade across the field, to catch surface-water, and carry it to the main drains. These water-furrows are
easily made, and will well repay the trouble of making them.
All drains, as well open as covered, should have fall enough to let the water run off gently ; but if the fall be too great, the stream will acquire so much force as to carry away the soil at the sides, which soon chokes up the drains. However formed, the drains should be conducted into a natural water-course, or else into a main drain communicating with one, so that the water may have a free outlet by which to escape.
Draining in all its branches is well deserving of the farmer's best attention; and a new kind, called Thorough-Draining, has been of late years much practised with the very best results. The mode of effecting this operation, to be followed by Subsoil-Ploughing, we will now describe.
THOROUGH-DRAINING, AND SUBSOIL-PLOUGHING.
These operations are independent of each other, and are performed at different periods, although the object of each is the same. They are both now extensively practised, and have invariably produced the most beneficial effects upon the soil, rendering it deeper and drier, and increasing the quantity and improving the quality of the crops.
Thorough-Draining.-Almost every description of land will be benefited by thorough-draining, but on wet heavy clays, and on soils having a hard retentive bottom, the effects are most striking. Land, which before grew nothing but sedges and the coarsest kind of grass, has been converted into a good mellow soil, and fitted for the culture of every description of crop, by means of thorough-draining.
The mode of proceeding to thorough-drain a field, is, in the first instance, to make a number of parallel drains, from 16 to 40 feet apart, according to the nature of the land, and as it is more or less exposed to wet, and either across or up and down the field, as circumstances may demand. If the land be low and wet, or if it consist of strong clay, the distance between the drains should not exceed 16 feet; if the subsoil is lighter and more porous, it may be 20, or 24, or 30 feet; and in very open subsoils the drains may be as much as 40 or 45 feet apart. When the ridges of a field are much raised, it will save cutting to run a drain up the furrow.
The drains must be 30 inches or 2 feet deep, and be filled with rubble or broken stones to the height of 12 inches from the bottom of the drain, leaving 16 to 18 inches clear from the top of the stones to the surface of the soil. Cover the stones with a thin sod, overlapping it at the joints, to prevent any of the loose earth getting in. The drains are then to be filled in, and a crop of grain taken off the land, after which the subsoil-plough must be put in operation, working transversely across the direction of the drains.
This is the usual way of thorough-draining, but the drains may be formed with tiles, where they can be procured at a cheap rate, or with flat stones set triangular fashion, thus A, or one side perpendicular and the other angular, thus , where suitable materials are at hand. In some cases shingle or large gravel may be obtained, or rubble-stones sufficiently small for filling the drains may be gathered off the land ; but where large stones only can be obtained, these must be broken into tolerably small pieces (say two or two and a half inches square), in order that the water may filter readily through them. When tiles are used, they should have a flat tile or piece of slate placed at bottom, as a sole, to prevent the edges of the tile from cutting into the soil, and thus lessening or destroying the opening for the water. Circular tiles are sometimes used, and they appear to answer well; and in some places a tile formed somewhat like a horseshoe is used, having its thick ends bent back, so as to form a kind of feet for the tile to rest upon, thus s, which prevents its cutting into the soil, and supersedes the necessity for a sole.
A free passage for the water below the surface is the great object to be accomplished in thorough-draining; and this must be so done as to leave 16 or 18 inches of soil above the materials used for the formation of the drain, in order that it may not be disturbed by the plough. Keeping this object in view, the thorough-drainer can hardly go wrong with respect to the depth of the drain, or the materials of which it is formed; and if he has provided a suitable main drain, into which these subsidiary drains may discharge the water which they have collected, the land will be left dry, and fitted for the production of crops.
The main drain, into which all the other drains must be carried, should run along the lowest part or hollow of the land, and if possible should communicate with some natural water-course, by which the water it discharges may be carried off. Its size must depend on the quantity of water expected, but it should be at least 6 inches deeper than the other drains. Submains will often be necessary along the bottom of a field, to receive the water from the smaller drains, and carry it into the main drain; and these ought likewise to be made somewhat deeper than the others discharging into them.
The water thus collected, may often be most advantageously employed for the purposes of irrigation, and this should never be omitted wherever it is practicable. Brooks and rivulets constitute the natural drains of the country, and should in like manner be applied to irrigation, whenever the levels admit of this being done. Nothing can be worse than to allow streams to run to waste, which, if properly applied, are capable of imparting the highest fertility to the land.
As regards the space between the drains, it is obvious that this must depend upon local circumstances, some stiff wet lands requiring the drains to be placed close to each other, in order to secure a dry seedbed for the crops, whilst in lighter soils the drains may be placed wider apart. As a general rule, however, it may be said that the drains should be formed at from 5 to 15 yards, or from 15 to 45 feet apart, according to the nature of the soil, and other circumstances, of which the farmer must in each case be the judge.