DRAINAGE, a process by which wet and unhealthy soils are rendered arable and healthy.
Benefits of Drainage.-1. Removal of superfluous water. Not only is the standing water at the surface carried off, but the water-table is lowered, in creasing the depth of soil.
2. Improves soil texture. Drained soils are more friable, less lumpy, offer less resistance to plant roots, and are of better texture in every way, than un drained soils.
3. Increases root pasturage. Agricul tural literature is full of testimony to the benefits of deep tillage. The deeper the soil is stirred the greater its produc tiveness.
4. Increases soil fertility. It prevents loss of fertility by water passing over the surface. It adds to the fertility by send ing summer showers down through the soil, instead of over them, enabling the crop to use the nitric acid and ammonia brought down. It increases the effect of manures by bringing them more quickly into solution and into more intimate con tact with plant roots.
5. Makes tillage easier. Waste land is reduced, and the better texture of soil, its finer tilth and greater friability decrease draft and increase the effectiveness of tillage implements.
6. Lengthens the growing season for crops. Frost comes out earlier in the spring and the land becomes earlier warmed. Evaporation lowers tempera ture, but drainage removes water without evaporation.
7. Assists disintegration. Frosts pene trate deeper in winter in drained soils, as sisting in unlocking the stores of mineral plant food.
8. Favors nitrification and bacterial ac tion. - Plants are largely dependent on the decomposition of organic matter in the soil for their supply of nitrogen. This change is brought about by the action of ferments or bacteria which thrive only under certain conditions of temperature and moisture. Drainage supplies the most favorable condition for their develop ment.
9. Prevents heaving. The effect of stool-ice in throwing out young plants in winter is often to diminish seriously and even destroy the crop. Drainage dries up the surface soil and prevents the for mation of stool-ice.
10. Lessens washing and diminishes violence of floods. By increasing the ab sorptive power of the soil less water is left to pass over the surface in a rainy season.
11. Improves the quantity and quality of crops. That the yield of crops is much greater on drained soils hardly needs to be substantiated. Rust, mildew, blight, etc., are much less prevalent in crops on drained soils.
12. Diminishes the effect of drought. By making the season earlier tillage can begin sooner and save moisture from wasting.
13. Healthfulness improved. So well known is this fact that large towns have undertaken the drainage of adjacent swamps to render the region more healthful.
Kinds of Drains.—Cobble-stone or so called blind drains are undoubtedly the most ancient covered drains ever made. They are trenches partly filled with boul ders picked up nearby and covered over with the earth thrown out.
Cobble duct. Two rows of boulders are laid in the bottom of the trench three or four inches apart, a third row is laid be tween on top, and these are covered with smaller stones and finally covered with the earth thrown out.
Brush drains are made by filling a trench with wide bottom full of brush laid in with stem ends downstream, treading them down, covering with sod, leaves or straw, and filling in. They are prone to cave in as the brush settles and decays, and are treacherous to animals.
French brush differ from common brush drains in having stakes driven X-wise in the bottom of the trench to raise the brush a few inches.
Box drains consist of two boards nailed together forming a V, laid in the bottom of trench with the apex up, and covered; or, of three boards, two set on edge three or four inches apart, with the third nailed across the top, placed in the trench open side down.
Plug drains are made by means of a plug, five or six feet long, consisting of four or five sections of wood with uni form elliptical cross sections, three or four inches in diameter, linked together by a short chain and bar for drawing the plug along the trench. Beginning at the upper end of the drain the plug is laid chain end downstream, in the bottom of the trench. A few inches of earth is tamped solidly over the plug; it is then drawn on by means of bar and chain, two-thirds of its length, and cov ered again, etc.
Mole drains are made with a mole plow, an implement constructed to draw an iron plug through the ground about three feet below the surface. This plow is usually drawn by a capstan with horses or oxen on the sweep.
Tile Dranage.—Drain tiles were in use at a very early date, probably during the Roman period. At first three bricks of common or special shape were used for the conduit, consisting of two set up edgewise a few inches apart, with a third across the top. Later a single brick was molded into the shape of the three as above laid. These were superseded by V-shaped tiles with broad soles on which to rest, and perforations along the back to admit the water. Plain cylindrical tiles are now generally used.
Outicts.—One of the weakest parts of a drain is the point of discharge. For this reason it is best not to have a sep arate outlet for each line of tikes, but rather to collect all into a system with a single outlet.
Minors or Laterals.—The smaller sub sidiary lines are so called in distinction from the main drain, which follows the lower part of the field and receives the discharge from the smaller drains.
Before construction, a drainage system should be carefully studied, surveyed and mapped out, both for greater accuracy of work and for location of drains after ward. Steam-power ditchers have been perfected, which have demonstrated their practicability where land is free from ob structions and the grade fairly even.