LAND-DRAINAGE

Field, Forest and Farm by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. LAND-DRAINAGE

CHAPTER XLII. LAND-DRAINAGE

“In the bottom of a flower-pot you will find a small round hole. Over this hole it is customary to lay a bit of broken tile, and on this, if the plant to occupy the pot is delicate, a few small pebbles. This done, the pot is filled with vegetable mold. Why this hole, this bit of tile, these pebbles? That is what we are now about to consider.

“Water is absolutely indispensable to plants, since it is the medium that dissolves the various nutritive ingredients of the soil and thus renders them capable of assimilation by the roots. Accordingly the soil penetrated by these roots must be constantly supplied with sufficient moisture either by rainfall or by artificial irrigation. But air is not less indispensable. It disinfects the soil and by causing slow combustion of the humus gives rise to a slight but uninterrupted liberation of carbonic acid gas, one of the nutritive substances required by vegetation. Should the roots be cut off from this life-giving agency, they would languish and finally decay. Thus it is that if vegetation is to thrive the soil in which it grows must have at the same time both air and water. But if the bottom of the flower-pot has no opening, or if its opening is stopped up, [215]the water from the watering-can will not flow through, nor will there be any air admitted from below, and for lack of this the roots will decay. On the other hand, if the water, after saturating the earth, runs out freely by the hole in the bottom of the pot, the damp soil will become a sort of sponge to which the air will have access from all sides, and the plant will thrive.

“This reasoning applies to the most extensive agricultural operations as well as to the care of a potted plant. After water has soaked into the ground it should find some channel to carry it off; otherwise the roots will decay for want of air. That is why clayey soils, which retain water when they are once saturated, are unsuited to agriculture, while light soils, having sand mixed with the clay and thus readily allowing the water to drain off, are well adapted to it. For the same reason, again, a sandy subsoil accelerates vegetation, and a clayey subsoil retards it. A sandy subsoil offers the same advantage as a flower-pot open at the bottom, whereas a clayey subsoil is like a flower-pot closed at the bottom. In the first case the surplus of water drains off and the air has free access; in the second the superabundant moisture finds no outlet and the air cannot reach the roots.

“Now let us suppose we have a marshy soil to deal with. Because of the stagnant water either on the surface or a little below it nothing can grow on this piece of ground except rushes or other hardy plants designed by nature for this kind of soil. Accordingly [216]we proceed to dig a number of small ditches, of a depth somewhat greater than that attained by plant-roots, and we fill the bottom of these ditches with small stones, on which we finally throw back the earth we have removed. These underground ditches are suitably inclined, and all empty at the lower end into a main canal. The water saturating the soil collects in these ditches, filters through the layer of pebbles, and empties into the main canal, which carries it off to some river or other stream. Our marshy soil is now like the potful of earth with a hole at the bottom, the bit of broken tile, and layer of little pebbles: the air has free access and brings fertility with it. This operation of ours is called drainage, a word formed from ‘drain,’ which is both a verb and a noun. In the latter sense we apply it to the narrow ditch dug for carrying off superfluous water.

“A drainage system like that just described is the simplest possible, but there is one serious objection to it: the layer of small stones soon becomes clogged with soil washed down by the water, and the latter can no longer run off. Hence it is customary to use fagots instead of stones, since they offer less obstruction. But still better results are obtained with earthenware conduits laid in the ditches. Sometimes these conduits take the form of drain-tiles such as are used on roofs, and they rest on sills or ground-pieces of the same material; or, again, they may be tubular in form, the successive sections loosely fitted together so that the water [217]to be carried off may enter where the sections join.

“The effect of drainage is not merely to carry off the superfluous water and thus promote the aëration of the soil to the depth reached by the roots; it also keeps the soil cool and moist by the constant presence of water in the drainage ditches or pipes. When a heap of sand is watered at its base, the moisture is seen to mount higher and higher until it reaches the top. In like manner the water collected in our drainage ditches soaks into the upper soil in a dry time and thus reaches the roots of plants growing there, so that water which is superfluous or even harmful at certain periods is held in reserve and gradually distributed at the right moment.

“Another advantage of a drainage system is that it prevents that cooling of the soil which would result from prolonged evaporation. In taking the form of vapor water chills the objects that help to promote the evaporation. For this reason we feel a decided chill on emerging from a bath; the film of moisture that covered us is passing off in vaporous form. Similarly a constant evaporation at the surface of a water-soaked tract of land chills the ground and we have a cold soil. But if the water is carried off by proper drainage, evaporation ceases and there is no further chilling of the surface soil. Now, a high temperature is always favorable to vegetation.

“Draining is so beneficial that it is not confined to marshy ground, which without it would be quite unproductive, but is applied also to ordinary arable [218]land. Wherever the soil is too clayey, or even where the surface soil is good but the subsoil clayey, rain-water cannot drain off readily and the ground remains soggy and cold. Eventually, however, it dries up, but there being no way for the air to permeate the soil, the latter is left hard and unyielding, so that the roots are by turns drowned in liquid mud and held fast in a tenacious paste that has been baked by the sun. Drainage overcomes these difficulties, and consequently all rich soils that hold rain-water for some time before infiltration are much improved by being properly drained.”

About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books.

This book is part of the public domain. Jean-Henri Fabre (2022). Field, Forest and Farm. Urbana, Illinois: Project Gutenberg. Retrieved October https://www.gutenberg.org/cache/epub/67813/pg67813-images.html

This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org, located at https://www.gutenberg.org/policy/license.html.