Draining for Profit, and Draining for Health | Page 4

circumstance soil in the mass is always more or less porous. If, however, we proceed to examine one of the smallest particles of which soil is made up, we shall find that even this is not always solid, but is much more frequently porous, like soil in the mass. A considerable proportion of this finely-divided part of soil, the impalpable matter, as it is generally called, is found, by the aid of the microscope, to consist of broken down vegetable tissue, so that when a small portion of the finest dust from a garden or field is placed under the microscope, we have exhibited to us particles of every variety of shape and structure, of which a certain part is evidently of vegetable origin.
[Illustration: Fig. 1 - A DRY SOIL.]
Fig. 1 - A DRY SOIL.
"In these figures I have given a very rude representation of these particles; and I must beg you particularly to remember that they are not meant to represent by any means accurately what the microscope exhibits, but are only designed to serve as a plan by which to illustrate the mechanical properties of the soil. On referring to Fig. 1, we perceive that there are two distinct classes of pores,--first, the large ones, which exist between the particles of soil, and second, the very minute ones, which occur in the particles themselves; and you will at the same time notice that, whereas all the larger pores,--those between the particles of soil,--communicate most freely with each other, so that they form canals, the small pores, however freely they may communicate with one another in the interior of the particle in which they occur, have no direct connection with the pores of the surrounding particles. Let us now, therefore, trace the effect of this arrangement. In Fig. 1 we perceive that these canals and pores are all empty, the soil being perfectly dry; and the canals communicating freely at the surface with the surrounding atmosphere, the whole will of course be filled with air. If in this condition a seed be placed in the soil, at a, you at once perceive that it is freely supplied with air, but there is no moisture; therefore, when soil is perfectly dry, a seed cannot grow.
[Illustration: Fig. 2 - A WET SOIL.]
Fig. 2 - A WET SOIL.
"Let us turn our attention now to Fig. 2. Here we perceive that both the pores and canals are no longer represented white, but black, this color being used to indicate water; in this instance, therefore, water has taken the place of air, or, in other words, the soil is very wet. If we observe our seed a now, we find it abundantly supplied with water, but no air. Here again, therefore, germination cannot take place. It may be well to state here that this can never occur exactly in nature, because, water having the power of dissolving air to a certain extent, the seed a in Fig. 2 is, in fact, supplied with a certain amount of this necessary substance; and, owing to this, germination does take place, although by no means under such advantageous circumstances as it would were the soil in a better condition.
[Illustration: Fig. 3 - A DRAINED SOIL.]
Fig. 3 - A DRAINED SOIL.
"We pass on now to Fig. 3. Here we find a different state of matters. The canals are open and freely supplied with air, while the pores are filled with water; and, consequently, you perceive that, while the seed a has quite enough of air from the canals, it can never be without moisture, as every particle of soil which touches it is well supplied with this necessary ingredient. This, then, is the proper condition of soil for germination, and in fact for every period of the plant's development; and this condition occurs when the soil is moist, but not wet,--that is to say, when it has the color and appearance of being well watered, but when it is still capable of being crumbled to pieces by the hands, without any of its particles adhering together in the familiar form of mud."
As plants grow under the same conditions, as to soil, that are necessary for the germination of seeds, the foregoing explanation of the relation of water to the particles of the soil is perfectly applicable to the whole period of vegetable growth. The soil, to the entire depth occupied by roots, which, with most cultivated plants is, in drained land, from two to four feet, or even more, should be maintained, as nearly as possible, in the condition represented in Fig. 3,--that is, the particles of soil should hold water by attraction, (absorption,) and the spaces between the particles should be filled with air. Soils which require drainage are not in this condition. When they are not