ON THE NATURE, AND COMPOSITION OF THE SOIL.
Plants absorb fluids through the extremities or spongioles of the roots, and it is thus that those portions of the substances which serve them as their food, and are derived from the soil, are carried into their system, in a state of solution: these spongioles are not strictly to be regarded as analogous to the mouths of animals, for they are not provided with openings, and cannot imbibe even the most impalpable powders; their action seems to be more analogous to that of the lacteals in animals, for these, as well as spongioles, serve to convey fluids only. These considerations render it necessary, that in the composition of soil for the growth of plants, the following important points should be held in consideration;—it should contain a sufficient ratio of organizable matter, that is of substances which can be rendered available as food to the plants; it should readily absorb fluids, since it is only when in a state of solution, that food can enter into the structure of the plants; it should be sufficiently retentive to avoid the risk of injury by reason of the evaporation, which takes place to a very great extent, when too great an abundance of silica is present, or when more than a due degree of porosity exists in its mechanical texture; and it should be sufficiently permeable, to prevent any thing like excess of moisture, by stagnation.
Soils composed either principally, or almost entirely of heath soil, or of vegetable mould, although very highly recommended for the growth of the Cucumber in winter, are nevertheless objectionable when applied alone, as will be evident if the foregoing principles are taken into view: it cannot however be assumed that the plants will not grow in these soils, for they grow vigorously for a period; neither can it be asserted that such soils do not contain the qualities which are necessary to administer to the nutrition of plants, for it is scarcely possible to conceive any substances which are more nutritious, or whose application in this respect is more effectual; but they are objectionable, in consequence of their becoming soon expended, and failing to maintain for any length of time, an equable degree of moisture. The cause which tends to produce this effect, is the porosity, or the want of mechanical combination in the texture of the soil; which being highly favourable to evaporation, is liable to render it speedily, and very materially dry, when exposed to the influence of powerful solar heat: the frequent application of water, does not entirely obviate the objection, for even when so applied, it soon becomes again evaporated, and thus tends to deteriorate the soil, and decrease its fertility; this it does, by taking up much of the soluble matter contained in it, and conveying it by evaporation into the atmosphere, instead of its being taken up by the roots whilst in a fluid state, and applied to the plant as a means of nutrition: when it is thus conveyed to the atmosphere, the leaves though they are enabled to take up a portion of their food from thence, are still incapacitated to do so fully, and hence, much of the fertilizing properties of the soil, is carried off by the first current of air which passes through the structure; and the plants decline by reason of starvation, though they had been seated in the midst of plenty.
The soil which I should recommend for the growth of the Cucumber, would be composed of ingredients, capable of supplying a sufficient portion of vegetable food; of retaining a due portion of moisture, when placed under powerful evaporation; and of securing the free passage of water through its mass: the former of these conditions would be secured, by the use of mould from the decaying leaves of trees, in the proportion of about three-eighths; the latter would be ensured, by employing about one-fourth part of turfy heath mould, and one-eighth part of clean coarse sand; and the remaining quality, would result by combining these ingredients with one-fourth part of good turfy loam. The preparation of this soil should take place in the dry weather of the summer months, just previous to its being used, so that it can be frequently turned and mixed, without incurring the danger of reducing it to an adhesive consistency, which would at once render it ungenial for the roots of plants: the turfy portions both of the loam and heath soil should be piled up reversely, until the herbage and roots of the grass, become partially decayed; when required for use, it should be chopped into pieces of from two to four inches square, by the spade, and then adding the other ingredients in a rough state, the whole should be well mixed, without sifting, or any other mechanical operation which would have the effect of destroying its open texture. It should always be prevented from becoming saturated with water; and moreover, should never be applied to the roots of plants which are growing in a warm medium, without having been previously submitted to a high temperature, for a sufficient length of time, to have absorbed at least an equal degree of heat, with that in which the plants might be already growing.
The admixture of charcoal with the soil, is said to be a means of adding to its nutritive qualities. Charcoal, which is nearly pure carbon, may be supposed continually to give off a portion of this gaseous substance during its decomposition, and this uniting with a portion of the oxygen contained in the air, would furnish a supply of carbonic acid gas, to the atmosphere immediately about the plants. It should however be borne in mind, that charcoal, is a substance whose decomposition except under the influence of heat, proceeds very slowly indeed, and therefore its chemical influence must not be overrated: doubtless however, the small portion which does combine with the oxygen of the air, is directly beneficial to the plants; for it is a function of the vegetable kingdom by the action of their leaves, when under the influence of light, to decompose carbonic acid, the oxygen of which is liberated, and the carbon fixed in the living tissue. It is therefore probable that a supply of carbonic acid, artificially maintained about the leaves and stems of plants, may be beneficial to them, by furnishing them directly with a portion of carbon, which they cannot absorb in a seperate state. When the charcoal is made from twigs, and the small branches of trees, its decomposition is often more rapid, than when it is obtained by the usual course of manufactering it: if the latter kind of charcoal is employed, it should be broken into pieces of a small size; and in ordinary cases, it should not be used in larger proportion than with about twice its bulk of soil, with which it should be intimately blended.
Besides its chemical action, which is probably beneficial, charcoal has a decidedly advantageous mechanical action in the composition of soils, and this is of a twofold nature:—first, in common with any similar materials, it renders the soil “open,” and thus effectually favours the free passage of water through its mass: secondly, it serves as a perpetual reservoir of moisture in the soil, for in consequence of its being extremely porous, it imbibes a great quantity of water, by its force of attraction, and this it parts with slowly to the soil; in this way, there is no doubt that its action is most salutary. Probably a few pieces of charcoal placed perpendicularly in the soil, and kept continually wet, by the action of some little capillary contrivance, would serve as the best possible means of conducting moisture, and distributing it to the roots of plants.
It will be observed that the application of dung, in any way whatever, has not been recommended; neither do I consider it to be at all requisite, or desirable, in the culture of winter Cucumbers: luxuriance is not a consummation which it is at all desirable to attain to, a moderate, well matured growth, being far preferable; and as some care is supposed to be used to provide suitable soil, it should be of such a nature as to possess the properties, which are requisite to effect the desired end. Dung containing as it does fertilizing properties, may do well to renew the fertility of exhausted soils, which may have been under a long course of cultivation; but it is questionable, whether it ought to be admissable to any extent in pot culture, or in the growth of forced plants, in preference to a supply of wholesome unexhausted natural soil.
A very great objection to the use of dung when applied in a solid state in the composition of soils, consists, in its being presented to the roots of plants, not only in the advanced periods of their existence, but equally so, during the early stages of their growth; here must be an error, for infants, whether they belong to the animal or vegetable kingdom, are certainly not capacitated to appropriate the same kind of food, in the same proportion, as adults. If only a small portion of soil is at first employed, and portions more and more enriched, are from time to time added, as the roots may extend, we are still liable to stumble on an objection, almost as important, though of a somewhat different nature; for we can in that case scarcely fail to injure the spongioles of the roots in a greater or less degree, and the injury thus sustained, will consequently act as a check in the progress of their developement. These considerations seem at once to mark the propriety of applying liquid manures in highly artificial cultivation; they can be supplied in this state, when the plants are in such a mature and advanced state of growth, as from time to time to require their aid; and their fertilizing properties being held in solution by the fluid medium in which they are conveyed, they are just in the condition to be taken up at once by the rootlets. It must still however be recollected, that whilst even impalpable powders cannot as such be made to minister to the nutrition of plants, so neither can gross liquids effect this purpose: it is clear limpid fluids, only, which can be received by the delicate spongioles, and therefore the so-called manure water, when applied of the consistency of mud, is not only in an unfit state to effect its purpose, except by the addition of a more bountiful supply of pure liquid, but it is also liable to act injuriously by reason of the concentration of the strength or powerful qualities of the manure, and by counteracting the open texture of the soil. Manure water, therefore, from whatever source it may be derived, though not necessarily a colourless, should without question, be a limpid fluid; if otherwise applied, it will at once destroy one of the best qualities a soil can possess, viz. porosity.