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.
Chap. VI.
ON THE APPLICATION OF MOISTURE.
From what has been stated in the preceeding chapter, it will be sufficiently evident, that a supply of water is required as a component of the soil, in which all plants are grown, in order to enable them to draw from it, other components, which form their food; and that, as it is necessary for them continually to take up a portion of this food, so is it necessary, that moisture should be continually present, in order to render it available by them.
Among other conditions to which the operation of applying water to the soil should be subjected, there are some which are specially important: it should never be either applied in excess, or unduly withheld; nor should it ever be applied when of a temperature below that of the atmosphere in which the plants to whose roots it is applied, are growing at the time of its application.
There is a liability of applying water in excess, when the particular stage of growth, the peculiar state of the weather, or the season of the year, are not duly regarded: thus, an adult plant will consume more water than an infant plant; and any plant, will decompose a larger quantity of water, in sunny weather, when evaporation is going on briskly, than in cloudy weather, when it is scarcely perceptible; again, in the summer season, a much larger quantity will be appropriated, than in the winter. Water has been applied in excess, whenever the soil becomes soddened or saturated therewith; but great as this evil is, it is equalled in its injurious effects, by falling into the opposite extreme, and withholding a quantity sufficient to render the constituents of the soil, available as food to the roots of plants placed in it.