Conversations on Chemistry Part 96

But pray what is the use of manuring the soil?

MRS. B.

Manure consists of all kinds of substances, whether of vegetable or animal origin, which have undergone the putrid fermentation, and are consequently decomposed, or nearly so, into their elementary principles.

And it is requisite that these vegetable matters should be in a state of decay, or approaching decomposition. The addition of calcareous earth, in the state of chalk or lime, is beneficial to such soils, as it accelerates the dissolution of vegetable bodies. Now, I ask you, what is the utility of supplying the soil with these decomposed substances?

CAROLINE.

It is, I suppose, in order to furnish vegetables with the principles which enter into their composition. For manures not only contain carbon, hydrogen, and oxygen, but by their decomposition supply the soil with these principles in their elementary form.

MRS. B.

Undoubtedly; and it is for this reason that the finest crops are produced in fields that were formerly covered with woods, because their soil is composed of a rich mould, a kind of vegetable earth, which abounds in those principles.

EMILY.

This accounts for the plentifulness of the crops produced in America, where the country was but a few years since covered with wood.

CAROLINE.

But how is it that animal substances are reckoned to produce the best manure? Does it not appear much more natural that the decomposed elements of vegetables should be the most appropriate to the formation of new vegetables?

MRS. B.

The addition of a much greater proportion of nitrogen, which const.i.tutes the chief difference between animal and vegetable matter, renders the composition of the former more complicated, and consequently more favourable to decomposition. The use of animal substances is chiefly to give the first impulse to the fermentation of the vegetable ingredients that enter into the composition of manures. The manure of a farm-yard is of that description; but there is scarcely any substance susceptible of undergoing the putrid fermentation that will not make good manure. The heat produced by the fermentation of manure is another circ.u.mstance which is extremely favourable to vegetation; yet this heat would be too great if the manure was laid on the ground during the height of fermentation; it is used in this state only for hot-beds, to produce melons, cuc.u.mbers, and such vegetables as require a very high temperature.

CAROLINE.

A difficulty has just occurred to me which I do not know how to remove.

Since all organised bodies are, in the common course of nature, ultimately reduced to their elementary state, they must necessarily in that state enrich the soil, and afford food for vegetation. How is it, then, that agriculture, which cannot increase the quant.i.ty of those elements that are required to manure the earth, can increase its produce so wonderfully as is found to be the case in all cultivated countries?

MRS. B.

It is by suffering none of these decaying bodies to be dissipated, but in applying them duly to the soil. It is by a judicious preparation of the soil, which consists in fitting it either for the general purposes of vegetation, or for that of the particular seed which is to be sown.

Thus, if the soil be too wet, it may be drained; if too loose and sandy, it may be rendered more consistent and retentive of water by the addition of clay or loam; it may be enriched by chalk, or any kind of calcareous earth. On soils thus improved, manures will act with double efficacy, and if attention be paid to spread them on the ground at a proper season of the year, to mix them with the soil so that they may be generally diffused through it, to destroy the weeds which might appropriate these nutritive principles to their own use, to remove the stones which would impede the growth of the plant, &c. we may obtain a produce an hundred fold more abundant than the earth would spontaneously supply.

EMILY.

We have a very striking instance of this in the scanty produce of uncultivated commons, compared to the rich crops of meadows which are occasionally manured.

CAROLINE.

But, Mrs. B., though experience daily proves the advantage of cultivation, there is still a difficulty which I cannot get over.

A certain quant.i.ty of elementary principles exist in nature, which it is not in the power of man either to augment or diminish. Of these principles you have taught us that both the animal and vegetable creation are composed. Now the more of them is taken up by the vegetable kingdom, the less, it would seem, will remain for animals; and, therefore, the more populous the earth becomes, the less it will produce.

MRS. B.

Your reasoning is very plausible; but experience every where contradicts the inference you would draw from it; for we find that the animal and vegetable kingdoms, instead of thriving, as you would suppose, at each other's expense, always increase and multiply together. For you should recollect that animals can derive the elements of which they are formed only through the medium of vegetables. And you must allow that your conclusion would be valid only if every particle of the several principles that could possibly be spared from other purposes were employed in the animal and vegetable creations. Now we have reason to believe that a much greater proportion of these principles than is required for such purposes remains either in an elementary state, or engaged in a less useful mode of combination in the mineral kingdom.

Possessed of such immense resources as the atmosphere and the waters afford us, for oxygen, hydrogen, and carbon, so far from being in danger of working up all our simple materials, we cannot suppose that we shall ever bring agriculture to such a degree of perfection as to require the whole of what these resources could supply.

Nature, however, in thus furnishing us with an inexhaustible stock of raw materials, leaves it in some measure to the ingenuity of man to appropriate them to its own purposes. But, like a kind parent, she stimulates him to exertion, by setting the example and pointing out the way. For it is on the operations of nature that all the improvements of art are founded. The art of agriculture consists, therefore, in discovering the readiest method of obtaining the several principles, either from their grand sources, air and water, or from the decomposition of organised bodies; and in appropriating them in the best manner to the purposes of vegetation.

EMILY.

But, among the sources of nutritive principles, I am surprised that you do not mention the earth itself, as it contains abundance of coals, which are chiefly composed of carbon.

MRS. B.

Though coals abound in carbon, they cannot, on account of their hardness and impermeable texture, be immediately subservient to the purposes of vegetation.

EMILY.

No; but by their combustion carbonic acid is produced; and this entering into various combinations on the surface of the earth, may, perhaps, a.s.sist in promoting vegetation.

MRS. B.

Probably it may in some degree; but at any rate the quant.i.ty of nourishment which vegetables may derive from that source can be but very trifling, and must entirely depend on local circ.u.mstances.

CAROLINE.

Perhaps the smoky atmosphere of London is the cause of vegetation being so forward and so rich in its vicinity?

MRS. B.

I rather believe that this circ.u.mstance proceeds from the very ample supply of manure, a.s.sisted, perhaps, by the warmth and shelter which the town affords. Far from attributing any good to the smoky atmosphere of London, I confess I like to antic.i.p.ate the time when we shall have made such progress in the art of managing combustion, that every particle of carbon will be consumed, and the smoke destroyed at the moment of its production. We may then expect to have the satisfaction of seeing the atmosphere of London as clear as that of the country. --But to return to our subject: I hope that you are now convinced that we shall not easily experience a deficiency of nutritive elements to fertilise the earth, and that, provided we are but industrious in applying them to the best advantage by improving the art of agriculture, no limits can be a.s.signed to the fruits that we may expect to reap from our labours.

CAROLINE.

Yes; I am perfectly satisfied in that respect, and I can a.s.sure you that I feel already much more interested in the progress and improvement of agriculture.

EMILY.

I have frequently thought that the culture of the land was not considered as a concern of sufficient importance. Manufactures always take the lead; and health and innocence are frequently sacrificed to the prospect of a more profitable employment. It has often grieved me to see the poor manufacturers crowded together in close rooms, and confined for the whole day to the most uniform and sedentary employment, instead of being engaged in that innocent and salutary kind of labour, which Nature seems to have a.s.signed to man for the immediate acquirement of comfort, and for the preservation of his existence. I am sure that you agree with me in thinking so, Mrs. B.?

MRS. B.

I am entirely of your opinion, my dear, in regard to the importance of agriculture; but as the conveniences of life, which we are all enjoying, are not derived merely from the soil, I am far from wishing to depreciate manufactures. Besides, as the labour of one man is sufficient to produce food for several, those whose industry is not required in tillage must do something in return for the food that is provided for them. They exchange, consequently, the accommodations for the necessaries of life. Thus the carpenter and the weaver lodge and clothe the peasant, who supplies them with their daily bread. The greater stock of provisions, therefore, which the husbandman produces, the greater is the quant.i.ty of accommodation which the artificer prepares. Such are the happy effects which naturally result from civilised society. It would be wiser, therefore, to endeavour to improve the situation of those who are engaged in manufactures, than to indulge in vain declamations on the hardships to which they are too frequently exposed.

But we must not yet take our leave of the subject of agriculture; we have prepared the soil, it remains for us now to sow the seed. In this operation we must be careful not to bury it too deep in the ground, as the access of air is absolutely necessary to its germination; the earth must, therefore, lie loose and light over it, in order that the air may penetrate. Hence the use of ploughing and digging, harrowing and raking, &c. A certain degree of heat and moisture, such as usually takes place in the spring, is likewise necessary.

CAROLINE.

One would imagine you were going to describe the decomposition of an old plant, rather than the formation of a new one; for you have enumerated all the requisites of fermentation.

MRS. B.

Do you forget, my dear, that the young plant derives its existence from the destruction of the seed, and that it is actually by the saccharine fermentation that the latter is decomposed?