Section Ii.—of the Chemical Method of Improving the Soil by the Use of

MANURES.

None of the above methods of improving the soil are mechanical only—they all involve some chemical alterations also, which are readily to be explained by a knowledge of elementary chemical principles. But the manuring of the land is more strictly a chemical operation, and may therefore with propriety be separated from those methods of improving its quality which involve at the same time important and expensive mechanical operations.

In commencing the tillage of a piece of land, the conscientious farmer may have three objects in view in regard to it.

1. He may wish to reclaim a waste, or to restore a neglected farm to an average condition of fertility.

2. Finding the land in this average state, his utmost ambition may be to keep it in its present condition; or,

3. By high farming he may wish to develope all its capabilities, and to increase its permanent productiveness in the greatest possible degree.

The man who aims at the last of these objects is not only the best tenant and the best citizen, but he is also his own best friend. The highest farming, skilfully and prudently conducted, is also the most remunerating.

But whichever of these three ends he aims at, he will be unable to attain it without a due knowledge of the various manures it may be in his power to apply to his land—what these manures are, or of what they consist—the general and special purposes they are each intended to serve—which are the most effective for this or that crop—how they are to be obtained in the greatest abundance, and at the least cost—how their strength may be economized,—and in what state and at what seasons they may be most beneficially applied to the land. Such are a few of the questions which the skilful farmer should be ready to ask himself, and should be able to answer.

By a manure is to be understood whatever is capable of feeding or of supplying food to the plant. And us plants require earthy and saline as well as vegetable food, gypsum and nitrate of soda are as properly called manures as farm-yard dung, bone-dust, or night-soil.

Manures naturally divide themselves into such as are of vegetable, of animal, and of mineral origin.

I. OF VEGETABLE MANURES.

There are two purposes which vegetable manure is generally supposed to serve when added to the soil. It loosens the land, opens its pores, and makes it lighter; and it also serves to supply organic food to the roots of the growing plant. It serves, however, a third purpose: it yields to the roots those saline and earthy matters which it is their duty to find in the soil, and which exist in decaying plants in a state more peculiarly fitted to enter readily into the circulating system of new races.

Decayed vegetable matters, therefore, are in reality mixed manures, and their value in enriching the land must vary considerably with the kind of plants and with the parts of those plants of which they are chiefly made up. This depends upon the remarkable difference which exists in the quantity and kind of inorganic matter present in different vegetable substances, as indicated by the ash they leave (see pages 52 to 62). Thus if 1000 lbs. of the saw-dust of the willow be fermented, and added to the soil, they will enrich it by the addition of only 4½ lb. of saline and earthy matter, while 1000 lbs. of the dry leaves of the same tree fermented, and laid on, will add 82 lbs. of inorganic matter. Thus, independent of the effect of the vegetable matter in each, the one will produce a very much greater effect upon the soil than the other.

It is owing to this large quantity of saline and other inorganic matter that fermented leaves form too strong a dressing for flower borders, and that gardeners therefore generally mix them up into a compost.

There are three states in which vegetable matter is collected by the husbandman for the purpose of being applied to the land—the green state; the dry state; and that state of imperfect decay in which it forms peat.

1. Green Manuring.—When grass is mown in the field, and laid in heaps, it speedily heats, ferments, and rots. But, if turned over frequently and dried into hay, it may be kept for a great length of time without undergoing any material alteration. The same is true of all other vegetable substances—they all rot more readily in the green state. The reason of this is, that the sap or juice of the green plant begins very soon to ferment in the interior of the stem and leaves, and speedily communicates the same condition to the moist fibre of the plant itself. When once it has been dried, the vegetable matter of the sap loses this easy tendency to decay, and thus admits of long preservation.

The same rapid decay of green vegetable matter takes place when it is buried in the soil. Thus the cleanings and scourings of the ditches and hedge-sides form a compost of mixed earth and fresh vegetable matter, which soon becomes capable of enriching the ground. When a green crop is ploughed into a field, the whole of its surface is converted into such a compost—the vegetable matter in a short time decays into a light, black mould, and enriches in a remarkable degree and fertilizes the soil.

Hence the practice of green manuring has been in use from very early periods. The second or third crop of lucerne was ploughed in by the ancient Romans—as it still is by the modern Italians. In Tuscany, the white lupin is ploughed in, in preference—in Germany, borage. In French Flanders, two crops of clover are cut, and the third is ploughed in. In Sussex, turnip seed has been sown at the end of harvest, and after two months again ploughed in, with great benefit to the land. Turnip leaves and potato tops decay more readily, and more perfectly, and are more enriching when buried in the green state. It is a prudent economy, therefore, where circumstances admit of it, to bury the potato tops on the spot from which the potatoes are raised. Since the time of the Romans, it has been the custom to bury the cuttings of the vine stocks at the roots of the vines themselves; and many vineyards flourish for a succession of years without any other manuring.

Buckwheat, winter tares, clover, and rape, are all occasionally sown for the purpose of being ploughed in. This should be done when the flower has just begun to open, and if possible at a season when the warmth of the air and the dryness of the soil are such as to facilitate decomposition.

That the soil should become richer in vegetable matter by this burial of a crop than it was before the seed of that crop was sown, and should also be otherwise benefitted, will be understood by recollecting (see page 42) that perhaps three-fourths of the whole organic matter we bury has been derived from the air—that by this process of ploughing in, the vegetable matter is more equally diffused through the whole soil than it could ever be by any merely mechanical means;—and that by the natural decay of this vegetable matter, ammonia and nitric acid are, to a greater extent (pages 33 and 34), produced in the soil, and its agricultural capabilities in consequence materially increased.

These considerations, while they explain the effect and illustrate the value of green manuring, will also satisfy the intelligent agriculturist that there are methods of improving his land without the aid either of town or of foreign manures—and that he overlooks an important natural means of wealth who neglects the green sods and crops of weeds that flourish by his hedgerows and ditches. Left to themselves, they ripen their seeds and sow them annually in his fields—collected in compost heaps they would materially add to his yearly crops of corn.

Sea-weeds.—Among green manures, the use of fresh sea-ware deserves especial mention, from the remarkably fertilizing properties it is known to possess, as well as from the great extent to which it is employed on all our coasts. The produce of the isle of Thanet in Kent is said to have been doubled or tripled by the use of this manure; the farms on the Lothian coasts are said to be let for 20s. or 30s. more rent when they have a right of way to the sea, where the weed is thrown on shore; and in the Western Isles the sea-ware, the shell-marl, and the peat-ash, are the three great natural fertilizers to which the agriculture of the district is indebted for the comparative prosperity to which it has in some of the islands already attained.

Sea-weeds decompose with great ease when collected in heaps or spread upon the land. During their decay, they yield not only organic food to the plant but saline matters also, to which much of their efficacy both on the grass and the corn crops is no doubt to be ascribed.

2. Manuring with dry Vegetable Matter.—Almost every one knows that the saw-dust of most common woods decays very slowly—so slowly, that it is rare to meet with a practical farmer who considers it worth the trouble of mixing with his composts. This property of slow decay is possessed in a certain degree by all dry vegetable matter. Heaps of dry straw alone, or even mixed with earth, will ferment with comparative difficulty and with great slowness. It is necessary, therefore, to mix it, as is usually done, with some substance that ferments more readily, and which will impart its own condition to the straw. Animal matters of any kind, such as the urine and droppings of cattle, are of this character; and it is by admixture with these that the straw which is trodden down in the farm-yard is made to undergo a more or less rapid fermentation.

The object of this fermentation is twofold—first, to reduce the particles of the straw to such a minute state of division, that they may admit of being diffused through the soil; and, second, that the dry vegetable matter may be so changed by exposure to the air, and other agencies, as to be fitted to yield both organic and inorganic food to the roots of the plants it is intended to nourish.

We have seen that this decomposition takes place very speedily, and of its own accord, when the vegetable matter is green, but that it can be induced or brought on in the case of dry straw by the agency of animal matter. The same means will cause the fermentation of any other vegetable substance which is in a minute state of division. Even saw-dust made into a compost heap with soil or sods, and watered regularly and copiously with the liquid manure of the farm-yards, may be thus converted into a fertilizing vegetable mould.

Differences of opinion have prevailed, and discussions have taken place, as to the relative efficacy of long and short—or of half fermented and of fully rotten dung. But if it be added solely for the purpose of yielding food to the plant, or of preparing food for it, the case is very simple. The more complete the state of fermentation—if not carried too far—the more immediate will be the agency of the manure; hence the propriety of the application of short dung to turnips and other plants it is desirable to bring rapidly forward; but if the manure be only half decayed, it will require time in the soil to complete the decomposition, so that its action will be more gradual and prolonged.

Though in the latter case the immediate action is not so perceptible, yet the ultimate benefit to the soil, and to the crops, may be even greater, supposing them to be such as require no special forcing at one period of the year. With a view to this slow amelioration, vegetable matter of any kind may be added with benefit, if in a sufficient state of division, to the soil. Even saw-dust applied largely to the land, has been found to improve it, though little at first, yet more during the second year after it was applied, still more during the third, and most of all in the fourth season after it was mixed with the soil. That any dry vegetable matter, therefore, does not produce an immediate effect, ought not to induce the practical farmer to despise the application to his land—either alone, or in the form of a compost—of every thing of the kind he can readily obtain. If his fields are not already very rich in vegetable matter, both he and they are likely to be ultimately benefitted by such additions to the soil.

Rape Dust.—It is from the straw of the corn-bearing plants, or from the stems and leaves of the grasses, that the largest portion of the strictly vegetable manures applied to the soil is generally obtained or prepared. But the seeds of all plants are much more enriching than the substance of their leaves and stems. These seeds, however, are in general too valuable for food to admit of their application as a manure. Still the refuse of some, as that of different kinds of rape-seed after the oil is expressed, and which is unpalatable to cattle, is applied with great benefit to the land. Drilled in with spring wheat, or scattered as a top-dressing in spring at the rate of 5 cwt. to an acre, it gives a largely increased and remunerating return. It is applied with equal success to the cultivation of potatoes, and generally it may be substituted for farm-yard manure at the rate of about 1 cwt. of rape dust for each ton of manure.

Malt Dust consists of the dried sprouts of barley, which, when the sprouted seed is dried in the process of malting, break off and form a coarse powder. This is found to be almost equal to rape dust in fertilizing power.

Charcoal Powder possesses the remarkable property of absorbing noxious vapours from the air and soil, and unpleasant impurities from water. It also sucks into its pores much oxygen from the air. Owing to these and other properties, it is a valuable substance for mixing with liquid manure, night-soil, farm-yard manure, ammoniacal liquor, or other rich applications to the soil. It is even capable by itself of yielding slow supplies of nourishment to living plants, and is said, in many cases, without any admixture, to have been used with advantage in practical agriculture. In moist charcoal the seeds of the gardener are found to sprout with remarkable quickness and certainty.

Soot, whether from the burning of wood or of coal, is of vegetable origin, and consists chiefly of a finely-divided charcoal, possessing the properties above mentioned. It contains, however, ammonia and certain other substances in small quantity, to which its well known, and especially its immediate, effects upon vegetation are in part to be ascribed.

3. The use of Peat.—In many parts of the world, and in none more abundantly, perhaps, than in Gt. Britain, is vegetable matter collected in the form of peat. This ought to supply an inexhaustible store of organic matter for the amelioration of the adjacent soils. We know that by draining off the sour and unwholesome water, and afterwards applying lime and clay, the surface of peat bogs may be gradually converted into rich corn-bearing lands. It must, therefore, be possible to convert peat itself by a similar process into a compost fitted to improve the condition of other soils.

The late Lord Meadowbank, who made many important experiments on this subject, found, that after being partially dried by exposure to the air, peat might be readily fermented, and brought into the state of a rich fertilizing compost by the same means which are adopted in the ordinary fermenting of straw. He mixed with it a portion of animal matter, which soon communicated its own fermenting quality to the surrounding peat, and brought it readily in to a proper heat. He found that one ton of hot fermenting manure, mixed in alternate layers with two of half dry peat, and covered by the same, was sufficient to ferment the whole; and subsequently that the vapours which rise from naturally fermenting farm-yard manure or animal matters, would alone produce the same effect upon peat, placed so as readily to receive and absorb them.

As ammonia is one of the compounds specially given off by putrifying animal substances, it is not unlikely that a watering with ammoniacal liquor would materially prepare the peat for undergoing fermentation. At all events it seems possible to prepare any quantity of valuable peat compost by mixing the peat with a still less quantity of fermented manure than was employed by Lord Meadowbank, provided the liquid manure of the farm-yard be collected in a cistern, and be thrown at intervals by means of a pump over the prepared heaps.

One important use also to which I think peat may be applied is, after it is partly dried, to build it into covered heaps, and half burn or char it till it become readily reducible into a fine powder. In this state it would be of great value as a mixture to preserve the virtues of liquid manures of all kinds, of night-soil, and of ammoniacal liquor.