CHAPTER VIII.
Of the Improvement of the Soil—Mechanical and Chemical Methods—Draining—Subsoiling—Ploughing, and Mixing of Soils—Use of Lime, Marl, and Shell-sand—Manures —Vegetable, Animal, and Mineral Manures.
Of the Improvement of the Soil—Mechanical and Chemical Methods—Draining—Subsoiling—Ploughing, and Mixing of Soils—Use of Lime, Marl, and Shell-sand—Manures —Vegetable, Animal, and Mineral Manures.
The soil is possessed of certain existing and obvious qualities, and of certain other dormant capabilities; how are these qualities to be improved,—these dormant capabilities to be awakened?
There are two distinct methods by which these ends may be, in some measure, attained,—by the use ofmechanical, and by the application ofchemical, means. Mechanical operations produce changeschieflyin the physical properties of the soil,—chemical means alter its elementary constitution. Ploughing, draining, mixing, &c. belong to the former class of operations; manuring and irrigation belong to the latter. It will be proper to consider these methods separately.
1.Draining.—The first step to be taken, in order to increase the fertility of nearly all the improveable lands of Great Britain, is to drain them. So long as they remain wet, they will continue to be cold. The heat of the sun’s rays, which is intended by nature to warm the soil, will be expended in evaporating the water from its surface; and thus the plants will never receive that genial warmth about their roots which so much favours their rapid growth. Where too much water is present in the soil also, that food of the plant which the soil supplies is so much diluted, that either a much greater quantity of fluid must be taken in by the roots,—much more work done,—or the plant will be scantily nourished. The presence of so much water in the stem and leaf keeps downtheirtemperature likewise, when the sunshine appears; an increased evaporation takes place from their surfaces, a lower natural heat, in consequence, prevails in the interior of the plant, and the chemical changes on which its growth depends proceed with less rapidity.
By the removal of the water, the physical properties of the soil also are in a remarkable degree improved. Dry pipe-clay can be easily reduced to a fine powder, but it naturally, and of its own accord, runs together when water is poured upon it. So it is with clays in the field. The soil expands, becomes close and adhesive, and excludes the air from the roots of the growing plant,—the access of which air appears to be almost an essential element in the healthy growth of the most important vegetable productions.
Open an outlet for the water below, and as it trickles away, the air from above will follow it and take its place among the pores of the soil, carrying to every root the salutary influences it is appointed to bear with it wherever it penetrates. When freed from water also, the stiff soil becomes more mellow; and when once stirred up to a considerable depth, more universally porous,—so that air can make its way everywhere, and the roots can find their easy way in every direction. The presence of vegetable matter,—whether existing naturally in a soil thus physically altered, or artificially added to it,—becomes of double value. When drenched with water, this vegetable matter either decomposes very slowly, or produces acid compounds more or less unwholesome to the plant, and even exerts injurious chemicalreactions upon the earthy and saline constituents of the soil. In the presence of air, on the contrary, this vegetable matter decomposes rapidly, produces carbonic acid in large quantity, as well as other compounds fit for food, and even renders the inorganic constituents of the soil more fitted to enter the roots, and thus to supply more rapidly what the several parts of the plant require.
Nor is it only stiff and clayey soils to which draining can with advantage be applied. It will be obvious to every one, that when springs rise to the surface in sandy soils, a drain must be made to carry off the water,—it will also readily occur, that where a sandy soil rests upon a hard or clayey bottom, drains may also be necessary; but it is not unfrequently supposed, that when the subsoil is sand or gravel, that drains can only in special cases be necessary.
Every one, however, is familiar with the fact, that when water is applied to the bottom of a flower-pot full of soil, it will gradually find its way to the surface, however light the soil may be. So it is in sandy soils or subsoils in the open field. If water abound at the depth of a few feet, or if it so abound at certain seasons of the year,thatwater will rise to the surface; and as the sun’s heat driesit off by evaporation, more water will follow to supply its place. This attraction from beneath will always go on when the air is dry and warm, and thus a double evil will ensue—the soil will be kept moist and cold, and instead of a constant circulation of air downwards, there will be a constant current of water upwards. Thus will the roots, the under soil, and the organic matter it contains, be all deprived of the benefits which the access of the air is fitted to confer. The remedy for these evils is to be found in an efficient system of drainage.
On this subject I shall add one important practical remark, which will readily suggest itself to the geologist who has studied the action of air and water on the various clay beds that occur here and there as members of the series of stratified rocks.There are no clays which do not gradually soften under the united influence of air and of running water. It is false economy, therefore, to lay down tiles without soles—however hard and stiff the clay subsoil may appear to be. In the course of ten or fifteen years the stiffest clays will soften, so as to allow the tile to sink; and many very much sooner. The passage for the water is thus gradually narrowed; and when the tile has sunk a couple of inches, the whole must be taken up. Thousands of milesof drains have been thus laid down, both in the low country of Scotland and in the southern counties of England, which have now become nearly useless; and yet the system still goes on. It would appear even as if the farmers and proprietors of each district—unwilling to believe in or to be benefitted by the experience of others—were determined to prove the matter in their own case also, before they will consent to adopt that surer system which, though demanding a slightly greater outlay at first, will return upon the drainer with no after-calls for either time or capital. If my reader live in a district where this practice is now exploded, and if he be inclined to doubt if other counties be farther behind the advance of knowledge than his own, I would invite him to spend a week in crossing the county of Durham, where he may find opportunities not only of satisfying his own doubts, but of scattering here and there a few words of useful advice among the more intelligent of our practical farmers.
2.Subsoiling.—The subsoil plough is an auxiliary to the drain. Though there are few subsoils through which the water will not at length make its way, yet there are some so stiff either naturally or from long consolidation, that the good effect of a well-arranged lineof drains is lessened by the slowness with which they allow the superfluous rains to pass through them. In such cases, the use of the subsoil plough is most advantageous in loosening the under layers of clay, and allowing the water to find a ready escape downwards and to either side until it reach the drains.
It is well known that if a piece of stiff clay be cut into the shape of a brick, and then allowed to dry, it will contract and harden—it will form an air-dried brick, almost impervious to any kind of gas—wet it again, it will swell and become still more impervious. Cut upwhile wet, it will only be divided into so many pieces, each of which will harden when dry, or the whole of which will again attach themselves and stick together if exposed to pressure. But tear it asunderwhen dry, and it will fall into many pieces, will more or less crumble, and will readily admit the air into its inner parts. So it is with a clay subsoil.
After the land is provided with drains, the subsoil being very retentive, the subsoil plough is used to open it up—to let out the water and to let in the air. If this is not done, the stiff under-clay will contract and bake as it dries, but it will neither sufficiently admit the air nor open a free passage for the roots. But let this operation be performed when the clay is still too wet, a good effectwill follow, in the first instance; but after a while, the cut clay will again cohere, and the former will pronounce subsoiling to be a useless expenseon his land. Defer the use of the subsoil plough till the clay is dry—it will thentearandbreakinstead ofcutting, and its openness will remain. Once give the air free access, and it, after a time, so modifies the drained clay, that it no longer has an equal tendency to cohere.
Mr. Smith of Deanston very judiciously recommends that the subsoil plough should never be used till at least a year after the land has been thoroughly drained. This in many cases will be a sufficient safeguard—will allow a sufficient time for the clay to dry; in other cases two years may not be too much. But this precaution has by some been neglected, and subsoiling being with them a failure, they have sought, in some supposed chemical or other qualityof their soil, for the cause of a want of success which is to be found in their own neglect of a most necessary precaution. Let not the practical man be toohastyin desiring to attain those benefits which attend the adoption of improved modes of culture; let him give every method a fair trial;and above all, let him make his trial in theway and with the precautions recommended by the author of the method, before he pronounce its condemnation.
3.Deep-ploughing, like subsoiling, aids the effect of the drains, and so far, and where it goes nearly as deep, more completely effects the same object. But independent of this, it has other uses and merits, and where it has been successfully applied, has improved the land by the operation of other causes.
Subsoiling only lets out the water, and allows access to the air and a free passage to the roots. Deep-ploughing, in addition to these, brings new earth to the surface, forms thus a deeper soil, and more or less alters both its physical qualities and its chemical constitution.
If the plough be made to bring up two inches of clay or sand, it will stiffen or loosen the soil, as the case may be, or it may affect its colour or density. It is clear and simple enough, therefore, that by deep-ploughing the physical properties of the soil may be altered.
But there are certain substances contained in every soil, whether in pasture or under the plough, which gradually make their way down towards the subsoil. They sink till they reach at last that pointbeyond which the plough does not usually penetrate. Every farmer knows that lime thus sinks. In peat-soils top-dressed with clay, the clay thus sinks. In sandy soils also which have been clayed, the clay sinks; and in all these cases, I believe, the sinking takes place more rapidly when the land is laid down to grass. Where soils are marled, the marl sinks; and the rains, in like manner, gradually wash out that which gives their fertilizing virtue to the under chalk-soils (see page 88), and render necessary a new application from beneath, to renovate its productive powers.
If this be the case with earthy substances such as those now mentioned, which are insoluble in water, it will be readily believed that those saline ingredients of the soil which are readily soluble will be still sooner washed out of the upper and conveyed to the under soil. Thus the subsoil may gradually become rich in those substances of which the surface-soil has been robbed. Bring up a portion of this subsoil by deep-ploughing, and you restore to the land a portion of what it has lost—substances, perhaps, which may render it much more fruitful than before. Such is an outline of the theory of deep-ploughing, and it is entirely unexceptionable.
But suppose the land to have originally contained something noxious to vegetation, which in process of time has been washed down into the subsoil, then to bring this again to the surface would be materially to injure the land. This also is true, and a sound discretion must no doubt be employed, in judging when and where such evil effects are likely to follow.
Such cases, however, are more rare than many suppose. There are few subsoils which a full and fair exposure to a winter’s frost will not in a great degree deprive of all their noxious qualities, and render fit to ameliorate the general surface of the poorer lands. If the reader doubt this fact, let him visit Yester, and give a calm consideration to the efforts produced by the use of deep-ploughing on the home-farm of the Marquis of Tweeddale.
In many cases the farmer fears, as he does in the county of Durham, to bring up a single inch of the yellow clay that lies beneath his soil. In the first inch lodges, among other substances, the iron worn from his plough, which in some soils, and after a lapse of years, amounts to a considerable quantity. Till it is exposed to the air, this iron is hurtful to vegetation, and one of the benefits of a winter’s exposure of such subsoils to the air, is the effect produced upon the iron it contains.
It is the want of drainage, however, and of the free access of air, that most frequently renders subsoils for a time injurious to vegetation. Let the lands be well drained—let the subsoils be washed for a few years by the rain-water passing through them,—and there are few of those which are clayey in their nature that may not ultimately be brought to the surface, not only with safety, but with advantage to the soil.
4.Ploughing.—Other benefits, again, attend upon the ordinary ploughings, hoeings, and workings of the land. Its parts are more minutely divided—the air gets access to every particle—it is rendered lighter, more open, more permeable to the roots. The vegetable matter it contains decomposes more rapidly by a constant turning of the soil, so that wherever the fibres of the roots penetrate, they find organic food provided for them, and an abundant supply of the oxygen of the atmosphere to aid in preparing it. The production of ammonia and of nitric acid also (see pages 33 to 36), and the absorption of one or both from the air, take place to a greater extent, the finer the soil is pulverised, and the more it has been exposed to the action of the atmosphere. The general advantage, indeed, to bederived from the constant working of the soil, may be inferred from the fact, that Tull reaped twelve successive crops of wheat from the same land by the repeated use of the plough and the horse-hoe. There are few soils so stubborn as not to shew themselves grateful in proportion to the amount of this kind of labour that may be bestowed upon them.
5.Mixing.—It has been shewn (page 114), that the physical properties of the soil have an important influence upon its average fertility. The admixture of pure sand with clay soils produces an alteration which is often beneficial, and which is wholly physical. The sand merely opens the pores of the clay, and makes it more permeable to the air.
The admixture of clay with sandy or peaty soils, however, produces both a physical and a chemical alteration. The clay not only consolidates and gives body to the sand or peat, but it also mixes with them certain earthy and saline substances useful or necessary to the plant, which neither the sand nor peat might originally contain in sufficient abundance. It thus alters its chemical constitution, and fits it for nourishing new races of plants.
Such is the case also with admixtures of marl, of shell-sand, and of lime. They slightly consolidate the sands and open the clays, and thusimprove the mechanical texture of both kinds of soil, but their main operation is chemical; and the almost universal benefit they produce depends upon the new chemical element they introduce into the constitution of the soil.
It is a matter of almost universal remark, that in our climate soils are fertile—clayey or loamy soils, that is—only when they contain an appreciable quantity of lime. In whatever way it acts, therefore, the mixing of lime in any of the forms above mentioned, with a soil in which little or no lime exists, is one of the surest practical methods of bringing it nearer in composition to those soils from which the largest returns of agriculture produce are usually obtained. Some of the chemical effects of the lime upon the soil will be explained in a subsequent section. (See page 195.)
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 chemicaloperation, 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. Byhighfarming 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 toserve—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 amanureis 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 ofvegetable, ofanimal, and ofmineralorigin.
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 theirduty 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 thekindof plants and with thepartsof those plants of which they are chiefly made up. This depends upon the remarkable difference which exists in thequantityandkindof 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.[17]
There are three states in which vegetable matter is collected by thehusbandman for the purpose of being applied to the land—thegreenstate; thedrystate; and that state of imperfect decay in which it formspeat.
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 intosuch 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 oflucernewas ploughed in by the ancient Romans—as it still is by the modern Italians. In Tuscany, thewhite lupinis ploughed in, in preference—in Germany,borage. In French Flanders, two crops ofcloverare cut, and the third is ploughed in. In Sussex,turnipseed 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 donewhen theflower 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 tothemselves, 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 knowsthat 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 alldryvegetable 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 beinducedor 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 addedsolelyfor 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 oneperiod 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 differentkinds 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 Dustconsists 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 Powderpossesses 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 inpractical 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 itsimmediate, 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 arich 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 withammoniacal liquorwould 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, afterit 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.
There are two principles on which the relative value of different vegetable substances, as manures, may be stated to depend—first, on the relative quantity and kind ofinorganic matterthey contain; andsecond, on the relative proportions ofnitrogenpresent in each.
1. Valued according to thequantityof inorganic matter they contain—the worth of the several kinds of straw and hay would be represented by the following numbers:—
that is, aton weightof each of these substances, when made into manure—provided nothing is washed out by the rains—will return to the soil the above quantities of inorganic matterin pounds. Generally, perhaps, these numbers will give the reader an idea of the relativepermanenteffect of these different kinds of vegetable matter when laid upon the soil. But, by a reference to the facts stated inpp. 58 to 64, in regard to thequalityof the inorganic matter contained in plants, he will satisfy himself, that the effect of these manures on particular crops is not to be judged of solely by the absolute quantity of earthy and saline matter they contain;—that which the turnip-top, for example, or the bean-stalk, returns to the soil, may not be exactly what will best promote the growth of wheat.
2. On the other hand, if the fertilizing value of vegetable substances is to be calculated by the relative quantities of nitrogen they severally contain, we should place them in the following order:—the number opposite to each substance representing that weight of it inpounds, which would produce the same effect as 100 pounds of farm-yard manure, consisting of the mixed droppings and litter of cattle.
This table again presents the same substances in a somewhat different order of value; shewing, for example, not only that such substances as rape dust and soot should produce a much more remarkable effect upon vegetation, than the same weight even of farm-yard manure, but also that certain dry vegetables, such as chaff and pea straw, will yield, when not unduly fermented, a more enriching manure than barley, oat, orwheat straw. It agrees, also, with the known effect of green manuring upon the land, since 80 pounds of meadow-grass ploughed in, will be equal in virtue to 100 of farm-yard manure.
Some writers ascribe theentireaction of these measures to the nitrogen they contain. This, however, is taking a one-side view of their real natural operation. The nitrogen, during their decay, is liberated chiefly in the form of ammonia—an evanescent substance, producing an immediate effect in hastening or carrying further forward the growth of the plant, but not remaining permanently in the soil. The reader, therefore, will form an opinion consistent alike with theory and with practice, if he conclude—
1. That theimmediateeffect of a vegetable manure, in hastening the growth of plants, is dependent, in a great degree, upon the quantity of nitrogen it contains and gives off during its decay in the soil.
2. That thepermanenteffect and value of manures is to be estimated chiefly by the quantity and quality of the inorganic matter they contain—of the ash they leave when burned.
The effect of the nitrogen may be nearly expended in a single season—that of the earthy and saline matter may not be exhausted for several years.
Nor is the carbon of vegetable substances without its important uses to vegetation. From the statements contained in the earlier chapters of the present work, it may be inferred that, however much influence we may allow to the nitrogen and to the earthy matter of plants in aiding the growth of future races—the soundest view of these important natural operations is that which considers each element present in decaying plants to be capable of ministering food to such as are still alive,—though we may not be able as yet, either to estimate the precise importance of each element to any particular kind of crop, or exactly to adjust their relative quantities in our manures, so as to promote the growth of such a crop in the greatest possible degree.