5.--_Chemical Changes that occur in the formation of Peat._ When a plant perishes, its conversion into humus usually begins at once. When exposed to the atmosphere, the oxygen of the air attacks it, uniting with its carbon producing carbonic acid gas, and with its hydrogen generating water. This action goes on, though slowly, even at some depth under water, because the latter dissolves oxygen from the air in small quant.i.ty,[2] and constantly resupplies itself as rapidly as the gas is consumed.

Whether exposed to the air or not, the organic matter suffers internal decomposition, and portions of its elements a.s.sume the gaseous or liquid form. We have seen that ripe peat is 10 to 12 _per cent._ richer in carbon and equally poorer in oxygen, than the vegetable matters from which it originates. Organic matters, in pa.s.sing into peat, lose carbon and nitrogen; but they lose oxygen more rapidly than the other two elements, and hence the latter become relatively more abundant. The loss of hydrogen is such that its proportion to the other elements is but little altered.

The bodies that separate from the decomposing vegetable matter are carbonic acid gas, carburetted hydrogen (marsh gas), nitrogen gas, and water.

Carbonic acid is the most abundant gaseous product of the peaty decomposition. Since it contains nearly 73 _per cent._ of oxygen and but 27 _per cent._ of carbon, it is obvious that by its escape the proportion of carbon in the residual ma.s.s is increased. In the formation of water from the decaying matters, 1 part of hydrogen carries off 8 parts of oxygen, and this change increases the proportion of carbon and of hydrogen. Marsh gas consists of one part of hydrogen to three of carbon, but it is evolved in comparatively small quant.i.ty, and hence has no effect in diminishing the _per cent._ of carbon.

The gas that bubbles up through the water of a peat-bog, especially if the decomposing matters at the bottom be stirred, consists largely of marsh gas and nitrogen, often with but a small proportion of carbonic acid. Thus Websky found in gas from a peat-bed

Carbonic acid 2.97 Marsh gas 43.36 Nitrogen 53.67 ------ 100.00

Carbonic acid, however, dissolves to a considerable extent in water, and is furthermore absorbed by the living vegetation, which is not true of marsh gas and nitrogen; hence the latter escape while the former does not. Nitrogen escapes in the uncombined state, as it always (or usually) does in the decay of vegetable and animal matters that contain it. Its loss is, in general, slower than that of the other elements, and it sometimes acc.u.mulates in the peat in considerable quant.i.ty. A small portion of nitrogen unites with hydrogen, forming ammonia, which remains combined with the humic and other acids.

PART II.

ON THE AGRICULTURAL USES OF PEAT AND SWAMP MUCK.

After the foregoing account of the composition of peat, we may proceed to notice:

1.--_The characters that adapt it for agricultural uses._

These characters are conveniently discussed under two heads, viz.:

Those which render it useful in improving the texture and physical characters of the soil, and indirectly contribute to the nourishment of crops,--characters which const.i.tute it an _amendment_ to the soil (_A_); and

Those which make it a direct _fertilizer_ (_B_).

A.--Considered as an amendment, the value of peat depends upon

_Its remarkable power of absorbing and retaining water, both as a liquid and as a vapor_ (I):

_Its power of absorbing ammonia_ (II):

_Its effect in promoting the disintegration and solution of mineral ingredients, that is the stony matters of the soil_ (III): _and_

_Its influence on the temperature of the soil_ (IV).

The agricultural importance of these properties of peat is best ill.u.s.trated by considering the faults of a certain cla.s.s of soils.

Throughout the State of Connecticut, for instance, are found abundant examples of light, leachy, hungry soils, which consist of coa.r.s.e sand or fine gravel; are surface-dry in a few hours after the heaviest rains, and in the summer drouths, are as dry as an ash-heap to a depth of several or many feet.

These soils are easy to work, are ready for the plow early in the spring, and if well manured give fair crops in wet seasons. In a dry summer, however, they yield poorly, or fail of crops entirely; and, at the best, they require constant and very heavy manuring to keep them in heart.

Crops fail on these soils from two causes, viz.; _want of moisture_ and _want of food_. Cultivated plants demand as an indispensable condition of their growth and perfection, to be supplied with water in certain quant.i.ties, which differ with different crops. Buckwheat will flourish best on dry soils, while cranberries and rice grow in swamps.

Our ordinary cereal, root, forage and garden crops require a medium degree of moisture, and with us it is in all cases desirable that the soil be equally protected from excess of water and from drouth. Soils must be thus situated either naturally, or as the result of improvement, before any steadily good results can be obtained in their cultivation.

The remedy for excess of water in too heavy soils, is thorough drainage.

It is expensive, but effectual. It makes the earth more porous, opens and maintains channels, through which the surplus water speedily runs off, and permits the roots of crops to go down to a considerable depth.

What, let us consider, is the means of obviating the defects of soils that are naturally too porous, from which the water runs off too readily, and whose crops "burn up" in dry seasons?

In wet summers, these light soils, as we have remarked, are quite productive if well manured. It is then plain that if we could add anything to them which would retain the moisture of dews and rains in spite of the summer-heats, our crops would be uniformly fair, provided the supply of manure were kept up.

But why is it that light soils, need more manure than loamy or heavy lands? We answer--because, in the first place the rains which quickly descend through the open soil, wash down out of the reach of vegetation the soluble fertilizing matters, especially the nitrates, for which the soil has no retentive power; and in the second place, from the porosity of the soil, the air has too great access, so that the vegetable and animal matters of manures decay too rapidly, their volatile portions, ammonia and carbonic acid, escape into the atmosphere, and are in measure lost to the crops. From these combined causes we find that a heavy dressing of well-rotted stable manure, almost if not entirely, disappears from such soils in one season, so that another year the field requires a renewed application; while on loamy soils the same amount of manure would have lasted several years, and produced each year a better effect.

We want then to _amend_ light soils by incorporating with them something that prevents the rains from leaching through them too rapidly, and also that renders them less open to the air, or absorbs and retains for the use of crops the volatile products of the decay of manures.

For these purposes, vegetable matter of some sort is the best and almost the only amendment that can be economically employed. In many cases a good peat or muck is the best form of this material, that lies at the farmer's command.

I.--_Its absorbent power for liquid water_ is well known to every farmer who has thrown it up in a pile to season for use. It holds the water like a sponge, and, according to its greater or less porosity, will retain from 50 to 100 or more _per cent._ of its weight of liquid, without dripping. Nor can this water escape from it rapidly. It dries almost as slowly as clay, and a heap of it that has been exposed to sun and wind for a whole summer, though it has of course lost much water, is still distinctly wet to the eye and the feel a little below the surface.

_Its absorbent power for vapor of water_ is so great that more than once it has happened in Germany, that barns or close sheds filled with partially dried peat, such as is used for fuel, have been burst by the swelling of the peat in damp weather, occasioned by the absorption of moisture from the air. This power is further shown by the fact that when peat has been kept all summer long in a warm room, thinly spread out to the air, and has become like dry snuff to the feel, it still contains from 8 to 30 _per cent._ (average 15 _per cent._) of water. To dry a peat thoroughly, it requires to be exposed for some time to the temperature of boiling water. It is thus plain, as experience has repeatedly demonstrated, that no ordinary summer heats can dry up a soil which has had a good dressing of this material, for on the one hand, it soaks up and holds the rains that fall upon it, and on the other, it absorbs the vapor of water out of the atmosphere whenever it is moist, as at night and in cloudy weather.

When peat has once become _air-dry_, it no longer manifests this avidity for water. In drying it shrinks, loses its porosity and requires long soaking to saturate it again. In the soil, however, it rarely becomes air-dry, unless indeed, this may happen during long drouth with a peaty soil, such as results from the draining of a bog.

II.--_Absorbent power for ammonia._

All soils that deserve to be called fertile, have the property of absorbing and retaining ammonia and the volatile matters which escape from fermenting manures, but light and coa.r.s.e soils may be deficient in this power. Here again in respect to its absorptive power for ammonia, peat comes to our aid.

It is easy to show by direct experiment that peat absorbs and combines with ammonia.

In 1858 I took a weighed quant.i.ty of air-dry peat from the New Haven Beaver Pond, (a specimen furnished me by Chauncey Goodyear, Esq.,) and poured upon it a known quant.i.ty of dilute solution of ammonia, and agitated the two together occasionally during 48 hours. I then distilled off at a boiling heat the unabsorbed ammonia and determined its quant.i.ty. This amount subtracted from that of the ammonia originally employed, gave the quant.i.ty of ammonia absorbed and retained by the peat at the temperature of boiling water.

The peat retained ammonia to the amount of 0.95 of _one per cent._

I made another trial at the same time with carbonate of ammonia, adding excess of solution of this salt to a quant.i.ty of peat, and exposing it to the heat of boiling water, until no smell of ammonia was perceptible.

The entire nitrogen in the peat was then determined, and it was found that the dry peat which originally contained nitrogen equivalent to 2.4 _per cent._ of ammonia, now yielded an amount corresponding to 3.7 _per cent._ The quant.i.ty of ammonia absorbed and retained at a temperature of 212, was thus 1.3 _per cent._

This last experiment most nearly represents the true power of absorption; because, in fermenting manures, ammonia mostly occurs in the form of carbonate, and this is more largely retained than free ammonia, on account of its power of decomposing the humate of lime, forming with it carbonate of lime and humate of ammonia.

The absorbent power of peat is well shown by the a.n.a.lyses of three specimens, sent me in 1858, by Edwin Hoyt, Esq., of New Canaan, Conn.

The first of these was the swamp muck he employed. It contained in the air-dry state nitrogen equivalent to 0.58 _per cent._ of ammonia. The second sample was the same muck that had lain under the flooring of the horse stables, and had been, in this way, partially saturated with urine. It contained nitrogen equivalent to 1.15 _per cent._ of ammonia.

The third sample was, finally, the same muck composted with white-fish.

It contained nitrogen corresponding to 1.31 _per cent._ of ammonia.[3]

The quant.i.ties of ammonia thus absorbed, both in the laboratory and field experiments are small--from 0.7 to 1.3 _per cent._ The absorption is without doubt chiefly due to the organic matter of the peats, and in all the specimens on which these trials were made, the proportion of inorganic matter is large. The results therefore become a better expression of the power of _peat_, in general, to absorb ammonia, if we reckon them on the organic matter alone. Calculated in this way, the organic matter of the Beaver Pond peat (which const.i.tutes but 68 _per cent._ of the dry peat) absorbs 1.4 _per cent._ of free ammonia, and 1.9 _per cent._ of ammonia out of the carbonate of ammonia.

Similar experiments, by Anderson, on a Scotch peat, showed it to possess, when wet, an absorptive power of 2 _per cent._, and, after drying in the air, it still retained 1.5 _per cent._--[Trans. Highland and Ag'l Soc'y.]

When we consider how small an ingredient of most manures nitrogen is, viz.: from one-half to three-quarters of one _per cent._ in case of stable manure, and how little of it, in the shape of guano for instance, is usually applied to crops--not more than 40 to 60 lbs. to the acre, (the usual dressings with guano are from 250 to 400 lbs. per acre, and nitrogen averages but 15 _per cent._ of the guano), we at once perceive that an absorptive power of one or even one-half _per cent._ is greatly more than adequate for every agricultural purpose.

III.--_Peat promotes the disintegration of the soil._

The soil is a storehouse of food for crops; the stores it contains are, however, only partly available for immediate use. In fact, by far the larger share is locked up, as it were, in insoluble combinations, and only by a slow and gradual change can it become accessible to the plant.

This change is largely brought about by the united action of _water_ and _carbonic acid gas_. Nearly all the rocks and minerals out of which fertile soils are formed,--which therefore contain those inorganic matters that are essential to vegetable growth,--though very slowly acted on by pure water, are decomposed and dissolved to a much greater extent by water, charged with carbonic acid gas.

It is by these solvents that the formation of soil from broken rocks is to a great extent due. Clay is invariably a result of their direct action upon rocks. The efficiency of the soil depends greatly upon their chemical influence.