FOOTNOTES:

Of what advantage are these differences to the farmer?Of what are plants composed?

Of what advantage are these differences to the farmer?

Of what are plants composed?

These differences are of great importance to the practical farmer, as by understanding what kind of plants use the most of one ingredient, and what kind requires another in large proportion, he can regulate his crops so as to prevent his soil from being exhausted more in one ingredient than in the others, and can also manure his land with reference to the crop which he intends to grow. The tables of analyses in the fifth section will point out these differences accurately.

FOOTNOTES:[J]This pectic acid gelatinizes food in the stomach, and thus renders it more digestible.[K]See Johnston's Elements, page 41.[L]Sifted through a fine cloth called a bolting cloth.

[J]This pectic acid gelatinizes food in the stomach, and thus renders it more digestible.

[K]See Johnston's Elements, page 41.

[L]Sifted through a fine cloth called a bolting cloth.

We have now learned as much about the plant as is required for our immediate uses, and we will carefully reconsider the various points with a view to fixing them permanently in the mind.

Plants are composed oforganicandinorganicmatter.

What is organic matter? Inorganic?Of what does organic matter consist? Inorganic?How do plants obtain their organic food?How their inorganic?How is ammonia supplied? Carbonic acid?

What is organic matter? Inorganic?

Of what does organic matter consist? Inorganic?

How do plants obtain their organic food?

How their inorganic?

How is ammonia supplied? Carbonic acid?

Organic matter is that which burns away in the fire. Inorganic matter is the ash left after burning.

The organic matter of plants consists of three gases, oxygen, hydrogen and nitrogen, and one solid substance carbon (or charcoal). The inorganic matter of plants consists of potash, soda, lime, magnesia, sulphuric acid, phosphoric acid, chlorine, silica, oxide of iron, and oxide of manganese.

Plants obtain their organic food as follows:—Oxygen and hydrogen from water, nitrogen from some compound containing nitrogen (chiefly from ammonia), and carbon from the atmosphere where it exists as carbonic acid—a gas.

They obtain their inorganic food from the soil.

The water which supplies oxygen and hydrogen to plants is readily obtained without the assistance of manures.

Ammonia is obtained from the atmosphere, by being absorbed by rain and carried into the soil, and it enters plants through their roots. It may be artificially supplied in the form of animal manure with profit.

Carbonic acid is absorbed from the atmosphere by leaves, and decomposed in the green parts of plants under the influence of daylight; the carbon is retained, and the oxygen is returned to the atmosphere.

When plants are destroyed by combustion or decay, what becomes of their constituents?How does the inorganic matter enter the plant?Are the alkalies soluble in their pure forms?Which one of them is injurious when too largely present?How may sulphuric acid be supplied?Is phosphoric acid important?How must silica be treated?From what source may we obtain chlorine?

When plants are destroyed by combustion or decay, what becomes of their constituents?

How does the inorganic matter enter the plant?

Are the alkalies soluble in their pure forms?

Which one of them is injurious when too largely present?

How may sulphuric acid be supplied?

Is phosphoric acid important?

How must silica be treated?

From what source may we obtain chlorine?

When plants are destroyed by decay, or burning, their organic constituents pass away as water, ammonia, carbonic acid, etc., ready again to be taken up by other plants.

The inorganic matters in the soil can enter the plant only when dissolved in water.Potash,soda,lime, andmagnesia, are soluble in their pure forms. Magnesia is injurious when present in too large quantities.

Sulphuricacid is often necessary as a manure, and is usually most available in the form of sulphate of lime or plaster. It is also valuable in its pure form to prevent the escape of ammonia from composts.

Phosphoricacid is highly important, from its frequent deficiency in worn-out soils. It is available only under certain conditions which will be described in the section on manures.

Silicais the base of common sand, and must be united to an alkali before it can be used by the plant, because it is insoluble except when so united.

Chlorineis a constituent of common salt (chlorideof sodium), and from this source may be obtained in sufficient quantities for manurial purposes.

What is the difference betweenperoxide andprotoxide of iron?How must the food of plants be supplied?What takes place after it enters the plant?What name is given to the compounds thus formed?How are proximates divided?Which class constitutes the largest part of the plant?Of what are animals composed, and how do they obtain the materials from which to form their growth?

What is the difference betweenperoxide andprotoxide of iron?

How must the food of plants be supplied?

What takes place after it enters the plant?

What name is given to the compounds thus formed?

How are proximates divided?

Which class constitutes the largest part of the plant?

Of what are animals composed, and how do they obtain the materials from which to form their growth?

Oxide of ironis iron rust. There are two oxides of iron, theperoxide(red) and theprotoxide(black). The former is a fertilizer, and the latter poisons plants.

Oxide of manganeseis often absent from the ashes of our cultivated plants.

The food of plants, both organic and inorganic, must be supplied in certain proportions, and at the time when it is required. In the plant, this food undergoes such chemical changes as are necessary to growth.

The compounds formed by these chemical combinations are calledproximates.

Proximates are of two classes, those not containing nitrogen, and those which do contain it.

The first class constitute nearly the whole plant.

The second class, although small in quantity, are of the greatest importance to the farmer, as from them all animal muscle is made.

Animals, like plants, are composed of both organic and inorganic matter, and their bodies are obtained directly or indirectly from plants.

What parts of the animal belong to the first class of proximates?What to the second?What is necessary to the perfect development of animals?Why are seeds valuable for working animals?What other important use, in animal economy, have proximates of the first class?Under what circumstances is animal fat decomposed?

What parts of the animal belong to the first class of proximates?

What to the second?

What is necessary to the perfect development of animals?

Why are seeds valuable for working animals?

What other important use, in animal economy, have proximates of the first class?

Under what circumstances is animal fat decomposed?

The first class of proximates in animals comprise the fat, and like tissues.

The second class form the muscle, hair, gelatine of the bones, etc.

In order that they may be perfectly developed, animals must eat both classes of proximates, and in the proportions required by their natures.

They require the phosphate of lime and other inorganic food which exist in plants.

Seeds are the best adapted to the uses of working animals, because they are rich in all kinds of food required.

Aside from their use in the formation offat, proximates of the first class are employed in the lungs, as fuel to keep up animal heat, which is produced (as in fire and decay) by the decomposition of these substances.

When the food is insufficient for the purposes of heat, the animal's own fat is decomposed, and carried to the lungs as fuel.

The stems, roots, branches, etc., of most plants consist principally ofwoody fibre.

Their seeds, and sometimes their roots, contain considerable quantities ofstarch.

Name the parts of the plant in which the different proximates exist.State what you know about flour.Do we know that different plants have ashes of different composition?

Name the parts of the plant in which the different proximates exist.

State what you know about flour.

Do we know that different plants have ashes of different composition?

Theproteinand theoilsof most plants exist most largely in theseeds.

The location of the proximates, as well as of the inorganic parts of the plant, show a remarkable reference to the purposes of growth, and to the wants of the animal world, as is noticed in the difference between the construction of the straw and that of the kernel of wheat.

The reason why the fine flour now made is not so healthfully nutritious as that which contained more of the coarse portions, is that it is robbed of a large proportion of protein and phosphate of lime, while it contains an undue amount of starch, which is available only to form fat, and to supply fuel to the lungs.

Different plants have ashes of different composition. Thus—one may take from the soil large quantities of potash, another of phosphoric acid, and another of lime.

By understanding these differences, we shall be able so to regulate our rotations, that the soil may not be called on to supply more of one ingredient than of another, and thus it may be kept in balance.

How are farmers to be benefited by such knowledge?

The facts contained in this chapter are thealphabet of agriculture, and the learner should not only become perfectly familiar with them, but should also clearly understand thereasonswhy they are true, before proceeding further.

What is a necessary condition of growth?

In the foregoing section, we have studied the character of plants and the laws which govern their growth. We learned that one necessary condition for growth is a fertile soil, and therefore we will examine the nature of different soils, in order that we may understand the relations between them and plants.

What is a fixed character of soils?How is the chemical character of the soil to be ascertained?What do we first learn in analyzing a soil?How do the proportions of organic or inorganic parts of soils compare with those of plants?Of what does the organic part of soils consist?

What is a fixed character of soils?

How is the chemical character of the soil to be ascertained?

What do we first learn in analyzing a soil?

How do the proportions of organic or inorganic parts of soils compare with those of plants?

Of what does the organic part of soils consist?

The soil is not to be regarded as a mysterious mass of dirt, whereon crops are produced by a mysterious process. Well ascertained scientificknowledge has proved beyond question that all soils, whether in America or Asia, whether in Maine or California, have certain fixed properties, which render them fertile or barren, and the science of agriculture is able to point out these characteristics in all cases, so that we can ascertain from a scientific investigation what would be the chances for success in cultivating any soil which we examine.

The soil is a great chemical compound, and its chemical character is ascertained (as in the case of plants) by analyzing it, or taking it apart.

We first learn that fertile soils contain both organic and inorganic matter; but, unlike the plant, they usually possess much more of the latter than of the former.

In the plant, the organic matter constitutes the most considerable portion of the whole. In the soil, on the contrary, it usually exists in very small quantities, while the inorganic portions constitute nearly the whole bulk.

Can the required proportion be definitely indicated?From what source is the inorganic part of soils derived?Do all soils decompose with equal facility?How does frost affect rocks?Does it affect soils in the same way?

Can the required proportion be definitely indicated?

From what source is the inorganic part of soils derived?

Do all soils decompose with equal facility?

How does frost affect rocks?

Does it affect soils in the same way?

The organic part of soils consists of the same materials that constitute the organic part of the plants, and it is in reality decayed vegetable and animal matter. It is not necessary that this organic part of the soil should form any particular proportionof the whole, and indeed we find it varying from one and a half to fifty, and sometimes, in peaty soils, to over seventy per cent. All fertile soils contain some organic matter, although it seems to make but little difference in fertility, whether it be ten or fifty per cent.

The inorganic part of soils is derived from the crumbling of rocks. Some rocks (such as the slates in Central New York) decompose, and crumble rapidly on being exposed to the weather; while granite, marble, and other rocks will last for a long time without perceptible change. Thecausesof this crumbling are various, and are not unimportant to the agriculturist; as by the same processes by which his soil was formed, he can increase its depth, or otherwise improve it. This being the case, we will in a few words explain some of the principal pulverizing agents.

1. The action of frost. When water lodges in the crevices of rocks, andfreezes, it expands, and bursts the rock, on the same principle as causes it to break a pitcher in winter. This power is very great, and by its assistance, large cannon may be burst. Of course the action of frost is the same on a small scale as when applied to largemasses of matter, and, therefore, we find that when water freezes in thepores[M]of rocks or stones, it separates their particles and causes them to crumble. The same rule holds true with regard to stiff clay soils. If they areridgedin autumn, and left with a rough surface exposed to the frosts of winter, they will become much lighter, and can afterwards be worked with less difficulty.

What is the effect of water on certain rocks?How are some rocks affected by exposure to the atmosphere? Give an instance of this.

What is the effect of water on certain rocks?

How are some rocks affected by exposure to the atmosphere? Give an instance of this.

2. The action of water. Many kinds of rock become so soft on being soaked with water, that they readily crumble.

3. The chemical changes of the constituents of the rock. Many kinds of rock are affected by exposure to the atmosphere, in such a manner, that changes take place in their chemical character, and cause them to fall to pieces. The red kellis of New Jersey (a species of sandstone), is, when first quarried, a very hard stone, but on exposure to the influences of the atmosphere, it becomes so soft that it may be easily crushed between the thumb and finger.

What is the similarity between the composition of soils and the rocks from which they were formed?What does feldspar rock yield? Talcose slate? Marls?Does a soil formed entirely from rock contain organic matter?How is it affected by the growth of plants?

What is the similarity between the composition of soils and the rocks from which they were formed?

What does feldspar rock yield? Talcose slate? Marls?

Does a soil formed entirely from rock contain organic matter?

How is it affected by the growth of plants?

Other actions, of a less simple kind, exert an influence on the stubbornness of rocks, and cause themto be resolved into soils.[N]Of course, the composition of the soil must be similar to that of the rock from which it was formed; and, consequently, if we know the chemical character of the rock, we can tell whether the soil formed from it can be brought under profitable cultivation. Thus feldspar, on being pulverized, yields potash; talcose slate yields magnesia; marls yield lime, etc.

The soil formed entirely from rock, contains, of course, no organic matter.[O]Still it is capable of bearing plants of a certain class, and when these die, they are deposited in the soil, and thus form its organic portions, rendering it capable of supporting those plants which furnish food for animals. Thousands of years must have been occupied in preparing the earth for habitation by man.

As the inorganic or mineral part of the soil is usually the largest, we will consider it first.

As we have stated that this portion is formedfrom rocks, we will examine their character, with a view to showing the different qualities of soils.

What is the general rule concerning the composition of rocks?Do these distinctions affect the fertility of soils formed from them?What do we mean by the mechanical character of the soil?Is its fertility indicated by its mechanical character?

What is the general rule concerning the composition of rocks?

Do these distinctions affect the fertility of soils formed from them?

What do we mean by the mechanical character of the soil?

Is its fertility indicated by its mechanical character?

As a general rule, it may be stated thatall rocks are either sandstones, limestones, or clays; or a mixture of two or more of these ingredients. Hence we find that all mineral soils are eithersandy,calcareous, (limey), orclayey; or consist of a mixture of these, in which one or another usually predominates. Thus, we speak of a sandy soil, a clay soil, etc. These distinctions (sandy, clayey, loamy, etc.) are important in considering themechanicalcharacter of the soil, but have little reference to its fertility.

Bymechanicalcharacter, we mean those qualities which affect the ease of cultivation—excess or deficiency of water, ability to withstand drought, etc. For instance, a heavy clay soil is difficult to plow—retains water after rains, and bakes quite hard during drought; while a light sandy soil is plowed with ease, often allows water to pass through immediately after rains, and becomes dry and powdery during drought. Notwithstanding those differences in their mechanical character, both soils may be very fertile, or one more so than the other, without reference to the clay and sand which they contain, and which, toour observation, form their leading characteristics. Thesame facts exist with regard to a loam, a calcareous (or limey) soil, or a vegetable mould. Their mechanical texture is not essentially an index to their fertility, nor to the manures required to enable them to furnish food to plants. It is true, that each kind of soil appears to have some general quality of fertility or barrenness which is well known to practical men, yet this is not founded on the fact that the clay or the sand, or the vegetable matter, enter more largely into the constitution of plants than they do when they are not present in so great quantities, but on certain other facts which will be hereafter explained.

What is a sandy soil? A clay soil? A loamy soil? A marl? A calcareous soil? A peaty soil?

As the following names are used to denote the character of soils, in ordinary agricultural description, we will briefly explain their application:

ASandy soilis, of course, one in which sand largely predominates.

Clay soil, one whereclayforms a large proportion of the soil.

Loamy soil, where sand and clay are about equally mixed.

Marlcontains from five to twenty per cent. of carbonate of lime.

Calcareous soilmore than twenty per cent.

Peaty soils, of course, contain large quantities of organic matter.[P]

How large a part of the soil may be used as food by plants?What do we learn from the analyses of barren and fertile soils?

How large a part of the soil may be used as food by plants?

What do we learn from the analyses of barren and fertile soils?

We will now take under consideration that part of the soil on which depends its ability to supply food to the plant. This portion rarely constitutes more than five or ten per cent. of the entire soil, sometimes less—and it has no reference to the sand, clay, and vegetable matters which they contain. From analyses of many fertile soils, and of others which are barren or of poorer quality, it has been ascertained that the presence of certain ingredients is necessary to fertility. This may be better explained by the assistance of the following table:

What can you say of the soils represented in the table of analyses?What proportion of the fertilizing ingredients is required?If the soil represented in the third column contained all the ingredients required except potash and soda, would it be fertile?What would be necessary to make it so?What is the reason for this?What are the offices performed by the inorganic part of soils?

What can you say of the soils represented in the table of analyses?

What proportion of the fertilizing ingredients is required?

If the soil represented in the third column contained all the ingredients required except potash and soda, would it be fertile?

What would be necessary to make it so?

What is the reason for this?

What are the offices performed by the inorganic part of soils?

The soil represented in the first column might still be fertile with less organic matter, or with a larger proportion of clay (alumina), and less sand (silica). These affect itsmechanicalcharacter; but, if we look down the column, we notice that there are small quantities of lime, magnesia, and the other constituents of the ashes of plants (except ox. of manganese). It is not necessary that they should be present in the soil in the exact quantity named above, butnot one must be entirely absent, or greatly reduced in proportion. By referring to the third column, we see that these ingredients are not all present, and the soil is barren. Even if it were supplied with all but one or two, potash and soda for instance, it could not support a crop without the assistance of manures containing these alkalies. The reason for this must be readily seen, as we have learned that no plant can arrive at maturity without the necessary supply of materials required in the formation of the ash, and these materials can be obtained only from the soil; consequently, when they do not exist there, it must be barren.

The inorganic part of soils has two distinct offices to perform. The clay and sand form amass of material into which roots can penetrate, and thus plants are supported in their position. These parts also absorb heat, air and moisture to serve the purposes of growth, as we shall see in a future chapter. The minute portions of soil, which comprise the acids, alkalies, and neutrals, furnish plants with their ashes, and are the most necessary to the fertility of the soil.

What is geology?Is the same kind of rock always of the same composition?How do rocks differ?

What is geology?

Is the same kind of rock always of the same composition?

How do rocks differ?

The relation between the inorganic part of soils and the rocks from which it was formed, is the foundation of Agricultural Geology. Geology may be briefly named thescience of rocks. It would not be proper in an elementary work to introduce much of this study, and we will therefore simply state that the same kind of rock is of the same composition all over the world; consequently, if we find a soil in New England formed from any particular rock, and a soil from the same rock in Asia, their natural fertility will be the same in both localities. Some rocks consist of a mixture of different kinds of minerals; and some, consisting chiefly of one ingredient, are of different degrees ofhardness. Both of these changes must affect the character of the soil, but it may be laid down as rule that,when the rocks of two locations are exactly alike, the soils formed from them will be of the same natural fertility, and in proportion as the character of rocks changes, in the same proportion will the soils differ.

What rule may be given in relation to soils formed from the same or different rocks?Are all soils formed from the rocks on which they lie?What instances can you give of this?

What rule may be given in relation to soils formed from the same or different rocks?

Are all soils formed from the rocks on which they lie?

What instances can you give of this?

In most districts the soil is formed from the rock on which it lies; but this is not always the case. Soils are often formed by deposits of matter brought by water from other localities. Thus the alluvial banks of rivers consist of matters brought from the country through which the rivers have passed. The river Nile, in Egypt, yearly overflows its banks, and deposits large quantities of mud brought from the uninhabited upper countries. The prairies of the West owe a portion of their soil to deposits by water. Swamps often receive the washings of adjacent hills; and, in these cases, their soil is derived from a foreign source.

We might continue to enumerate instances of the relations between soils and the sources whence they originated, thus demonstrating more fully the importance of geology to the farmer; but it would be beyond the scope of this work, and should be investigated by scholars more advanced than those who are studying merely theelementsof agricultural science.

The mind, in its early application to any branchof study, should not be charged with intricate subjects. It should master well therudiments, before investigating those matters which shouldfollowsuch understanding.

In what light will plants and soils be regarded by those who understand them?

By pursuing the proper course, it is easy to learn all that is necessary to form a good foundation for a thorough acquaintance with the subject. If this foundation is laid thoroughly, the learner will regard plants and soils as old acquaintances, with whose formation and properties he is as familiar as with the construction of a building or simple machine. A simple spear of grass will become an object of interest, forming itself into a perfect plant, with full development of roots, stem, leaves, and seeds, by processes with which he feels acquainted. The soil will cease to be mere dirt; it will be viewed as a compound substance, whose composition is a matter of interest, and whose care is productive of intellectual pleasure. The commencement of study in any science must necessarily be wearisome to the young mind, but its more advanced stages amply repay the trouble of early exertions.

FOOTNOTES:[M]The spaces between the particles.[N]In very many instances the crevices and seams of rocks are permeated by roots, which, by decaying and thus inducing the growth of other roots, cause these crevices to become filled with organic matter. This, by the absorption of moisture, may expand with sufficient power to burst the rock.[O]Some rocks contain sulphur, phosphorus, etc., and these may, perhaps, be considered as organic matter.[P]These distinctions are not essential to be learned, but are often convenient.

[M]The spaces between the particles.

[N]In very many instances the crevices and seams of rocks are permeated by roots, which, by decaying and thus inducing the growth of other roots, cause these crevices to become filled with organic matter. This, by the absorption of moisture, may expand with sufficient power to burst the rock.

[O]Some rocks contain sulphur, phosphorus, etc., and these may, perhaps, be considered as organic matter.

[P]These distinctions are not essential to be learned, but are often convenient.

What proportion of organic matter is required for fertility?How does the soil obtain its organic matter?How does the growth of clover, etc., affect the soil?

What proportion of organic matter is required for fertility?

How does the soil obtain its organic matter?

How does the growth of clover, etc., affect the soil?

It will be recollected that, in addition to its mineral portions, the soil contains organic matter in varied quantities. It may be fertile with but one and a half per cent. of organic matter, and some peaty soils contain more than fifty per cent. or more than one half of the whole.

The precise amount necessary cannot be fixed at any particular sum; perhaps five parts in a hundred would be as good a quantity as could be recommended.

The soil obtains its organic matter in two ways. First, by the decay of roots and dead plants, also of leaves, which have been brought to it by wind, etc. Second, by the application of organic manures.

When organic matter decays in the soil, what becomes of it?Is charcoal taken up by plants?Are humus and humic acid of great practical importance?

When organic matter decays in the soil, what becomes of it?

Is charcoal taken up by plants?

Are humus and humic acid of great practical importance?

When a crop of clover is raised, it obtains its carbon from the atmosphere; and, if it be plowed under, and allowed to decay, a portion of this carbon is deposited in the soil. Carbon constitutes nearly the whole of the dry weight of the clover, aside from the constituents of water; and, when we calculate the immense quantity of hay, and roots grown onan acre of soil in a single season, we shall find that the amount of carbon thus deposited is immense. If the clover had been removed, and the roots only left to decay, the amount of carbon deposited would still have been very great. The same is true in all cases where the crop is removed, and the roots remain to form the organic or vegetable part of the soil. While undergoing decomposition, a portion of this matter escapes in the form of gas, and the remainder chiefly assumes the form of carbon (or charcoal), in which form it will always remain, without loss, unless driven out by fire. If a bushel of charcoal be mixed with the soil now, it will be the same bushel of charcoal, neither more nor less, a thousand years hence, unless some influence is brought to bear on it aside from the growth of plants. It is true that, in the case of the decomposition of organic matter in the soil, certain compounds are formed, known under the general names ofhumusandhumic acid, which may, in a slight degree, affect the growth of plants, but their practical importance is of too doubtful a character to justify us in considering them. The application of manures, containing organic matter, such as peat, muck, animal manure, etc., supplies the soil with carbon on the same principle, and the decomposing matters alsogenerate[Q]carbonic acid gas while being decomposed. The agricultural value of carbon in the soil depends (as we have stated), not on the fact that it enters into the composition of plants, but on certain other important offices which it performs, as follows:—

On what does the agricultural value of the carbon in the soil depend?Why does it make the soil more retentive of manure?What is the experiment with the barrels of sand?

On what does the agricultural value of the carbon in the soil depend?

Why does it make the soil more retentive of manure?

What is the experiment with the barrels of sand?

1. It makes the soil more retentive of manures.

2. It causes it to appropriate larger quantities of the fertilizing gases of the atmosphere.

3. It gives it greater power to absorb moisture.

4. It renders it warmer.

1. Carbon (or charcoal) makes the soil retentive of manures, because it has in itself a strong power to absorb, and retain[R]fertilizing matters. There is a simple experiment by which this power can be shown.

Ex.—Take two barrels of pure beach sand, and mix with the sand in one barrel a few handfuls of charcoal dust, leaving that in the other pure. Pour the brown liquor of the barn-yard through the pure sand, and it will pass out at the bottom unaltered. Pour the same liquor through the barrel, containing the charcoal, and pure water will be obtained as a result. The reason for this is that thecharcoal retains all of the impurities of the liquor, and allows only the water to pass through. Charcoal is often employed to purify water for drinking, or for manufacturing purposes.

Will charcoal purify water?If a piece of tainted meat, or a fishy duck be buried in a rich garden soil, what takes place?What is the reason of this?How does charcoal overcome offensive odors?How can you prove that charcoal absorbs themineralimpurities of water?

Will charcoal purify water?

If a piece of tainted meat, or a fishy duck be buried in a rich garden soil, what takes place?

What is the reason of this?

How does charcoal overcome offensive odors?

How can you prove that charcoal absorbs themineralimpurities of water?

A rich garden-soil contains large quantities of carbonaceous matter; and, if we bury in such a soil a piece of tainted meat or a fishy duck, it will, in a short time, be deprived of its odor, because the charcoal in the soil will entirely absorb it.

Carbon absorbs gases as well as the impurities of water; and, if a little charcoal be sprinkled over manure, or any other substance, emitting offensive odors, the gases escaping will be taken up by the charcoal, and the odor will cease.

It has also the power of absorbingmineralmatters, which are contained in water. If a quantity of salt water be filtered through charcoal, the salt will be retained, and the water will pass through pure.

We are now able to see how carbon renders the soil retentive of manures.

1st. Manures, which resemble the brown liquor of barn-yards, have their fertilizing matters taken out, and retained by it.

How does charcoal in the soil affect the manures applied?Why does charcoal in the soil cause it to appropriate the gases of the atmosphere?What fertilizing gases exist in the atmosphere?How are they carried to the soil?Does the carbon retain them after they reach the soil?What can you say of the air circulating through the soil?How does carbon give the soil power to absorb moisture?

How does charcoal in the soil affect the manures applied?

Why does charcoal in the soil cause it to appropriate the gases of the atmosphere?

What fertilizing gases exist in the atmosphere?

How are they carried to the soil?

Does the carbon retain them after they reach the soil?

What can you say of the air circulating through the soil?

How does carbon give the soil power to absorb moisture?

2d. The gases arising from the decomposition (rotting) of manure are absorbed by it.

3d. The soluble mineral portions of manure, which might in some soils leach down with water, are arrested and retained at a point at which they can be made use of by the roots of plants.

2. Charcoal in the soil causes it to appropriate larger quantities of the fertilizing gases of the atmosphere, on account of its power, as just named, to absorb gases.

The atmosphere contains results, which have been produced by the breathing of animals and by the decomposition of various kinds of organic matter, which are exposed to atmospheric influences. These gases are chiefly ammonia and carbonic acid, both of which are largely absorbed by water, and consequently are contained in rain, snow, etc., which, as they enter the soil, give up these gases to the charcoal, and they there remain until required by plants. Even the air itself, in circulating through the soil, gives up fertilizing gases to the carbon, which it may contain.

3. Charcoal gives to the soil power to absorb moisture, because it is itself one of the best absorbents in nature; and it has been proved by accurate experiment that peaty soils absorb moisture with greater rapidity, and part with it more slowly than any other kind.

How does it render it warmer?Is the heat produced by the decomposition of organic matter perceptible to our senses?Is it so to the growing plant?What is another important part of the organic matter in the soil?

How does it render it warmer?

Is the heat produced by the decomposition of organic matter perceptible to our senses?

Is it so to the growing plant?

What is another important part of the organic matter in the soil?

4. Carbon in the soil renders it warmer, because it darkens its color. Black surfaces absorb more heat than light ones, and a black coat, when worn in the sun, is warmer than one of a lighter color. By mixing carbon with the soil, we darken its color, and render it capable of absorbing a greater amount of heat from the sun's rays.

It will be recollected that, when vegetable matter decomposes in the soil, it produces certain gases (carbonic acid, etc.), which either escape into the atmosphere, or are retained in the soil for the use of plants. The production of these gases is always accompanied byheat, which, though scarcely perceptible to our senses, is perfectly so to the growing plant, and is of much practical importance. This will be examined more fully in speaking of manures.

How is it obtained by the soil?What offices does the organic matter in the soil perform?

How is it obtained by the soil?

What offices does the organic matter in the soil perform?

Another important part of the organic matter in the soil is that which containsnitrogen. This forms but a very small portion of the soil, but it is of the greatest importance to vegetables. As the nitrogen in food is of absolute necessity to the growth ofanimals, so the nitrogen in the soil is indispensable to the growth of cultivated plants. It is obtained by the soil in the form of ammonia (or nitric acid), from the atmosphere, or by the application of animal matter. In some cases, manures callednitrates[S]are used; and, in this manner, nitrogen is given to the soil.

We have now learned that the organic matter in the soil performs the following offices:—

Organic matter thoroughly decomposed iscarbon, and has the various effects ascribed to this substance on p. 79.

Organic matter in process of decay produces carbonic acid, and sometimes ammonia in the soil; also its decay causes heat.

Organic matter containingnitrogen, such as animal substances, etc., furnish ammonia, and other nitrogenous substances to the roots of plants.

FOOTNOTES:[Q]Produce.[R]By absorbing and retaining, we mean taking up and holding.[S]Nitrates are compounds of nitric acid (which consists of nitrogen and oxygen), and alkaline substances. Thus nitrate of potash (saltpetre), is composed of nitric acid and potash: nitrate of soda (cubical nitre), of nitric acid and soda.

[Q]Produce.

[R]By absorbing and retaining, we mean taking up and holding.

[S]Nitrates are compounds of nitric acid (which consists of nitrogen and oxygen), and alkaline substances. Thus nitrate of potash (saltpetre), is composed of nitric acid and potash: nitrate of soda (cubical nitre), of nitric acid and soda.

What effect has clay besides the one already named?How does it compare with charcoal for this purpose?

What effect has clay besides the one already named?

How does it compare with charcoal for this purpose?

The offices performed by the inorganic constituents of the soil are many and important.

These, as well as the different conditions in which the bodies exist, are necessary to be thoroughly studied.

Those parts which constitute the larger proportion of the soil, namely the clay, sand, and limy portions, are useful for purposes which have been named in the first part of this section, while theclayhas an additional effect in the absorption of ammonia.

For this purpose, it is as effectual as charcoal, the gases escaping from manures, as well as those existing in the atmosphere, and in rain-water, being arrested by clay as well as charcoal.[T]

What particular condition of inorganic matter is requisite for fertility?What is the fixed rule with regard to this?What is the condition of the alkalies in most of their combinations? Of the acids?What is said of phosphate of lime?

What particular condition of inorganic matter is requisite for fertility?

What is the fixed rule with regard to this?

What is the condition of the alkalies in most of their combinations? Of the acids?

What is said of phosphate of lime?

The more minute ingredients of the soil—those which enter into the construction of plants—exist in conditions which are more or less favorable or injurious to vegetable growth. The principal condition necessary to fertility iscapacity to be dissolved, it being (so far as we have been able to ascertain) a fixed rule, as was stated in the first section, thatno mineral substance can enter into the roots of a plant except it be dissolved in water.

Thealkaliespotash, soda, lime, and magnesia, are in nearly all of their combinations in the soil sufficiently soluble for the purposes of growth.

Theacidsare, as will be recollected, sulphuric and phosphoric. These exist in the soil in combination with the alkalies, as sulphates and phosphates, which are more or less soluble under natural circumstances. Phosphoric acid in combination with lime as phosphate of lime is but slightly soluble; but, when it exists in the compound known assuper-phosphate of lime, it is much more soluble, and consequently enters into the composition of plants with much greater facility. This matter will be more fully explained in the section on manures.

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