CHAPTER X
ATMOSPHERIC FERTILIZERS
Are the gases in the atmosphere manures?
What would be the result if they were not so?
It is not common to look on the gases in the atmosphere in the light of manures, but they are decidedly so. Indeed, they are almost the only organic manure ever received by the uncultivated parts of the earth, as well as a large portion of that which is occupied in the production of food for man.
If these gases were not manures; if there were no means by which they could be used by plants, the fertility of the soil would long since have ceased, and the earth would now be in an unfertile condition. That this must be true, will be proved by a few moments' reflection on the facts stated in the first part of this book. The fertilizing gases in the atmosphere being composed of the constituents of decayed plants and animals, it is as necessary that they should be again returned to the form of organized matter, as it is that constituents taken from the soil should not be put out of existence.
AMMONIA
How is ammonia used by plants?
How may it be carried to the soil?
How may the value of organic manures be estimated?
What effects has ammonia beside supplying food to plants?
The ammonia in the atmosphere probably cannot be appropriated by the leaves of plants, and must, therefore, enter the soil to be assimilated by roots. It reaches the soil in two ways. It is either arrested from the air circulating through the soil, or it is absorbed by rains in the atmosphere, and thus carried to the earth, where it is retained by clay and carbon, for the uses of plants. In the soil, ammonia is the most important of all organic manures. In fact, the value of organic manure may be estimated, either by the amount of ammonia which it will yield, or by its power of absorbing ammonia from other sources.
The most important action of ammonia in the soil is the supply of nitrogen to plants; but it has other offices which are of consequence. It assists in some of the chemical changes necessary to prepare the matters in the soil for assimilation. Some argue that ammonia stimulates the roots of plants, and causes them to take up increased quantities of inorganic matter. The discussion of this question would be out of place here, and we will simply say, that it gives them such vigor that they require increased amounts of ashy matter, and enables them to take this from the soil.
To how great a degree can the farmer control atmospheric fertilizers?
What should be the condition of the soil?
What substances are good absorbents in the soil?
How may sandy soils be made retentive of ammonia?
Although, in the course of nature, the atmospheric fertilizers are plentifully supplied to the soil, without the immediate attention of the farmer, it is not beyond his power to manage them in such a manner as to arrest a greater quantity. The precautions necessary have been repeatedly given in the preceding pages, but it may be well to name them again in this chapter.
The condition of the soil is the main point to be considered. It must be such as to absorb and retain ammonia—to allow water to pass through it, and be discharged below the point to which the roots of crops are searching for food—and to admit of a free circulation of air.
The power of absorbing and retaining ammonia is not possessed by sand, but it is a prominent property of clay, charcoal, and some other matters named as absorbents. Hence, if the soil consists of nearly pure sand, it will not make use of the ammonia brought to it from the atmosphere, but will allow it to evaporate immediately after a shower. Soils in this condition require additions of absorbent matters, to enable them to use the ammonia received from the atmosphere. Soils already containing a sufficient amount of clay or charcoal, are thus far prepared to receive benefit from this source.
Why does under-draining increase the absorptive power of the soil?
How do plants obtain their carbonic acid?
How does carbonic acid affect caustic lime in the soil?
The next point is to cause the water of rains to pass through the soil. If it lies on the surface, or runs off without entering the soil, or even if it only enters to a slight depth, and comes in contact with but a small quantity of the absorbents, it is not probable that the fertilizing matters which it contains will all be abstracted. Some of them will undoubtedly return to the atmosphere on the evaporation of the water; but, if the soil contains a sufficient supply of absorbents, and will allow all rain water to pass through it, the fertilizing gases will all be retained. They will be filtered (or raked) out of the water.
This subject will be more fully treated in Section IV. in connection with under-draining.
Besides the properties just described, the soil must possess the power of admitting a free circulation of air. To effect this, it is necessary that the soil should be well pulverized to a great depth. If, in addition to this, the soil be such as to admit water to pass through, it will allow that circulation of air necessary to the greatest supply of ammonia.
CARBONIC ACID
What power does it give to water?
What condition of the soil is necessary for the reception of the largest quantity of carbonic acid?
May oxygen be considered a manure?
What is the effect of the oxidation of the constituents of the soil?
Carbonic acid is received from the atmosphere, both by the leaves and roots of plants.
If there is caustic lime in the soil, it unites with it, and makes it milder and finer. It is absorbed by the water in the soil, and gives it the power of dissolving many more substances than it would do without the carbonic acid. This use is one of very great importance, as it is equivalent to making the minerals themselves more soluble. Water dissolves carbonate of lime, etc., exactly in proportion to the amount of carbonic acid which it contains. We should, therefore, strive to have as much carbonic acid as possible in the water in the soil; and one way, in which to effect this, is to admit to the soil the largest possible quantity of atmospheric air which contains this gas.
The condition of soil necessary for this, is the same as is required for the deposit of ammonia by the same circulation of air.
OXYGEN
How does it affect the protoxide of iron?
How does it neutralize the acids in the soil?
How does it affect its organic parts?
How does it form nitric acid?
How may it affect excrementitious matter of plants?
What effect has it on the mechanical condition of the soil?
Oxygen, though not taken up by plants in its pure form, may justly be classed among manures, if we consider its effects both chemical and mechanical in the soil.
1. By oxidizing or rusting some of the constituents of the soil, it prepares them for the uses of plants.
2. It unites with the protoxide of iron, and changes it to the peroxide.
3. If there are acids in the soil, which make it sour and unfertile, it may be opened to the circulation of the air, and the oxygen will prepare some of the mineral matters contained in the soil to unite with the acids and neutralize them.
4. Oxygen combines with the carbon of organic matters in the soil, and causes them to decay. The combination produces carbonic acid.
5. It combines with the nitrogen of decaying substances and forms nitric acid, which is serviceable as food for plants.
6. It undoubtedly affects in some way the matter which is thrown out from the roots of plants. This, if allowed to accumulate, and remain unchanged, is often very injurious to plants; but, probably, the oxygen and carbonic acid of the air in the soil change it to a form to be inoffensive, or even make it again useful to the plant.
7. It may also improve the mechanical condition of the soil, as it causes its particles to crumble, thus making it finer; and it roughens the surfaces of particles, making them less easy to move among each other.
These properties of oxygen claim for it a high place among the atmospheric fertilizers.
WATER
Why may water be considered an atmospheric manure?
What classes of action have manures?
What are chemical manures? Mechanical?
Water may be considered an atmospheric manure, as its chief supply to vegetation is received from the air in the form of rain or dew. Its many effects are already too well known to need farther comment.
The means of supplying water to the soil by the deposit of dew will be fully explained in Section IV.
CHAPTER XI
RECAPITULATION
Manures have two distinct classes of action in the soil, namely, chemical and mechanical.
Chemical manures are those which enter into the construction of plants, or produce such chemical effects on matters in the soil as shall prepare them for use.
Mechanical manures are those which improve the mechanical condition of the soil, such as loosening stiff clays, compacting light sands, pulverizing large particles, etc.
What are the three kinds of manures?
What are organic manures, and what are their uses? Mineral? Atmospheric?
Manures are of three distinct kinds, namely, Organic, mineral, and atmospheric.
Organic manures comprise all vegetable and animal matters (except ashes) which are used to fertilize the soil. Vegetable manures supply carbonic acid, and inorganic matter to plants. Animal manures supply the same substances and ammonia.
Mineral manures comprise ashes, salt, phosphate of lime, plaster, etc. They supply plants with inorganic matter. Their usefulness depends on their solubility.
Many of the organic and mineral manures have the power of absorbing ammonia arising from the decomposition of animal manures, as well as that which is brought to the soil by rains—these are called absorbents.
Atmospheric manures consist of ammonia, carbonic acid, oxygen and water. Their greatest usefulness requires the soil to allow the water of rains to pass through it, to admit of a free circulation of air among its particles, and to contain a sufficient amount of absorbent matter to arrest and retain all ammonia and carbonic acid presented to it.
What rule should regulate the application of manures?
How must organic manures be managed? Atmospheric?
Manures should never be applied to the soil without regard to its requirements.
Ammonia and carbon are almost always useful, but mineral manures become mere dirt when applied to soils not deficient of them.
The only true guide to the exact requirements of the soil is chemical analysis; and this must always be obtained before farming can be carried on with true economy.
Organic manures must be protected against the escape of their ammonia and the leaching out of their soluble parts. One cord of stable manure properly preserved, is worth ten cords which have lost all of their ammonia by evaporation, and their soluble parts by leaching—as is the case with much of the manure kept exposed in open barn-yards.
Atmospheric manures cost nothing, and are of great value when properly employed. In consequence of this, the soil which is enabled to make the largest appropriation of the atmospheric fertilizers, is worth many times as much as that which allows them to escape.
SECTION FOURTH.
MECHANICAL CULTIVATION
CHAPTER I
THE MECHANICAL CHARACTER OF SOILS
What is the first office of the soil?
How does it hold water for the uses of the plant?
How does it obtain a part of its moisture?
The mechanical character of the soil is well understood from preceding remarks, and the learner knows that there are many offices to be performed by the soil aside from the feeding of plants.
1. It admits the roots of plants, and holds them in their position.
2. By a sponge-like action, it holds water for the uses of the plant.
3. It absorbs moisture from the atmosphere to supply the demands of plants.
How may it obtain heat?
What is the use of the air circulating among its particles?
Could most soils be brought to the highest state of fertility?
What is the first thing to be done?
Should its color be darkened?
4. It absorbs heat from the sun's rays to assist in the process of growth.
5. It admits air to circulate among roots, and supply them with a part of their food, while the oxygen of that air renders available the minerals of the soil; and its carbonic acid, being absorbed by the water in the soil, gives it the power of dissolving, and carrying into roots more inorganic matter than would be contained in purer water.
6. It allows the excrementitious matter thrown out by roots to be carried out of their reach.
All of these actions the soil must be capable of performing, before it can be in its highest state of fertility. There are comparatively few soils now in this condition, but there are also few which could not be profitably rendered so, by a judicious application of the modes of cultivation to be described in the following chapters.
The three great objects to be accomplished are:—
1. To adopt such a system of drainage as will cause all of the water of rains to pass through the soil, instead of evaporating from the surface.
2. To pulverize the soil to a considerable depth.
3. To darken its color, and render it capable of absorbing atmospheric fertilizers.
Name some of the means used to secure these effects.
Why are under-drains superior to open drains?
The means used to secure these effects are under-draining, sub-soil and surface-plowing, digging, applying muck, etc.
CHAPTER II
UNDER-DRAINING
The advantages of under-drains over open drains are very great.
When open drains are used, much water passes into them immediately from the surface, and carries with it fertilizing parts of the soil, while their beds are often compacted by the running water and the heat of the sun, so that they become water tight, and do not admit water from the lower parts of the soil.
The sides of these drains are often covered with weeds, which spread their seeds throughout the whole field. Open drains are not only a great obstruction to the proper cultivation of the land, but they cause much waste of room, as we can rarely plow nearer than within six or eight feet of them.
There are none of these objections to the use of under-drains, as these are completely covered, and do not at all interfere with the cultivation of the surface.
With what materials may under-drains be constructed?
Describe the tile.
Under drains may be made with brush, stones, or tiles. Brush is a very poor material, and its use is hardly to be recommended. Small stones are better, and if these be placed in the bottoms of the trenches, to a depth of eight or ten inches, and covered with sods turned upside down, having the earth packed well down on to them, they make very good drains.
TILE DRAINING
The best under-drains are those made with tiles, or burnt clay pipes. The first form of these used was that called the horse-shoe tile, which was in two distinct pieces; this was superseded by a round pipe, and we have now what is called the sole tile, which is much better than either of the others.
Fig. 4—Sole Tile.
Why is the sole tile superior to those of previous construction?
How are these tiles laid?
How may the trenches be dug?
This tile is made (like the horse-shoe and pipe tile) of common brick clay, and is burned the same as bricks. It is about one half or three quarters of an inch thick, and is so porous that water passes directly through it. It has a flat bottom on which to stand, and this enables it to retain its position, while making the drain, better than would be done by the round pipe. The orifice through which the water passes is egg-shaped, having its smallest curve at the bottom. This shape is the one most easily kept clear, as any particles of dirt which get into the drain must fall immediately to the point where even the smallest stream of water runs, and are thus removed. An orifice of about two inches is sufficient for the smaller drains, while the main drains require larger tiles.
These tiles are laid, so that their ends will touch each other, on the bottoms of the trenches, and are kept in position by having the earth tightly packed around them. Care must be taken that no space is left between the ends of the tiles, as dirt would be liable to get in and choke the drain. It is advisable to place a sod—grass side down—over each joint, before filling the trench, as this more effectually protects them against the entrance of dirt. There is no danger of keeping the water out by this operation, as it will readily pass through any part of the tiles.
Fig. 5.
Upton tool.
Spade and hoe.
In digging the trenches it is not necessary (except in very stony ground) to dig out a place wide enough for a man to stand in, as there are tools made expressly for the purpose, by which a trench may be dug six or seven inches wide, and to any required depth. One set of these implements consists of a long narrow spade and a hoe to correspond, such as are represented in the accompanying figure.
With these tools, and a long light crowbar, for hard soils, trenches may be dug much more cheaply than with the common spade and pickaxe. Where there are large boulders in the soil, these draining tools may dig under them so that they will not have to be removed.
When the trenches are dug to a sufficient depth, the bottoms must be made perfectly smooth, with the required descent (from six inches to a few feet in one hundred feet). Then the tiles may be laid in, so that their ends will correspond, be packed down, and the trenches filled up. Such a drain, if properly constructed, may last for ages. Unlike the stone drain, it is not liable to be frequented by rats, nor choked up by the soil working into it.
The position of the tile may be best represented by a figure, also the mode of constructing stone drains.
Why are small stones better than large stones in the construction of drains?
On what must the depth of under-drains depend?
It will be seen that the tile drain is made with much less labor than the stone drain, as it requires less digging, while the breaking up of the stone for the stone drain will be nearly, or quite as expensive as the tiles. Drains made with large stones are not nearly so good as with small ones, because they are more liable to be choked up by animals working in them.34
Fig. 6.
a—Tile drain trench.
b—Stone drain trench.
c—Sod laid on the stone.
Describe the principle which regulates these relative depths and distances. (Blackboard.)
Which is usually the cheaper plan of constructing drains?
The depth of the drains must depend on the distances at which they are placed. If but twenty feet apart, they need be but three feet deep; while, if they are eighty feet apart, they must be five feet deep, to produce the same effect. The reason for this is, that the water in the drained soil is not level, but is higher midway between the drains, than at any other point. It is necessary that this highest point should be sufficiently far from the surface not to interfere with the roots of plants, consequently, as the water line between two drains is curved, the most distant drains must be the deepest. This will be understood by referring to the following diagram.
Fig. 7.
aa—5 feet drains, 80 ft. apart. bb—3 feet drains, 20 ft. apart.
The curved line represents the position of the water.
In most soils it will be easier to dig one trench five feet deep, than four trenches three feet deep, and the deep trenches will be equally beneficial; but where the soil is very hard below a depth of three feet, the shallow trenches will be the cheapest, and in such soils they will often be better, as the hard mass might not allow the water to pass down to enter the deeper drains.
By following out these instructions, land may be cheaply, thoroughly, and permanently drained.
CHAPTER III
ADVANTAGES OF UNDER-DRAINING
The advantages of under-draining are many and important.
1. It entirely prevents drought.
2. It furnishes an increased supply of atmospheric fertilizers.
3. It warms the lower portions of the soil.
4. It hastens the decomposition of roots and other organic matter.
5. It accelerates the disintegration of the mineral matters in the soil.
6. It causes a more even distribution of nutritious matters among those parts of soil traversed by roots.
7. It improves the mechanical texture of the soil.
8. It causes the poisonous excrementitious matter of plants to be carried out of the reach of their roots.
9. It prevents grasses from running out.
10. It enables us to deepen the surface soil.
By removing excess of water—
11. It renders soils earlier in the spring.
12. It prevents the throwing out of grain in winter.
13. It allows us to work sooner after rains.
14. It keeps off the effects of cold weather longer in the fall.
15. It prevents the formation of acetic and other organic acids, which induce the growth of sorrel and similar weeds.
16. It hastens the decay of vegetable matter, and the finer comminution of the earthy parts of the soil.
17. It prevents, in a great measure, the evaporation of water, and the consequent abstraction of heat from the soil.
18. It admits fresh quantities of water from rains, etc., which are always more or less imbued with the fertilizing gases of the atmosphere, to be deposited among the absorbent parts of soil, and given up to the necessities of plants.
19. It prevents the formation of so hard a crust on the surface of the soil as is customary on heavy lands.
How does under-draining prevent drought?
1. Under-draining prevents drought, because it gives a better circulation of air in the soil; (it does so by making it more open). There is always the same amount of water in and about the surface of the earth. In winter, there is more in the soil than in summer, while in summer, that which has been dried out of the soil exists in the atmosphere in the form of a vapor. It is held in the vapory form by heat, which acts as braces to keep it distended. When vapor comes in contact with substances sufficiently colder than itself, it gives up its heat—thus losing its braces—contracts, and becomes liquid water.
This may be observed in hundreds of common operations.
Why is there less water in the soil in summer than in winter, and where does it exist?
What holds it in its vapory form?
How is it affected by cold substances?
Describe the deposit of moisture on the outside of a pitcher in summer.
What other instances of the same action can be named?
It is well known that a cold pitcher in summer robs the vapor in the atmosphere of its heat, and causes it to be deposited on its own surface. It looks as though the pitcher were sweating, but the water all comes from the atmosphere, not, of course, through the sides of the pitcher.
If we breathe on a knife-blade, it condenses in the same manner the moisture of the breath, and becomes covered with a film of water.
Stone houses are damp in summer, because the inner surfaces of the walls, being cooler than the atmosphere, cause its moisture to be deposited in the manner described. By leaving a space, however, between the walls and the plaster, this moisture is prevented from being troublesome.
How does this principle affect the soil?
Explain the experiment with the two boxes of soil.
Nearly every night in the summer season, the cold earth receives moisture from the atmosphere in the form of dew.
A cabbage, which at night is very cold, condenses water to the amount of a gill or more.
The same operation takes place in the soil. When the air is allowed to circulate among its lower and cooler particles, they receive moisture from the same process of condensation. Therefore, when, by the aid of under-drains, the lower soil becomes sufficiently open to admit of a circulation of air, the deposit of atmospheric moisture will keep the soil supplied with water at a point easily accessible to the roots of plants.
If we wish to satisfy ourselves that this is practically correct, we have only to prepare two boxes of finely pulverized soil, one, five or six inches deep, and the other fifteen or twenty inches deep, and place them in the sun at mid-day in summer. The thinner soil will be completely dried, while the deeper one, though it may have been perfectly dry at first, will soon accumulate a large amount of water on those particles which, being lower and more sheltered from the sun's heat than the particles of the thin soil, are made cooler.
With an open condition of subsoil, then, such as may be secured by under-draining, we entirely overcome drought.
How does under-draining supply to the soil an increased amount of atmospheric fertilizers?
How does it warm the lower parts of the soil?
2. Under-draining furnishes an increased supply of atmospheric fertilizers, because it secures a change of air in the soil. This change is produced whenever the soil becomes filled with water, and then dried; when the air above the earth is in rapid motion, and when the comparative temperature of the upper and lower soils changes. It causes new quantities of the ammonia and carbonic acid which it contains to be presented to the absorbent parts of the soil.
3. Under-draining warms the lower parts of the soil, because the deposit of moisture (1) is necessarily accompanied by an abstraction of heat from the atmospheric vapor, and because heat is withdrawn from the whole amount of air circulating through the cooler soil.
When rain falls on the parched surface soil, it robs it of a portion of its heat, which is carried down to equalize the temperature for the whole depth. The heat of the rain-water itself is given up to the soil, leaving the water from one to ten degrees cooler, when it passes out of the drains, than when received by the earth.
There is always a current of air passing from the lower to the upper end of a well constructed drain; and this air is always cooler in warm weather, when it issues from, than when it enters the drain. Its lost heat is imparted to the soil.
How does it hasten the decomposition of roots and other organic matter in the soil?
How does it accelerate the disintegration of its mineral parts?
Why is this disintegration necessary to fertility?
This heating of the lower soil renders it more favorable to vegetation, partially by expanding the spongioles at the end of the roots, thus enabling them to absorb larger quantities of nutritious matters.
4. Under-draining hastens the decomposition of roots and other organic matters in the soil, by admitting increased quantities of air, thus supplying oxygen, which is as essential in decay as it is in combustion. It also allows the resultant gases of decomposition to pass away, leaving the air around the decaying substances in a condition to continue the process.
This organic decay, besides its other benefits, produces an amount of heat perfectly perceptible to the smaller roots of plants, though not so to us.
5. Draining accelerates the disintegration of the mineral matters in the soil, by admitting water and oxygen to keep up the process. This disintegration is necessary to fertility, because the roots of plants can feed only on matters dissolved from surfaces; and the more finely we pulverize the soil, the more surface we expose. For instance, the interior of a stone can furnish no food for plants; while, if it were finely crushed, it might make a fertile soil.
Any thing, tending to open the soil to exposure, facilitates the disintegration of its particles, and thereby increases its fertility.
How does under-draining equalize the distribution of the fertilizing parts of the soil?
Why does this distribution lessen the impoverishment of the soil?
How does under-draining improve the mechanical texture of the soil?
How do drains affect the excrementitious matter of plants?
6. Draining causes a more even distribution of nutritious matters among those parts of soil traversed by roots, because it increases the ease with which water travels around, descending by its own weight, moving sideways by a desire to find its level, or carried upward by attraction to supply the evaporation at the surface. By this continued motion of the water, soluble matter of one part of the soil may be carried to some other part; and another constituent from this latter position may be carried back to the former. Thus the food of vegetables is continually circulating around among their roots, ready for absorption at any point where it is needed, while the more open character of the soil enables roots to occupy larger portions, making a more even drain on the whole, and preventing the undue impoverishment of any part.
7. Under-drains improve the mechanical texture of the soil; because, by the decomposition of its parts, as previously described (4 and 5), it is rendered of a character to be more easily worked; while smooth round particles, which have a tendency to pack, are roughened by the oxidation of their surfaces, and move less easily among each other.
8. Drains cause the excrementitious matter of plants to be carried out of the reach of their roots. Nearly all plants return to the soil those parts of their food, which are not adapted to their necessities, and usually in a form that is poisonous to plants of the same kind. In an open soil, this matter may be carried by rains to a point where roots cannot reach it, and where it may undergo such changes as will fit it to be again taken up.
Why do they prevent grasses from running out?
9. By under-draining, grasses are prevented from running out, partly by preventing the accumulation of the poisonous excrementitious matter, and partly because these grasses usually consist of tillering plants.
These plants continually reproduce themselves in sprouts from the upper parts of their roots. These sprouts become independent plants, and continue to tiller (thus keeping the land supplied with a full growth), until the roots of the stools (or clumps of tillers), come in contact with an uncongenial part of the soil, when the tillering ceases; the stools become extinct on the death of their plants, and the grasses run out.
The open and healthy condition of soil produced by draining prevents the tillering from being stopped, and thus keeps up a full growth of grass until the nutriment of the soil is exhausted.