The Elements of Agriculture

What takes place when a dead animal is exposed to the atmosphere for a sufficient time?

What often assist the evaporation of solids?

Evaporation is the changing of a solid or liquid body to a vapory form. Thus common smelling salts, a solid, if left exposed, passes into the atmosphere in the form of a gas or vapor. Water, a liquid, evaporates, and becomes a vapor in the atmosphere. This is the case with very many substances, and in organic nature, both solid and liquid, they are liable to assume a gaseous form, and become mixed with the atmosphere. They are not destroyed, but are merely changed in form.

As an instance of this action, suppose an animal to die and to decay on the surface of the earth. After a time, the flesh will entirely disappear, but is not lost. It no longer exists as the flesh of an animal, but its carbon, hydrogen, oxygen, and nitrogen, still exist in the air. They have been liberated from the attractions which held them together, and have passed away; but (as we already know from what has been said in a former section) they are ready to be again taken up by plants, and pressed into the service of life.

The evaporation of liquids may take place without the aid of any thing but heat; still, in the case of solids, it is often assisted by decay and combustion, which break up the bonds that hold the constituents of bodies together, and thus enable them to return to the atmosphere, from which they were originally derived.

What is the cause of odor?

When we perceive an odor, what is taking place?

Why do manures give off offensive odors?

How may we detect ammonia escaping from manure?

It must be recollected that every thing, which has an odor (or can be smelled), is evaporating. The odor is caused by parts of the body floating in the air, and acting on the nerves of the nose. This is an invariable rule; and, when we perceive an odor, we may be sure that parts of the material, from which it emanates, are escaping. If we perceive the odor of an apple, it is because parts of the volatile oils of the apple enter the nose. The same is true when we smell hartshorn, cologne, etc.

Manures made by animals have an offensive odor, simply because volatile parts of the manure escape into the air, and are therefore made perceptible. All organic parts in turn become volatile, assuming a gaseous form as they decompose.

We do not see the gases rising, but there are many ways by which we can detect them. If we wave a feather over a manure heap, from which ammonia is escaping, the feather having been recently dipped in manure, white fumes will appear around the feather, being the muriate of ammonia formed by the union of the escaping gas with the muriatic acid. Not only ammonia, but also carbonic acid, and other gases which are useful to vegetation escape, and are given to the winds. Indeed it may be stated in few words that all of the organic part of plants (all that was obtained from the air, water, and ammonia), constituting more than nine tenths of their dry weight, may be evaporated by the assistance of decay or combustion. The organic part of manures may be lost in the same manner; and, if the process of decomposition be continued long enough, nothing but a mass of mineral matter will remain, except perhaps a small quantity of carbon which has not been resolved into carbonic acid.

What remains after manure has been long exposed to decomposition?

What gaseous compounds are formed by the decomposition of manures?

The proportion of solid manure lost by evaporation (made by the assistance of decay), is a very large part of the whole. Manure cannot be kept a single day in its natural state without losing something. It commences to give out an offensive odor immediately, and this odor is occasioned, as was before stated, by the loss of some of its fertilizing parts.

Animal manure contains, as will be seen by reference to p. 100 (#x4_x_4_i88), all of the substances contained in plants, though not always in the correct relative proportions to each other. When decomposition commences, the carbon unites with the oxygen of the air, and passes off as carbonic acid; the hydrogen and oxygen combine to form water (which evaporates), and the nitrogen is mostly resolved into ammonia, which escapes into the atmosphere.

Describe fire-fanging.

What takes place when animal manure is exposed in an open barn-yard?

What does liquid manure lose by evaporation?

If manure is thrown into heaps, it often ferments so rapidly as to produce sufficient heat to set fire to some parts of the manure, and cause it to be thrown off with greater rapidity. This may be observed in nearly all heaps of animal excrement. When they have lain for some time in mild weather, gray streaks of ashes are often to be seen in the centre of the pile. The organic part of the manure having been burned away, nothing but the ash remains,—this is called fire-fanging.

Manures kept in cellars without being mixed with refuse matter are subject to the same losses.

When kept in the yard, they are still liable to be lost by evaporation. They are here often saturated with water, and this water in its evaporation carries away the ammonia, and carbonic acid which it has obtained from the rotting mass. The evaporation of the water is rapidly carried on, on account of the great extent of surface. The whole mass is spongy, and soaks the liquids up from below (through hollow straws, etc.), to be evaporated at the surface on the same principle as causes the wick of a lamp to draw up the oil to supply fuel for the flame.

Liquid Manure containing large quantities of nitrogen, and forming much ammonia, is also liable to lose all of its organic part from evaporation (and fermentation), so that it is rendered as much less valuable as is the solid dung.[24 - It should be recollected that every bent straw may act as a syphon, and occasion much loss of liquid manure.]

When does the waste of exposed manure commence?

What does economy of manure require?

What is the effect of leaching?

Give an illustration of leaching.

From these remarks, it may be justly inferred that a very large portion of the value of solid and liquid manure as ordinarily kept is lost by evaporation in a sufficient length of time, depending on circumstances, whether it be three months or several years. The wasting commences as soon as the manure is dropped, and continues, except in very cold weather, until the destruction is complete. Hence we see that true economy requires that the manures of the stable, stye, and poultry-house, should be protected from evaporation (as will be hereafter described), as soon as possible after they are made.

LEACHING

The subject of leaching is as important in considering the inorganic parts of manures as evaporation is to the organic, while leaching also affects the organic gases, they being absorbed by water in a great degree.

A good illustration of leaching is found in the manufacture of potash. When water is poured over wood-ashes, it dissolves their potash which it carries through in solution, making ley. If ley is boiled to dryness, it leaves the potash in a solid form, proving that this substance had been dissolved by the water and removed from the insoluble parts of the ashes.

How does water affect decomposing manures?

Does continued decomposition continue to prepare material to be leached away?

How far from the surface of the soil may organic constituents be carried by water?

In the same way water in passing through manures takes up the soluble portions of the ash as fast as liberated by decomposition, and carries them into the soil below; or, if the water runs off from the surface, they accompany it. In either case they are lost to the manure. There is but a small quantity of ash exposed for leaching in recent manures; but, as the decomposition of the organic part proceeds, it continues to develope it more and more (in the same manner as burning would do, only slower), thus preparing fresh supplies to be carried off with each shower. In this way, while manures are largely injured by evaporation, the soluble inorganic parts are removed by water until but a small remnant of its original fertilizing properties remains.

What arrests their farther progress?

What would be the effect of allowing these matters to filter downwards?

What does evaporation remove from manure? Leaching?

It is a singular fact concerning leaching, that water is able to carry no part of the organic constituents of vegetables more than about thirty-four inches below the surface in a fertile soil. They would probably be carried to an unlimited distance in pure sand, as it contains nothing which is capable of arresting them; but, in most soils, the clay and carbon which they contain retain all of the ammonia; also nearly all of the matters which go to form the inorganic constituents of plants within about the above named distance from the surface of the soil. If such were not the case, the fertility of the earth must soon be destroyed, as all of those elements which the soil must supply to growing plants would be carried down out of the reach of roots, and leave the world a barren waste, its surface having lost its elements of fertility, while the downward filtration of these would render the water of wells unfit for our use. Now, however, they are all retained near the surface of the soil, and the water issues from springs comparatively pure.

Evaporation removes from manure—

Carbon, in the form of carbonic acid.

Hydrogen and oxygen, in the form of water.

Nitrogen, in the form of ammonia.

Leaching removes from manure—

The soluble and most valuable parts of the ash in solution in water, besides carrying away some of the named above forms of organic matter.

CHAPTER IV

ABSORBENTS

What substances are called absorbents?

What is the most important of these?

What substances are called charcoal in agriculture?