ents 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.

FOOTNOTES:

[X] It should be recollected that every bent straw may act as a syphon,
and occasion much loss of liquid manure.

CHAPTER IV.

ABSORBENTS.

[What substances are called absorbents?

What is the most important of these?

What substances are called charcoal in agriculture?

How is vegetable matter rendered useful as charcoal?]

Before considering farther the subject of animal excrement, it is
necessary to examine a class of manures known as _absorbents_. These
comprise all matters which have the power of absorbing, or soaking up,
as it were, the gases which arise from the evaporation of solid and
liquid manures, and retaining them until required by plants.

The most important of these is undoubtedly _carbon_ or charcoal.

CHARCOAL.

_Charcoal_, in an agricultural sense, means all forms of carbon, whether
as peat, muck, charcoal dust from the spark-catchers of locomotives,
charcoal hearths, river and swamp deposits, leaf mould, decomposed spent
tanbark or sawdust, etc. In short, if any vegetable matter is decomposed
with the partial exclusion of air (so that there shall not be oxygen
enough supplied to unite with all of the carbon), a portion of its
carbon remains in the exact condition to serve the purposes of charcoal.

[What is the first-named effect of charcoal? The second?
Third? Fourth?

Explain the first action.]

The offices performed in the soil by carbonaceous matter were fully
explained in a former section (p. 79, Sect. 2), and we will now examine
mere