.

[What must a farmer know in order to avoid failures?

Can this be learned entirely from observation?

What kind of action have manures?

Give examples of each of these.

May mechanical effects be produced by chemical action?

How does potash affect the soil?]

To understand the science of _manures_ is the most important branch of
practical farming. No baker would be called a good practical baker who
kept his flour exposed to the sun and rain. No shoemaker would be called
a good practical shoemaker, who used morocco for the soles of his shoes,
and heavy leather for the uppers. No carpenter would be called a good
practical carpenter, who tried to build a house without nails, or other
fastenings. So with the farmer. He cannot be called a good practical
farmer if he keeps the materials, from which he is to make plants, in
such a condition, that they will have their value destroyed, uses them
in the wrong places, or tries to put them together without having every
thing present that is necessary. Before he can avoid failures _with
certainty_, he must know what manures are composed of, how they are to
be preserved, where they are needed, and what kinds are required. True,
he may from observation and experience, _guess_ at results, but he
cannot _know_ that he is right until he has learned the facts above
named. In this section of our work, we mean to convey some of the
information necessary to this branch of _practical farming_.

We shall adopt a classification of the subject somewhat different from
that found in most works on manures, but the _facts_ are the same. The
action of manures is either _mechanical_ or _chemical_, or a combination
of both. For instance: some kinds of manure improve the mechanical
character of the soil, such as those which loosen stiff clay soils, or
others which render light sandy soils compact--these are called
_mechanical_ manures. Some again furnish food for plants--these are
called _chemical_ manures.

Many mechanical manures produce their effects by means of chemical
action. Thus _potash_ combines chemically with sand in the soil. In so
doing, it roughens the surfaces of the particles of sand, and renders
the soil less liable to be compacted by rains. In this manner, it acts
as a _mechanical_ manure. The compound of sand and potash,[U] as well as
the potash alone, may enter into the composition of plants, and hence it
is a _chemical_ manure. In other words, potash belongs to both