|
Loss during the analysis | 1.4 | 3.6-1/2 | .4
+--------------+-------------+----------
|100.0 |100.0 |100.0
---------------------------+--------------+-------------+----------

[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 its _mechanical_ character; 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, but _not 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 a mass 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.

GEOLOGY.

[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
w