hese manures are needed, from which we may
learn what rules are to be observed in their application.

[Relate what you know of the properties of vegetable ashes?

How does this relate to the fertility of the soil?

According to what two rules may we apply mineral manures?

What course would you pursue to raise potatoes on a soil containing a
very little phosphoric acid and no potash?]

1st. Those which are used as food by plants. It will be recollected that
the _ash_ left after burning plants, and which formed a part of their
structures, has a certain chemical composition; that is, it consists of
alkalies, acids, and neutrals. It was also stated that the ashes of
plants of the same kind are always of about the same composition, while
the ashes of different kinds of plants may vary materially. Different
parts of the same plant too, as we learned, are supplied with different
kinds of ash.

For instance, _clover_, on being burned, leaves an ash containing
_lime_, as one of its principal ingredients, while the ash of _potatoes_
contains more of _potash_ than of any thing else.

In the second section (on soils), we learned that some soils contain
every thing necessary to make the ashes of all plants, and in sufficient
quantity to supply what is required, while other soils are either
entirely deficient in one or more ingredients, or contain so little of
them that they are unfertile for certain plants.

[Would you manure it in the same way for wheat?

Why?]

From this, we see that we may pursue either one of two courses. After we
know the exact composition of the soil--which we can learn only from
correct analysis--we may manure it with a view either to making it
fertile for all kinds of plants or only for one particular plant. For
instance, we may find that a soil contains a very little phosphoric
acid, and no potash. If we wish to raise potatoes on such a soil, we
have only to apply potash (if the soil is good in other particulars),
which is largely required by this plant, though it needs but little
phosphoric acid; while, if we wish to make it fertile for wheat, and all
other plants, we must apply more phosphoric acid as well as potash. As a
universal rule, it may be stated that to render a soil fertile for any
particular plant, we must supply it (unless it already contains them)
with those matters which are necessary to _make_ the ash of that plant;
and, if we would render it capable of producing _all_ kinds of