ments in food, and the purposes they
severally subserve in sustaining life, let me now direct your
attention to a scarcely less interesting and equally important
subject--the means of obtaining from a given surface of the earth
the largest amount of produce adapted to the food of man and
animals.

Agriculture is both a science and an art. The knowledge of all the
conditions of the life of vegetables, the origin of their elements,
and the sources of their nourishment, forms its scientific basis.

From this knowledge we derive certain rules for the exercise of the
ART, the principles upon which the mechanical operations of farming
depend, the usefulness or necessity of these for preparing the soil
to support the growth of plants, and for removing every obnoxious
influence. No experience, drawn from the exercise of the art, can be
opposed to true scientific principles, because the latter should
include all the results of practical operations, and are in some
instances solely derived therefrom. Theory must correspond with
experience, because it is nothing more than the reduction of a
series of phenomena to their last causes.

A field in which we cultivate the same plant for several successive
years becomes barren for that plant in a period varying with the
nature of the soil: in one field it will be in three, in another in
seven, in a third in twenty, in a fourth in a hundred years. One
field bears wheat, and no peas; another beans or turnips, but no
tobacco; a third gives a plentiful crop of turnips, but will not
bear clover. What is the reason that a field loses its fertility for
one plant, the same which at first flourished there? What is the
reason one kind of plant succeeds in a field where another fails?

These questions belong to Science.

What means are necessary to preserve to a field its fertility for
one and the same plant?--what to render one field fertile for two,
for three, for all plants?

These last questions are put by Art, but they cannot be answered by
Art.

If a farmer, without the guidance of just scientific principles, is
trying experiments to render a field fertile for a plant which it
otherwise will not bear, his prospect of success is very small.
Thousands of farmers try such experiments in various directions, the
result of which is a mass of practical experience forming a method
of cultivation which accomplishes the desired end for certain
places; but the same method frequently does not s