r land, and pay on land that has been badly tilled for years, yet the
ashes of the Parsnip contain thirty-six per cent. of potash, eleven per
cent. of lime, eighteen per cent. of phosphoric acid, six per cent. of
sulphuric acid, three per cent. of phosphate of iron, and five per cent.
of common salt. How does the Parsnip obtain its mineral food in a soil
which for other crops appears to be exhausted? Simply by pushing down
for it into a mine that has hitherto been but little worked, though
Cabbage might fail on the same plot because the superficial stratum has
been overtaxed.

Having attempted a general, we now proceed to a particular application.
In the first place, good land, well tilled and abundantly manured,
cannot be soon exhausted; but even in this case a rotation of crops is
advisable. It is less easy to say why than to insist that in practice we
find it to be so. The question then arises--What is a rotation of crops?
It is the ordering of a succession in such a manner that the crops will
tax the soil for mineral aliments in a different manner. A good rotation
will include both chemical and mechanical differences, and place
tap-roots in a course between surface roots, as, for example, Carrot,
Parsnip, and Beet, after Cabbage, Cauliflower, and Broccoli; and light,
quick surface crops, such as Spinach, to serve as substitutes for
fallows. The cropping of the kitchen garden should be, as far as
possible, so ordered that plants of the same natural families never
immediately succeed one another; and, above all things, it is important
to shift from place to place, year after year, the Cabbages and the
Potatoes, because these are the most exhaustive crops we grow. In a ton
of Potatoes there are about twelve pounds of potash, four pounds of
sulphuric acid, four pounds of phosphoric acid, and one pound of
magnesia. We may replace these substances by abundant manuring, and we
are bound to say that the best rotation will not obviate the necessity
for manuring; but even then it is well to crop the plot with Peas,
Spinach, Lettuce, and other plants that occupy it for a comparatively
brief space of time, and necessitate much digging and stirring; for
these mechanical agencies combine with the manure in preparing the plot
to grow Potatoes again much better than if the land were kept to this
crop only from year to year. If we could mark out a plot of ground into
four parts, we should devote one plot to permanent crops--such as