ROTATION 
matter which the different cultivated crops con- 
tribute to the ground at the time of their being 
mown or pulled or otherwise reaped or gathered. 
A seventh is the singular and exceedingly varied 
character and action of the excrementitious mat- 
ter deposited by crops,—that of any one crop 
being fitted to injure a succeeding crop of the 
same or similar kind, and yet to benefit a pro- 
perly selected succeeding crop of a different kind. 
An eighth is the tendency of any one crop, when 
repeated, to encourage the ruinous prolificity of 
such insects as prey upon its roots and stems, 
and such cryptogams as send up their sporules 
from the soil to feed upon its organisms,—and 
the contrary tendency of each of the different 
crops of a series to starve out all the insects and 
eryptogams which prey upon the others. Anda 
ninth is the mighty facilities which are afforded 
by alternations of widely different kinds of crops 
so to modify and regulate their adaptations to 
one another, and their individual treatment, and 
the methods of disposing of them, as to control 
or retard or counteract any or all of the exhaust- 
ing processes of a rotation by concurrent or al- 
ternate ameliorating processes, 
The practical rules which ought to regulate 
rotations are easily deducible from what we have 
said, and do not require any separate proof or 
illustration. Some of the most obvious and im- 
portant of them are, that plants which have long 
perpendicular roots should succeed those which 
have spreading and superficial roots,—that crops 
of the same or similar species of plants should 
not follow in succession, but should return at as 
distant intervals as shall be found to comport 
with general convenience and profit,—that two 
kinds of crops which alike or similarly encourage 
the growth of weeds should not follow in succes- 
sion,—that crops which abstract phosphates and 
sulphates and nitrogenous principles from the 
soil, and secrete them in seeds or other forms 
which are not returned again to the field, should 
alternate with crops and with methods of treat- 
ing and consuming them which shall not carry 
away but rather augment the remainder of these 
salts and principles in the soil,—that, on every 
farm which has been long under cultivation, 
crops which require much of either these or 
other scarce and valuable principles shall be 
raised only on soil which has been recently en- 
riched with them by means of artificial manur- 
ings, and shall be followed or alternated, at suf- 
ficiently short intervals, with either crops or 
fallowings which shall give back to the soil as 
much of the rare salts and principles as they 
have abstracted,—that the several members of a 
rotation should follow one another in an order 
of succession studiously adapted to the conditions 
and changes of the soil in the successive years 
after fallowing or special manuring,—and that 
the laying down of land to grass, in a sys- 
tem of alternating lea with tillage, should be 
done when the soil is both clean and fertile. 
OF CROPS. 91 
The cereal grasses, wheat, barley, oats, and rye, 
as grown for the maturing and carrying away of 
their seeds, are the greatest exhausters; the pulse 
plants, the pea and the bean, as grown for the 
maturing and carrying away of their seeds, are 
exhausters of less severity than the cereal grasses, 
and afford considerable compensatory action by 
means of their succulent roots and of the horse- 
hoe method of culture; the fibre-yielding and 
oleaginous plants, flax and hemp, are either ex- 
ceedingly slight exhausters when pulled in flower 
and made to contribute only their fibre, but ex- 
ceedingly severe exhausters when grown to ma- 
turity and made to contribute the entire sub- 
stance of their seeds; and either the turnip, the 
rape, and cther brassicas, when raised only for 
their roots and leaves, and consumed upon the 
farm,—or the beet, the parsnip, the carrot, the 
potato, and other plants of similar habit, when 
raised only for their roots and tubers and consum- 
ed upon the farm,—or the clover, the tare, the lu- 
cern, and other forage leguminous plants, when cut 
green or in flower and consumed upon the farm, 
are more or less non-exhausters in the ordinary 
method of cultivating them, and can, in most in- 
stances, be rendered powerful ameliorators either 
by special modes of consuming them on the ground, 
or by sending back to the soil the putrescent 
rejectamenta of their eaten produce in combina- 
tion with the litter of the farm-yard. Or, to 
make another practical classification, the cereal 
crops are exhausting and befouling; the horse- 
hoed pulse crops are exhausting and cleaning; 
the green forage crops are ameliorating and 
sometimes befouling; the green fallow crops are 
ameliorating and cleaning; and the sown grass 
crops, continued into lea, are ameliorating and 
capable of being made most thoroughly cleaning. 
All particular rotations, however, whether for 
an entire farm of homogeneous character, or for 
coadjacent fields of diversified character, ought 
to be determined with due reference to soils, 
local circumstances, and market profits. “ Lu- 
cern and sainfoin,” remarks Chaptal, “are classed 
among the plants which should have a place in 
the system of a rotation of crops; nevertheless, 
it is to be remembered that these plants require 
a deep soil, and at the same time not too com- 
pact, in order that they may freely penetrate 
the earth with their long perpendicular roots. 
Hemp, flax, and the cereal plants, require good 
ground, and should not be admitted into a course 
of crops, except in such soils as are abundantly 
fertile and thoroughly prepared. Light, dry soils 
are unsuited to the same succession of plants, as 
would be appropriate to those of a compact na- 
ture, and which are constantly humid. Each 
kind of soil, therefore, demands a particular 
course of crops; and every agriculturist should 
arrange his system according to the nature and 
properties of the soil which he has to cultivate. 
Inasmuch as in each different situation, soils will 
present some shades of dissimilarity, more or less 
