ARE ROTATIONS OF CROPS NECESSARY ? 
361 
out the expense of applying various items, some 
of which, might, for the time, be entirely super¬ 
fluous ; and where an analysis could not be con¬ 
veniently made, experiments on a small scale, 
even on a single rod, might give the desired in¬ 
formation. 
There is no doubt, that while every substance 
found in a plant is equally necessary to its perfec¬ 
tion in all cases, (after providing for the few in¬ 
stances of substitution in some of them, as of soda 
for potash, and the like,) yet there is not an equal 
necessity for their being found in the soil. Thus, 
while the mineral or earthy portion of plants (al¬ 
though usually constituting about one fortieth of 
the whole) are indispensable to plants, and can not 
be obtained by them unless in the soil and within 
reach of the roots; yet the organic, as carbon, 
oxygen, hydrogen, and nitrogen, may be, and un¬ 
questionably are, drawn in large quantity from the 
atmosphere and rains and dews, and this effect is 
generally in proportion to the judicious arrange¬ 
ment and proper combination of the inorganic 
materials of the soil. Experiments have proved 
this position beyond cavil, as an artificial soil, 
formed of pure siiicious sand, with the sole addi¬ 
tion of the mineral ingredients of the plant, with 
a supply of air and water, has been found entirely 
adequate to mature it. But at the same time that 
we may readily acknowledge the success of such 
experiments, and are aware from numerous ob¬ 
servations, that the atmosphere is the ever-abun- 
dant storehouse for the supply of a large portion 
of the substances of plants, experience teaches us 
with equal certainty, that the addition of these 
materials to the soils in putrescent and other ma¬ 
nures, muck, &c., is of the highest advantage to 
the speedy maturity and fullest development of 
vegetables, and consequently it is of the greatest 
interest to the farmer that they be adequately 
furnished to the plant in the soil. 
When the proper measure of fertility is ac¬ 
quired for any given crop, we see no reason, and 
can conceive of none, why the same process of 
cultivation, the same quality of seed, and the 
same or equally favorable seasons, should not pro¬ 
duce an equal amount of crop, provided the same 
materials , and in equal proportions , which fur¬ 
nished the lasty are again intimately blended with 
the soil. We might then open an account current 
with a field, and charge all the materials added, 
and credit the ultimate constituents of the crop 
taken off, adding sufficient for drainage, and, if ne¬ 
cessary, the escape by evaporation, and we should 
always be sure of sustaining the full measure of its 
highest condition of fertility, and this , loo , for 
any one crop , a thousand times successively re¬ 
peated. We can see, indeed, a remote exception 
to this rule, in a soil so long cultivated, that its 
mechanical structure has become so altered by 
constant tillage, and the coarser particles of the 
soil, having become so thoroughly comminuted or 
broken down by the chemical action of the roots of 
vegetation and their disposing influences upon the 
various materials constituting the soils, that it 
would be necessary to add portions of a less con¬ 
stantly cultivated foreign soil, or what is always 
at hand, and generally, perfectly adapted to the 
purpose, the subsoil lying directly beneath. It 
has been found necessary, in parts of Europe, 
which have been subjected to a close tillage for 
ages, to adopt this system, even when the super¬ 
soil was fully supplied with every element of fer¬ 
tility, and the effect has been immediate and pe¬ 
culiarly striking. 
The practice of constant cropping with the 
same species of vegetation, may, it is true, in 
many cases, be attended with peculiar objections. 
Such are the nourishing of such insects, worms, 
or grubs, as are destructive of the crop, by con¬ 
stantly furnishing them food of a kind adapted to 
their most successful growth and productiveness; 
or the increase of weeds, which the necessary 
mode of cultivation will not readily admit of ex¬ 
terminating. In these cases, an occasional change 
of crop, may not only be the most economical, but 
the most effectual mode of eradicating its ene¬ 
mies. 
An objection has been frequently made to con¬ 
tinued cropping of a single species of vegetation, 
from the fancied theory of prejudicial excretions 
of the roots, a theory advanced and ingeniously 
supported by Decandolle, but which the closest 
scrutiny, of the most able and scientific observers 
since, has failed to establish, and it is confidently 
believed no difficulty may be apprehended from 
this cause. 
It may, and doubtless is, beneficial in many, and 
perhaps all cases, that some additional material 
be added to the soil beyond what is taken off in 
the crop, or otherwise escapes. Such are lime 
and gypsum, which, in addition to the food they 
yield directly to plants, serve an important office 
in drawing the organic materials from the atmo¬ 
sphere, and combining with them, in which condi¬ 
tion they are retained for the growing plant; and 
they are useful, also in predisposing such chemical 
action in the constituents of soils, as will most effect¬ 
ually subserve the great objects desired. Such, 
too, has charcoal been found, in hoarding up car¬ 
bonic acid and ammonia for plants, though yielding 
no perceptible portion of itself to the soil or plant. 
Lime, also, is frequently absolutely essential in 
neutralizing deleterious vegetable acids, and min¬ 
eral carbonates and oxides existing in the soil. 
An additional quantity of some of the materials 
requisite to the perfection of a crop may be ne¬ 
cessary, from inability in a single season to mix 
them intimately with all parts of the soil, so that 
not only every root, but every fibre and spongiole 
shall be able to drink in a full supply of its appro¬ 
priate nutriment, that no time be lost in matur¬ 
ing and giving the fullest perfection to the plant. 
An excess of some of the materials beyond what 
may be required for present use, therefore, if not 
so great as to be positively injurious, will, in many 
cases, be found indispensable to the greatest suc¬ 
cess; and this excess need be attended with no 
further loss than the interest of the outlay till it 
becomes sufficiently blended with the mass to 
yield itself up to the constant demands of the 
plant. 
These conditions being fully considered and 
provided for, we believe a thousand successive 
crops may be taken from the same field without 
