284 On the Maintenance of Fertility in new Arable Land. 
following remarks are directed exclusively to tlie grounds on 
which the first of the above " reasons" rests : — 
Landowners generally object to the conversion of grass lands ; 
and very naturally and reasonably too^ for they find that a pasture 
ploughed up soon loses its fertility, and becomes of less annual 
value per acre. Grass, by the very fact that it j'ields less acre- 
able produce per annum than any other plant, and by the fact 
that this is generally all consumed on the land, proves itself the 
crop which least exhausts the soil. Any other plant, wheat for 
instance, or the turnip or potato, yields indeed more food per 
acre ; but this very circumstance causes it to diminish the fertility 
of the soil from which it is taken. New arable land thus rapidly 
deteriorates in quality, and of course in value also, till ultimately 
it produces less food and yields less rent than the pasture out of 
which it was broken. But I am sure that this is no necessary 
consequence of growing other crops than grass, nor is this the 
universal experience of landowners and tenants on this subject. 
And I shall be very glad if a short statement of the grounds on 
which correct practice in this particular will be generally allowed 
to rest, along with the description of an experience in accordance 
with them, shall result in convincing any owners of pasture land 
farmed by intelligent tenants, that their own interest, in common 
with that of every other class in the nation, requires its subjection 
to arable culture. 
The question for consideration is: — How can any given 
DEGREE or FERTILITY IN LAND BE MAINTAINED? ProfcSSOr 
Johnston has conclusively answered it, where he says — " Soils 
which are chemically and physically alike are agriculturally 
equal." Given, a soil whose net annual produce shall be a 
certain acreable sum ; and you preserve its agricultural identity — 
its capability of annually raising similar crops, simply by taking 
care that its composition and its texture shall remain unaltered. 
This is what 'Theory' says upon the subject, and one does not 
see what objection can be made to a statement whose truth is so 
nearly self-evident. Agriculture is just to be considered as a 
manufacture, by which certain substances contained in the soil 
are converted into vegetable and animal produce ; and its results, 
or, to use other terms, the fertility of land must therefore depend 
on the occurrence of those substances in abundance, and in due 
relative proportion. Let them be present tlms, and let the great 
mass of the soil — the mixed clay and sand and lime in it — be of 
such a texture as permits a sufficiently free passage through it 
both to air and water, and the soil will be at its highest pitch of 
fertility. Let cither its texture or its composition fail of this 
standard, and its productiveness will diminish. And there is no 
