208 
Experiments on the Growth of Wheat. 
corn crop in succession, was condemned as bad in principle ; 
and when we consider what was the amount of produce generally 
obtained in the second year, it must be admitted that, under the 
circumstances then existing, the practice could not be easily jus- 
tified. The increased sources, however, of artificial manures 
which have of late years been opened up, and more especially 
the comparatively large and cheap supplies of that valuable agent 
ammonia, have furnished the agriculturist of the present day 
with a means of increasing, and in many cases of repeating, his 
corn crops, which was not possessed by his predecessor. To 
those heavy lands on which root crops were considered but as a 
necessary evil, these comparatively cheap and abundant sources of 
ammonia may be considered almost as great a boon as the ap- 
plication of the four-course system to the light soils by the late 
Earl^of Leicester. The limit, however, up to which the growth 
of corn by means of artificial manures may safely be extended 
on different descriptions of soil, has yet to be fixed by the aid 
either of practical experience, or of more direct experiment. 
Leaving out of the question for the moment the important in- 
fluence of the subsoil in modifying the character and fertility of 
different descriptions of land, it may be said that, whilst in the 
" heavy " soil certain elements of fertility are comparatively more 
inexhaustible, though capable of liberation in but small quan- 
tities each year, — in the " liglit " soil, on the other hand, there 
is generally a less store of the elements of fertility, though 
they will yield up more rapidly those which are added to 
them in the form of manure. There is, however, an almost in- 
finite variety in the characters of our soils ; in some parts of 
our island we have those of the most opposite description within 
a short distance of each other ; and there are some which so 
combine the qualities of " light " and " heavy " land, as to render 
it difficult on which side to classify them. There are others, 
again, which are decidedly light in character so far as the surface 
soil is concerned, but which possess in their subsoil a vast store- 
house of some of the native elements of fertility ; and hence whilst 
they are amenable to the same mechanical and other general 
management of the so-called light soils, they are more nearly 
allied to the heavy soils so far as the native resource of fertility 
is concerned. Whilst, then, a broad distinction must always 
exist between soils which can without injury be trodden by sheep 
in the wettest weather and those which under the same circum- 
stances will scarcely bear a foot to be put upon them — and it 
may be convenient to apply to them the current designations of 
"Zi^^/ii" or '■^ heavy" accordingly — it must at the same time be 
remembered that these terms, as applied to a surface-soil, afford 
a very imperfect indication of the probable native resources, and 
