Experiments on the Groioth of Wheat. 
221 
mulated available minerals in tlie soil considerably in excess of 
the accumulated nitrogen available for the growth of tlie crop ; 
and that it was the limited amount of the latter, and not of the 
former, which fixed the limit to the amount of produce of the 
unmanured plot in the first season — that is, so far as the greater 
amount of it that year was due to manurial constituents inde- 
pendently of the climatic variations of the different seasons. In 
a word, the practical fact is elicited, that by the growth of corn 
in a soil which has been cultivated in an ordinary manner with 
rotation and home-manuring, the supplies of available minerals 
are not nearly so soon exhausted as those of the available nitrogen. 
In fact, the soil has been reduced from a comparatively high 
wheat-growing condition to a very low one, by the exhaustion of 
its immediately available floating stock of nitrogen ; and it was 
in this very low wheat-growing condition, notwithstanding that the 
mineral elements of fertility still existed in it in such an excess 
in relation to the natural resources of nitrogen, as was sufficient 
for an increase of crop during a succession of years, provided 
only that nitrogen was artificially added to it. 
What, then, is the lesson to practical farming which these 
experiments should teach us ? It will not be supposed, that be- 
cause it is here shown that in a cultivated soil of a comparatively 
light character an increased growth of wheat may be obtained 
over a continuous series of years by the use of nitrogenous 
manures alone — that hence rotation and home-manuring should 
be abandoned, and that corn-crops should be grown continuously 
by means of nitrogenous artificial manures ? There cannot, 
however, be a doubt of the legitimacy of the inference from these 
and other experiments, that provided the land receive in a course 
of years a due share of the home manures derived from feeding of 
horses and other stock on the farm, the mineral supplies of the soil 
will be amply sufficient to sustain an increased and even repeated 
growth of corn, by means of nitrogenous artificial manures, con- 
siderably beyond that which is recognised by the leases or the 
current practices of the day ; and a further assurance that the 
necessary minerals are not likely to become deficient, under the 
judicious adoption of such an increased growth of corn, is to be 
found in the fact that there are few really large sources of nitro- 
genous manures which do not, at the same time, bring upon the 
land a considerable .amount of some of the more important 
minerals also. 
