220 
Experiments on the Groivth of Wheat. 
drainajje, to which all might be subject, the nitrogen, in several 
of its forms of combination, is alsp volatile, and may be exhaled 
into the atmosphere and lost, but this is not the case with the 
mineral constituents of manure. 
Upon the whole, then, a careful study of the various experi- 
ments has proved, — 
That the soil, even with the most unusual and very exhausting 
process of carrying off the land the total grain and straw of 
several successive corn-crops, after a root-crop which had also 
been drawn from the land, still contained a larger annual available 
supply of minerals than the annual natural supplies of other con- 
stituents, nitrogen or carbon, were adequate to turn to account ; — 
That the excess of the annual supply of minerals in the soil 
over that required to appropriate the natural resources of nitrogen, 
is proved, by the effects of ammoniacal salts alone, to have been 
equal to the further growth, during 4 years, of about 32 bushels 
of wheat, or an average of about 8 bushels per annum ; — 
That beyond the increased annual produce which the supply 
of minerals in the soil was adequate annually to provide when 
nitrogen was not wanting, the average capabilities of the climate 
were competent for the maturing of a still greater produce, if 
additional minerals as well as the ammoniacal salts were pro- 
vided ; and, in that case, from once and a half to twice as much 
corn was grown as the natural supplies of nitrogen, even with a 
most liberal supply of minerals, were sufficient to produce ; — 
That carbonaceous organic matters (such as are contained in 
rape-cake and farm-yard dung) are of themselves of little or no 
effect in increasing the growth of wheat. 
We can now have little difficulty in deciding to what accu- 
mulated elements of growth to attribute the higher " condition " 
or greater fertility of the first year, as compared with the suc- 
ceeding ones. Mineral manures alone have had no effect in 
restoring the fertility which was exhausted by the first experi- 
mental crop. Ammonia alone gave a produce of several bushels 
more than the unmanured plot in the first year, and has, on the 
average of the last 3 years, given half as much again of produce 
as either the unmanured or the mineral manui'ed plot; and the addi- 
tion of minerals to this ammonia, has restored a further increment 
of the lost fertility. In no case, however, have the artificial manures 
of subsequent years entirely restored the original fertility : or 
rather, in no case (with it is true a difference of season), has 
there since been a produce quite equal to that of the unmanured 
space of 1851. From the above facts it is obvious that in the 
first year there existed in the soil a larger supply both of avail- 
able minerals and of available nitrogen tlian in any of the 
succeeding years ; but that in the first year there existed accu- 
