362 Report of Experiments on the Growth of Barley, 
nitrogen than was supplied in the manure, the average produce 
of tlie subsequent courses would appear, by calculation, to have 
removed much less than was supplied ; and, as most of that 
which was supplied was in the form of rape-cake, there would 
doubtless be an effective residue left within the soil. 
To sum up the results on the point: — As in other experi- 
ments, so also in these, in which barley was grown in rotation, 
and under three very different conditions as to manuring, the 
evidence is sufficiently conclusive, and, therefore, corroborative 
of that in the other cases, that an essential condition for the 
growth of a full crop of barley, whether in rotation, or under 
less usual conditions, is a liberal supply of available nitrogen 
within the soil. 
Section VI. — Summary and General Conclusions, showing 
THE Practical Bearings of the Kesults. 
In a former paper it was shown, that wheat had been suc- 
cessfully grown for twenty years in succession on the same land ; 
that the produce without manure had, during that period, 
diminished comparatively little ; and that that by farmyard- 
manure, and by certain artificial manures, had increased con- 
siderably. The thirtieth wheat crop is now growing, and shows 
no deterioration, in either quantity or quality, where the proper 
manures, natural or artificial, have been supplied. The most 
prominent result was, and still is, that mineral manures alone 
increase the produce scarcely at all ; that nitrogenous manures 
alone increase it very considerably ; but that the largest crops are 
obtained when nitrogenous and mineral manures are applied 
together. 
How far do the results now recorded in regard to harlei/ accord 
with those which have been obtained with its botanical ally — 
wheat ? 
The results on the growth of barley, without manure, by farm- 
yard manure, and by a great variety of artificial mixtures, each 
used for twenty years in succession on the same land, have been 
given in detail in the foregoing pages ; and they have been com- 
pared with those obtained with wheat under corresponding con- 
ditions. They have been classified, and given in separate 
sections, and at the conclusion of the sections they have been 
more or less formally summarised. It remains to call attention 
here to the most prominent results of the inquiry as a whole, 
with as little reference to detail as may be consistent with clear- 
ness, referring the reader to the detailed discussion of individual 
points, and to the summaries, given at the conclusion of pre- 
ceding sections, for any further illustration or confirmation that 
may be needed. 
