for Twenty Years in succession on the same Land. 371 
nevertheless yielded larger crops. Still, there is a large amount 
of the nitrogen of the dung not yet satisfactorily accounted for ; 
but, whether there will be an ultimate loss of a greater or less 
proportion of that supplied, than when ammonia-salts or nitrate 
of soda is used, the data at present at command do not enable us 
to determine with certainty. 
It is, then, established, that there is a great liability to loss by 
drainage of the nitrogen of manures, the available amount of 
which, more than of any other constituent, rules the amount of 
produce, under the existing conditions of British agriculture. The 
mineral constituents being, however, equally essential for growth, 
it is obviously important to have some direct experimental evi- 
dence showing whether or not they are also liable to such loss. 
The field experiments with wheat have afforded conclusive 
evidence of the marked effect of potass and phosphoric acid 
supplied more than twenty years previously, when nitrogenous 
manures were afterwards applied to render them available ; 
and, not only are the results of the analysis of the produce con- 
sistent with this, but the analysis of the soils has shown their 
accumulation, and that of the drainage-waters their compara- 
tively little liability to loss in that way. Indeed, it may be con- 
cluded that, at any rate in the case of the heavier soils, these 
constituents, which, by the sale of corn and meat, would other- 
wise be the most likely to become relatively deficient, and which 
in that point of view are the most important to consider, are 
almost wholly retained within the reach of the roots. 
Let it be granted^ — that, in one field at Rothamsted, wheat, 
and in another barley, have been grown for many years in 
succession, the same manure being applied to the same plot year 
after year ; that, under these circumstances, it has been found 
that mineral manures alone have little or no effect, that nitro- 
genous manures alone have very much more, and that nitrogenous 
and mineral manures together will continue to yield as large 
crops as farmyard manure annually applied, and much larger 
than the average produce of the country under rotation. It may 
still be asked, whether conclusions drawn from results obtained 
under such unusual conditions may be trusted as any guide to 
the requirements of the crops when grown on any other land, or 
in the ordinary course of farming ? 
In our paper on the growth of wheat for twenty years in suc- 
cession on the same land (vol. xxv., pp. 491-494), we adduced the 
results of direct experiments, made not only in another field at 
Rothamsted, but also in other localities, on soils of verv different 
description, and in very different condition. The result in each 
case was, as in the experimental field, that there was but little 
increase by mineral manures alone, much more by ammonia-salts 
alone, and more still by ammonia-salts and mineral manure 
VOL. IX. — s. S. 2 C 
