498 
Agricultural Cliemistry. 
of the cereal grains, are not measurable by the amount of the 
additional mineral food of plants liberated thereby, these being, 
under ordinary cultivation, in excess of the assimilable nitrogen 
existing in or condensed within the soil in the same period of 
time. The amount of the latter therefore — the available 
vitroqen — is the measure of the increased produce of grain 
wiiicli will be obtained. 
4. That the beneficial effects of rotation, in increasing the pro- 
duction of saleable produce (so far as they are chemical), are not 
explained by the fact of one plant taking from the soil more of 
the different mineral constituents than another, but depend on 
the property of the so-called green or falloic crops of bringing, 
or conserving, upon the farm, more substance rich in nitrogen 
than is yielded to them in manure ; whilst the crops to which they 
are subservient, are both largely exported from the farm, and 
^ ield in their increase considerably less nitrogen than is given to 
them in manure. 
5. Finally — that, in the existing condition of British agricul- 
ture, a full production of the saleable cereal (/rains, with other 
exportable produce, is only attainable, Avhether by manures, falloic, 
or rotation, provided there be an accumulation of available 
nitrogen icithin the soil itself. 
Ilothamstcd, December, 1855. 
Note. — It is due to tlie authors of this pa])cr to state, tliat in consequence 
of want of space, it Las unavoidably been somewhat condensed. — Ed. 
The foregoing article is so much more controversial in its 
nature than any which have hitherto appeared in the Royal Agri- 
cultural Society's Journal, that some explanation seems to be 
required of the circumstances which have led to its insertion. 
It will not bs necessary on this occasion tO' discuss the general 
question, whether controv^ersy is or is not the best mode of 
eliciting truth ; and hy limiting t!ie following remarks to the par- 
ticular case in point, it may be shown in few words, that to have 
declined to accept Mr. Lawes's paper because it consisted in great 
part of a defence of the principles embodied in his previous pub- 
lications, would have been a tacit abandonment of the opinions 
previously advocated in this Journal, as well as a great loss to 
tlie supporters of sound agricultural science. 
It will be in the recollection of all who have watched the rise 
and progress of this important controversy that, in the year 1840, 
Baron Liebig first published in this country his great work on 
Agricultural Chemistry. At that time a very general impression 
prevailed that British agriculture was capable of great develop- 
