THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 
435 
and conclusions of Boussifgault, and others, in connexion with this question, from the 
date above mentioned up to the present time, we shall have to refer pretty fully further 
on. It may here be mentioned, however, that already at that early period Bous- 
SIXGAULT had so far advanced in his inquiries into the chemical statistics of certain agri- 
cultural practices on the large scale, as to be apparently led by them to see the import- 
ance of investigating much more closely the sources of the Nitrogen periodically yielded 
by a given area of land, over and above that which was artificially supplied to it. 
We fully admit the pertinence of the considerations, and the sagacity of the observa- 
tions adduced on this head, more than twenty years ago, by Boussingault. It will, 
nevertheless, be well to preface the discussion of our own experimental evidence regard- 
ing the som-ces of the nitrogen of plants, by the statement of a few prominent and 
striking facts, established by investigations conducted here, at Eothamsted, illustrative 
of the amounts of nitrogen yielded by difierent crops over a given area of land, and of 
the relation of these amounts to certain measured, or kno'wn, sources of it. Of these 
points, however, we profess to speak only in a very brief and summary manner on the 
present occasion. The discussion in detail, of the evidence relating to them, would 
indeed itself exhaust the limits of our Paper, Moreover, we have already treated of 
this subject in a separate form, elsewhere*; and it is our intention to consider it much 
more fully at some futiu'e opportunity. 
Section II.— ANNUAL YIELD OF NITROGEN PEE ACRE, IN DIFFERENT CROPS f. 
A. — Yield of Nitrogen jper acre iclien the same Croj) is grown year after year 
on the same Land. 
The following Summary Table shows the average annual amounts of nitrogen yielded 
per acre, in the crops enumerated, when each was grown for a number of years con- 
secutively on the same land, without manure. 
Table I. 
Description of Crop. 
Dates of the Experi- 
ments. 
Number of Years. 
Average Annual yield of 
Nitrogen per acre, 
without Slanure. 
lbs. 
Wheat 
1844 — 1859 inclusive 
16 
24*4 
Bariev 
18.52 — 1 8.5Q ineliisivp 
8 
24*7 
Meadow Hay 
1856 — 1859 inclusive 
4 
39-4 
Beans 
1847 — 1858 inclusive 
12 
47-8 
There were obtained, then, in each of the Cereal crops (wheat and barley) about 
24|lbs. of Nitrogen per acre, per annum, without manm'e. In the case of each of the 
crops the land was, in an agricultural sense, exhausted at the commencement of the 
* Britisli Association for the Advancement of Science, Leeds Meeting (1858), Section B. 
t The results given in this Section have been revised, and in some cases the periods over which the 
estimates are taken extended, since the reading of the Paper. 
