QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 21 
Table IX.—Nitrogen per cent., and per acre, in the surface soils, before and after the 
growth of the barley and clover. Geescrofb Field, E-othamsted. 
Nitrogen in sifted dry soil. 
Per cent. 
Per acre. 
1883. 
1885. 
1883. 
1885. 
1885 
+ or - 1883. j 
1. Without manure. 
2. With mineral manure containing potash . 
3. With mineral manure and nitrogen .... 
p. c. 
0-0993 
0-1087 
0-1163 
p. c. 
0-1083 
0-1149 
0-1225 
lbs. 
2441 
2672 
2859 
lbs. 
2662 
2824 
3011 
lbs. i 
-h 221 
+ 152 
+ 152 
Without assuming that the figures represent accurately the amounts of nitrogen 
accumulated per acre, it cannot be doubted that the surface soils had become con¬ 
siderably richer. If, for the sake of illustration, we assume that 300 lbs. of nitrogen 
were removed per acre in the crops, and 200 lbs. were accumulated in the surface soil, 
we have 500 lbs. to account for as gathered by the crops, and chiefly by the clover, 
within about 2 years. 
In our former paper, when we assumed that perhaps 200 lbs. would be removed in 
the crops, we admitted that there was in the experimental results no conclusive 
evidence as to the source of so large an amount of nitrogen, but that it must 
obviously have been derived either from the atmosphere or from the subsoil; and 
assumiirg it to be the subsoil rather thair the atnrosphere, the question arose whether 
it was taken up as iritric acid, as ammoiria, or as organic nitrogen ? It was poiirted 
out that as yet no direct proof existed that green-leaved plants did take up the 
organic nitrogeir of the soil as such; and that although there was more evidence 
from analogy iu favour of a nitric acid source than of any other, proof was equally 
wanting to establish the conclusion that so much nitrogen had been available as nitric 
acid. The much larger airrounts irow known to have been gathered by the clover 
crop, of course renders this explanation still less adequate. 
On a review ’of the whole of the results that have been adduced, it cannot be 
doubted that nitric acid is an important source of the nitrogen of the Leguminosse. 
Indeed, so far as existing experimental evidence goes, that relating to nitric acid 
carries us quantitatively further than any other line of explanation. But it is 
obviously quite inadequate to account for the facts of growth, either in the case of 
the Medicago sativa grown on the clover-exhausted land, or in that of the clover on 
the bean-exhausted land. There is, in fact, nothing in the results relating to the 
clover experiment to justify the conclusion that there had been such a large production 
of nitric acid in the subsoil, due to the increased development of the nitrifying 
organisms under the influence of the leguminous growth and crop-residue, and their 
