26 
SIR J. B. LAWES AND PROFESSOR J. H. GILBERT ON THE 
the wheat-fallow subsoils, those bj the white clover subsoils were more marked; but 
this was especially the case with the lucerne plot subsoils, of which more samples, and 
those from a greater depth. Induced nitrification. The same is also observable on a 
comparison of the results obtamed by the samples from the wheat-fallow plot, with 
those from the rotation red clover plot. 
It is then established that the nitrogenous matters of raw clay subsoils are 
susceptible of nitrification, if the organisms, with the other necessary conditions, are 
present. It is further indicated, not only that the action is more marked under the 
influence of leguminous than of gramineous growth and crop-residue, but that the 
organisms become distributed to a considerable depth even in raw clay subsoils, 
especially where deep-rooted and free-growing Leguminosse have grown. 
The next question is, how far, in a quantitative sense, do the results aid us in 
explaining the source of the large amounts of nitrogen taken up by some leguminous 
crops—as for instance in the case of the Medicago sativa growm on the clover- 
exhausted land, and of the red clover grown on the bean-exhausted land. 
In the case of the three leguminous crop subsoils there was, over the total period, 
only about 1 part of nitrogen nitrified per million of soil; and as the subsoil to the 
dej^th experimented on would weigh about 30 million lbs. per acre, the amount of 
nitrification supposed would represent only about 30 lbs. per acre. Obviously, the 
conditions of nitrification in which the samples are exposed in the laboratory are very 
different from those of the subsoil in situ. Thus, whilst in the case of the samples in 
the laboratory, the conditions as to temperature and aeration would be the more 
favourable, the successive extractions by water under pressure would be liable to 
remove, not only the mineral matters essential for the development of the organisms, 
and for the production of nitric acid, but the organisms themselves, whereas in the 
case of the natural subsoil the tendency would be to multiplication. 
Compared with the small amount of nitrification of the nitrogen of the raw clay 
subsoils shown in the foregoing experiments, in which some of the conditions were 
more and others less favourable than in the natural subsoil, the following results 
obtained by Mr. Warington (‘Chem. Soc. Trans.,' 1887, pp. 127-9), show how very 
large may be the amount of nitrification of the nitrogen of such subsoils under more 
favourable circumstances than those of them natural condition. Thus, he mixed raw 
clay subsoil with an equal weight of coarsely powdered flint, seeded the mixture with 
rich garden soil, moistened it, and placed it in a vessel allowing for free access of 
washed air. Under these conditions he found, when no mineral food wms added, in 
one case 2‘4, and in another 3‘0 per cent, of the total nitrogen of the subsoil nitrified ; 
and when mineral food was added, he found in one case 4 per cent., and in another 
3‘6 per cent, of the total nitrogen was nitrified. 
Indeed, the greatest difficulty in the way of the supposition that much nitrogen is 
available to plants by the nitrification of the nitrogen of the subsoil, is, in fact, the 
want of sufficient aeration. Independently of the greater or less porosity of the sub- 
