QUESTION OP THE SOURCES OP THE NITROGEN OP VEGETATION. 
103 
absence of dead vegetable matter. Indeed, if there were such loss during growth 
when there was no decay, either in M. Boussingault’s experiments or in our own, it 
must have been almost exactly balanced by corresponding gain; an assumption which 
is without any proof, but which has nevertheless had its advocates. 
In fact we conclude, that under the existing conditions of practical agriculture 
in temperate climates, the annual loss of combined nitrogen over a given area, by 
cropping and otherwise, is by no means so great as has been assumed ; that the 
restoration requmed to compensate the loss is therefore correspondingly less; and 
further, that the known facts relating to the maintenance or the reduction of the 
fertility of soils, do not point to the conclusion that such loss as actually does take 
place, is compensated by such restoration. 
The well-known accumulation of nitrogen which takes place in the surface soil 
within a few years, when arable land is laid down to grass, is, it may be admitted, not 
conclusively explained. At the same time, there is, to say the least, quite as much 
evidence in favour of the assumption of a subsoil, as of an atmospheric, source. At 
Bothamsted, for example, there is, in soil and subsoil, to the depth at which the 
action of some deep-rooted and large nitrogen-accumulating plants has been proved, 
a store of about 20,000 lbs. of already combined nitrogen per acre. It is true that 
whilst many other soils and subsoils will contain as much, or more, many ^vill contain 
much less. Still, if further investigation should confirm the indications given in this 
and former papers, that in the case of the deep and strong rooting, and high nitrogen- 
yielding, Leguminosse, much at any rate of their nitrogen probably has its source in 
the combined nitrogen of the subsoil, and that the accumulation in the surface soil is 
due to nitrogenous crop-residue, the nitrogen of which has come from the subsoil, it 
is obvious that a like explanation would be applicable to the accumulation which takes 
place when arable land is laid down to grass, including herbage of various root-ranges, 
and various habits of root-collection. 
Then, again, as to the supposition that the gains of nitrogen in argillaceous matters 
of very low initial nitrogen contents, which gains are attributed to the fixation of free 
nitrogen, serve to explain the gradual formation of vegetable soils, there cannot be 
any doubt that, so far as nitrogen is concerned, the natural fertility of most soils is 
due to the accuniulation of ages of natural vegetation with little or no removal of 
it, by animals or otherwise. If the amounts of nitrogen even now brought into 
combination over a given area under the influence of electricity in Equatorial regions, 
were not exceeded in the earlier periods of the history of our globe, that would be 
quite sufficient, with growth and with little or no removal, through the ages which 
modern science teaches us to reckon upon, for the ascertained accumulations in natural 
prairie, or forest lands; and it is these which have to a great extent furnished us with 
our meadows and pastures, and arable soils. Frequently the natural forests have been 
on the more elevated, or the more undulating lands, and the soils they have formed 
