nds, therefore, on the method of sampling and the basis of
calculation adopted; and it may be that this may occasionally explain,
to some extent at least, the great discrepancies in the estimation of
the quantities of nitrogen present in different soils as found by
different investigators.

_Peat-soils richest in Nitrogen._

Of all soils, peat-soils are richest in nitrogen. Professor S. W.
Johnson found the nitrogen in fifty separate samples of peat to range
from .4 per cent to 2.9 per cent, the average being 1.5 per cent. On the
other hand, marls and sandy soils are poorest, the analyses of a number
of these soils showing only from .004 to .083 per cent for the former,
and .025 to .074 for the latter. As a general rule most arable soils
contain over one-tenth per cent of nitrogen, or, say, over 3500 lb. per
acre. A good pasture-soil, taken to a depth of 9 inches at Rothamsted,
was found to contain about a quarter per cent. In ten samples of soil,
taken to a depth of 9 inches, from different parts of Great Britain and
Ireland, Munro found from .128 to .695 per cent of nitrogen, the average
being .3278 per cent. The Rothamsted soils, it may be pointed out, are
probably poor in nitrogen compared with most soils. A. Mueller's
investigations showed that in some of the soils he has analysed, the
nitrogen amounted to little short of one per cent, while for the others
the average was over half a per cent; even the poorer soils he examined
contained about one quarter per cent on an average. Anderson's analyses
of Scottish wheat-soils showed a variation of from .074 to .22 in the
surface-soil, while he found in their subsoil from .15 to .92 per cent.
Boussingault's results are also very much higher. The amount of nitrogen
in a number of loams coming from widely different localities he examined
contained from 6000 to 30,000 lb. per acre--the soil taken to a depth of
17 inches.[74]

_Nature of the Nitrogen in the Soil._

When we compare the amount of nitrogen removed by different crops
(which, even in the case of those most exhaustive of nitrogen, does not
often amount to more than 150 lb. per acre), with the amount contained
in the soil, the former amount seems very insignificant when compared to
the latter. Such being the case, it would seem at first sight that the
addition of nitrogen in the form of manures is quite superfluous. We
must remember, however, that while the _total_ amount of nitrogen is
relatively large whe